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With the introduction of stringent emission norms for two wheeler applications, and need to reduce green house gases emission, it is a challenging task to improve the performance of the engine, especially at part throttle conditions. The typical drawback of spark ignition engine is poor part throttle performance and the Indian driving cycle (IDC) predominantly covers these part throttle operations. Contrary to popular belief, carbureted two wheelers with engine capacity up to 250cc are able to meet regulation Euro III with add-ons like secondary valve and catalyst. Vehicles with EFI systems are more expensive and they are not able to provide any fuel economy benefit or improvement in drivability. Under these circumstances, carburetor designers are working continuously to improve its performance. In order to improve the performance, optimization of slow speed to high speed fueling circuit dividing ratio is of immense importance.

Gasoline direct injection (GDI) technology is already in use in four wheeler applications owing to the additional benefits in terms of better combustion and fuel economy. The air-assisted in-cylinder injection is the emerging technology for gasoline engines which works with low pressure injection systems unlike gasoline direct injection (GDI) system. GDI systems use high pressure fuel injection, which provides better combustion and reduced fuel consumption. It envisages small droplet size and low penetration rate which will reduce wall wetting and hydrocarbon emissions. This study is concerned with a CFD analysis of an air-assisted injection system to evaluate mixture spray characteristics. For the analysis, the air injector fitted onto a constant volume chamber (CVC) maintained at uniform pressure is considered. The analysis is carried out for various CVC pressures, mixture injection durations and fuel quantities so as to understand the effect on mixture spray characteristics.