![]() Therefore, the two-stroke engine design works well for large high-power engines with its slower speed and fewer strokes. As engine size and power increase, the size and weight of the internal components also increase, which limits their ability to reciprocate quickly. Some of the largest engines in the world are two-stroke engines. Most two-stroke engines are the slow to mid-speed variety (400 to 700 rpm), primarily because of lubricating concerns and because the crankshaft is turning only once per cycle. Another method, commonly used on small two-stroke engines, is to combine a prescribed amount of oil with the fuel so that it lubricates the engine as the air/fuel mixture passes through the crankcase. Lubrication of the engine is accomplished by an auxiliary lubricator that injects a prescribed amount of oil into critical areas. Lubricating a two-stroke engine is also unique compared with other engines because the engine does not have a traditional valve arrangement that separates the crankcase from the combustion chamber. Exhaust gas is evacuated between 5 and 6 when the exhaust port is open and fuel mixture is drawn in between 6 and 1 when the intake port is open. For example, 1 through 4 are the compression stroke and 4 back to 1 is the combustion/expansion stroke. Numbers signify the beginning of various events in the two-stroke cycle. 1-Idealized P-V diagram for a two-cycle engine. As the power stroke reaches its end, the cycle begins again.įig. The burning of the air/fuel mixture pushes the piston through the power stroke. The compression stroke compresses the air/fuel mixture that is then ignited by a spark plug. ![]() Because some of the air/fuel mixture can be lost in this process, some two-stroke engines are equipped with fuel injection systems that raise their fuel efficiency close to that of a four-stroke engine. These ports allow the exhaust to escape under its own pressure and then be displaced by the incoming air/fuel mixture. As the piston moves downward during the power stroke, first the exhaust port is uncovered and then the intake port is uncovered. 1, the process of filling the cylinder with an air/fuel mixture and exhausting the burned gases occurs almost simultaneously near the end of the power stroke. The two-stroke engine is unique because it does not control the release of exhaust or the admission of an air/fuel mixture into the cylinder with a traditional valve arrangement, one intake and one exhaust.Īs shown in Fig. The two strokes are the power and compression strokes. Two-stroke cycle engines or two-cycle engines complete their combustion cycle in two piston strokes that are accomplished with one revolution of the crankshaft. The combustion cycle and fuel type required to complete this task are what distinguish the three engine types from each other. There are three main types of engine combustion.Īll three types of engine combustion convert the chemical potential energy found in the fuel to mechanical kinetic energy. ![]()
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