A.N. Kraiko , A.D. Egoryan
DOI Number XXX-YYY-ZZZ
Conference Number HiSST 2018_3000970
In connection with the allegations of a possible significant increase in thrust characteristics when replacing air-breathing jet engines with deflagration combustion (RAMJET) to engines with combustion in detonation waves (pulsating – PDE and rotating – RDE), a comparison of ramjet engines of different schemes with deflagration and detonation combustion was performed. The comparison is based on the simplest models of thermodynamics, detonation wave, air braking, expansion of combustion products in perfectly adjustable nozzles and unsteady flows in combustion chambers. Within such models, with a fixed adiabatic index, the characteristics of each engine depend on two parameters — the flight Mach number and the dimensionless calorific value of the combustible mixture. The comparison for the real values of these parameters with the analysis of thermodynamic cycles and one-dimensional unsteady calculations (for engines with combustion in detonation waves or at a constant volume) confirmed the importance of taking into account nonstationary processes in combustion chambers. Statements about the advantages of detonation combustion are made on the basis of comparison of ideal thermal coefficients of efficiency and calculated on them also ideal specific thrust and impulses. If the process in the combustion chamber is unsteady, and even with the shock waves arising from the reflection of the detonation wave from its ends, the recalculation of thrust and impulse according to thermal efficiency is wrongful. The validity of the above for multi-chamber PDE was confirmed by unsteady calculations with instantaneous opening and closing of the detonation chamber valve and instantaneous initiation of the detonation wave without energy costs. According to the calculations, the PDE thrust is obtained less than the thrust of a RAMJET, starting from small supersonic Mach numbers. A similar calculation for RDE is wrongful due to the strong (even for narrow cylindrical chambers) spatial non-uniformity of the parameters and non-inertiality of rotating reference frame.