The document discusses the Otto, Diesel, and Dual combustion cycles. It states that in the Otto cycle combustion occurs at constant volume, while in the Diesel cycle it occurs at constant pressure. However, in reality combustion cannot happen instantly at either constant volume or constant pressure. The Dual cycle is a compromise between the two. For the same heat input and compression ratio, the Otto cycle has the lowest heat rejection and highest efficiency, while the Diesel cycle has the highest heat rejection and lowest efficiency. The Dual cycle efficiency is between the two.