An ideal diesel engine has a compression ratio of 20 and uses air as the working fluid. The state of air at the beginning of the compression process is 101 kPa and 20°C. The maximum temperature in the cycle is not to exceed 2200 K. The gas constant of air is R = 0.287 kJ/kg·K. Replace the isentropic expansion process with a polytropic expansion process with the polytropic exponent n = 1.35. Use variable specific heats.