Experimental Investigation of Cyclic Variation and Combustion Phases in a Lean Burn Two-Stroke SI Engine

The problem of cyclic variation in combustion has been investigated by measuring 2000 continuous in-cylinder pressure traces. The experimental work was carried out in a single cylinder two-stroke SI engine loaded by an eddy current dynamometer. The air-fuel ratio was varied form rich to lean by a modified carburetor. The pressure traces were recorded by a piezo-electric pressure pickup and PC based data acquisition system. Cyclic variation in combustion was identified by the variation in peak pressure (Pmax) and indicated mean effective pressure (IMEP). The results show that cyclic variation increases when the air-fuel mixture becomes lean. It also indicates the existence of combustion phasing and different modes of combustion. The combustion variation and its effect on the performance of the engine is more severe in two-stroke engine as compared to a four-stroke engine. One of the causes of cyclic variation in a two-stroke engine is the variation in mass of trapped charge inside the cylinder.