Physics of Heat-Release in Rotating Detonation Engines

Abstract

Rotating detonation engines (RDEs), along with the well-studied Pulsed Detonation Engine (PDEs), represent an alternative for obtaining propulsion and power generation using the high efficiency detonation cycle. In the last half decade, the RDE has been studied aggressively internationally due to its advantages over conventional PDEs. Many previous studies have focused on the main characteristics and performance of RDEs in various configurations and conditions. The performance of any combustor is tied closely to the local heat-release conditions in the combustor. Unlike more conventional combustors or even the closely related Pulsed Detonation Engines, heat-release occurs under a wide range of conditions within RDEs from detonation to deflagration to even non-premixed burning, and so describing it solely as a "detonation cycle engine" is not completely accurate. In this paper we use a deflagration model in simulations with different configurations to try to more accurately pinpoint where heat is being released, and how this affects the performance of the resulting engine. In particular, we examine how changing the pressure, the injector configuration, and the mixedness of the reactants may change the different heat-release regimes and ultimately the performance of the RDE. Results show that for cases using the ideal injection model, low pressure reactions are insignificant and have only a small effect on performance. When computing finite-sized injectors, a separate low pressure reaction model has to be used due to overprediction of deflagration and recovery zone reactions that eventually cause the detonation wave to fail. In these cases, less than half of the reactants are burned within the detonation wave, although the detonation wave is still the dominant feature of the flow-field. Detonation wave speeds varied from 1637 m/s to 1844 m/s, and specific impulses varied from 4650 s to 4980 s for 10 atm feed stagnation pressure. Nomenclature= ratio of micro-injector throat area to injection face area, non-dimensional !,! = specific heat at constant pressure for species k, ergs/(gm K) !,! = specific heat at constant volume for species k, ergs/(gm K) = total specific energy, ergs/gm = pressure, dynes/cm 2 = mixture ideal gas constant, ergs/(gm K) ! = ideal gas constant for species k, ergs/(gm K) = temperature, K !"# = induction time, s = velocity of gas, cm/s = reaction rate for reactant, gm/cm 3 ∆ = heat-release per gram of reactant, ergs/gm = mixture specific heat ratio ! = specific heat ratio for species k = density, gm/cm 3 ! = density for species k = induction parameter 1 Mechanical Engineer, Code 6041, Naval Research Laboratory, AIAA Senior Member.

A Review of Pressure Gain Combustion Solutions for Aerospace Propulsion

“…The comparison between premixed and non-premixed cases, as in [113], shows that the number of waves and location of the detonation wave are different for premixed and non-premixed case. Schwer et al [114] investigated the distribution of heat release in an RDE with the variation in different critical parameters such as air/fuel injection pressure, injector size and mixing ratios. The fluid particle trajectory is studied by Zhou et al [115], and has reported that while the deflagration wave doesn't deflect the particle, the detonation wave or oblique shock changes the flow parameters rapidly.…”

Combustion Characteristics in Rotating Detonation Engines

“…There may be one or several rotating detonation waves (RDWs) moving tangentially in the RDE combustor [7]. Chemical reactions mainly occur inside the detonation wave, although there may still be deflagrative combustion near the walls [8] or between the reactants and products [9]. The rotating propagation and pressure-gain combustion together make the detonation wave continuous.…”