DIESEL POLLUTANTS & THEIR EFFECT ON PUBLIC HEALTH-MULTIPLE TECHNOLOGIES DEVELOPED FOR EMISSION CONTROL
vijay tharad
Director Operations at Corporate Professional Academy for Technical Training & Career Development
MULTIPLE TECHNOLOGIES AVAILABLE AND ARE BEING DEVELOPED TO CONTROL EMISSION
With mounting evidence that diesel exhaust poses major health hazards, reducing diesel pollution has become a public priority.
Health impacts of diesel pollution
Diesel-powered vehicles, vessels, locomotives, and equipment account for over 60 percent of all nitrogen oxides (NOx) and more than 70 percent of all fine particulate matter (PM2.5) emissions from US transportation sources. Heavy-duty vehicles powered by diesel, like big-rigs and garbage trucks account for 20 percent of all NOx and 25 percent of PM2.5 pollution emitted by vehicles in the country.
The World Health Organization (WHO) classifies diesel exhaust as carcinogenic to humans, and ample research demonstrates that its components, which include PM 2.5 and NOx, a ground-level ozone precursor, are harmful for human health even at low concentrations and through short-term exposures.?
Fine particulate pollution
Particulate matter, sometimes called soot, is created during the incomplete combustion of diesel fuel. Though just a fraction of the width of a human hair, particulate matter varies in size from coarse particulates (less than 10 microns in diameter, known as PM 10) to fine particulates (less than 2.5 microns, known as PM 2.5) to ultrafine particulates (less than 0.1 microns). Ultrafine particulates, which are small enough to penetrate the cells of the lungs, make up 80 to 95 percent of diesel soot pollution. ?
Particulate matter irritates the eyes, nose, throat, and lungs, contributing to respiratory and cardiovascular illnesses and even premature death. Although everyone is susceptible to particulate pollution, children, the elderly, and individuals with preexisting respiratory conditions are the most vulnerable. A recent study found that the rates of nine common causes of death, including cardiovascular disease, lung cancer, and other prevalent fatal conditions, were associated with exposure even at concentrations of fine particulates lower than the current federal standards.
The larger body of science clearly shows that communities of color and socioeconomically disadvantaged communities bear disproportionately higher exposures to PM 2.5 pollution, and despite significant reductions in ambient concentrations over the past 40 years, these communities remain exposed at similarly proportioned higher levels.7 ?
Impacts from nitrous oxides (NOx)
Heavy duty diesel vehicles also emit significant levels of NOx, especially at lower speeds while driving through urban neighborhoods. NOx is particularly dangerous as it is both a pollutant itself and a precursor chemical leading to the creation of fine particulate and ground-level ozone pollution. Exposure to NOx pollution has been shown to inflict a number of respiratory health issues over both short- and long-term exposure, including reduced lung function and inflammation.
Long-term exposure to NOx has been directly linked to the development of asthma, while short-term exposure can trigger asthmatic symptoms.9 ?
Ground-level ozone
Diesel emissions of NOx contribute to the formation of ground-level ozone, which irritates the respiratory system, causing coughing, choking, and reduced lung capacity. Ground-level ozone pollution, formed when NOx and hydrocarbon emissions combine in the presence of sunlight, presents a hazard for both healthy adults and individuals suffering from respiratory problems. Urban ozone pollution has been linked to increased hospital admissions for respiratory problems such as asthma, even at levels below the federal standards for ozone.
Exposure is particularly harmful for more vulnerable populations, including the elderly and those with preexisting conditions. A recent study found a significant relationship between mortality among the Medicare population with small, short-term increases in ozone concentrations. Ground-level ozone has also been shown to damage crops leading to measurable reductions in agricultural output worldwide and climate change will only further these impacts. ?
Pollutant Emissions
In modern internal combustion engines, two primary systems are responsible for the formation and reduction of pollutants:
The combustion system includes the combustion chamber, its shape and characteristics such as charge composition, charge motion, and fuel distribution. This is where pollutants such as NOx, CO and PM are created as well as where incomplete oxidation of fuel occurs. What happens in the combustion system is greatly influenced by other engine systems such as the intake charge management system and the fuel injection system. In fact, the primary purpose of these secondary systems is to influence what happens during the combustion process. Numerous options are available to limit the formation of pollutants resulting from the combustion system. Once exhaust gas leaves the combustion system, its composition is essentially frozen until it reaches the emission aftertreatment system (ATS, also abbreviated EAT or EATS) where further reductions in pollutants can be realized and also where secondary emissions such as N2O, NO2 and NH3 can originate.
The aftertreatment system consists of catalytic reactors that attempt to further lower pollutants. In some cases, such as stoichiometric spark ignition (SI) engines, a single three-way catalyst (TWC) is sufficient to achieve very significant reductions in pollutants. In other cases such as lean burn diesel engines, a number of catalytic devices are required. Secondary systems are required to ensure the ATS works as intended. These include: control of exhaust gas composition through control of exhaust stoichiometry or supply of additional reactants not normally found in exhaust gas or not present in sufficient quantity (e.g., urea, additional HCs, additional air or O2), thermal management to ensure the catalysts operate within the required temperature window, systems to ensure contaminants and pollutants that might accumulate are removed (regeneration of filters, sulfur management, urea deposits,) and systems to minimize the formation of secondary pollutants such as the ammonia slip catalyst (ASC).
It would be a mistake to consider the combustion system and the ATS as separate systems. In order maximize their effectiveness, a high degree of integration is required. A classic example is air-to-fuel ratio (AFR) in SI engines where a very high level of control precision is required to ensure the TWC performance is maximized. Thermal management of the ATS can be carried out by adjustments within the engine to affect the temperature of the exhaust gas leaving the cylinder. In some cases, additional fuel required by the ATS (e.g., for thermal management) can be supplied by the engine’s fuel injectors.
It is important to realize that the objective of engine optimization is not to minimize the pollutant emissions from the combustion system or maximize the reduction of pollutants in the ATS. Rather the objective is to achieve a target level of emissions from the entire system. The target is generally sufficiently below the regulatory limit to allow for production variability. Doing so may require the emission of some pollutants from the combustion system to increase if ATS performance is sufficiently high to still allow design target to be met. For example, NOx emissions from engines equipped with a urea-SCR catalyst can be allowed to increase to minimize GHG emissions (due to the NOx-BSFC trade-off) if high NOx conversion in the SCR catalyst is achieved.
Fuels and lubricants are an important “partner” in the combined engine and aftertreatment system. Low emissions over the life of the engine would not be possible unless fuel contaminants such as sulfur and some inorganic minerals are controlled to very low levels.
EMISSION CONTROL TECHNOLOGIES EXPLAIED :
1. Positive Crankcase Ventilation :
A crankcase ventilation system (CVS) removes unwanted gases from the crankcase of an internal combustion engine. The system usually consists of a tube, a one-way valve and a vacuum source (such as the inlet manifold).
The unwanted gases, called "blow-by", are gases from the combustion chamber which have leaked past the piston rings. Early engines released these gases to the atmosphere simply by leaking them through the crankcase seals. The first specific crankcase ventilation system was the 'road draught tube', which used a partial vacuum to draw the gases through a tube and release them to the atmosphere. Positive crankcase ventilation (PCV) systems— first used in the Second World War and present on most modern engines— send the crankcase gases back to the combustion chamber, as part of the vehicle emission control in order to reduce air pollution .In the crankcase—the portion of the engine block below the cylinders where the crankshaft is located—leaked combustion gases are combined with ventilating air and returned to the intake manifold for reburning in the combustion chamber. The device that performs this function is known as the positive crankcase ventilation valve, or PCV valve
Blow-by, as it is often called, is the result of combustion material from the combustion chamber "blowing" past the piston rings and into the crankcase. These blow-by gases, if not ventilated, inevitably condense and combine with the oil vapor present in the crankcase, forming oil sludge. Excessive crankcase pressure can furthermore lead to engine oil leaks past the crankshaft seals and other engine seals and gaskets. Therefore, it becomes imperative that a crankcase ventilation system be used.
The CCV system, also known as the "PCV system" (Positive Crankcase Ventilation), is now widespread and even compulsory on new vehicles. What's special about it? It prevents the release of noxious gases into the atmosphere. How does it work? Gases and vapors are drawn into the system. They are passed through a coalescing filter. Thanks to its filter media, this retains the oil and contaminants present in the combustion gases. The oil is returned to the crankcase, while the gases are reintroduced into the intake manifold via the PCV valve to be burnt during combustion.
Advantages of a ccv system
2. Evaporative Emission Control
Evaporative emission control systems (EVAP) are used in cars' fuel systems to prevent gasoline fumes from leaking into the atmosphere. The EVAP system runs diagnostics for possible fuel vapor leaks and will trigger a fault code if they’re present. It will also activate the check engine light on the dashboard.?
How The EVAP System Works
The EVAP system comprises the fuel tank, a vapor storage canister, valves, hoses, and the fuel tank gas gap. To prevent the gasoline vapors from escaping directly into the atmosphere, vent lines from the fuel tank pass the fumes or vapor to the vapor storage canister, which is confined and stored until the vehicle starts. Once the vehicle is running, and the engine is warmer, the storage canister releases the vapors through a purge valve opened by the vehicle's powertrain control module (PCM) into the intake manifold. The vapors are then burnt together with the air-fuel mixture inside the engine.?
EVAP systems are active systems and require no maintenance. However, faults can develop, and the system may not function as designed. Hence the vehicle's PCM monitor runs self-checks to verify if there is airflow from the canister to the engine and whether there are no leaks in the fuel tank, the canister, fuel lines, and vents. The system will trigger a fault code and illuminate the check engine light even if a leak smaller than the size of a pinprick is detected.?
EVAP System Components And Their Functions
Powertrain Control Module (PCM)
The PCM is responsible for assessing the integrity of the EVAP system by running an EVAP diagnostic monitor during certain driving conditions to detect evaporative leaks. It will set a diagnostic fault code (DTC) and the accompanying check engine light if leaks occur. The PCM is also responsible for adequately metering the stored gasoline vapor back into the engine by monitoring engine and vehicle operating conditions, fuel level, cycle times, and ambient temperature.
Fuel Tank
The fuel tank stores fuel until the engine requires it. It also stores some fuel vapor before passing them to the EVAP storage canister. The fuel tank is air-tight, with seals at access points where fuel and vapor pass to the engine and canister. Any breakages or ruptures below the fuel tank lead to fuel leakages, whiles those above the tank results in gasoline vapors escaping into the atmosphere. The EVAP system will identify and trigger a fault code when such problems occur.
