Why internal combustion engines for road transportation are single acting?
Engine efficiency is determined primarily be difference between the maximum temperature and the exhaust temperature. The number of power strokes is not a factor. Common automobile engines are 4-stroke which means 1 power stroke for 2 rotations. 2-stroke engine have 1 power stroke for each rotations. They have lubrication problems and are used only for small engines. A double action engine (2 power strokes per rotation) would have worse lubrication problems plus a complicated linkage to the crankshaft.
