Modelling the Influence of Fuel Injection Parameters on Diesel Engine Emissions 980789

Rate shaping of the fuel injection process is known to significantly impact emissions production in diesel engines. To demonstrate the ability of multidimensional engine modeling to quantify and explain the effect of rate shaping and injection duration, three injection profiles typical of common diesel fuel injection systems were investigated for three injection durations and injection timings. The present study uses an improved version of the KIVA-II engine simulation code employing the characteristic time combustion model, the Kelvin-Helmholtz and the Rayleigh-Taylor spray atomization mechanisms, the extended Zeldovich thermal NO_x production model, and a single species soot model. Together, these models satisfactorily reproduce the known trends in engine behavior with respect to injection rate shaping and injection duration for a representative high-load high-speed operating condition at a fixed fueling rate; namely, increased NO_x with decreased injection duration; decreased soot production with decreased injection duration. At high injection pressures, the falling injection profile produces more NO_x and less soot than either the square or rising injection profile. The rising injection profile produces more soot and less NO_x than the square profile. The computational results are also used to explain the origin of anomalous soot-NO_x tradeoff trends where soot minima are seen as the injection timing is varied.