Gas Cap
The gas cap prevents fuel vapors or actual fuel from getting into the atmosphere due to the gasoline evaporation in the fuel tank. It also allows fresh air into the fuel tank to replace the fuel transferred into the engine. It, therefore, is an essential component of the fuel system and must be correctly designed, calibrated, and installed to provide an air-tight seal. Gas caps come As vented or unvented and must be replaced with the same type if missing. Otherwise, the EVAP system will trigger a fault code.?
Fuel Tank Pressure Sensor
The fuel tank pressure sensor measures positive and negative pressure in the fuel tank. During EVAP monitoring, the PCM uses this pressure to detect vapor leakages in the fuel tank and will trigger a fault code and illuminate the check engine light when a leak is detected or if the sensor fails.
EVAP Canister
The EVAP canister is usually a plastic container filled with activated charcoal and connected to the fuel tank by a vent line. It absorbs and confines the gasoline vapors until the vehicle's engine starts. As the vehicle drive, the canister purge valve opens to allow the intake vacuum to draw vehicles into the engine for combustion.
Canister Purge Valve
The canister purge valve is usually electrically operated and allows the engine vacuum to draw fuel vapors. The valve, however, can get clogged or be held open by charcoal particles or debris drawn from the canister. The vehicle's PCM assesses the valve condition and activates the check engine light if an issue is detected.
Leak Detection Pump LDP
The leak detection pump provides pressure for conducting positive pressure testing of the EVAP system by pumping air into the fuel tank and charcoal canister. The PCM measures the EVAP system's pressure detail once the system is pressurized.
Summary
Vehicle pollution encompasses more than just tailpipe emissions. Gasoline fumes escaping from the engine and fuel tank are also a significant source of hydrocarbon pollution, whether the engine is running or not, and can continue to pollute the atmosphere until there's no fuel left in the engine or fuel tank. EVAP systems prevent these hydrocarbons from escaping and prompt the driver whenever a leak occurs.
3. EXHAUST GAS RECIRCULATION SYSTEM (EGR)
EGR is a system developed to incorporate some of the exhaust gases in the cylinder into the combustion process with the intake air. The purpose here is to lower the combustion end temperature and thus the NOx emission values by deteriorating the combustion performance, because high temperature is the main influence in the formation of NOx emissions. The use of the EGR system reduces the amount of oxygen in the cylinder, and therefore resulting in a decrease in the combustion end pressure and temperature. The decrease in the amount of oxygen suppresses the formation of NOx. The exhaust gas recirculated in the cylinder and containing large amounts of CO2 and H2O increases the specific heat capacity of the intake charge, and this reduces the temperature values in the compression and combustion processes . Displacement of some of the oxygen content in the intake charge by the exiting exhaust gases reduces the air excess coefficient and increases the ignition delay by diluting the intake charge. This slows the mixture of oxygen with fuel and therefore the combustion rate.
The EGR system developed to reduce the combustion end temperature in the cylinder has been widely used by automobile manufacturers since the past. The circulation of the exhaust gas with the intake air can be achieved in two different ways; external and internal . In the external exhaust gas recirculation, the exhaust gas taken from the exhaust manifold is sent to the intake stream through a valve and a coolant. In the internal exhaust gas recirculation, unlike the external exhaust gas recirculation, some of the combustion exhaust gas is withdrawn to the combustion chamber before exiting the exhaust valve. This is accomplished by delaying the camshaft and closing the exhaust valves a little later than normal. The late closing of the exhaust valve allows the piston to draw a portion of the exhaust gas at the outlet of the exhaust valve into the cylinder while the piston is moving downward at intake stroke. The engines, which have the internal EGR systems, are run with variable valve timing. Compared with external EGR, the internal EGR system remains weak in controlling exhaust gas into the cylinder. In addition, since no cooling operation can be performed on the recirculated exhaust gas, desired reductions in NOx emission values are not achieved. The internal EGR system is generally preferred for gasoline engines, which have lower NOx emissions compared to diesel engines. On the other hand, external EGR systems are widely used in diesel engines.
Figure 4 shows the structure of a conventional EGR system used in diesel engines. The system simply consists of valve, control unit and coolant. The EGR valve mounted on the intake manifold is controlled by the control unit. The function of the EGR valve is to control the flow of exhaust gas to intake port depending on the engine load. The amount of exhaust gas sent to the intake port may constitute a maximum of 50% of the air taken into the combustion chamber . Because of the high exhaust gas content included in the combustion, the combustion performance is greatly affected; therefore the engine performance can decrease significantly. For this reason, the exhaust gas content mixed with the intake air does not exceed 20% in practice.
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Figure 4. Exhaust gas recirculation (EGR).
The cooling of the exhaust gas included in the combustion process in the EGR system allows the higher amount of exhaust gas to be included in the combustion process and at the same time the combustion chamber temperature and hence NOx emissions can be further reduced. For this reason, in the EGR systems, the exhaust gas is passed through a cooler and sent to the intake stream. Cooling is carried out using engine coolant. In an electronically controlled cooling system, the cooling process is optimized depending on different engine loads, temperatures and conditions.
In turbocharged diesel engines, the use of EGR takes place in two different ways; high pressure and low pressure. In a high-pressure EGR system, the exhaust gas is recirculated to the intake channel before the exhaust gas goes to the turbine and in the low-pressure EGR system the exhaust gas is recirculated after passing through the turbine.?
Thanks to the EGR system, the NOx emission in diesel engines can be reduced by up to 50% ]. However, in this method, combustion is worsened, engine performance decreases, and other pollutants, especially particulate emissions (PM) slightly increases. At the same time, the EGR system leads to an increase of about 2% in fuel consumption . Due to the flow of the exhaust gas, EGR system can affect the quality of lubrication oil and the engine durability negatively, and erosion on piston rings and cylinder liner can increase . These disadvantages and developed aftertreatment emission control technologies have overshadowed the EGR system .
EGR Disadvantages
1. By reducing the amount of oxygen available for combustion, the EGR system reduces the power and performance available to a vehicle.
2. By introducing exhaust gas into the combustion chamber, the EGR system may cause soot deposits on glow plugs, intake valves, cylinder heads, turbochargers etc.
Exhaust gas recirculation (EGR), the process of recirculating some of the exhaust gas back into the intake system, is an important technology that has allowed modern diesel engines to achieve very low engine out NOx emissions. As can be imagined, introducing relatively high temperature exhaust gas into the intake air can have significant impacts on the temperature and composition of the combustion air supplied to the combustion chamber. In order to ensure proper functioning of an engine with EGR, various hardware components, such as valves and coolers have to be introduced to control the flow, temperature and distribution of EGR supply and the resulting mixture with intake air. As well, turbocharger sizing and technology choices can also be affected and steps must be taken to ensure sufficient oxygen is still available for combustion and sufficient EGR flow is available at all engine operating conditions.
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4. AIR INJECTION SYSTEM
In a typical air-injection system, an engine-driven pump injects air into the exhaust manifold, where the air combines with unburned hydrocarbons and carbon monoxide at a high temperature and, in effect, continues the combustion process. In this way a large percentage of the pollutants that were formerly discharged through the exhaust system are burned (though with no additional generation of power).
SECONDARY AIR INJECTION (commonly known as air injection) is a vehicle emissions control strategy, wherein fresh air is injected into the exhaust stream to allow for a fuller combustion of exhaust gases. Secondary air injection system is one of the method to control Carbon Monoxide and Hydrocarbon emission in engines. There are various methods used to reduce emissions in engines. Secondary air injection is the cheapest method to reduce carbon monoxide and hydrocarbon emission. In order to meet government emission norms and also to prevent environment from global warming. There is a need to introduce a additional system to reduce emission.
II. WORKING PRINCIPLE
Secondary Air injection (SAI) pushes air into the exhaust system right after the exhaust manifold, to help intercept and burn those unburned fuels. The system is critical to help cars achieve government emissions standards. So, the law says you need a secondary air injection system.
There are various methods to control emissions in engines. Some of them are as follows:
? Thermal converters,
? Catalytic Converters,
? Particulate Traps,
? Exhaust Gas Recirculation (EGR),
? Air Injection,
? Evaporative Emissions Control,
? Ceramic Engine Coatings and Other Methods.
Since we are going to reduce emission in lower CC engine, secondary air injection is one the best method and also cost wise it will be very cheaper. Here we are going to take a separate path from air filter to cylinder block which will carry O2 with it. There is a separate connecting passage introduced between Cylinder block to cylinder head exhaust port in order to transfer the O2 into it. The harmful hydrocarbon and Carbon monoxide which comes out from combustion chamber will reacts with Oxygen to form Water and Carbon dioxide.
The below figure clearly explains about the function of secondary air injection system in automotive engine.
Motor vehicles produce more than two-thirds of the man made carbon monoxide in the atmosphere. Carbon monoxide reduces the volume of oxygen that enters the bloodstream and can slow reflexes, cause drowsiness, impair judgment and vision and even cause death.
Hydrocarbons are unburned fuel vapors. The chemical balancing equation of hydrocarbon, Carbon monoxide which reacts with Oxygen are as follows:
Hydrocarbon reacts with Oxygen:
4 HC + 5 O2 = 4 CO2 + 2 H2O
Carbon monoxide reacts with Oxygen:
2 CO(g) + O2(g) = 2 CO2(g)
Hence by using Secondary air injection system in engine exhaust system, there would be a significant reduction in Carbon monoxide and hydrocarbons. Secondary Air injection (SAI) System is one of the best methods to reduce Carbon monoxide and hydrocarbons in exhaust emission. Hence to achieve the future emission norms in lower CC engines, Secondary air injection system to be used in all kind of vehicles in order to control the emissions and also to save the environment from global warming.
5. CATALYTIC CONVERTER
Catalytic Converter and Emission Control?
Catalytic Converter?Efficiency and Emission: Catalytic converters are critical in reducing harmful emissions from internal combustion engines in automobiles and other vehicles. The? catalytic converter?is a key component of a vehicle’s exhaust system, designed to convert toxic exhaust gases like carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful carbon dioxide, water vapor, and nitrogen.
With stricter emission regulations coming into effect in the 1970s, catalytic converters were widely adopted and have become standard equipment in gasoline-powered vehicles in the US and around the world. They aid in controlling air pollution by reducing emissions of major air pollutants.
The efficiency of the catalytic converter directly impacts a vehicle’s emission levels and ability to meet emissions standards. Therefore, evaluating and maintaining proper catalytic converter efficiency is an important area of focus for automotive manufacturers and vehicle owners alike.
