Propulsion System Cycles

The most important cycles used for practical air vehicle propulsion systems are discussed and analyzed, including their relative thermal efficiencies and various other attributes that determine their suitability for specific propulsion applications. This includes the fundamental thermodynamic performance of the most widely used heat engine cycles, such as the Otto and Diesel cycles, which are widely used in reciprocating engines, the Brayton cycle, which is used in continuous-flow systems such as gas turbines and ramjet engines, and the Humphrey cycle, which is relevant to various wave-driven propulsion systems including pulse jets and pulse detonation engines. Classical ideal cycle results are obtained for each case, and discussion of real cycle effects shows where the performance of practical systems departs from the ideal cycles. Performance metrics for the various cycles are compared, and realistic values for modern systems are used to assess the relative merits of practical propulsion systems based on each these heat engine cycles.