冷起动首循环瞬态HC排放特性试验研究

Transient HC Emissions of the First Firing Cycle at Cold Start on an LPG SI Engine

从循环控制的角度,详细研究了LPG点燃式发动机冷起动首循环瞬态HC排放特性。试验在一台电控LPG进气道喷射单缸风冷四冲程、125 mL发动机上进行。通过高速采集系统记录发动机首循环瞬态HC排放、瞬时缸压和转速,分析了瞬态HC排放与其他参数之间的关系。研究表明:随着过量空气系数的变化,首循环瞬态HC排放在一个较宽的混合气浓度变化范围内平缓变化,并稳定在较低的水平。首循环瞬态HC排放的最小值出现在缸内燃烧最好的燃空当量比附近。当首循环混合气浓度过浓或者是过稀时,瞬态HC排放迅速增加。首循环瞬态HC排放随点火角度的推迟,其变化规律为先增加再减少,随点火角度不断推迟,在膨胀行程中氧化的燃料不断增加,当点火角度推迟到一定限值,缸内燃烧不能进行,瞬态HC排放急剧增加。

Based on the analysis of engine＇ s first firing cycle （ FFC）, this paper presents transient HC emission characteristics at cold-start in a small electronic fuel injected （EFI） SI engine fuelled with LPG. The results show that the transient HC emission of the first firing cycle gives a moderately pattern versus excess air ratio over a wide range. Minimum exhaust HC emissions correspond to maximum peak cylinder pressure occurrence. The HC emissions are increased remarkably when the mixture concentration becomes too lean or too rich. The engine-out HC emissions of the first firing cycle increased with delaying ignition timing at first, and then decreased with delaying ignition timing due to increasing oxidation of hydrocarbons during the expansion stroke. When ignition delaying exceeds a limited value, misfire will occur and HC emissions will increase greatly.