The invention aims to provide an environment-friendly engine capable of avoiding wetting walls and provided with good fuel economy. The engine comprises a piston, cylinders, oil atomizers and a spark plug. Especially, an oil atomizer is arranged in each cylinder of the engine, the oil atomizer is arranged in the centre of a cylinder cover, and the spark plug is close to an oil injection nozzle of the oil atomizer and inclines towards the oil injection nozzle of the oil atomizer, the side electrode of the spark plug deviates from the oil injection nozzle of the oil atomizer and locates in the edge of spray sprayed by the oil injection nozzle. The engine has simple structure, solves the problem of wetting walls of the prior engine, has good fuel economy and environmental protection, and accords with development tendency of the modern engine.