1. Most of the working gas is in contact with the hot cylinder walls , it has been heated and expansion has pushed the hot piston to the top of the cylinder. Expansion continues in the cold cylinder piston, which is 90o behind the hot piston in its cycle, extracting still more work from the hot gas.

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1. Most of the working gas is in contact with the hot cylinder walls , it has been heated and expansion has pushed the hot piston to the top of the cylinder. Expansion continues in the cold cylinder piston, which is 90o behind the hot piston in its cycle, extracting still more work from the hot gas.