직접분사식 커먼레일 디젤엔진의 실시간 연소위상검출 알고리즘에 관한 연구

Abstract

For developing eco-friendly diesel engines, the accurate combustion phase control is important due to its significant effects on harmful emissions and fuel efficiency. In order to control the combustion phase accurately, the detection of combustion phase should be preceded the control system design. In general, the combustion phase has been detected by the location of 50% mass fraction burned (MFB50) because of its close correlation with emissions and fuel efficiency. Nevertheless, it is not easy to be implemented in real-time applications since the calculation of MFB50 requires a large amount of in-cylinder pressure data and excessive computational load. For this reason, a combustion phase indicator with simple algorithm is demanded for real-time combustion control. In this study, we propose a new combustion phase indicator, called the average location of normalized difference pressure (ANDP) between the firing pressure and motoring pressure. The ANDP indicates the average crank angle position of the two locations where the normalized difference pressure (NDP) reaches 90% of the maximum value before peak (NDPbp90) and 70% of the maximum value after peak (NDPap70). The NDPbp90 and NDPap70 are highly correlated with MFB50. By using average location, these locations demonstrate the closer relationship with MFB50, which is validated by correlation analysis between the locations of fuel mass fraction burned (MFB) and the NDP. The ANDP is represented by a fixed quadratic polynomial with MFB50 regardless of 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, the ANDP requires remarkably fewer in-cylinder pressure data samples, calculation steps and less computation time compared to MFB50. These results show great potential of the ANDP to be a substitute of MFB50 for real-time combustion control. Consequently, the proposed combustion phase detection algorithm is expected to be used effectively for real-time combustion phase detection and control.