Parametric ideal cycle analysis of a scramjet engine at a constant combustion mach number

Abstract

The 1920’s and 1930’s saw the development of the turbojet engine and turbofan engine,respectively. Supersonic combustion ramjet or scramjet engine development began in the United States the early 1950’s after the development of the ramjet engine in the late 1940’s. However, unlike the research completed on the ideal cycle engine analysis for turbofans and turbojets little analysis has been published on the ideal scramjet engine cycle. Employing isentropic assumptions of the Brayton Cycle, this research project will examine the published literature on the ideal cycle for the scramjet engine including six parametric measures common to the ideal engine cycle analysis for turbojets and turbofans; specific thrust, fuel-to-air mass flow ratio, thrust specific fuel consumption, thermal, propulsive, and overall all efficiencies as well as a seventh parameter, thrust flux, across a range of freestream Mach numbers at various constant combustion Mach numbers and altitudes. By design, a ramjet engine’s combustion Mach number is approximately zero thus some discussion and comparison of a ramjet ideal engine cycle will be included. Additionally, a qualitative discussion of the losses creating a non-ideal engine cycle will be discussed. Finally, due to the supersonic speed of the flow inside the combustion chamber discussion regarding constant Mach versus constant velocity will be examined. At the conclusion of this project the reader should come away with a better understanding of why a constant combustion velocity is a more practical model for the burner due to the pressure losses in the combustor. Additionally, it will also be shown that the new, seventh parametric measure, thrust flux, is a better indicator of at what flight Mach number the scramjet engine thrust will peak rather than the formerly assumed parametric measure, thrust specific fuel consumption.