Automobile Diesel engines - Optimization

tuning automotive diesel engines on the engine test bench is an essential phase in optimizing the various trade-offs between performance, emissions, cold start, reliability and noise.

The characteristic feature of combustion in diesel engines is that it takes place :

• in a very heterogeneous environment, the air-fuel mixture in the chamber being very rich in the vicinity of the fuel jet, resulting in the formation of soot particles;

• with excess air, resulting in the presence of oxygen in the exhaust gases, making post-treatment of the nitrogen oxides in the exhaust very difficult.

Controlling nitrogen oxide and particulate emissions therefore remains at the heart of the Diesel engine optimization issue. In direct injection, reducing particulate emissions requires small-diameter injector holes, which is contradictory to the quest for performance; reducing nitrogen oxide emissions is achieved by recirculating part of the exhaust gases to the intake, which results in higher particulate emissions. The importance of compromises is thus constantly apparent during the development process.