The Evolution of Emission Control Technologies
The introduction of Volvo’s three-way catalytic converter?in 1975 marked a breakthrough in emission control. Catalytic converters could simultaneously reduce hydrocarbons, carbon monoxide, and nitrogen oxide emissions in a single device. This three-way catalytic converter became standard on new cars in the US after regulations required their use starting in 1975.
Further advancements in the 1980s and 90s led to the use of more efficient ultra-low emission vehicles (ULEV) and super ultra-low emission vehicles (SULEV) converters. Modern vehicles now utilize a complex system of sensors and emission control devices to meet the latest standards.
Catalytic converters are emissions control devices installed on vehicle exhaust systems. They contain a catalyst coated on a substrate inside a stainless steel housing. As hot exhaust gases pass through, the catalyst facilitates chemical reactions that convert harmful pollutants into less toxic compounds.
The most common type is the three-way catalytic converter that reduces hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). Diesel vehicles often use oxidation catalysts to reduce CO and HC or NOx absorbers/adsorbers to reduce NOx.
Types of Catalytic Converters
There are three major types of catalytic converters:
Based on the substrate material, converters can be categorized as ceramic, metallic, or zeolite types. Ceramic converters with a monolithic honeycomb structure are most common.
Other specialty converters include heated, electric, and three-way plus oxidation converters. The performance also depends on catalyst composition – commonly a mixture of precious metals like platinum, palladium, and rhodium.
How Catalytic Converters Work
Catalytic converters use a combination of chemical and thermal processes to treat exhaust ?emissions. Their main function is to convert toxic gases like CO, HC, and NOx into harmless compounds via oxidation and reduction reactions.
This is facilitated by the catalyst coating on the substrate, which activates the chemical reactions. Common catalyst compounds include platinum, palladium, rhodium, and cerium oxide. The substrate provides a high surface area for catalysis.
The catalyst helps oxidize CO and HC to form CO2 and H2O as hot exhaust passes. It also reduces NOx to N2. Performance is optimal at high temperatures around 300-900°C. The converter has an insulated casing to retain heat and reach operating temperature quickly.
The efficiency of a catalytic converter determines how much it can reduce the emissions of CO, HC, and NOx in exhaust gases. Higher converter efficiency correlates with lower tailpipe emissions.
Even a small drop in efficiency can result in emission levels exceeding mandated limits, failing emission tests, and increasing air pollution. Poorer fuel economy is another negative outcome of lowered catalytic converter performance.
Factors Affecting Catalytic Converter Efficiency
Some key factors impacting catalytic converter efficiency include:
The most common sensors used for monitoring catalytic converter function are:
Function and Purpose of Catalyst Monitoring Sensors
Catalyst monitoring sensors serve a few key functions:
Common Issues with Catalyst Monitoring Sensors
Some common problems encountered with catalyst monitoring sensors include:
Importance of Regularly Checking and Replacing Sensors
Since catalyst monitoring sensors are critical for the proper functioning of the converter, they should be regularly checked and replaced as needed. Problems with sensors will inhibit effective catalyst monitoring and control.
Replacing aging oxygen, temperature, and NOx sensors is important for continued accurate readings. Manufacturers often recommend replacing oxygen sensors every 80,000-100,000 miles. Diagnostic scan tools help identify any sensor issues.
Methods for Evaluating Emission Control Performance
There are several methods used to evaluate the performance of emission control systems:
Common Factors Affecting Catalytic Converter Efficiency
Catalytic converter efficiency degrades with vehicle age and mileage as the catalyst becomes contaminated, damaged, and unable to function properly. Efficiency can drop by 15-20% at around 80,000 to 100,000 miles.
Higher mileage also results in greater soot accumulation, masks catalyst active sites, and decreases efficiency. Conversion of pollutants drops from around 95% in a new converter to 60-75% in an older high-mileage converter.
Influence of Fuel Quality on Catalytic Converter Efficiency
Lower-quality fuels with higher sulfur content can poison the catalyst and lower converter efficiency. Lead and other additives in older gasoline formulations impair catalyst function.
Ultra-low sulfur fuels help sustain catalyst activity. Gasoline detergent additives help minimize deposit build-up on the converter, which can lower efficiency due to restricted??exhaust ?flow.
Environmental Impact of Catalytic Converters
The use of catalytic converters has significantly reduced vehicle emissions of major air pollutants:
This has led to major improvements in urban air quality and associated health benefits over the past 40+ years.
Potential Environmental Concerns
Some concerns related to catalytic converters include:
Emerging Technologies in Catalytic Converters
Some emerging catalytic converter technologies include:
Potential Benefits and Challenges
Key benefits of newer technologies include better cold start emissions, faster light-off, improved efficiency, lower back pressure, compact packaging, and diesel NOx control.
However, for adoption, increased cost, complexity, durability concerns, regeneration needs (for NOx adsorbers), and integration into existing designs must be addressed.
Three-way catalysts
Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce - Carbon Monoxide, Hydrocarbon and Nitrogen Oxides. The converter uses different types of catalysts, for reducing and oxidizing the pollutants within a single monolith and an oxidization catalyst.
Both types consist of a ceramic structure coated with a metal catalyst, usually Platinum, Rhodium and / or Palladium. The idea is to create a structure that exposes the maximum surface area of a catalyst to the exhaust stream, while also minimizing the amount of catalyst required as they are expensive. The conventional three-way catalyst technology used on petrol engines needs a 'richer' environment with less oxygen in the exhaust than is available on these engines to be able to reduce NOx
A three-way catalytic converter:
Most cars today use a honeycomb structure.
6. Oxidation catalyst
The oxidation catalyst reduces the unburned Hydrocarbons and Carbon Monoxide (CO) by burning (oxidizing) them over a Platinum and Palladium catalyst.
For example: 2CO + O2 ----> 2CO2 But where did this oxygen come from?
The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is an oxygen sensor mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter is. This sensor tells the engine control unit (ECU) the amount oxygen in the exhaust. The ECU can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the ECU to make sure that the engine is running at close to the stoichiometric point, and also to make sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.
7. Diesel Oxidation Catalyst (DOC)
DOC’s reduce emissions of the organic fraction of particulate Matter (PM), gas-phase hydrocarbons and carbon monoxide.
Ceramic Honeycomb Catalyst Structure
Diesel engines are lean-burn engines hence require oxidation catalyst alone. To reduce NOx in an oxidation rich environment requires new approaches. Selective Catalytic Reduction, Lean De-NOx catalysts and NOx adsorbers are technologies that can be used in these lean applications.
It is a device that is used to reduce?oxides of nitrogen?(NO and NO2) emissions from a?lean burn?internal combustion engine.
8. NOx Adsorbers (NOx traps)
The NOx?adsorber was designed to avoid the problems that EGR and SCR experienced as NOx?reduction technologies. The theory is that the?zeolite?will trap the NO and NO2?molecules - in effect acting as a molecular sponge. Once the trap is full (like a sponge full of water) no more NOx?can be absorbed and it is passed out of the exhaust system. Various schemes have been designed to "purge" or "regenerate" the adsorber. Injection of diesel fuel (or other reactant) before the adsorber can purge it, the NO2?in particular is unstable and will join with?hydrocarbons?to produce?H2O?and?N2. Use of?hydrogen?has also been tried, with the same results, however hydrogen is difficult to store. Some experimental engines have mounted?hydrogen reformers?for on board hydrogen generation; however fuel reformers are not mature technology.
9. Selective Catalytic Reduction (SCR)
The new clean diesel system involves three pieces: cleaner diesel fuel, lower-emitting diesel engines and advanced emissions control devices. Selective Catalytic Reduction (SCR) is one of the latest technologies designed to further reduce emissions of nitrogen oxides and to meet stringent new air quality regulations.
What is SCR?
Selective Catalytic Reduction is a technology that injects urea – a liquid-reducing agent –into the exhaust stream of a diesel engine. The urea sets off a chemical reaction that converts nitrogen oxides into nitrogen and water in the catalyst, which is then expelled through the vehicle tailpipe. While urea is the primary operating fluid presently used in SCR systems, alternatives to the urea agent are currently being explored. One option involves the use of diesel fuel to transform NOx into harmless gases.
Why is SCR important?
SCR technology is one of the most cost-effective and fuel-efficient technologies available to help reduce emissions. SCR can reduce NOx emissions up to 90 percent while simultaneously reducing HC and CO emissions by 50-90 percent, SCR systems can also be combined with a diesel particulate filter to achieve even greater emission reductions for PM. SCR technology may play a key role in achieving emissions reductions that allow light-duty diesel vehicles to meet the most stringent emission regulation to be phased in US, Europe and Japan.
Where is SCR used?
SCR has been used to reduce stationary source emissions since the 1980s. In addition, more than 100 marine vessels worldwide have been equipped with SCR technology, including cargo vessels, ferries and tugboats.
While SCR has been installed on both highway and non-road engines in diesel retrofit demonstration projects throughout the U.S., SCR systems have become the technology of choice for many of Europe’s heavy-duty diesel truck and bus manufacturers where the urea agent is commonly known as Ad Blue. SCR technology may become more prevalent in the United States as both light and heavy-duty engine manufacturers work to meet future emissions reduction standards starting in 2009. In fact, several light-duty diesel manufacturers have already indicated that they are considering the use of SCR in future products.
10. Lean De-NOx catalysts (Hydrocarbon SCR)
Lean De-NOx Catalysts, also known as hydrocarbon-SCR systems use different catalyst to reduce NOx; Hydrocarbon like Ethanol or diesel is dosedin order to create a rich 'microclimate' reduction of NOx happens, while the overall exhaust remains lean.
11. Gasoline Particulate Filter (GPF)
Gasoline Direct Injection (GDI) is a key technology of gasoline engine development to reduce CO2?emissions while improving torque and power output. However the drawback of GDI engines is an increase in particle number (PN) emissions compared to conventional Port Fuel Injection (PFI) engines.
Most of the GDI particles are formed during the cold-start phase, catalyst heating mode and dynamic engine modes. Therefore, the injection system including injection operating programme (e.g. number of injections, timing, and amount of injection) has been further developed in order to improve air-fuel mixture in the cold-start phase.?Furthermore, internal engine measures such as improved mixture homogenization and minimized amount of injected fuel striking the walls helps to avoid the formation of particles. Thus, latest GDI vehicles can achieve the PN limit of 6×1011/km on the regulatory test cycle (NEDC or WLTC). The RDE procedure however also includes particle counting in a wide range of engine map operation. The Gasoline Particulate Filter (GPF) technology has been derived from successful experience with DPF and is available. It ensures control of ultrafine particles from Gasoline Direct Injection engines under real-world driving conditions.
