1992-02-01

Exhaust-Gas Recirculation - A Measure to Reduce Exhaust Emissions of DI Diesel Engines 920725

It can be expected that the high speed DIdiesel enginewill play a major role as a drive system for passenger cars and light duty vehicles. The reason is its fuel consumption which is the lowest of all combustion engines. Of course, low exhaust emission levels expecially particulates (PM) and nitric oxides NOx are a requirement in this context. Exhaust gas recirculation (EGR) can contribute decisively to achieve acceptable emission levels with high speed DI diesel engines.
On the basis of fundamental investigations into the influence of EGR on the combustion process of DI diesel engines, it will be shown how the exhaust gas should be recirculated to obtain effective emission reductions.
In particular, it was found that so called “Hot EGR” which keeps the temperature of the recirculated exhaust gases at a very high level, not only helps to reduce NOx but also contributes distinctly to achieve lower hydrocarbon (HC) and PM emissions. In addition, there is no adverse affect of EGR on the fuel economy. Very positive effects of EGR can be achieved especially at low loads and up to medium loads.
EGR can be combined advantageously with other emission reducing measures such as flexible injection timing control or application of catalytic converters. Most promising results were obtained with a closed loop control of the EGR rate which allows a precise adjustment in the amount of recirculated exhaust gases at various engine operating points.

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