|M.Sc Thesis||Department of Aerospace Engineering|
|Supervisor:||Prof. Emeritus Gany Alon|
|Full Thesis text|
The promising performance of the hydrogen-fueled supersonic combustion ramjet (scramjet) engine in the hypersonic flight speed range and specifically its apparent potential for achieving near-orbital speeds, has drawn increasing attention on hypersonic flight missions and, especially, on the elegant single-stage-to-orbit (SSTO) aerospace plane concept.
Air breathing engines for operation in the hypersonic speed regime have been studied for over forty years. The heart of these engine systems is the supersonic combustion ramjet (scramjet) cycle, which potentially offers better cycle efficiency compared to the conventional, subsonic combustion ramjet in this flight speed range.
A scramjet is a type of air-breathing engine which is designed to operate at the hypersonic speed range normally associated with rocket propulsion. It differs from a rocket by using air from the atmosphere to burn its fuel, as opposed to an oxidizer carried with the vehicle itself.
The objective of this work has been to analyze the effect of individual flow and combustion process efficiencies (inlet, combustion chamber, nozzle) as well as different operating parameters on the overall scramjet cycle performance. The investigation has been applied to hydrogen and JP4 (kerosene) fueled scramjet engines.
The results of the work show that scramjet engine cycle exhibits much higher specific impulse with hydrogen than with JP4 fuel. Hydrogen fueled scramjet engine starts to be more efficient than the subsonic combustion ramjet from about Mach number of 5. It can continue to be efficient and to produce enough thrust to overcome drag till about Mach number of 11 for nominal drag coefficient. Also, efficient JP4 fueled scramjet cycle with reasonable Isp and thrust greater than drag can exist till about Mach≈9-10 for nominal drag coefficient. For a greater than nominal drag coefficient, the achievable flight speed should be lower.
As opposed to the scramjet cycle, the work reveals that the subsonic combustion ramjet cycle cannot be used in practice above flight Mach @ 8. According to thermochemical calculations, in these operating conditions it is impossible to add sensible heat to a subsonic flow combustor via hydrogen or JP4 reaction with air, as chemical energy at the corresponding static temperatures is almost entirely converted to dissociation energy.
Also, according to the current work results, primary parameters that affect scramjet engine cycle performance for a given fuel are inlet pressure recovery, combustion chamber pressure recovery, combustion chamber efficiency, and fuel to air ratio.