Fuel-Injection Strategy for PCCI Engine Fueled by Mineral Diesel and Biodiesel Blends

Premixed-charge compression ignition (PCCI) combustion is a novel combustion concept, whereby a partially homogeneous fuel-air mixture burns predominantly in a premixed combustion phase, which results in lower emissions of nitrogen oxides (NOx) and particulates. This experimental study explored the possibility of PCCI combustion using three test fuels, namely, 20% (v/v) biodiesel blended with mineral diesel (B20), 40% (v/v) biodiesel blended with mineral diesel (B40), and baseline mineral diesel. To investigate the combustion, performance, and emission characteristics of the PCCI engine, experiments were performed in a single-cylinder research engine equipped with a common rail direct injection (CRDI) system. The effects of the fuel-injection pressure (FIP) and the timing of the start of main injection (SoMI) were investigated by varying the FIP from 400 to 1000 bar and the SoMI timing from 12 degrees to 24 degrees bTDC, respectively. Detailed investigations of the particulate morphology, particulate numbersize distribution, and particulate-bound trace metals were also carried out. The results showed that PCCI combustion was significantly influenced by the fuel-injection parameters and that the combustion improved with increasing FIP (up to 700 bar). Further increasing the FIP resulted in inferior engine performance because of intense knocking. Increasing the FIP (up to 700 bar) reduced the NOx and particulate emissions through it improved fuel-air mixing. Among the three test fuels, B40 showed the best combustion and performance characteristics, and B20 showed emission characteristics superior to baseline mineral diesel. Because of inferior fuel-air mixing in the combustion chamber, B20 and B40 showed relatively higher particle number emissions compared to mineral diesel under identical conditions. Overall, this study suggests that fuel-injection parameters for optimized PCCI combustion vary with the properties of the test fuel.