Impact of Fuel and Injection Timing on Partially Premixed Charge Compression Ignition Combustion

Advanced combustion modes have drawn much attention from researchers due to increasingly strict emissions regulations. Partially premixed compression ignition (PCCI) combustion creates a partially premixed charge inside the cylinder before ignition occurs. As a result, NOx and particulate matter (PM) emissions can be reduced simultaneously relative to those of conventional diesel combustion. The basic operating mechanism of PCCI combustion is to prolong the time period for mixing of the fuel air mixture by separating the end of injection and start of combustion. Three different fuels, ultralow sulfur diesel (ULSD), diesel fuel produced via a low temperature Fischer-Tropsch process (LTFT), and a renewable diesel (RD), which is a hydrotreated camelina oil, are tested in this study. Engine combustion performance, PM, NO; CO, total hydrocarbon (THC) emissions, particle size distribution, soot morphology, and nanostructure are examined for conventional combustion and various PCCI conditions. PCCI combustion can effectively reduce NOx and soot emissions with similar or slightly increased CO and THC emissions. Both LTFT and RD can reduce gaseous emissions compared to ULSD during PCCI combustion. However, because of the high viscosity of the renewable diesel used in this study, CO, THC, and PM emissions are higher than emissions from LTFT fuel during PCCI combustion.