Differences between 2-stroke and 4-stroke engines

The so-called four stroke engine means that every two revolutions of the engine crankshaft, the engine completes a work cycle through four strokes of intake, compression, power and exhaust, while the two-stroke engine only needs the crankshaft to rotate for one revolution and undergo two strokes to complete a work cycle.

From the structural point of view, the two-stroke engine is relatively simple in structure, mainly composed of cylinder head, cylinder, piston, piston ring and other parts, and the cylinder block is provided with an air inlet, an exhaust hole and an air change hole; The opening and closing of the air hole are determined by the position of the piston. Compared with the four stroke engine, there is no complex valve train and lubrication system, and the cooling system is generally air-cooled, which is greatly simplified in structure.

From the performance point of view, when the crankshaft speed is the same, the number of work done per unit time of the two-stroke engine is twice that of the four stroke engine. Theoretically, the power of the two-stroke engine should be twice that of the four stroke engine (but only 1.5~1.7 times in fact). The engine has higher power, better power performance and less vibration.

In addition, the two-stroke engine is light in weight, low in manufacturing cost, low in failure rate, convenient in maintenance and flexible in use.

The fatal disadvantages of two-stroke engine are fuel consumption and environmental protection. Due to its poor ventilation quality and low fuel efficiency, the fuel consumption of the whole vehicle is relatively high; In terms of exhaust emissions, there is a lot of pollution. The exhaust pollution of a two stroke motorcycle engine with a displacement of 50ml is roughly equivalent to that of five 2.0L sedan engines. This is the main reason for the elimination of two-stroke engines.

Advantages of the four stroke engine: the intake, compression, expansion (explosion) and exhaust processes are carried out separately, so the work is reliable, efficient and stable, and the speed range from low speed to high speed is wide. There is no blowby and backflow loss like the two-stroke engine, and the fuel consumption is low. It operates stably at low speed and is lubricated by the lubrication system, so it is not easy to overheat. The intake process and compression process take a long time, and the volumetric efficiency and average effective pressure are high. The heat load is less than that of a two-stroke engine. Don't worry about deformation and ablation. With large displacement, it can be designed as a high-power engine.

To sum up, four stroke engines are more widely used. The vast majority of automobiles and construction machinery are equipped with four stroke engines.And our H&S all use 4 stroke gas lawn mower.