Diesel NO x emissions—A simple correlation technique forintake air effects

Abstract

A correlation technique for the effects of intake gas addition (N2, O2, Ar), exhaust gas recirculation and elevated intake air temperature on diesel NOx emissions is presented. NOx emissions were obtained from two different single-cylinder divided-chamber diesel engines operating over a wide range of engine speeds, loads, and intake air compositions and temperatures. Since the major portion of the combustion event in diesel engines is diffusion controlled in a manner similar to that in steady spray flames, variations in the calculated stoichiometric adiabatic flame temperature are used to correlate NOx emissions. The NOx correlation yields an apparent activation energy which is relatively independent of engine speed, load or combustion chamber configuration, indicating that the NOx kinetics are not significantly altered by variations of the air-fuel mixing process. However, this apparent activation energy is considerably lower than the one obtained for steady-spray flames. Several possible reasons for this difference are discussed. In the absence of detailed theoretical models describing the diesel combustion process, the simple flame-temperature correlation provides a useful method of correlating and predicting the effects of intake air composition and temperature on NOx emissions from divided-chamber diesel engines.