12. Fuel Injection and Ignition System Controls
Introduction to Fuel Injection Systems
Modern internal combustion engines are not complete without fuel injection systems, which offer precise control over fuel supply and are therefore essential for controlling emissions, performance, and economy. The basic ideas, forms, and parts of fuel injection systems are covered here.
Basic Principles of Fuel Injection
The carefully regulated procedure of injecting gasoline into the engine's combustion chamber is known as fuel injection. The following are the main ideas behind fuel injection:
Controlled Metering: Optimal combustion and lower waste and emissions are made possible by precise control over the amount of fuel injected.
Spray Atomization: To ensure full combustion and increase efficiency, fuel is sprayed in tiny droplets.
Timing Control: By delivering fuel at the appropriate stage of the engine cycle, injection timing adapts to changes in load and speed.
Types of Fuel Injection Systems
Different fuel injection system designs have been created to accommodate different engine needs.
Direct Injection (DI)
Port Injection (PI)
Sequential Fuel Injection (SFI)
Throttle Body Injection (TBI)
Components of Fuel Injection Systems
Fuel injection systems are made up of many essential parts:
Injectors: Accurate tools that precisely dispense fuel into the engine. There are several designs available for different uses.
Fuel Rails: These are the pipes that supply fuel to the injectors while preserving the required pressure.
Fuel Pump: They are used to transfer fuel from tanks to fuel rails; they frequently come along with pressure regulators to regulate fuel pressure.
Engine Control Unit (ECU): The engine control unit (ECU) is the brain of the system; it uses sensor inputs to determine the necessary amount of fuel and the timing of injections.
Sensors: The ECU receives real-time data from a variety of sensors, such as mass airflow and oxygen sensors, to enable adaptive control.
Figure 1: Depiction of a Typical Fuel Injection System
In many applications, fuel injection systems have taken the place of carburetors as a fundamental component of contemporary internal combustion engines. Fuel injection systems provide increased responsiveness and efficiency using highly regulated atomization, timing, and metering. Fuel injection may be customized to work with a broad range of engine types and operating situations thanks to the variety of kinds and components that allow for design freedom. Gaining an understanding of the fundamentals and elements of fuel injection systems paves the way for investigating the integrations and control schemes that drive contemporary engine management.
Fuel Injection Control Strategies
Modern internal combustion engines depend on accurate fuel injection regulation to function, which affects efficiency, emissions, and performance. The primary control schemes for fuel injection systems will be discussed here, with an emphasis on air-fuel ratio management, timing and duration control of injections, and adaptive controls for changing engine and environmental circumstances.
Air-Fuel Ratio Control
The amount of fuel to air in the engine's intake mixture is known as the air-fuel ratio, or AFR. To preserve fuel efficiency, minimize emissions, and achieve efficient combustion, precise control of AFR is essential. Important elements consist of:
Stoichiometric AFR: This is the optimal ratio, which for gasoline is typically about 14.7:1 when all of the fuel is utilized with the available oxygen. In many driving situations, it is a target and reduces hazardous emissions.
Lean and Rich Mixtures: Higher AFR lean mixes can boost fuel economy, but there is a danger of increased NOx emissions and engine knocking. To boost power, rich mixes (lower AFR) may be utilized, however, this will result in worse fuel efficiency and more CO emissions.
Lambda Control: Oxygen sensors, also known as lambda sensors, are used to detect the amount of oxygen in exhaust. They then provide the ECU with input so that the AFR may be adjusted appropriately.
Closed-Loop Control: A feedback control system that continually modifies the injector pulse width while taking temperature, load, and other variables into account in order to maintain the intended AFR.
Injection Timing and Duration Control
For optimal engine performance and economy, fuel injection timing and duration are also critical factors.
Injection Timing: When the fuel injection begins in relation to the engine's cycle, is referred to as injection timing. It might occur before, during, or after the intake stroke, based on the kind of engine and the circumstances of operation.
Injection Duration: This indicates how long the injector is left open, which affects how much fuel is supplied. The throttle position, engine speed, and load are some of the variables that the ECU uses to determine the necessary time.
Multiple Injections: With the ability to carry out several injections in a single cycle, modern systems offer more exact control over emissions, noise, and combustion.
Adaptive Controls for Varying Engine and Environmental Conditions
A broad range of operating variables, including variations in load, temperature, altitude, and fuel quality, must be accommodated by modern engines. Important coping mechanisms include: Load Sensing: This ensures efficient engine performance at both idle and maximum power by adjusting the fuel injection to meet the engine's load.
Temperature Compensation: While hot engines can need tweaks to stop banging, cold engines need a richer mixture.
Altitude Compensation: Since there is less oxygen in the air at higher elevations, the AFR must be adjusted.
Fuel Quality Sensing: Engines may adjust the injection method based on the properties of different fuels.
Modern engine management systems are based on fuel injection control techniques, which provide accurate combustion control to fulfill strict pollution regulations and performance goals. Modern fuel injection systems contribute to the intricate orchestration needed to run the wide variety of internal combustion engines that are available today by dynamically altering the air-fuel ratio, injection timing, and reacting to different engine and environmental circumstances. Fuel injection control is an area of constant innovation and optimization because of the advancement of sensors, algorithms, and hardware.
Introduction to Ignition Systems
An essential component of internal combustion engines, ignition systems light the air-fuel combination, starting the combustion process. A well-thought-out ignition system has to provide a spark with sufficient energy and timing to guarantee thorough and effective combustion. The fundamentals of ignition and the many kinds of ignition systems frequently used in automobile engines are covered in this chapter's section.
Basic Principles of Ignition
The compressed air-fuel combination in the engine's cylinder is ignited by a spark, which starts the ignition process and causes quick combustion and energy release. Among the fundamental ideas are:
Spark Creation: A spark is produced by passing a high-voltage electric current between the electrodes of a spark plug. An ignition coil provides the energy for this by converting the low-voltage electrical supply of the car into the necessary high-voltage.
Ignition Timing: The timing of the spark is crucial to the engine's operation. Typically, it happens shortly before the piston hits the Top Dead Center (TDC) during the compression stroke. For the best engine performance, fuel efficiency, and emissions management, timing is essential.
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Energy Transfer: The spark must have sufficient energy to ignite the mixture, but not so much that it gradually erodes the spark plug electrodes or other parts.
Types of Ignition Systems
Diverse ignition system types have been created to accommodate different engine needs and technology developments. Among the primary kinds are:
Distributor Ignition System: In this conventional setup, high voltage is sent to the appropriate spark plug at the appropriate moment using a distributor that is mechanically operated. Timing changes are frequently performed mechanically, or by using vacuum and electrical controllers.
Distributor less Ignition System (DIS): This system uses separate coils for one or more cylinders, eliminating the need for a distributor. To adjust spark timing, it frequently uses a computer-controlled module that collects inputs from sensors.
Coil-on-Plug (COP) Ignition System: With this more recent method, each spark plug has a single ignition coil immediately on top of it, providing more precise control and increased energy efficiency. The COP system eliminates energy loss and improves ignition dependability by shortening the spark's distance of travel.
Wasted Spark System: This system uses two cylinders in pairs to fire two spark plugs concurrently using one coil. One spark is "wasted" in an exhaust stroke cylinder, while the other ignites the mixture in its cylinder. Though less effective than COP, it is easier.
From distributor systems that were mechanically controlled to intricate electronically controlled designs, ignition systems have developed throughout time. The objective is still the same: to ignite the air-fuel mixture with a prompt, powerful spark. Automotive engineers must optimize ignition systems for cost, performance, emissions, and dependability, thus they must have a thorough understanding of the fundamentals and variants of these systems. The drive in automobile design towards more control, efficiency, and environmental responsibility is reflected in the tendency toward more accurate and efficient systems, such as the Coil-on-Plug.
Ignition System Control Strategies
With the development of the engine control unit (ECU), where exact management methods are necessary for maximum engine performance, the current ignition system has become a highly complicated component. Important tactics include knock detection and management, ignition timing control, and spark advance and retard schemes. The importance of these techniques in automobile engineering is discussed in more detail in this section.
Ignition Timing Control
Definition and Importance: The exact instant the spark plug should ignite, in order to ignite the air-fuel combination within the cylinder is referred to as ignition timing. To maximize power, reduce emissions, and maximize fuel efficiency, this timing must be properly controlled.
Static vs. Dynamic Timing
Control Methods
Challenges
Ignition timing management may be difficult to implement when competing needs like performance, efficiency, and emissions need to be balanced.
Spark Advance and Retard Strategies
Spark Advance
Spark Retard
Knock Detection and Control
Engine Knock: A premature and uncontrollably burning combination of air and gasoline that can harm an engine.
Knock Sensors: It uses piezoelectric sensors to identify knock induced vibrations.
Control Strategies:
Importance of Control: Well-executed knock control protects the engine from any harm while optimizing performance and fuel economy.
A crucial component of contemporary engine management is the use of ignition system control techniques. Engineers may maximize pollution control, fuel efficiency, and engine performance by comprehending and putting these techniques into practice. These techniques are essential for the development of automotive technology because of the rising demand for ecologically friendly automobiles. Students who pursue further education in this discipline will be better prepared to innovate and make valuable contributions to the dynamic field of automotive engineering.
Integrating Fuel Injection and Ignition Controls
Modern internal combustion engines must integrate their fuel injection and ignition control systems in order to provide the best possible performance, efficiency, and emissions control. This part explores the intricacies and innovations of this integration, emphasizing coordinated control for peak performance and going over the problems and solutions that come with it.
Coordinated Control for Optimal Performance
Interdependence of Fuel and Ignition: To guarantee ideal combustion, the timing of the ignition spark and fuel injection must be precisely synchronized. Variations in engine speed, load, temperature, and other factors must be handled by both systems.
Control Objectives
The goal of coordinated control is:
Techniques
Benefits
Challenges and Solutions in Integration
Challenges
Solutions
A key component of contemporary engine technology is the integration of fuel injection and ignition controls, which significantly improves engine performance, efficiency, and compliance with environmental standards. Although there are many engineering hurdles associated with this integration, substantial advancements have been made possible by breakthroughs in hardware, algorithms, and standards.
For both professionals and engineering students, comprehending this connection will be crucial as the automobile industry develops further. It highlights how multidisciplinary automotive engineering is and how knowledge in fluid mechanics, thermodynamics, control systems, and other fields is necessary. This subject is a fascinating one for further innovation and study as future improvements may involve more integration with other subsystems like exhaust after-treatment and hybrid powertrain controls.
