Hello chemists, need some help here. I'm trying to calculate the power output of a certain otto cycle using different fuels, specifically gasoline, ethanol and different combinations of the two like 85% ethanol and 15% gasoline or 50% ethanol and 50% gasoline. However I have found it difficult to find a reliable source for the heat of combustion values of those mixed substances so I wondered if I just calculated the average heat of combustion given the proportions of the substances used or if there is some weird chemical stuff going on that I'm not aware of, this is out of my area of expertise so I figured I should ask somebody that knows. The short version is: can I just assume that the heat of combustion value of a mixture of substances to be the average value of the heats of combustion of the substances that make the mixture given the proportions or not? For example: If gasoline has a heat of combustion of 47,000 Kj/Kg and ethanol 28,500 Kj/Kg would it be correct to assume that the heat of combustion of a mixture of 50% ethanol and 50% gasoline has a heat of combustion of: (47,000+28,500)/2 = 37,750 KJ/Kg is that correct?