Partially premixed combustion (PPC) is a combustion concept between homogeneous charge compression ignition (HCCI) and conventional diesel combustion. By running a start of injection timing (SOI) sweep from early in the intake stroke to a timing close to the top dead center (TDC), the transition of fuel-air mixture stratification condition and combustion process can be divided into three regimes: the HCCI regime, the Transition regime, and the PPC regime. Different types of fuel distributions and heat releases were observed when comparing the operating points in the three regimes. The differences in fuel distribution and combustion also led to different efficiency performance. Within the Transition regime, part of the fuel spray was trapped inside of the piston crevices and ultimately turned to incomplete combustion emissions; thus, the combustion efficiency was generally low. In addition, operating points in the PPC regime had the highest gross indicated efficiencies compared to those in other regimes. To gain a deeper understanding of the causes of different efficiency, from each of the three regimes, one or two operating points were selected and operated at constant load and three engine speeds: 900 rpm, 1200 rpm, and 1500 rpm. The results showed that the operating points in the early PPC regime gained the best indicated efficiency at all engine speeds while those in the late PPC regime achieved the highest combustion efficiency. Sorting the operating points by their gross indicated efficiencies, from the highest to the lowest, they were in the early PPC regime, late PPC regime, HCCI regime, and Transition regime, respectively. According to energy balance calculations, heat transfer losses were the biggest difference of the operating points in different regimes.
第二届世界内燃机大会The 2nd World Congress on Internal Combustion Engines