13. High pressure common rail fuel injection System
The Common Rail Direct Injection (CRDI) system stands as a cornerstone of modern diesel engine technology, revolutionising the efficiency, performance, and emissions characteristics of these powertrains. By precisely controlling the fuel delivery process through a high-pressure common rail, the CRDI system has transformed combustion dynamics, resulting in enhanced power output, reduced fuel consumption, and decreased emissions. This innovative approach has reshaped the landscape of diesel engines, ushering in an era of cleaner, more fuel-efficient, and environmentally conscious transportation.
In this discussion, an attempt shall be made to uncover all the aspects of Common Rail Direct Injection System, its working, functions and advantages.
Common Rail Direct Injection System
The Common Rail Direct Injection (CRDI) system is a cutting-edge technology for diesel engines. It stores fuel at high pressure in a common rail, allowing precise and efficient fuel delivery to each cylinder. CRDI enhances combustion efficiency, reducing emissions, improving fuel economy, and delivering more power, making it a staple in modern diesel engines.
What is Common Rail Direct Injection System?
The term 'CRDi' is commonly associated with diesel engines, while a comparable technology used in petrol engines is known as Gasoline Direct Injection (GDI) or Fuel Stratified Injection (FSI). Both CRDi and GDI/FSI technologies share a similar design, featuring a common "fuel rail" supplying fuel to injectors. However, they substantially differ in terms of fuel pressures and types.?
With common rail fuel injection, the combustion process can be optimized to achieve low pollutant levels combined with lower fuel consumption. Fuel is injected into the combustion chamber from a common rail under high pressure. The electronic control system ensures that the start of injection, the quantity and time are independent of the engine speed.
Fig 1: Common rail Direct injection system
In the case of Common Rail Direct Injection, combustion initiation occurs directly within the primary combustion chamber situated in a cavity on the piston crown. Presently, manufacturers employ CRDi technology to address the limitations of traditional diesel engines, which historically exhibited sluggishness, noise, and subpar performance in passenger vehicles. The CRDi technology collaborates with the engine's Electronic Control Unit (ECU), which receives inputs from various sensors.
Components of Common Rail Direct Injection System
A Common Rail Direct Injection (CRDI) system consists of key components: a high-pressure fuel rail, injectors, a fuel pump, and a pressure regulator. The fuel rail stores and distributes high-pressure fuel to injectors, which precisely spray fuel into the combustion chamber. A high-pressure pump maintains the required fuel pressure, while a regulator controls it for optimal engine performance.
The components of CRDI system are:
High-Pressure Fuel Pump
The high-pressure fuel pump is a key component responsible for supplying pressurised fuel from the fuel tank to the common fuel rail. It ensures that the fuel is delivered at the required pressure to meet the precise injection demands of the engine, contributing to efficient combustion.
Common Fuel Rail
The common fuel rail serves as a distribution system that receives pressurised fuel from the high-pressure pump and delivers it to the individual injectors. It maintains consistent fuel pressure throughout the system, optimising injection accuracy and engine performance.
Injectors
Injectors are crucial components that directly introduce fuel into the combustion chambers. They are precisely controlled by the engine control unit (ECU) to deliver the right amount of fuel at the right time, ensuring efficient combustion, power generation, and emissions control.
Engine Control Unit (ECU)
The engine control unit, often referred to as the ECU or engine control module (ECM), is the brain of the CRDi system. It receives input from various sensors that monitor engine conditions and adjust the fuel injection process accordingly. The ECU optimises fuel delivery for performance, efficiency, and emissions compliance, ensuring the CRDi system's seamless operation.
In a common rail system, arbitrary timing and multiple injections are available for NOx reduction. The high injection pressure enhances the fuel/air mixing and improves combustion leading to lower NOx and PM emissions.
Fig. 2: Fuel flow and injection sequence for multiphase injection mtu divides the fuel injection sequence into as many as three separate phases. The main injection phase delivers the fuel, a preinjection phase reduces the load on the crankshaft drive gear, and a post-injection phase reduces particulate emissions. This enables both fuel consumption and emissions to be reduced.
Injection rate: pre-, main and post injection
The injection rate determines when and how much fuel is injected into the cylinder. In order to reduce emissions and fuel consumption, the present evolution stage of the injection system formtuengines divides the fuel injection sequence into as many as three separate phases (see Figure 2). The timing of the start of injection, the duration and amplitude are userdefined in accordance with engine performance map. The main injection phase supplies the fuel for generating the engine’s power output. A preinjection phase initiates advance combustion to provide controlled combustion of the fuel in the main injection phase. This reduces nitrogen oxide emissions, because the abrupt combustion prevents high peak temperatures. A post injection phase shortly after the main injection phase reduces particulate emissions. It improves the mixing of fuel and air during a late phase of combustion to increase temperatures in the combustion chamber, which promote soot oxidation. Depending on the engine’s operating point, the main injection phase can be supplemented as required by including pre- and/or post injection phases.
Comparison of injector sizes for engines with different cylinder capacities, including injectors for the current mtu Series 1600, 2000, 4000 and 8000 engines. (light grey: non-mtu engines)
Fig. 3: Change in injection pressures since 1996 for Series 4000 engines Since 1996, mtu has steadily increased the injection pressures to further reduce consumption and particulate emissions. Since 2000, mtu has used advanced versions of the common rail system on the Series 4000, amongst others, in which each fuel injector has its own fuel reservoir. The advantage is that even with large injection quantities, the fuel rail remains free of pressure fluctuations and the injection sequences of the individual cylinders do not interfere with each other.
Fig. 4: Injector with integrated fuel reservoir The use of injectors with an integrated fuel reservoir prevents pressure fluctuations in the common rail system and, therefore, a momentary undersupply or oversupply of fuel to the injectors.
Diesel common rail direct injection (CRDI) and its benefits
Common rail is a fuel injection system found in modern diesel engines. Common rail systems provide a level of flexibility which can be exploited for class leading emission control, power and fuel consumption. This enables Original Equipment Manufacturers (OEMs) to design for optimum performance and exceptional end-user value across a range of machines and applications.
An increasing number of modern diesel engines employ common rail direct injection (CRDi) fuel systems for the flexibility they provide while meeting the most stringent emission control standards.
In common rail systems, the fuel is supplied to the engine under pressure with electronically controlled precision. This provides a level of flexibility which can be exploited for class leading levels of emission control, power and fuel consumption.
Perkins applies CRDi technology to its electronic product offerings in the 400, 1100 and 1200 Series.
How does CRDi work?
The fuel in an electronically controlled engine is stored at variable pressure in a cylinder or ‘rail’ connected to the engine’s fuel injectors via individual pipes, making it a ‘common rail’ to all the injectors. The pressure is controlled by a fuel pump but it is the fuel injectors, working in parallel with the fuel pump, that control the timing of the fuel injection and the amount of fuel injected. In contrast earlier mechanical systems rely on the fuel pump for pressure, timing and quantity.
A further advantage of the CRDi system is that it injects the fuel directly into the combustion chamber. The indirect injection (IDI) system in older engines injected fuel into a pre-combustion chamber which then fed the main combustion chamber.
What is the advantage of CRDi?
CRDi ensures the fuel injection timing, quantity of fuel and atomisation or fuel spray are controlled electronically using a programmable control module. This allows multiple injections at any pressure at any time (within pre-defined limits), providing a level of flexibility which can be exploited for better power, fuel consumption and emission control.?
How will you notice the benefits of common rail?
Noise, vibration and harshness (NVH) are improved with CRDi as a result of the timing flexibility. Your engine sounds quieter and has a better quality of sound. It also runs smoother. You will see fuel consumption benefits as well because greater injection pressure produces a finer spray of fuel (atomisation) that burns more efficiently.
Better combustion efficiency is a key part of meeting emission standards. Less fuel is wasted as soot or particulates in the exhaust and deposits in the engine. A cleaner running engine is good for the environment – and for the cost of ownership. Cleaner running improves the long-term durability and reliability of your engine.
Lower emissions due to combination with other key technologies
With combustion optimization by internal engine design features there is a three-way interaction between nitrogen-oxide formation, the production of soot particulates and fuel consumption: the more intensive the combustion and thus the energy conversion, the lower the particulate emissions and consumption and the higher the nitrogen oxide emissions. Conversely, retarded combustion leads to lower nitrogen oxide formation, but also to higher fuel consumption and particulate emission levels. The job of the engine developers is to find a compromise between these extremes for every point on the engine performance map. When doing so, they must harmonize the effect of the fuel injection system with that of other internal engine measures such as exhaust gas recirculation, which primarily reduces nitrogen oxide emissions, and external exhaust aftertreatment systems. As a pioneer in this field, mtu can draw from many years of experience with fuel injection systems produced by Rolls-Royce Power Systems brand L’Orange and other suppliers. In the course of this period, mtuhas acquired comprehensive expertise in the integration of the common rail fuel injection system into the engine. This has enabled the company to fully utilize the potential of the fuel injection system in combination with other key technologies for refining the combustion process. The two key parameters in fuel injection that affect fuel consumption and emissions are injection rate and injection pressure.
“A cleaner running engine is good for the environment – and for the cost of ownership. Cleaner running improves the long-term durability and reliability of your engine.”
HIGH PRESSURE RAIL FOR COMMON RAIL FUEL SYSTEM
The high-pressure rail gives its name to the common-rail system and binds the pump and injectors together as the central hydraulic component. It stores the compressed fuel and supplies this to the injectors. A rail pressure sensor and - independent of the system configuration - an additional pressure control valve or pressure limiting valve are always fitted on the high-pressure rail as rail assembled components. over 60,000 pressure checks per minute to regulate the fuel injection high pressure resistance thanks to high-tech production technologies
reduction of the CO2 emissions through reduction of weight rail assembled components adjusted to the system
High-pressure rail: Robust fuel tank with pressure monitoring
The rail consists of a forged steel tube into which the rail pressure sensor (RPS) and pressure control valve (PCV) are screwed. Independent of the high-pressure pump used, the rail has one or two fuel lines to connect to the high-pressure pump. Corresponding to the number of cylinders, further high-pressure connections for the fuel lines leading to the injector are present. The PCV-controlled fuel is conveyed back to the tank via the low-pressure connection.
Customized variants for every segment
High-pressure rails made by Bosch are available for pressure levels between 1,400 bar and 2,700 bar. They are used for all on-highway applications in cars up to heavy duty vehicles and for all off-highway applications. The rails have a modular construction and can be specifically adapted to the customer's needs or adjusted to the application specifications. The variants tailor-made for each application scenario differentiate themselves with regard to, for example, the rail assembled components, rail length, number of high-pressure connections, installation concept on the motor, and lifetime.
Frequently Asked Question and Answers
What is a high-pressure common rail fuel injection system?
