Gasoline Direct Injection (GDI)

In internal combustion engines, Gasoline Direct Injection (GDI), also known as Petrol Direct Injection or Direct Petrol Injection or Spark Ignited Direct Injection (SIDI) or Fuel Stratified Injection (FSI), is a variant of fuel injection employed in modern two-stroke and four-stroke gasoline engines. The gasoline is highly pressurized, and injected via a common rail fuel line directly into the combustion chamber of each cylinder, as opposed to conventional multi-point fuel injection that happens in the intake tract, or cylinder port.

Theory of GDI technology:–

THE major advantage of this?GDI technology engine?is that it increased fuel efficiency and high power output.

Therefore, including emissions levels can also be controlled more accurately with the?GDI technology, GDI system majorly operates on the two different modes

Firstly, fully lean equivalence ratio composition during low load and low-speed operation.

Secondly,?homogeneous stoichiometric mode on higher with higher speed. at medium load area charge will be lean or stoichiometric.

The engine management system?majorly decides from these three combustion modes written below:-

1. Lean burn
2. Stoichiometric
3. Full power output mode

Each and every mode is classified by air-fuel ration. The stoichiometric air-fuel ratio for gasoline is 14.7:1 by mass (weight).

But in this ultra-lean mode the ratio can be high as 65:1( only for limited periods ) this mixture is much leaner than a conventional engine which reduces the fuel consumption

Ultra lean mode:-

This mode is used for light load running, Although the condition where high acceleration is not required.

Where the combustion chamber is designed in toroidal or an oval the shape also is known as the cavity which produces swirl in the combustion chamber for the complete mixing of air and fuel ( the design can vary from one producer to another )

In this type of system, the fuel is not injected in the suction stroke but Injected in the latter stages of the compression stroke.

Stoichiometric model:-

This is the medium load condition experienced by the engine during this period the fuel is injected during the suction stroke in the homogeneous?air-fuel mixture?formation.

Because of this stoichiometric air-fuel mixture, the overall burning of fuel results in the form of clean exhaust which gets further cleaned by a?catalytic converter

Full power mode:-

The full power mode is all about rapidly

accelerating the vehicle, climbing the hill areas or while

experiencing offroading. during this mode the?air-fuel

mixture?Is slightly richer than the stoichiometric feed

similarly, the air-fuel mixture is feed during the suction

stroke as the?stoichiometric mode.

Now if talking about the changes made in GDI engines from PFI engines, there are numerous changes. But basic changes lie in Injector, Fuel Pump, Common Rail, Electronic System ETC.

GDI Fuel Injectors:–?As discussed earlier the fuel is injected directly into the combustion chamber in GDI. Also, the injection pressure is high as compared to the PFI engine (20MPa in GDI).

So, To bear this high pressure the Injector design in GDI engines is different from that used in PFI engines. Also in GDI engine, the injectors are placed directly into the combustion Chambers which mean the injectors have to face high temperature of combustion which PFI injector is safe from.

GDI Fuel Pump:–?The fuel pump used in the PFI system is of low pressure. Whereas the one used in GDI Engine is of a high-pressure type. Which pumps fuel at high pressure and makes it possible to be injected directly into the combustion chamber.

Common Rail:?Because of high strength materials of the common rail. It is used in GDI System, which is able to bear the high pressures generated by the GDI Fuel pump.

Engine Management System (EMS):?The EMS in GDI is more complex and advanced. As Computer needs to do more computations for air, fuel quantity ETC.

Catalytic Converter:–?The Catalytic Converter used in GDI System is different from the one used in the PFI system due to the emissions of Nitrox in Stratified Mode. In other words, we can say that it reduces the amount of Emissions Norms.

Exhaust Gas Recirculation (EGR):–?The technique used to reduce Nitrox Emissions are know as EGR and It involves the recirculation of exhaust gases back into the combustion chamber. That is around 25% of Total exhaust gases.

EMISSIONS BY GDI ENGINE:-

Gasoline direct injection engine produces carbon dioxide particles which are 10 times more than that of normal diesel engine. High emissions were caused Because of the uneven mixing of the air/fuel mixture.

Nowadays, Various technologies used in automotive to control the rate of Pollution,?most importantly?are as follow:-

• Mixing urea to exhaust gases.
• Adding oxygen to exhaust.
• Catalytic convertor.

Advantages of GDI technology:-

• Increased fuel efficiency and performance.
• High power output.
• Fast acceleration and deceleration (due to shortage of travel path ).
• No need of choke In the winter season.
• The engine starts in single cranking.

Disadvantages of GDI technology:-

• Higher manufacturing cost for the engine.
• Non-uniform distribution of?air-fuel mixture in a multi-cylinder engine, therefore, reduced the loss of thermal energy.
• Loss of volumetric efficiency due to the restrictions of airflow mixture, as a result, increasing the chances of misfiring.