Cycle variations in a hydrogen internal combustion engine

The cycle variation characteristics of a port fuel injection hydrogen internal combustion engine (PFI-HICE) have been extensively investigated. The covariance of indicated mean effective pressure (COVimep) is the best parameter for evaluating the cycle variations in the PFI-HICE. COVimep decreases as fuel–air ratio increases from 1000 to 5500 rpm, and engine speed minimally affects COVimep. The effect of ignition advance angle on COVimep is determined by fuel–air ratio. The ignition advance angles that correspond to the minimum COVimep of the PFI-HICE decrease as fuel–air ratio increases. The effect of ignition advance angle on COVimep diminishes as fuel–air ratio increases. The COVimep of the PFI-HICE rapidly decreases as throttle increases when the throttle is less than 20%. Injection timing only slightly affects COVimep under high-speed conditions, and COVimep increases when hydrogen is injected in intake periods under low-speed conditions. These results indicate that studying COVimep improves the stability of PFI-HICEs.