Common rail direct fuel injection is a direct fuel injection system built around a high-pressure (over 2,000 bar or 200 MPa or 29,000 psi) fuel rail feeding solenoid valves, as opposed to a low-pressure fuel pump feeding unit injectors (or pump nozzles).
What does a high-pressure fuel rail do?
The high-pressure rail binds the pump and injectors together as the central hydraulic component. It stores the compressed fuel and supplies this to the injectors. Pressure pulses occur in the high-pressure rail as a result of the injection process. The stored high-pressure volume reduces these to a minimum.
How is fuel rail pressure controlled on a common rail diesel fuel injection system?
In many systems, the rail pressure is controlled by a metering valve at the pump and a pressure regulator on the rail. A sensor measures pressure in the rail and provides the data to the ECU, which compares the actual pressure with a set value, which depends on engine speed and injection quantity.
What is the working principle of common rail fuel injection system?
Working of Common Rail Direct Injection System A high-pressure pump pressurises the fuel. A pressure regulating valve is attached to the high-pressure pump which gets input from ECU. The ECU receives signals from the throttle position sensor, temperature sensor, speed sensor and manifold pressure sensor.
What are the advantages of common rail fuel injection system?
Your engine sounds quieter and has a better quality of sound. It also runs smoother. You will see fuel consumption benefits as well because greater injection pressure produces a finer spray of fuel (atomisation) that burns more efficiently. Better combustion efficiency is a key part of meeting emission standards.
What is high pressure injection system?
The high injection pressure enhances the fuel/air mixing and improves combustion leading to lower NOx and PM emissions. The high-pressure common rail fuel injection system has been applied to marine diesel engines, such as W32CR engine , RT Flex engines , MAN 32/44CR engines and MAN 48/60 CR engines.
What causes high fuel pressure in common rail?
So, then, what causes high fuel pressure? As we discussed, high fuel pressure means that the air to fuel ratio is off-kilter. The causes for this imbalance of fuel pressure typically include either a bad fuel regulator or a clogged return line.
What is the benefit of a high pressure fuel pump?
In simple terms, a high pressure fuel pump is a device that delivers fuel to the engine at a significantly higher pressure than regular fuel pumps. Its purpose is to ensure that the engine receives the right amount of fuel with the necessary pressure for combustion.
What is the purpose of a fuel rail?
A fuel rail, one of the critical components of the fuel injector, is responsible for stably supplying fuel, such as gasoline, to the injector. Used in advanced direct-injection gasoline engines, a fuel rail helps achieve high levels of fuel efficiency and environmental performance.
What is the difference between fuel rail and common rail?
The primary difference between the two systems is how they are controlled. Conventional fuel injection systems are controlled mechanically while a common rail injection system is controlled using an electronic control unit. The electronic control unit regulates how much fuel is injected and the amount of pressure used.
What is the problem with common rail diesel?
Today's common rail systems are extremely susceptible to contamination due to the extreme conditions they operate within. Contaminated or clogged filters and injector deposits cause an uneven or incomplete fuel burn, resulting in a dirty area around the exhaust and the release of white smoke from the exhaust pipe.
What type of injector is common rail?
Common Rail Injector types Solenoid-type injectors control fuel injection by opening and closing the control valve with magnetic force, using a solenoid on the actuator. Piezo-type injectors achieve faster responsiveness than solenoid types by using piezo elements on the actuators.
What are the disadvantages of common rail direct injection system?
Disadvantages of Common Rail Direct Injection System
Advantages of Direct Injection
14. Variable Valve Timing (VVT)
VVT systems adjust the timing and duration of the engine’s intake and exhaust valves, optimizing airflow and combustion for better performance and reduced emissions.
Variable valve timing (VVT) is the process of altering the timing of a VALVE lift event in an INTERNAL COMBUSTION ENGINE, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing many automotive manufacturers to use VVT systems.
Theory
The valves within an internal combustion engine are used to control the flow of the intake and exhaust gases into and out of the combustion chamber timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing is the same for all engine speeds and conditions, therefore compromises are necessary. An engine equipped with a variable valve timing actuation system is freed from this constraint, allowing performance to be improved over the engine operating rang
Piston engines normally use valves which are driven by camshafts. The cams open (lift) the valves for a certain amount of time (duration) during each intake and exhaust cycle. The timing of the valve opening and closing, relative to the position of the crankshaft, is important. The camshaft is driven by the crankshaft through timing belts, gears or chains.
An engine requires large amounts of air when operating at high speeds. However, the intake valves may close before enough air has entered each combustion chamber, reducing performance. On the other hand, if the camshaft keeps the valves open for longer periods of time, as with a racing cam, problems start to occur at the lower engine speeds. Opening the intake valve while the exhaust valve is still open may cause unburnt fuel to exit the engine, leading to lower engine performance and increased emissions. According to engineer David Vizard's book "Building Horsepower", when both intake & exhaust are open simultaneously, the much-higher-pressure exhaust pushes the intake-charge back, out from the cylinder, polluting the intake-manifold with exhaust, in worst cases.
Continuous versus discrete
Early variable valve timing systems used discrete (stepped) adjustment. For example, one timing would be used below 3500 rpm and another used above 3500 rpm.
More advanced "continuous variable valve timing" systems offer continuous (infinite) adjustment of the valve timing. Therefore, the timing can be optimized to suit all engine speeds and conditions.
Cam phasing versus variable duration
The simplest form of VVT is cam-phasing, whereby the phase angle of the camshaft is rotated forwards or backwards relative to the crankshaft. Thus the valves open and close earlier or later; however, the camshaft lift and duration cannot be altered solely with a cam-phasing system.
Achieving variable duration on a VVT system requires a complex system, such as multiple cam profiles or oscillating cams.
Typical effect of timing adjustment
Late intake valve closing (LIVC) The first variation of continuous variable valve timing involves holding the intake valve open slightly longer than a traditional engine. This results in the piston actually pushing air out of the cylinder and back into the intake manifold during the compression stroke. The air which is expelled fills the manifold with higher pressure, and on subsequent intake strokes the air which is taken in is at a higher pressure. Late intake valve closing has been shown to reduce pumping losses by 40% during partial load conditions, and to decrease nitric oxide (NOX) emissions by 24%. Peak engine torque showed only a 1% decline, and hydrocarbon emissions were unchanged.
Early intake valve closing (EIVC) Another way to decrease the pumping losses associated with low engine speed, high vacuum conditions is by closing the intake valve earlier than normal. This involves closing the intake valve midway through the intake stroke. Air/fuel demands are so low at low-load conditions and the work required to fill the cylinder is relatively high, so Early intake valve closing greatly reduces pumping losses. Studies have shown early intake valve closing reduces pumping losses by 40%, and increases fuel economy by 7%. It also reduced nitric oxide emissions by 24% at partial load conditions. A possible downside to early intake valve closing is that it significantly lowers the temperature of the combustion chamber, which can increase hydrocarbon emissions.
Early intake valve opening Early intake valve opening is another variation that has significant potential to reduce emissions. In a traditional engine, a process called valve overlap is used to aid in controlling the cylinder temperature. By opening the intake valve early, some of the inert/combusted exhaust gas will back flow out of the cylinder via the intake valve, where it cools momentarily in the intake manifold. This inert gas then fills the cylinder in the subsequent intake stroke, which aids in controlling the temperature of the cylinder and nitric oxide emissions. It also improves volumetric efficiency, because there is less exhaust gas to be expelled on the exhaust stroke.
Early/late exhaust valve closing Early and late exhaust valve closing timing can be manipulated to reduce emissions. Traditionally, the exhaust valve opens, and exhaust gas is pushed out of the cylinder and into the exhaust manifold by the piston as it travels upward. By manipulating the timing of the exhaust valve, engineers can control how much exhaust gas is left in the cylinder. By holding the exhaust valve open slightly longer, the cylinder is emptied more and ready to be filled with a bigger air/fuel charge on the intake stroke. By closing the valve slightly early, more exhaust gas remains in the cylinder which increases fuel efficiency. This allows for more efficient operation under all conditions
Challenges
The main factor preventing this technology from wide use in production automobiles is the ability to produce a cost-effective means of controlling the valve timing under the conditions internal to an engine.n engine operating at 3000 revolutions per minute will rotate the camshaft 25 times per second, so the valve timing events have to occur at precise times to offer performance benefits. Electromagnetic and pneumatic camless valve actuators offer the greatest control of precise valve timing,
15. Combustion Chamber Design
Improved?mixture?formation?may?be?achieved?through?the?design?(shape)?of the combustion chamber and the location of the fuel injector, leading to reductions in both NOx and PM emission. However, problems in the areas of structural durability and emission control durability have been attributed to these configurations, especially in larger engines. Compression ratio is another engine design parameter that impacts emission control. In general, lower?compression ratios cause a?reduction?in NOx?emissions?and?decreased?fuel?economy,?but?also?cause?an?increase?in PM emissions. Also, low?compression ratios can lead to difficulty?in starting a cold engine. However, lower compression ratio does play a part in lowering the loads imposed on the components of the engine and, as a result, may increase the durability of the units.
Combustion chamber modifications have the potential to reduce unwanted fuel spread and fuel impingement on walls, which further lowers the carbon monoxides (CO), hydrocarbons (HC) and soot emissions
Bathtub or Heart-shapedThe bathtub designation is generally reserved for any chamber that's not a wedge or hemispherical. Most domestic engines of pushrod design have used it in varying forms. In some instances the shape of the combustion chamber was almost oval, with the latest trends being the efficient heart shape.
16. Charge Air System
A significant portion of PM emissions is produced during engine accelerations.?The?acceleration?effect ,known?as?“turbo?lag”,?is?especially critical on turbocharged engines. PM emissions can be reduced by supplying additional combustion air during engine acceleration. Such increased?flexibility?can?be?provided?by?variable geometry?turbochargers (VGT), which can be programmed to deliver variable quantities of air depending on operating conditions. Another option is to use electrically driven superchargers to supply additional intake air during engine acceleration from low engine speeds .
In modern engines, it is also important to ensure the temperature of the charge does not become excessive. In modern boosted engines, this is a real possibility. Excessive temperatures can lead to reduced charge density and higher combustion temperatures which can affect torque, power and emissions.
