CFD Predictions of the Effect of Fuel Temperature on Heavy Duty Diesel Engine NOx and Soot Emissions

Computational fluid dynamics (CFD) has been used to investigate the influence of the injected fuel temperature on diesel combustion and emissions. A series of three dimensional, moving piston simulations were performed for four different fuel temperature scenarios involving the fuel injection rate and period. The predictions of specific fuel consumption, NOx and soot indicated that fuel temperature effects were significant only for scenario I, where the injection period was fixed and the injection rate change was in proportion to the relative change in fuel density due to the temperature change. Under these conditions it was predicted that NOx can be reduced by 10% with a 2% penalty in BSFC, for a 100K reduction in the injected fuel temperature.

To put the predicted fuel temperature effects into context, a further series of simulations were performed dealing with the effects of in-cylinder swirl, air/fuel ratio, in-cylinder gas temperature and injection pressure on combustion and emissions. The predictions showed that fuel temperature effects were less significant than changes to these variables. The predictions also showed that both in-cylinder gas temperature and air/fuel ratio changes with constant boost pressure had a dominant effect on NOx. Air/fuel ratio changes made while keeping the boost temperature constant were predicted to have little effect on NOx and a significant effect on soot. A 100K reduction in TDC gas temperature was predicted to yield a 24% reduction in NOx with a 1% gain in BSFC.