Experimental study on the factors affecting lean combustion limit of S.I. hydrogen-natural gas engine

An experimental study was conducted on a spark ignition engine to investigate the factors that affect the lean combustion limit of hydrogen-natural gas engine. The effects of ignition timing, hydrogen mixing ratio, engine speed, throttle opening, lubricant oil and coolant temperature were examined. The engine speed was 1500-3000 r/min, the throttle opening was 10%-40%, the lubricant temperature was 75°C-95°C, and the coolant temperature was 65°C-85°C during experience. The hydrogen mixing ratio varied from 0 to 40%, and the lean-combustion limit ignition timing was defined and adopted. The result shows that both over-retarded and over-advanced ignition timing would baffle the extension of lean-combustion limit. The lean-combustion limit increases with hydrogen mixing ratio, slightly increases with throttle opening, and decreases when the engine speed is raised. Besides, it decreases with the increase in lubricant temperature. Warming-up coolant is positively related to enlarge the lean-combustion limit.