Further restrictions on NOx emissions and the extension 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.
This paper presents an analysis of the effects of varying injection timing, fuel mass distributions in split injections and fuel rail pressure on emissions, combustion noise and fuel consumption during the medium load operation (≥10 bar IMEP) at high EGR rates (41%) of a single-cylinder test engine, with the overall objective to optimize a triple injection strategy. The results of some of the test cases are compared with those obtained from modelling in KIVA-3V.
Using an optimized triple injection strategy, soot and NOx emission levels from the test engine could be reduced to < 0.04 g/kWh and < 0.4 g/kWh, respectively, at the medium engine load of 10 bar IMEP.