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Carburetors are widely used for two wheeler applications in India as well as countries like Taiwan, Indonesia and China. These carburetors are characterized by simple design and low cost. As the emission norms are becoming more and more stringent, matching the carburetors for vehicle application becomes very challenging. Earlier it was widely believed that, for meeting the Euro-3 regulations, even two wheelers with small engine capacity had to employ electronic fuel injection. However, many vehicle manufacturers have successfully developed carburetors for meeting Euro-3 norms by employing catalytic converters without any electronic control. This development has been essentially motivated by the need for low cost. Flow variation is inherent in mass produced carburetors because there are many parts, which contribute to the air-fuel ratio delivered by the carburetor. Carburetors with the mixture control pilot systems were mass-produced and compared for results with air control system.

In modern direct injection gasoline engines, air-fuel mixing has a strong influence on combustion and emission characteristics, which in turn largely depends on in-cylinder fluid motion. However, in-cylinder fluid motion dependent on many engine parameters viz., piston shape, engine speed, intake manifold orientation, compression ratio, fuel injection timing, duration, etc. Among them, piston shape has significant influence on the in-cylinder fluid motion. Therefore, this study aims on evaluating the effect of piston shape on in-cylinder flows in a direct injection engine using CFD. In this study, a single-cylinder, two-valve, four-stroke direct injection engine designed for two-wheeler application in India is considered for the analysis. ‘STAR-CD’ and és-ice’ are used for CFD analysis. Pressure boundary values obtained from measurements in the actual engine are employed. Two piston-shapes viz., flat and bowl types at wide-open-throttle under non-firing conditions are considered.