Rotating Detonation Engine Research Articles

Numerical Research on the Toroidal Shock Wave Focusing Detonation Initiation

Abstract Pressure gain combustion (PGC) is considered to be a potential technology to increase the cycle efficiency of gas turbine. As one viable candidate for PGC, rotating detonation engine (RDE) draws more attention due to its significant advances in continuous mode of operation. In practical, one of the basic challenges for RDE application is to reliably initiate detonation wave. For this purpose, both detonation initiation mechanism and enhancement approach are urgently needed to be understood. In this work, a toroidal shock wave focusing detonation initiator is presented. On this basis, the two-dimensional numerical simulations are carried out to investigate the detonation initiation characteristics by using the toroidal shock wave focusing. All of the flame acceleration, shock wave focusing, detonation wave forming, and propagation are analyzed in detail. The numerical results show that the toroidal shock wave focusing initiator developed in this study can rapidly realize the detonation initiation over a short distance and performs significantly better than the traditional smooth or obstructed tube based imitators under different operating conditions. Under the same operating condition, the novel developed initiator decreases time of 59.2% and distance of 84.7% for the smooth tube based initiator, and time of 52% and distance of 78.9% for the obstructed one. Besides, the multifield analysis indicates that both the local explosion induced by shock wave focusing in concave cavity and the entrainment vortex generated by shock wave and jet flame in front of diaphragm are important mechanisms to initiate detonation wave. This study is expected to enhance the understanding of the physical mechanism of shock wave focusing detonation initiation and contribute to the development of detonation propulsion technology.

Design and Operation of a Radial Rotating Detonation Engine

Recently, there has been a need for compact rapid-response power generators on aircraft. A novel solution to this problem comes in the form of coupling a rotating detonation engine (RDE) with a turbine generator. To improve power density, a new type of RDE, referred to as the radial RDE, has been developed. This design was based on a disk-shaped device within which reactants flow from the outer radius, detonate, and exit the inner radius. This was coupled into a compact centrifugal turbocharger turbine to extract the power. The first step in this process was to design a modular unit that would enable an understanding of the parameters that enable detonation in this type of device. Control over the throat area, channel area, and nozzle exit area enabled a range of area ratios to be evaluated. Other primary controls included the mass flow and equivalence ratio within the device. Initial results confirmed detonation operation between mass flow rates of at equivalence ratios ranging from 0.67 to 1.10. Operating frequencies and wave speeds are reported. Lastly, high-speed images of the exhaust as well as pressure traces are shown as confirmation of detonation, and reveal multiwave operation for various conditions.

The Influence of the Method of Supplying Fuel Components on the Characteristics of a Rotating Detonation Engine

ABSTRACT The computational technology jointly developed by the N. N. Semenov Federal Research Center for Chemical Physics (ICP) and AVL LIST GmbH is used for simulating the operation process in a Rotating Detonation Engine (RDE) with an annular combustor and separate supply of fuel (natural gas (NG)) and oxidizer (gaseous oxygen). Particular attention is paid to turbulent and molecular mixing of fuel and oxidizer in the combustor and its effect on the RDE operation process. Two different schemes of fuel and oxidizer supply are considered at fixed values of their mass flow rates. In the first, the oxidizer is supplied axially through the annular slot, whereas the fuel is supplied radially through the belt of multiple distributed holes in the outer wall of the combustor. In the second, the oxidizer and fuel replace each other while their mass flow rates are kept fixed. Such a replacement is shown to lead to restructuring of the operation process: the mode with three equidistant detonation waves (DWs) rotating over the fire head of the RDE is replaced by the mode with a single rotating DW, which is the indication of approaching the marginal operation conditions. Moreover, such a replacement leads to a significant decrease in the combustion completeness of the fuel components and to the decrease in the average pressure in the RDE combustor.

