I want to compare the Ideal Diesel, Otto and Dual cycles with constant specific heats. I am interested in knowing the relationship between r (compression) and nth (efficiency). I am unable to determine the common inputs to all three which can give me the efficiency for all the cycles. r with temperature and pressure is an obvious choice. But I also need cut off ratio to calculate diesel and dual cycle's efficiency and it is not there in otto cycle. And I need pressure ratio for otto's efficiency which is not there in the other two cycles. I was wondering if taking a common Qin (heat input) would do ? Any suggestions please.