Development of a Real Time NOx Prediction Model Based on Heat Release Analysis in a Direct Injection Diesel Engine

Abstract

A prediction model, which describes linear relationship between the nitrogen oxides (NOx) emissions and the incylinder heat release rate in a directinjection diesel engine, was developed through numerical simulations. A modified KIVA3 V code was used to calculate NOx formations and to conduct heat release analyses in a directinjection diesel engine under different operating conditions. The numerical simulation results indicated that the NOx formation amount was related to both the magnitude and the timing of the peak heat release rate in each engine cycle. Based on the above observations, a controloriented dynamic NOx model was constructed and then implemented into a feedback emission control system on a small diesel engine. A new parameter—combustion acceleration—was proposed in this research to describe the intensity of the premixed combustion. Experimental work was also conducted to measure the realtime incylinder pressure at each crankangle when the engine was running and the heat release rate was calculated instantaneously to control an exhaust gas recirculation (EGR) valve. The experimental results showed that the proposed NOx prediction model was effective in controlling NOx emissions under high rpm conditions.