Delayed-Charging and Low-Pressure Fuel Injection: a Step towards less Consumption and less Pollution in Small Two-Stroke Engines

The classical two-stroke engine is well known for its mechanical simplicity, its high power-to-weight ratio but also, unfortunately, for its poor fuel utilization effectiveness due to large losses of fuel during scavenging leading to a high specific consumption and a high hydrocarbon pollution rate. A very simple system, called Delayed-Charging (D.-C.), was proposed in earlier papers, improving fuel utilization by separating the scavenging and charging functions, the latter being retarded. In this paper, comparisons are made between a 50 cc production engine and D.-C. modified 50 cc engines equipped with a pressurized carburetter or a low-pressure injector feeding the air flow into the charging-transfer duct (i.e. various engines including parameter changes such as injector location, fuel jet angle, jet direction, injection closing angle, D.C.-transfer duct geometry, number of scavenging transfer ducts,…). With electronic fuel injection, one notices a further marked reduction in fuel-consumption and HC pollution, with figures down to respectively 310 and 36 g/kWh, associated with low CO production, which is at the expense of the slightly lower b.m.e.p..