Fast mass-fraction-burned calculation using the net pressure method for real-time applications

The mass fraction burned (MFB) is determined from the analysis of measured in-cylinder pressure data. In this paper, a net pressure method (model 2) is used to evaluate the MFB curves at different load conditions (3.3 bar indicated mean effective pressure and wide-open throttle) using a constant polytropic index. Results are compared with the well-known Rassweiler-Withrow method (model 1), which is a linear model for the polytropic index. Model 2 showed good agreement with model I at high-load conditions; however, it predicts slower combustion at part-load conditions than that of model 1. It is found that the proper selection of the polytropic index n and the determination of the end of combustion are the important parameters for calculating the MFB curves using model 2. The modified form of model 2 compares well with the results of model I for evaluating the MFB at part-load conditions. The MFB results of the modified form (of model 2) also show good agreement with model I at high-load conditions. Model 2 has an advantage that the data-processing time is short enough to allow for online processing.