Development of Optimized Split Fuel Injection and EGR Strategy for Diesel-PCCI Combustion Engine

Abstract

As compared to traditional CI combustion mode, premixed charge compression ignition (PCCI) removes locally rich fuel-air mixtures and lowers combustion temperature in an engine combustion chamber, resulting in extremely low PM and NOx emissions while retaining relatively superior engine performance. In order to achieve PCCI combustion in a production-grade diesel engine, this experimental study established an optimized split fuel injection and EGR strategy. Experiments were carried out to determine the performance and emissions characteristics of diesel PCCI combustion at a constant engine speed (1500 rpm) with varying loads (4.5 bar brake mean effective pressure (BMEP)). The effects of different fuel injection pressures (FIPs), start of main injection (SoMI) timings, start of pilot injection (SoPI) timings, and exhaust gas recirculation (EGR) rates on engine output and regulated emissions were investigated. Firstly, the effect of FIP was analyzed during which the experiments were conducted at 400, 700 and 1000 bar FIP at constant SoPI timing (35° bTDC), 15% EGR and at three different SoMI timings (10, 15 and 20° bTDC). Secondly, the effect of EGR rate was investigated during which the experiments were performed at (0%, 15% and 30%) EGR rates at SoMI timings (10°, 15° and 20° bTDC). For all cases, SoPI timing and FIP were kept constant at 35° bTDC and 700 bar, respectively. On the basis of overall experimental analysis, it was concluded that the 700 bar FIP and 15% EGR rate were the best FIP and EGR rate for achieving PCCI combustion in a production grade diesel engine at medium engine loads. Based on these results, an optimized split fuel injection and EGR strategy was developed to see whether PCCI combustion could be achieved in a commercial diesel engine.