Rodriguez, J. and Cheng, W., "Effect of Operation Strategy on First Cycle CO, HC, and PM/PN Emissions in a GDI Engine," SAE Int. J. Engines 8(3):1098-1106, 2015, doi:10.4271/2015-01-0887.
The impact of the operating strategy on emissions from the first combustion cycle during cranking was studied quantitatively in a production gasoline direct injection engine. A single injection early in the compression cycle after IVC gives the best tradeoff between HC, particulate mass (PM) and number (PN) emissions and net indicated effective pressure (NIMEP). Retarding the spark timing, it does not materially affect the HC emissions, but lowers the PM/PN emissions substantially. Increasing the injection pressure (at constant fuel mass) increases the NIMEP but also the PM/PN emissions.