What are the latest advancements in diesel engine combustion technology?

1 Low-temperature combustion

One of the main goals of diesel engine combustion research is to achieve low-temperature combustion (LTC), which is a mode of operation that reduces the formation of nitrogen oxides (NOx) and particulate matter (PM), two of the most regulated emissions from diesel engines. LTC relies on high levels of exhaust gas recirculation (EGR), advanced injection timing, and multiple injections to create a more homogeneous and lean air-fuel mixture that burns at lower temperatures and pressures. LTC can also improve fuel efficiency and noise reduction, but it poses challenges in terms of engine stability, control, and compatibility with conventional diesel fuels.

2 Reactivity controlled compression ignition

One of the promising approaches to achieve LTC is reactivity controlled compression ignition (RCCI), which is a dual-fuel strategy that uses a low-reactivity fuel (such as gasoline or natural gas) and a high-reactivity fuel (such as diesel or biodiesel) to create a stratified charge with varying reactivity. By adjusting the ratio and timing of the two fuels, RCCI can optimize the combustion phasing and duration, resulting in lower NOx and PM emissions, higher efficiency, and lower peak pressure and temperature. RCCI requires sophisticated fuel injection and mixing systems, as well as advanced sensors and controllers, to ensure optimal performance and operability.

3 Gasoline compression ignition

Another way to achieve LTC is gasoline compression ignition (GCI), which is a single-fuel strategy that uses gasoline or a gasoline-like fuel to ignite under compression, similar to diesel engines. GCI can reduce NOx and PM emissions by using a low-octane fuel that has a higher resistance to auto-ignition and a lower sooting tendency than diesel. GCI can also improve fuel efficiency by using a higher compression ratio and a lower boost pressure than diesel engines. However, GCI faces challenges in terms of ignition control, knock prevention, and fuel availability and quality.

4 Diesel water emulsion

A simple but effective method to improve diesel engine combustion and emissions is to use diesel water emulsion (DWE), which is a mixture of diesel and water that forms a stable suspension with the help of surfactants. DWE can reduce NOx and PM emissions by lowering the combustion temperature and oxygen concentration, as well as by suppressing the formation of soot and NOx precursors. DWE can also improve fuel economy by enhancing the evaporation and atomization of the fuel, as well as by reducing the heat losses and friction losses in the engine. DWE can be used in existing diesel engines with minor modifications, but it requires careful preparation and storage to prevent phase separation and corrosion.

5 Diesel oxidation catalyst

A widely used aftertreatment technology to reduce diesel engine emissions is the diesel oxidation catalyst (DOC), which is a device that uses a metal-based catalyst (such as platinum or palladium) to oxidize the unburned hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas into water and carbon dioxide. DOC can also oxidize some of the NOx into nitrogen dioxide (NO2), which can enhance the performance of other downstream devices, such as the diesel particulate filter (DPF) and the selective catalytic reduction (SCR) system. DOC can improve the fuel efficiency and the durability of the engine by reducing the backpressure and the soot deposition in the exhaust system.

6 Selective catalytic reduction

Another widely used aftertreatment technology to reduce diesel engine emissions is the selective catalytic reduction (SCR), which is a device that uses a urea-based reductant (also known as diesel exhaust fluid or DEF) and a metal-based catalyst (such as vanadium or copper) to convert the NOx in the exhaust gas into nitrogen and water. SCR can achieve high NOx reduction rates (up to 90%) under various operating conditions, as well as reduce the fuel consumption and the CO2 emissions of the engine. SCR requires a reliable and accurate dosing and injection system for the reductant, as well as a proper thermal management and control strategy for the catalyst.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?