An Alternative Method to MFB50 for Combustion Phase Detection and Control in Common Rail Diesel Engines

Abstract

Although injection timing does not change at every cycle in compression ignition engines, the variations in combustion phase may occur. The variations in combustion phase are directly related to emission dispersion, torque variation, and fuel economy; therefore, the variations should beminimized by combustion phase detection and control. In this study, we propose a novel combustion indicator: location of 20% of initial heat release after the peak (IHRap20) that is an alternative to MFB50 to detect and control combustion phase in real time. IHRap20 is extracted from IHR, which is a simplified heat release model derived by the product of in-cylinder volume and the gradient of difference pressure between firing pressure and motoring pressure. IHRap20 is confirmed with engine experiment that it is highly correlated to MFB50 with RMSE of 0.2790 degrees crank angle and R-2 of 0.9873 under various operating conditions such as injection timing, mass air flow, boost pressure, and rail pressure changes. In addition, IHRap20 is able to detect combustion phase in real time with fewer number of in-cylinder pressure data and computational load compared to MFB50. Furthermore, IHRap20 is more robust to in-cylinder pressure sensor noise than MFB50. Consequently, IHRap20 is promising for real-time combustion phase detection.