4. Conclusions
1. One hundred fifty cycles are sufficient for studying the
cycle variations in HICEs.
2. The COVimep of HICEs decreases as fuel-air ratio increases
at 1000e5000 rpm, especially when the COVimep is less than
5% at a fueleair ratio greater than 0.2. Engine speed has
little effect on the COVimep of HICEs. The variation trend of
COVimep with fuel-air ratio tends to be the same at different
speeds.
3. COVimep decreases as fuel-air ratio increases. The best
ignition advance angles that correspond to the minimum
COVimep also decrease with increasing fuel-air ratio. The
effect of ignition advance angle on COVimep diminishes with
a richer mixture, and COVimep gradually varies with ignition