Reduction of Fuel Consumption and Emissions for a Small Capacity Two-Stroke Cycle Engine 932393

The emissions produced from a simple carburetted crankcase scavenged two-stroke cycle engine primarily arise due to losses of fresh charge from the exhaust port during the scavenging process. These losses lead to inferior fuel consumption and a negative impact on the environment. Pressure on exhaust emissions and fuel consumption has reduced the number of applications of the two-stroke cycle engine over the years, however the attributes of simplicity, high power density and potential low manufacturing costs have ensured its continuing use for mopeds and motorcycles, small outboard engines and small utility engines. Even these last bastions of the simple two-stroke engine are being challenged by the four stroke alternative as emissions legislation becomes tighter and is newly formulated for many categories of engines. A simple solution is described which reduces short circuit and scavenge losses in a cost effective way. Air is introduced into the top of the transfer passages during the crankcase induction phase, this air is then used to initiate the scavenging process. A preliminary experimental evaluation has shown that brake specific fuel consumption can be reduced by about 10% and brake specific hydrocarbon emissions by around 40 % at wide open throttle operation.