Transient control of low-temperature premixed combustion using ISG motor dynamic torque compensation

The use of low-temperature premixed combustion can significantly reduce NOx and soot emission of diesel engines. However, due to application of high EGR rate, the combustion process is sensitive to the variation of the intake fresh air amount. In engine transient operating conditions, the reduction of oxygen concentration of the fuel-air mixture will lead to deterioration of soot emission and the thermal efficiency. Limiting the transient air-fuel ratio by reducing the fuel injection amount is a feasible solution to eliminate the soot emission peak. However it will result in insufficient power output of the engine. In order to solve this problem, an ISG motor, which has the advantage of fast torque response, is integrated on the diesel engine. An in-cylinder pressure based engine torque on-board estimation method is designed and verified. Through calculating the difference between the desired engine torque and the actual engine output torque, a strategy using ISG motor dynamic torque compensation to improve transient power performance is designed. Experiments with different transient control strategies are carried out. The result shows that, by using air-fuel ratio limitation and ISG motor dynamic torque compensation in transient operation conditions of low-temperature premixed combustion, the soot emission can be reduced substantially, while the engine keeps good power performance.