The basic two-stroke cycle was described in Chapter 1 and the operation of this type of engine can now be amplified. Fig. 12.1 shows a typical indicator diagram for a two-stroke, and it can be seen that because the ports open during the stroke the compression and expansion phases are restricted. Also the inlet period is much shorter than that of the four-stroke, so the volumetric efficiency of the engine is low. As compression cannot begin until the exhaust port is shut, the compression ratio calculated from the swept and clearance volumes is much higher than the actual ratio achieved.
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