Additional injection timing effects on first cycle during gasoline engine cold start based on ion current detection system

摘要

This paper focuses on the first firing cycle of a cold start process as a means to improve combustion performance and reduce emissions during the cold start of a combined injection strategy engine. A novel additional firing strategy, based on a modified form tandem ion current (IC) signal detection system, was applied to avoid an in cycle misfire condition. Specifically, by detecting the misfire with the IC signal and then using an additional injection and spark ignition strategy, misfire can be avoided in the current cycle by successful survival combustion. However, if the quantity of additional injection fuel is improper, a misfire may still happen even if this strategy is applied. Furthermore, the requirement for additional fuel was found to be sensitive to the primary ignition timing. Thus, the effects of different ignition timings on the combustion and emissions of the first cycle were also studied. If the additional injection occurs near top dead centre, less fuel needs to be injected to avoid misfire. Having the additional injection timing occur too early or too late were both disadvantageous for additional spark ignition. This is determined by spray condition and piston movement in the cylinder, which is explained in detail by numerical simulation in this paper. Increasing the amount of additional injection fuel can stabilise combustion, but this also increases the hydrocarbon (HC), particulate number (PN), and particulate mass (PM) emissions. If the additional spark ignition fails to cause the combustion after additional injection and ignition, the HC emissions will not dramatically increase compared with basic misfire operation, but the PM will. However, the PM emissions are still at the same level as in normal combustion because the basic misfire condition causes ultra-low PM emissions.