Influence of EGR unequal distribution from cylinder to cylinder on NOx–PM trade-off of a HSDI automotive Diesel engine

The influence of cylinder-to-cylinder variation in EGR distribution on the NOx–PM trade-off (while varying EGR rate) is studied on an automotive high-speed direct injection Diesel engine. Experiments have been conducted on an engine test bench with and without air-EGR mixer and demonstrate that variations in cylinder-to-cylinder EGR distribution results in a deteriorated NOx–PM trade-off (increased NOx emissions level at a given PM emissions level, or increased PM emissions level at a given NOx emissions level) compared to the well mixed configuration with equal EGR rate for all the cylinders. A qualitative study as well an original experiment is conducted to explain this emissions increase induced by unequal distribution of EGR. When recirculating hot exhaust gases, the emissions increase is due to cylinder-to-cylinder variations in intake gas composition and temperature.