Lesson 2/Learning Event 1
FIGURE 42. COMPRESSION STROKE.
During the compression stroke, the piston moves up with both valves closed. This upward movement squeezes
the air into a very small area. This is a much smaller area than is used in the same size gasoline spark-ignited
engine. Squeezing the air causes it to get hot, reaching a temperature of 800F to 1,000 at about 500 PSI. Just
before the piston reaches the end, or top, of the compression stroke, fuel is injected into the hot air in the
combustion chamber by the injector nozzle. The fuel is ignited by the hot air and then burns.
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