Optimization of a Light Aircraft Spark-Ignition Engine

The aim of this study was to find a convenient set-up for an innovative engine dedicated to light aircraft through a numerical one-dimensional simulation. Six different engine layouts were analyzed in order to find the highest power/weight ratio and the least voluminous configuration. The first was a four cylinder, four stroke, horizontally opposed, naturally aspirated, water cooled engine with 16 valves that delivered 75 kW (∼100 bhp) at 2400 rpm for an estimated weight of 65 kg. A gearbox was also used in the naturally aspirated model to decrease the displacement, the weight and the overall dimensions. The other solutions involved these two engines in a turbocharged layout in order to gain a further downsizing. The supercharging was obtained through a centrifugal compressor driven by an exhaust-gas driven turbine, which also allows the power to be restored at cruising altitude. The other engines were two-stroke turbocharged engines (compressor driven by gas-turbine) with and without a gearbox. The most important innovations of the two-stroke engines concern the turbo-charge group, an unidirectional-flow scavenging scheme with four all-acting exhaust valves, a forced-fed lubricating system and a direct fuel injection in order to reduce fuel consumption and pollution. The results have shown that the four and the two-stroke turbocharged engines are the most promising as far as the power/weight ratio and dimension reduction are concerned.