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Short-circuiting of the fuel air mixture during scavenging is the main reason for high fuel consumption and hydrocarbon (HC) emissions in two-stroke SI engines. Though direct injection of the fuel after the closure of ports has advantages, it is costly and complex. In this work, in a 2S-SI, single cylinder, automotive engine, LPG (liquefied Petroleum Gas) was injected through the boost port to reduce short-circuiting losses. A fuel injector was located on one of the boost ports and the air alone was fed through the other transfer and boost ports for scavenging. Experiments were done at 25% and 70% throttle openings with different injection timings and optimal spark timing at 3000 rpm. Boost port injection (BPI) of LPG reduced HC emissions at all conditions as compared to LPG-MI (Manifold Injection). Particularly significant reductions were seen at high throttle conditions and rich mixtures. HC reductions with BPI were 19% and 25% as compared to LPG-MI and gasoline-MI respectively.

Engine operation at low temperatures is of considerable interest from the standpoint of exhaust gas emissions and fuel economy. A semi-empirical film model is developed to study the transient cold starting process. Variation of air-to-fuel ratio reaching the cylinder during the starting is estimated. Film-model uses some inputs from the CFD simulation and essentially avoids the multiple cycle CFD simulation. CFD simulation was carried out with unsteady boundary condition obtained from the experiment. The experiments were conducted at different temperatures inside cold chamber. Air-to-fuel ratio variations were recorded after starting which is used for qualitative comparison with the film model. The model is able to capture the qualitative trends observed in the experiment.