In order to further reduce exhaust gas emissions, an investigation was carried out concerning premixed charge compression ignition (PCCI) combustion, which is achieved by the early injection of conventional diesel fuel to the combustion chamber.
The engine used for the experiments was a single cylinder version of a modern passenger car type common rail engine with a displacement of 550(cm3). An injector with a narrower corn angle was used to prevent interaction of the spray and the cylinder liner. Also, the compression ratio was decreased in order to avoid an excessively advanced ignition situation. Additionally, a large degree of cooled exhaust gas recirculation (EGR) was applied.
These measures led to a significantly reduction in NOX emissions. However, a fuel wall-film, which was formed on the surface of the piston bowl wall, caused increases in soot, HC and CO emissions. Also observed was a reduction in indicated mean effective pressure (IMEP), as well as deteriorate in Coefficient of Variation-IMEP (COV IMEP), both of which result from excessively advanced ignition and the formation of lean air-fuel mixture. A measure, consisting of an EGR increase and a small amount of secondary injection, improved IMEP and COV IMEP. It was also effective in reducing soot.