Interaction between rotating detonation wave propagation and reactant mixing

Rotating detonation engines (RDEs) are widely studied because of their compact configurations and high thermal cycle efficiency. In previous literatures, many investigations on the mixing process in an RDE and the rotating detonation wave (RDW) propagation under non-premixed conditions have been published. However, the two issues were investigated separately, and the interaction between the RDW propagation and reactant mixing has not been studied yet. In this paper, a series of three-dimensional numerical simulations of the mixing process and the RDW propagation in an RDE are performed. The transient explicit density-based solver in ANSYS Fluent is used to perform the simulations. In the cold mixing flowfield, as the back pressure at the chamber exit increases, the axial velocity decreases, and the average resident time of reactant in the chamber increases. Thus the fuel has more time to mix with air in the chamber to provide a better mixing quality. The RDW velocity is very stable during the operation time, whose average value is about 1895 m/s. The velocity deficit is very small. After RDW initiation, the pressure in the combustion chamber increases due to the detonation process. The increased pressure slows down the flowing of the reactant, thus the average resident time of reactant within the height of the RDW increases, making the mixing quality better. The enhanced mixing quality of reactant in turn makes the RDW stronger. Thus, there is a positive feedback between RDW propagation and the reactant mixing.

Effect of blockage ratio on the existence of multiple waves in rotating detonation engine

The effect of blockage ratio on the existence of multiple waves in rotating detonation engine was investigated through experimental approach. It has been shown experimentally that four typical detonation propagation modes (single wave, hybrid mode of single wave and double waves, double waves, longitudinal pulsed detonation) were obtained by varying blockage ratios and air mass flow rates at the global equivalence ratio of around 1.60. The results show that the increase of blockage ratio reduces the critical mass flow rate for the occurrence of multiple waves. The occurrence of multiple waves experiences coexistence of single wave and two co-rotating detonation waves, and steady two co-rotating detonation waves. The increase of blockage ratio intensifies the effect of reflected oblique shock waves on fresh reactants and elevates average pressure in the combustor, which play important role in the occurrence of multiple waves. Moreover, the increase of blockage ratio elevates the pre-combustion pressure. The high pre-combustion pressure resulting from high blockage ratio leads to the existence of volumetric explosion immediately after ignition, which extends the formation time of rotating detonation wave. Further increasing of blockage ratio triggers the longitudinal pulsed detonation (LPD), and the highly decreased injection pressure ratio is considered to be the main reason for the occurrence of LPD.

Influence of Inlet Flow Parameters on Rotating Detonation

The measurement of pseudototal pressure is used to study the impact that a set of guide vanes, called a swirler, has on flow direction in a rotating detonation engine. In experiments, a special swirler redirected the flow ahead of the detonation chamber, and the flow direction downstream of the chamber was determined using a rotatable pseudopitot tube. The study revealed that the flow did not change direction after passing through the detonation wave propagating in the chamber. This leads to the conclusion that hot-flow direction can be controlled through guide vanes placed in the cold flow upstream of the detonation chamber.

Detonation limits in methane-hydrogen-oxygen mixtures: Dominant effect of induction length

New-concept detonation combustors, for example, rotating detonation engines (RDEs), motivate investigations of the phenomena and theory relevant to detonation limits. Because CH4–H2 binary fuel mixtures have excellent combustion performance in engines, it is interesting to investigate the application possibilities of such mixtures in advanced detonation engines. Therefore, the detonation characteristics (e.g., initiation, propagation and failure) and their mechanisms for methane-hydrogen mixtures under different thermodynamic conditions need further study. In this work, the physical connection between detonation limits and induction length (ΔI) of detonation structures for CH4–H2–O2 mixtures is investigated; the dominant effect of induction length on the detonation limits is examined. The results show that a single-headed spinning structure is a unique feature of detonation limits; hence, the detonation limits can be qualitatively estimated by this phenomenon. The relation between λ and ΔI is proportional, and the proportionality factor is 34.62; this relation is applicable in methane/hydrogen and oxygen mixtures with various fuel contents. By scaling the critical pressure pc with ΔI near the detonation limits, the relation between them is shown to be an exponential function: ΔI = 201.2·(1+pc)−2.1.

