Real-Time Combustion Phase Detection Using Central Normalized Difference Pressure in CRDI Diesel Engines

Abstract

To develop eco-friendly diesel engines, accurate combustion phase control is important due to its significant effects on harmful emissions and fuel efficiency. In order to accurately control the combustion phase, the detection of the combustion phase should precede control system design. Currently, combustion phase detection is done by the location of 50% mass fraction burned (MFB50), because of its close correlation with emissions and fuel efficiency. However, this method is not easily implemented in real-time applications because the calculation of MFB50 requires a large amount of in-cylinder pressure data and an excessive computational load. For this reason, a combustion phase indicator with a simple algorithm is required for real-time combustion control. In this study, we propose a new combustion phase indicator, called the “Central normalized difference pressures (CNDP).” The CNDP indicates the center of the two crank angles where the normalized difference pressure between firing pressure and motoring pressure (NDP) reaches 90% of the maximum value before peak (NDPbp 90), and 70% of the maximum value after peak (NDPap 70). The NDPbp 90 and NDPap 70 are highly correlated with MFB50 and the correlation is enhanced as the center between the two points obtained. The CNDP is represented by a fixed quadratic polynomial with MFB50 that robust to changes in various engine operating conditions such as engine speed, main injection timing, injected fuel quantity, fuel-rail pressure, exhaust gas recirculation (EGR) rate and boost pressure. Furthermore, in performance evaluation, the CNDP requires remarkably fewer in-cylinder pressure data samples, calculation steps and less computation time compared to MFB50. These results show great potential for the CNDP to be a substitute for the MFB50 since the proposed combustion phase detection algorithm can be used effectively for real-time combustion phase detection and control.