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 turbocharge 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.