Injection Strategy Optimization for a Light Duty DI Diesel Engine in Medium Load Conditions with High EGR rates

Paper in proceeding, 2009

Further restrictions on NOx emissions and the expansion of current driving cycles for passenger car emission regulations to higher load operation in the near future (such as the US06 supplement to the FTP-75 driving cycle) requires attention to low emission combustion concepts in medium to high load regimes. One possibility to reduce NOx emissions is to increase the EGR rate. The combustion-temperature reducing effects of high EGR rates can significantly reduce NO formation, to the point where engine-out NOx emissions approach zero levels. However, engine-out soot emissions typically increase at high EGR levels, due to the reduced soot oxidation rates at reduced combustion temperatures and oxygen concentrations. The work presented in this paper focuses on the optimization of a triple injection strategy to study the effect of injection timing, fuel mass distribution over the different injections and fuel rail pressure on emissions, combustion noise and fuel consumption for operation at medium load (10 bar IMEP and upwards) and high EGR rates (41%). The results of some of the test cases are compared with those obtained from modelling in KIVA-3V. By using an optimized triple injection strategy, soot emission levels could be reduced to below 0.04 g/kWh and NOx emissions to below 0.4 g/kWh at a medium engine load of 10 bar IMEP in a single cylinder research engine.