Experimental Study of EGR Mixture Design and its Influence on EGR Distribution Across the Cylinder for NOx - PM Tradeoff

Future emissions regulations like BSIV and above in India, Diesel engine manufacturers are forced to find complex ways to reduce exhaust gas pollutant emissions, in particular NOx and particulate matter (PM). Exhaust gas recirculation (EGR) into the engine intake is an established technology to reduce NOx emissions. The distribution of EGR in each cylinder plays vital role in combustion process and hence it will affect exhaust emissions. The influence of EGR mixture design and its effect on distribution across the cylinder has significant impact on the NOx-PM trade-off which is studied on light duty direct injection diesel engine. A simulation and experimental study of EGR mixer design is conducted to explain this effect and the distribution of EGR across the cylinder at different EGR flow rate. Experiments have been conducted on an engine test bench with and without air-EGR mixer and demonstrated that variations in cylinder-to-cylinder EGR distribution results in a deteriorated NOx-PM trade-off (increased NOx emission level at a given PM emission level, or increased PM emission level at a given NOx emission level) as compared to the well mixed with EGR mixture configuration with equal EGR rate for all the cylinders. The aim of this study is to show that EGR mixture effect & cylinder-to-cylinder variations in EGR can lead to higher NOx and PM emissions as compared to a configuration where the EGR is equally distributed amongst all cylinders. The influence of the NOx-PM trade-off has been experimentally studied in details.