There is an ever-increasing need for improving efficiency and decreasing the harmful emissions from automobiles. Since in our country, about 84% of the automobiles sold each year are in the two- and three-wheeler segments, the application of improved combustion technologies in these systems is essential. Gasoline direct-injection (GDI) engines that are gradually gaining popularity can use higher compression ratios and lean to ultra-lean mixtures, and therefore, have the potential to boost fuel economy and reduce emissions. However, to date this technology has not been applied in small engines due to challenges like lack of space on the engine cylinder head, high fuel impingement on combustion chamber walls, need for low flow rate direct injectors and pumps.

In this work, a small GDI engine for two and three-wheeler applications has been developed by introducing a high-pressure injection system, sensors and electronic controls from a commercially available carburetted spark-ignition engine. The engine was coupled to the dynamometer and was instrumented for the analysis of combustion, performance and emission characteristics. As charge motion and fuel-air mixture preparation are the key factors controlling the performance and emission characteristics, CFD studies were carried out to analyse the in-cylinder flow, fuel injection, air-fuel mixture preparation and distribution, fuel wall impingement, in-cylinder combustion and emission formation. Detailed experiments were also conducted to optimize the fuel injection timing, the number of injections, rail pressure, injector location and combustion chamber shape. The results obtained from the CFD simulations helped in understanding and optimizing the in-cylinder strategies, and modifications required on the engine. This presentation will discuss the CFD results related to the mixture formation, combustion and emissions under selected operating conditions, details of the experimental setup and results obtained with required modifications to the engine. Comparisons are also provided with the operation under port fuel injection mode.