Boost Port Injection of LPG in a Two - Stroke SI Engine for Reduction in HC Emissions 2013-01-0584

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. BPI resulted in almost the same efficiency as LPG-MI except at lean mixtures, particularly at high throttle conditions. At 25% throttle the brake thermal efficiency with BPI was similar to LPG-MI. With lean mixtures at 70% throttle conditions lower heat release rates were observed with BPI. NO emissions are higher with BPI as compared to LPG-MI when the mixture was rich due to improved heat release rates. However, the peak value of NO is always lower than gasoline-MI.