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

A prediction model, which describes linear relationship between the nitrogen oxides (NOx) 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 NOx formations and to conduct heat release analyses in a direct-injection 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 control-oriented 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 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 NOx prediction model was effective in controlling NOx emissions under high rpm conditions.