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

A prediction model, which describes linear relationship between the nitrogen oxides (NO_x) emissions and the in-cylinder heat release rate in a direct-injection diesel engine, was developed through numerical simulations. A modified KIVA-3 V code was used to calculate NO_x formations and to conduct heat release analyses in a direct-injection diesel engine under different operating conditions. The numerical simulation results indicated that the NO_x 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 control-oriented dynamic NO_x 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 real-time in-cylinder pressure at each crank-angle 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 NO_x prediction model was effective in controlling NO_x emissions under high rpm conditions.