Development and Testing of a Novel Direct Mixture Injection System for a Two Stroke SI Engine

In this work a novel mixture injection system has been developed and tested on a two stroke scooter engine. This system admits finely atomized gasoline directly into the combustion chamber. It employs many components that were individually developed, fabricated, tested and then coupled together. A small compressor driven by the engine sends pressurized air at the correct crank angle through a timing valve. This is connected to a mechanical injector through a high pressure pipe. Fuel is metered into the high pressure pipe using a standard low pressure injector. The developed mixture injection system resulted in considerable improvements in thermal efficiency and reduction in HC emissions over the manifold injection method at all engine outputs. A considerable reduction in short circuiting losses was seen. The highest brake thermal efficiency achieved was 25.5% as against 23% with the manifold injection system. The minimum HC level is 460 ppm where as for manifold injection it is 1360 ppm. Better combustion with the developed system lead to a small increase in the peak NO level as compared to the manifold injection system. Further improvements are possible by redesigning the compressor and combustion chamber.