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Study on the Influence of High-altitude on Performance of an Opposed-Piston Gasoline Engine

The engine performance test was carried out on the high-performance test bench of opposed-piston engine of UAV (unmanned aerial vehicle) from 0m to 7000m altitudes. The influence of altitudes on power, torque, fuel consumption, and heat balance (cylinder surface temperature and heat flow distribution) of the engine were analyzed. The results showed that power and torque of the engine gradually decrease with the altitudes increasing. The power and torque were reduced by about 11.25% and 12.5% respectively, and the fuel consumption rate increased by 14.4% and 2.8% respectively at low-speed and high-speed with altitude rises 1000m. At the altitude of 0-3000m, the temperature and the surface temperature of the cylinder surface decreased by 18.7 and 7.9 degrees respectively with altitude of sea level per 1000m. At the altitude of 3000m-7000m, the temperature and the surface temperature of the cylinder surface decreased by 31.9 and 21.2. The outlet temperature of cooling water increased first and then decreased with altitudes increasing, and the extent of variation at high-speeds was greater than that at low-speeds. The effective thermal efficiency of the engine is less than 5%, while the percentage of lost heat is over 30% under 3000rpm speed at the altitude of 6000m.