Effects of Variable Total Pressures on Instability and Extinction of Rotating Detonation Combustion

Instability, extinction and re-initiation of rotating detonation in a two-dimensional Rotating Detonation Engine (RDE) configuration are numerically investigated, and the emphasis is laid on the effects of variable total pressures on the above combustion dynamics. Two conditions, i.e. different constant pressures and time-varying pressures, are considered to investigate the combustion instability in RDE. It is seen that under constant pressure condition the rotating detonation is more prone to instability at low pressure, due to the instability from the deflagrative surface. The intrinsic frequency for the unstable cases with different pressures is close, and maybe related to the RDE configuration and/or fuel properties. For the time-varying pressures with various specified frequencies, the RDE shows the different levels of instability characterized by multiple frequencies. The dominant frequencies vary, depending on the competition between the forced external frequency and the intrinsic one induced by the RDE system. About the extinction of continuously rotating detonation, it can be found that when the total pressure is reduced to a relatively lower value the detonation is quenched and left with deflagrative combustion. Furthermore, when the total pressure is increased based on the extinguished flow fields, detonation fronts are re-initiated due to the local high pressure. The stochasticity in RDE re-initiation has been found, in terms of the location and number of initial detonation front, the propagation direction, their interaction and final stabilization.

Three-dimensional numerical study on rotating detonation engines using reactive Navier-Stokes equations

Three-dimensional simulations on the rotating detonation engine (RDE) are conducted by solving the Navier-Stokes equations in stoichiometric hydrogen/air mixtures. Free-slip wall and non-slip wall boundary conditions are considered. The emphasis is placed on the effects of the viscosity, mass diffusion and thermal conduction on the detonation wave in the RDE, especially in the boundary layer. The simulation results show that the detonation wave propagates with a lower velocity in the Navier-Stokes solutions compared with that in the Euler solutions. This is mainly due to the effects of mass diffusion and thermal conduction. Meanwhile, the two effects above reduce the pressure of the detonation wave in the mainstream. Moreover, the detonation wave height is higher in the Navier-Stokes solutions than that in the Euler solutions. The temperature behind the detonation wave near the walls is much higher than that inside the chamber due to the existence of the boundary layer. Therefore, the viscosity, mass diffusion and thermal conduction impact the detonation velocity, pressure, the detonation wave height and temperature in the RDE.

Rotating detonation engines with two fuel orifice schemes

Hollow combustors without centerbodies are becoming popular for rotating detonation engines. The present experimental study compares detonation and pressure gain performances of hollow combustors with two fuel orifice schemes to choose a better one. Hydrogen and air sources at room temperatures of 280–285 K are used as propellants. The combustors are optically accessible by embedding a piece of quartz glass in the outerbody. The hollow combustor channel here has an outer diameter of 100 mm. Fuel is injected into the combustor from 150 cylindrical orifices in a diameter of 0.8 mm or 90 orifices in a diameter of 2 mm, and air is injected through a circular channel with a throat width of 1 mm. Results show that the hollow combustor with 150 cylindrical orifices in a diameter of 0.8 mm has a better detonation performance and a higher pressure gain performance than the other one. High-speed images show the wall surface roughness affects the RDW strength greatly.

Numerical investigation of a non-premixed hollow rotating detonation engine

Rotating detonation engines (RDEs) are widely studied because of their compact configurations and high thermal cycle efficiency. In this paper, a series of numerical investigations of a non-premixed hollow RDE are performed. The transient explicit density-based solver in ANSYS Fluent is used to perform the simulations. For a hollow RDE without Laval nozzle, there is only one rotating detonation wave in the combustion chamber. Compared to the traditional annular RDE, the mixing quality is deteriorated, and the thrust of the engine decreases and becomes more unstable. When the hollow RDE is attached with a Laval nozzle, there are two rotating detonation waves in the combustion chamber. The pressure within the combustion chamber increases while the axial velocity decreases. The mixing quality is improved. The height of detonation waves decreases with larger contraction ratio of the nozzle. A Laval nozzle is beneficial for a hollow RDE to achieve steadier operation and higher thrust output. When the contraction ratio is 4, the propulsive performance of the engine is the highest. The maximum thrust achieved is 840 N.

Experimental investigation on n-decane plasma cracking in an atmospheric-pressure argon environment

In order to solve the problem of the difficulty of igniting and steadily propagating a continuous rotating detonation engine when using liquid hydrocarbon fuel, an experiment was carried out using a dielectric barrier discharge excited by a nanosecond power supply to crack n-decane, the single alternative fuel to aviation kerosene, in a pre-heated argon environment. By changing the voltages and the discharge frequencies, the concentrations of different components as well as a number of different species were acquired. The generating mechanism of olefins and alkanes together with their competition mechanism were acquired. The influence of the voltage on isomer products was also analyzed. The results demonstrate that the bond energy distribution and the species generating condition are the main factors affecting the formation of the products. With the increasing of voltage and discharge frequency, small molecule olefins, large molecular olefins, large molecular alkanes, small molecular alkanes, and hydrogen were detected, and in turn, their concentrations were also increased except for ethylene; what is more, when the voltage was increased over 8.5 kV, the n-butene converted to trans-butene, and the n-pentene converted to isoamylene.

