Compression and expansion lines are polytropes with a variable polytropic exponent. The indicator diagram does not reflect changes in the temperature and direction of the heat flow.
This is clearly shown in the diagram T-s (Fig. 1, b). At the beginning of compression (point "a"), the gas temperature is lower than the temperature of the piston and cylinder walls. The process occurs with a heat input at a polytropic exponent greater than the adiabatic exponent. During compression, the temperature of the gas rises, and the direction of heat exchange changes at the moment when the temperature of the gas is higher than the wall temperature, and it begins to give off heat. The polytropic index varies from n> k at the beginning of compression to n> k at the end of compression.
https://plus.google.com/111825209396211167612/posts/JamtC1p8G1c
https://plus.google.com/106858352641162810807/posts/2wg6aMhoW27
https://plus.google.com/+ElizabethBrowns/posts/2oWAsTt3nFJ
https://plus.google.com/108505800356485925022/posts/Sdqrymsj8uw
This is clearly shown in the diagram T-s (Fig. 1, b). At the beginning of compression (point "a"), the gas temperature is lower than the temperature of the piston and cylinder walls. The process occurs with a heat input at a polytropic exponent greater than the adiabatic exponent. During compression, the temperature of the gas rises, and the direction of heat exchange changes at the moment when the temperature of the gas is higher than the wall temperature, and it begins to give off heat. The polytropic index varies from n> k at the beginning of compression to n> k at the end of compression.
https://plus.google.com/111825209396211167612/posts/JamtC1p8G1c
https://plus.google.com/106858352641162810807/posts/2wg6aMhoW27
https://plus.google.com/+ElizabethBrowns/posts/2oWAsTt3nFJ
https://plus.google.com/108505800356485925022/posts/Sdqrymsj8uw