While turbochargers and superchargers increase charge air density, they also increase the temperature of the air in the intake manifold. This arrangement with intake air compression with no subsequent cooling was suitable for applications such as North American heavy-duty diesel engines until the 1990s. As emission standards became increasingly stringent, additional increases in charge air density were needed. While this could be achieved through compression to higher pressures, this would require more expensive compression equipment and would further increase cycle temperatures. On the other hand, if intake manifold temperature could be reduced, the intake density could be further increased and more air could be supplied to the engine without necessarily increasing the intake manifold pressure. While this would require a compressor capable of higher flow, the cost would be considerably less than a compressor that was also capable of higher pressures. Cooling the air with a heat exchanger as it leaves the compressor is a common way to achieve this charge air cooling. Such a heat exchanger is referred to as a charge air cooler (CAC), intercooler or aftercooler (Figure 1). These terms are commonly used interchangeably. The term intercooler refers to the fact that this heat exchanger performs its task in between two stages of compression, i.e., between compression in the compressor and compression in the cylinder of the engine. The term aftercooler refers to the charge air being cooled after being compressed in the compressor. Increasing demand for improvements in fuel economy and exhaust emissions has made the charge air cooler an important component of most modern turbocharged engines.
17. Diesel Fuels
Changes?in?diesel?fuel?properties?can?impact?diesel?exhaust?emissions.?For instance, decreasing the aromatic content of diesel fuel, which is closely correlated with increased cetane rating, seems to have a potential for decreasing both PM and NOx emissions. Increasing the kinematic viscosity?of?diesel?fuel?has?been?also?correlated?with?reduced?PM?emissions However, it must be kept in mind that the magnitude of emission reduction due to fuel properties is small to moderate, at best, when compared with the emission reductions achieved by aftertreatment and/or certain advanced engine design methods. In other words, diesel fuel can be considered only a secondary emission driver in modern engines, after exhaust aftertreatment and engine design.
Many of the aftertreatment technologies that have been mentioned, including?NOx?adsorbers?and?certain?types?of?catalytic?diesel?particulate filters, are sensitive to sulfur. Therefore fuels of reduced sulfur content became the technology enabler for advanced diesel emission control systems. Compatibility with catalytic emission controls is by far the most important reason for the worldwide introduction of ultra low sulfur diesel fuels; decreases in sulfur oxide and sulfate particulate emissions are only?of?marginal?importance?(however,?SO2 control?may?be?still?very?important?in fuels of very high sulfur content, such as marine fuels with sulfur levels as high as 2-5%).
Another direction in fuel development are alternative fuels. For instance, PM?emissions?can?be?reduced?using?biodiesel?or,?to?even?larger?degree,?by converting to natural gas power. Several emission –driven niche markets were created for such fuels in the 1990’s. However, since similar emission levels can be achieved today using advanced, emission controlled diesel engines, the choice of the fuel-engine technology remains a simple question of economy. The real significance of alternative fuels is shifting away from emissions of exhaust pollutants towards greenhouse gas emissions and energy security issues in the wake of depletion of world’s petroleum and natural gas reserves.
LOW SULFUR DIESEL FUEL KEY TO LOWER VEHICLE EMISSIONS
Diesel vehicles are the engines of choice for heavy-duty applications. They provide important fuel economy and durability advantages for large heavy-duty trucks, buses, and non-road equipment used in, for example, construction and agriculture. Recent technological innovations have greatly improved the performance of diesel engines. This, along with their higher fuel economy compared to petrol vehicles, is making their use in passenger vehicles increasingly popular. Diesel exhaust emissions are a complex mixture of gases, liquid aerosols, and particles. The emissions of concern for diesel vehicles are particulate matter (PM) and NOx, while emissions of HC and CO are low. PM comprises three basic fractions: ? solids (elemental carbon particles); ? soluble organics (heavy hydrocarbons which attach to the carbon particles);and ? sulphates, produced from oxidation of the sulphur burned. The relative proportions of carbon, organics, and sulphates depend on both vehicle technology and fuel sulphur content. PM emissions from diesel vehicles are an order of magnitude higher than PM emissions from properly functioning petrol vehicles. Vehicles without any controls will benefit from lower sulphur fuel by directly reducing SO2 and particulate emissions. Vehicles with diesel after-treatment emission control technologies treat engine exhaust to remove pollutants. As part of the exhaust system, the control devices convert or capture pollutants before they leave the tailpipe. All these technologies are sensitive to fuel sulphur to some degree. New Diesel Vehicles Europe, the United States, Canada,and Japan are currently in the process of implementing, or are about to implement very stringent vehicle emission standards. In each case, these countries have also acted to reduce fuel sulphur to ensure that the required emission control technologies operate appropriately and with the greatest efficiency. These latest emission standards will require sulphur to be reduced to ultra low levels (e.g.15 ppm and below). Engine Developments Over the last 15 years, engine manufacturers have introduced a variety of engine modifications to reduce emissions, improve performance and increase efficiency. These modifications include direct injection, high-pressure injection, computer controls, multiple injections, exhaust gas recirculation (EGR),and aftercooling. .In the US these modifications have led to significant reductions in overall emissions, including PM and NOx, when compared to uncontrolled diesel engines. Although most of these technologies by themselves do not require specific fuel sulphur levels, most if not all, will be more durable with lower sulphur fuel, which reduces fuel injector corrosion, piston ring corrosion, oil acidification, and overall engine wear. Exhaust Gas Recirculation (EGR) is a modified engine design where exhaust gas is recycled back to the engine inlet system, which reduces combustion temperature and hence NOx formation. This technique is widely used on many modern engines, but cannot be retrofitted. The EGR control valve can become corroded with high sulphur levels; hence sulphur levels should be restricted to maximum 500 ppm. High pressure injection systems are used to improve the efficiency of the burning of the diesel/ air mixture in the cylinders ,and thus increase fuel efficiency and reduce emissions. One such system that is now introduced, especially in Europe is the so-called commonrail diesel engine. As this systems works with very high pressure (up to 1,800 bar) it puts high demands on the diesel fuel quality, which should not contain any contamination (e.g. water and particulate matter).With the global move to near zero sulphur fuels such new technology is increasingly only tested– and approved– by international manufacturers for high quality low sulfur fuel markets.
LOW SULFUR DIESEL FUEL KEY TO LOWER VEHICLE EMISSIONS
Diesel vehicles are the engines of choice for heavy-duty applications. They provide important fuel economy and durability advantages for large heavy-duty trucks, buses, and non-road equipment used in, for example, construction and agriculture. Recent technological innovations have greatly improved the performance of diesel engines. This, along with their higher fuel economy compared to petrol vehicles, is making their use in passenger vehicles increasingly popular. Diesel exhaust emissions are a complex mixture of gases, liquid aerosols, and particles. The emissions of concern for diesel vehicles are particulate matter (PM) and NOx, while emissions of HC and CO are low. PM comprises three basic fractions: ? solids (elemental carbon particles); ? soluble organics (heavy hydrocarbons which attach to the carbon particles);and ? sulphates, produced from oxidation of the sulphur burned. The relative proportions of carbon, organics, and sulphates depend on both vehicle technology and fuel sulphur content. PM emissions from diesel vehicles are an order of magnitude higher than PM emissions from properly functioning petrol vehicles. Vehicles without any controls will benefit from lower sulphur fuel by directly reducing SO2 and particulate emissions. Vehicles with diesel after-treatment emission control technologies treat engine exhaust to remove pollutants. As part of the exhaust system, the control devices convert or capture pollutants before they leave the tailpipe. All these technologies are sensitive to fuel sulphur to some degree. New Diesel Vehicles Europe, the United States, Canada, and Japan are currently in the process of implementing, or are about to implement very stringent vehicle emission standards. In each case, these countries have also acted to reduce fuel sulphur to ensure that the required emission control technologies operate appropriately and with the greatest efficiency. These latest emission standards will require sulphur to be reduced to ultra low levels (e.g.15 ppm and below). Engine Developments Over the last 15 years, engine manufacturers have introduced a variety of engine modifications to reduce emissions, improve performance and increase efficiency. These modifications include direct injection, high-pressure injection, computer controls, multiple injections, exhaust gas recirculation (EGR),and aftercooling. .In the US these modifications have led to significant reductions in overall emissions, including PM and NOx, when compared to uncontrolled diesel engines. Although most of these technologies by themselves do not require specific fuel sulphur levels, most if not all, will be more durable with lower sulphur fuel, which reduces fuel injector corrosion, piston ring corrosion, oil acidification, and overall engine wear. Exhaust Gas Recirculation (EGR) is a modified engine design where exhaust gas is recycled back to the engine inlet system, which reduces combustion temperature and hence NOx formation. This technique is widely used on many modern engines, but cannot be retrofitted. The EGR control valve can become corroded with high sulphur levels; hence sulphur levels should be restricted to maximum 500 ppm. High pressure injection systems are used to improve the efficiency of the burning of the diesel/ air mixture in the cylinders ,and thus increase fuel efficiency and reduce emissions. One such system that is now introduced, especially in Europe is the so-called commonrail diesel engine. As this systems works with very high pressure (up to 1,800 bar) it puts high demands on the diesel fuel quality, which should not contain any contamination (e.g. water and particulate matter).With the global move to near zero sulphur fuels such new technology is increasingly only tested– and approved– by international manufacturers for high quality low sulfur fuel markets.
18. Lubricating Oils
Reductions in PM emissions can be obtained by changes in the composition of lubricating oil and by reducing the amount of lubricating oil consumed. Refiners are conducting research to formulate such lubricating oils that form less PM. One possibility is to replace the metal additives commonly used in lubricating oil with nonmetallic compounds in order to reduce the?noncombustible (ash) portion?of the?oil. This approach?may?also increase the?durability?of catalytic aftertreatment devices, as?many?metal?oil additives, such as phosphorus, are known catalyst poisons. Low ash oils can also extend the service intervals for ash cleaning in diesel particulate filters.?Lube?oil?derived?HCs?have?been?identified?as?the?major?contributor?to the particulate’s SOF material. The SOF formation may be reduced by using specially formulated oils, e.g., synthetic or partial synthetic oils.
Conventional?formulations?of?lubricating?oil?evaporate?over?a wide?range?of temperatures. The portion that evaporates at lower temperatures may evaporate in the crankcase and diffuse into the combustion chamber, increasing PM emissions. Synthetic oils can be formulated to evaporate over?a?narrow,?high?-temperature range.?Using?such?a?synthetic?lubricating oil would reduce the contribution of oil evaporation to PM emissions.
19. Intake Boosting
Emission Impact : Primary emissions impact is to lower soot (PM) production. Also important for efficiency gains.
Higher intake pressure increases air/fuel ratio for given fuel injection amount and lowers soot production. Can be an important measure to offset unwanted decreases in performance and increased emissions with NOx control measures such as EGR. Often accompanied by improved intake charge cooling capabilities. Enables engine downsizing for efficiency gains. Introduces challenges such as turbocharger lag that can require complex solutions. Enhancing Turbochargers. Turbochargers add pressurized engine exhaust to the combustion chamber. This allows more fuel to be injected for an increase in engine power. It also reduces engine emissions.
