A Proposal on Heat Engines, a topic in Chemical Engineering Thermodynamics. This work aim at studying the process involved in the conversion of heat energy to mechanical work and in effect the principles which engine operate. Heat engines are systems that convert heat or thermal energy to mechanical energy which can then be used to do mechanical work. This is done basically by bringing a working substance from a higher state temperature to a lower state temperature. The working substance is brought to a high temperature by a heat source which generates thermal energy. This energy is converted to work by exploiting the proportion of the working substance during which the heat is transferred to the colder destination until it reaches a lower temperature state. The conversion of this heat to mechanical work follow certain routes which ends at the start point and hence are called cycles. This work will in essence focus on these cycles. Otto cycle, Atkinson cycle and brayton cycle are some of the cycle that represent models for heat engine operations. The condition to which the working fluid is subjected in the process, is what distinguishes one cycle from the other.