Hydrocarbon emissions during cold start and subsequent engine warm-up constitute the majority of hydrocarbons emitted during an FTP test. Reducing HC emissions during this portion of the test is necessary to meet current and future HC emissions regulations. This paper summarizes the results of a study which quantified the influence of fuel injector configuration and engine calibration on HC emissions prior to catalyst light-off, in a contemporary four-valves-per-cylinder engine. The fuel-injector parameters investigated included dual versus single spray, air-assist versus non-air-assist, and different spray characteristics (cone angle, droplet size). Control parameters investigated included injection timing, air-fuel ratio, and spark timing. Design and calibration merits were assessed according to combustion stability, cumulative hydrocarbon emissions during cold start and warm-up, and catalyst light-off time.
For all injector configurations tested, closed-intake-valve injection always produced more favorable results than open-intake-valve injection. In addition, when fuel was injected on closed intake valves, neither the use of dual sprays nor air-assist provided significant benefits.
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