During the expansion process of the ideal Otto cycle, the gas is a mixture whose volumetric composition is 30 percent nitrogen, 10 percent oxygen, 35 percent water, and 25 percent carbon dioxide. Calculate the thermal efficiency of this cycle when the air at the beginning of the compression is at 90 kPa and 15oC; the compression ratio is 8; and the maximum cycle temperature is 1100oC. Model the heat-addition and heat-rejection processes using constant gas properties that are the average of the air and the expansion gas properties.