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SAE 960633

Mechanism of Soot and NOx Emission Reduction Using Multiple Injection in A Diesel Engine

By: Zhiyu Han, Ali Uludogan, Greg J. Hampson, Rolf D. Reitz


Laboratory experiments have shown that with high-pressure multiple injections (two or more injection pulses per power cycle), the soot-NOx trade-off curves of a diesel engine can be shifted closer to the origin than those with single-pulse injection, reducing both soot and NOx emissions significantly. In order to understand the mechanism, multidimensional computations were carried out for a heavy-duty diesel engine with multiple injections. Different injection schemes and timings were considered. The predicted cylinder pressure, heat release rate and soot and NOx emissions are compared with the measured data. Agreements between prediction and measurement are achieved after improvements on models were made. The improvements include using a RNG k-e turbulence model, adopting a new wall heat transfer model and introducing the nozzle discharge coefficient to model the contraction of fuel jet at the nozzle exit. Based on the computations, a mechanism of emissions reductions using multiple-injection is suggested.