Modeling no and soot emissions with gas compressibility

A multidimensional engine combustion code was used to model NO and soot emissions from a heavy duty Cummins Diesel engine with a compression ratio of 16. The code solves the gas calculation in a moving curvilinear coordinate system. The code includes a 13 species chemistry model that calculates the rate of formation of each species from the fuel conversion time and the species equilibrium concentration. The code also models fuel injection, spray impingement and secondary spray breakup. The engine was tested with 10% EGR in the intake by mass, a swirl ratio of 2.1 and an engine speed of 1500 rpm. The engine was tested at 3 different injection timings. The consequence of including compressibility effects is also studied. The Redlich-Kwong model was used to calculate the deviation of the gases within the combustion chamber from ideal gas behavior. The computational results were compared to the values of pressure, NO and soot emissions obtained from experiments. At the high compression ratio that the engine operates under, the ideal gas equation was found to under-predict the peak cylinder pressure by about 4%. The soot emissions were closely matched in both value and trend. Due to the inaccuracy of the equilibrium-based chemical model, the calculated NO emissions were higher than the experimental values. The evolution of the NO and soot emissions during the cycle was studied. The processes that form these emissions were identified.