Since it's the oxygen in the air that combines with fuel to make the engine run and produce power — and that air-fuel balance is kept at a relatively stable ratio — the more air you can get into the engine, the more power you can get out.
Intake boosting is an important feature of modern engines, directly benefiting the specific power output and indirectly responsible for improvements in efficiency. It is also essential to compensate for the loss of power brought about by combustion systems that are designed to limit engine emissions. Intake boosting is done by superchargers and turbochargers. By far, the most common method of boosting is by turbocharging, which is the main focus of this chapter, but supercharging and charge air cooling also feature. The principal components of the turbocharger are the compressor and turbine, and their performance parameters and maps are described. The operational characteristics of a turbocharged engine are largely determined by the match between the engine and the turbocharger. The performance characteristics of each component and the ways in which they interact in automotive engines are discussed in detail. From this, the need for boost control devices such as wastegates and variable geometry turbines becomes apparent. Other intake boosting systems, including series turbochargers, turbo compounding, electric assist, and pressure wave superchargers, are also described.
20. Intake temperature management
Emission effect Most direct impact on NOx emissions. Can lower soot emissions as well.
Increased boosting and/or EGR can increase intake manifold temperature. Intake charge cooling capability improvements are required to limit intake charge temperature and minimize associated NOx emission increases, reductions in air-fuel ratio and losses in power density.
Managing the temperature of the cylinder contents at the time of fuel injection in diesel engines is critical to ensure proper engine operation. Steps to limit this temperature can be taken in the intake system as well as in-cylinder. There are two aspects of intake charge temperature management:
If charge temperatures are too high, the intake charge density will be lower and combustion temperatures can become too high. This can limit engine output and lead to increased exhaust emissions. If temperatures are too low, starting the engine at low temperatures can be problematic and/or emissions during engine warm-up can become excessive. Various pieces of engine hardware are commonly used to achieve proper charge temperature. In boosted engines, charge air coolers are used to keep charge temperatures from becoming too high, these can transfer heat from the charge air to the engine coolant, the ambient air or a separate lower temperature liquid. Ensuring sufficient charge air temperature for cold starting and to maintain it during warm-up can be achieved with glow plugs, electric grid heaters or flame-type aids.
21.. Hybridization
Emission Impact Primarily to reduce fuel consumption
Hybridization with battery electric drive can enable the engine to operate longer in regions of higher thermal efficiency and less at low efficiency points such as idle and low load. Electric motor boost enables the use of efficiency technologies that might otherwise not be practical because of detrimental performance impacts.
22. Diagnostics
Emission Impact OBD ensures long term emissions compliance.
Intended to detect malfunctions that would cause emissions over the certification test to increase beyond a defined threshold.
23. Controls
Emission Impact Electronic controls ensure accurate control of numerous emissions and powertrain control components can be maintained over the life of the vehicle. Variations in ambient conditions, system integration and system aging effects can be accommodated.
Diesel engine controls include: EGR control, intake boost pressure control, fuel injection timing control and combustion control. Aftertreatment system controls include: urea dosing, temperature management to ensure high emission reduction efficiency, regeneration control to ensure accumulated materials such as soot, sulfur and urea deposits are regularly removed. ntegrated system controls: Some control functions require a strongly integrated approach to ensure the engine and aftertreatment system work together. Examples include the NOx adsorber catalyst that require the engine’s air/fuel ratio to be enriched regularly to remove accumulated NOx; adjustment of engine parameters such as fuel injection timing to raise exhaust temperature for keeping the aftertreatment system efficiency high; and DPF regeneration which may require the engine operation to be strictly controlled to avoid damaging the DPF.
S.I. ENGINES
SI engine controls include: Air/fuel ratio control, spark timing control, idle speed control.
Aftertreatment system controls include: thermal management to ensure rapid warm-up and high emission reduction efficiency; and air/fuel ratio control to ensure maximum conversion of the TWC. Integrated system controls: The need to accurately control the air/fuel ratio is driven by the very narrow air/fuel ratio window where high conversion of NOx, HC and CO is possible in a TWC.
24. Water Emulsions : Water in diesel emulsions: Improved efficiency with reduced emissions
Water-fuel emulsions?are?one?of?the?few?methods?that?can?simultaneously control PM and NOx emissions. Depending on the engine, emulsions containing 20% water can reduce PM emissions by as much as 50%. It should be noted that other methods of water addition, such as direct injection, are not effective in controlling PM.
Diesel internal combustion engines are widely used in powering automobiles, mechanical engines, and power generators. However, there are issues that diesel engines are a major source of air pollution that can be damaging to human health. One method of reducing these harmful emissions is the introduction of water into the fuel by using a water in oil emulsion. This has the advantage of reducing the emissions of particulates, CO2 and NOx whilst increasing the efficiency of combustion resulting in improved economy.
The introduction of water in the form of a water in oil emulsion, where the oil is the external phase, produces a fuel with similar properties to the base oil. Typical emulsions contain up to 20% water however, higher levels of water can be used but this can have adverse effects on power output without modification to the fuel injection systems. The emulsion technology can be used with both traditional fossil fuels and biobased fuel or mixtures.
The introduction of water beneficially effects the combustion process by burst evaporation. As the temperature of the fuel droplet containing the water increases during the compression stage, the water rapidly evaporates inside the fuel droplet. This rapid evaporation breaks down the fuel into a smaller droplet size which increases the combustion efficiency and significantly reduces the mass of particulate matter with a resulting reduction in visible emissions and smoke. The loss of energy during the evaporation of the water decreases the combustion temperature slowing down the reaction between oxygen and nitrogen, providing an overall reduction in NOx formation.
Lankem have developed an emulsifier that can produce a stable water in oil emulsions in a range of diesel and biobased fuel. Lansurf LKD1484 was independently tested at Manchester University using a light duty diesel engine. These tests showed that at higher engine loads significant benefits were observed, with the particle mass having reductions of >50%, with an overall reduction in particle size, lower emissions of NOx were also observed with >40% reduction. Benefits were also seen in fuel consumption with an overall reduction being observed.
Key Findings
Compared to standard diesel, the Lankem fuel emits:
? Less NOx and CO2 at the higher engine load
? Comparable NOx and more CO2 at the lower engine load
? Less NO at higher engine load and more NO2 at lower engine load
? Substantially less particulate matter mass at all tested engine load conditions
? Substantially more particulate number at all tested engine conditions
? Substantially more small particles with a modal size of 10nm
Importantly, these findings appear to be generally true when normalising the data for engine
power or for CO2 emissions as a proxy for fuel consumption.
25. Electrostatic Precipitators
Development work continues in electrostatic PM control methods . In electrostatic?devices, charged?particles?migrate?in?electrical?field?towards?an electrode, where they become trapped.
26. Plasma Devices
Non-thermal?plasma?devices?were?proposed,?where?trapped?particulates are oxidized utilizing plasma generated nitrogen dioxide.
Non-thermal plasma (NTP) discharges in exhaust gas have been studied as a potential method to reduce NOx and PM emissions in diesel exhaust as well as NOx and cold start hydrocarbons in lean gasoline exhaust. Vehicle exhaust gases, both diesel and gasoline, undergo chemical changes when exposed to plasma. Logically, oxidation processes dominate in the presence of oxygen. These reactions include oxidation of hydrocarbons, carbon monoxide, and, to a degree, diesel particulate matter. Nitric oxide (NO) can be oxidized by plasma to NO2. The oxidation properties of plasma have been utilized in the treatment of flue gases from power plants . In the power plant flue gas treatment the purpose of the plasma is to oxidize NO to NO2 and subsequently to nitric acid. The desired products, in the form of ammonium salts, are then obtained by reacting the formed acid with ammonia. Industrial plasma systems have also been demonstrated for VOC removal.
Obviously, this method of NOx removal is not applicable for trucks or cars. The objective in the plasma treatment of exhaust gases from internal combustion engines is the reduction, as opposed to oxidation, of NOx. Contrary to some earlier literature reports, there is now a wide consensus that plasma alone, due to its oxidizing character, is not a viable NOx control method. However, combinations of plasma with catalysts, referred to as “plasma-assisted catalysts” or simply “plasma catalysts”, have been suggested for NOx reduction. The plasma is believed to show potential to improve catalyst selectivity and removal efficiency. Current “state-of-the art” plasma catalysts have efficiencies comparable to those of active DeNOx systems, removing about 50% of NOx at a fuel economy penalty of less than 5% [Hoard 2000]. While such performance would not be sufficient to reduce NOx in heavy-duty engines from the US2004 level of about 2 g/bhp-hr to the 2010 level of 0.20 g/bhp-hr, it could be sufficient to reach NOx levels of about 1 g/bhp-hr, as will be needed during the 2007-2009 phase-in period of the NOx standard.
In the case of diesel exhaust a removal of particulate matter emissions would be also a valuable benefit of plasma systems. Plasma systems have been shown to be capable of reducing of diesel particulate matter by low temperature oxidation. It is not currently clear whether the NOx and PM control functions by plasma can be combined in one device, i.e., if NTP reactors can be designed for the simultaneous control of NOx and PM.
An increasing number of research reports are published in the literature increasing our understanding of plasma chemistry in the engine exhaust gases. However, this technology has still a novel character and published results need to be evaluated with caution. Since many studies are conducted in small scale laboratory experiment, as opposed to a full-flow engine experiment, erratic interpretation of data is frequently suspected. It is very easy to overlook a formation of unidentified chemical compounds in the plasma or to confuse adsorption and storage of material in the test equipment with its steady-state removal. For vehicle plasma applications, it is very important to make a distinction between NO removal by chemical oxidation and NO removal by chemical reduction. The desired overall process is chemical reduction to benign products, such as nitrogen and oxygen. In the plasma processing literature many authors use the term “NO reduction” even when the NO removal is accomplished by oxidation to NO2 and nitric acid. It is not sufficient for a plasma experimental work to record a decrease of the NO or NOx concentration. Possible reaction products may include many other nitrogen species which may be not acceptable. Several of these by-products may be also difficult to detect in the laboratory setup. Besides nitrous and nitric acids these products may include nitrates, nitrites or organonitrites which can be deposited on reactor walls, on particulates, or on the pellets material if a packed bed reactor is used. Even if chemical reduction of NO dominates, the products may include nitrous oxide N2O which, although not a regulated emission, is not an acceptable product. Commercialization of non-thermal plasma technology for emission control from mobile sources requires significant advancements and much more development work. The plasma may or may not become a viable choice for lean NOx or PM removal systems.
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