On the response of annular injectors to rotating detonation waves

A series of three-dimensional, unsteady simulations have been conducted to illuminate the behavior of annular gaseous injectors that are frequently used in rotating detonation engine combustors. The strength (detonation overpressure history) and number of detonation waves in the combustor are investigated as operational parameters along with the injector design (area ratio and length) to assess the impact on the unsteady response of the injection system to the imposed detonation model. Attenuation of the imposed overpressure and reflection off the assumed mass flow inlet boundary are features that are highlighted. The unsteady flow at the exit of the injector as a result of these interactions is found to fluctuate by $$+$$ 80 to − 200%. Strong wave attenuation in the near-exit region of the injector is observed, but acoustic perturbations are seen to propagate throughout the injector, which along with the corresponding reflections persist during the transient injection.

Characterization of Rotating Detonation Engine Injector Response Using Laser-Induced Fluorescence

Rotating detonation engine (RDE) fuel injector response was characterized in a lab-scale linear testing platform. The experimental design consists of a linear extrusion of an RDE cross section and allows rapid interchanging of modular, 3D printed inlet geometries. An array of helium jets was established within a channel, and a single combustion-driven shock pulse was presented at one end. The subsequent injector interruption and recovery were quantified using high-speed acetone planar-laser-induced fluorescence (PLIF). A quartz wall provided optical access to the channel and the injector response was visualized at up to 30 kHz. Three dynamic pressure transducers allowed the shock strength to be quantified along the length of the channel. Timescales associated with jet interruption and recovery were determined by analysis of instantaneous PLIF images and considered in conjunction with the dynamic pressure measurements. Results are presented as a function of pertinent nondimensional parameters and compared with available experimental and computational data in a full, research-scale RDE.

Effects of air injection throat width on a non-premixed rotating detonation engine

Rotating detonation engines are widely studied because of their compact configurations and high thermal cycle efficiency. For simplification, most of the numerical simulations of rotating detonation engines used premixed reactant mixtures. The rotating detonation waves under non-premixed conditions are not studied enough. The width of air injection throat is an important design parameter for a non-premixed rotating detonation engine. Here, a series of three-dimensional numerical simulations of a non-premixed rotating detonation engine with different air injection throat widths are performed. Cases with three different throat widths of 0.4 mm, 1.0 mm and 2.0 mm are calculated. The transient explicit density-based solver in ANSYS Fluent is used to perform the simulations. Detonation combustion happens in different radial domains for different air injection throat widths. When the air injection throat width is 1.0 mm, there is only one rotating detonation wave in the combustion chamber when the total mass flow rate is 272.3 g/s or 500 g/s. When the total mass flow rate is further increased to 1000 g/s, there are two co-rotating detonation waves in the combustion chamber. While for air injection throat width 0.4 mm, the transition to two-wave mode happens at a smaller total mass flow rate of 500 g/s. When the air injection throat width is too large, the interaction between the injection process and the propagating of rotating detonation wave becomes very strong, and the detonation wave quenches due to the insufficient injected reactants. The engine requires a larger total mass flow rate to sustain the continuous propagation of the rotating detonation wave.

Supersonic driven detonation dynamics for rotating detonation engines

In this paper we present the first exploration of detonation wave propagation dynamics in premixed supersonic flows using a novel rotating detonation engine (RDE) configuration. An RDE with a coupled linear extension, referred to as ρDE, is used to divide detonations traveling radially in the RDE into linearly propagating waves. A tangential propagating wave is directed down a modular tangential linearized extension to the engine for ease of optical diagnostics and hardware configuration investigations. A premixed Mach 2 supersonic linear extension is coupled to the ρDE to investigate the effects of varying crossflow configurations for detonation propagation, particularly the interaction between detonations and supersonic reactive mixtures. Detonation waves are generated at the steady operating frequency of the RDE and visualized using high speed schlieren and broadband OH* chemiluminescence imaging. The stagnation pressure was varied from over- to ideally-expanded supersonic regimes. Experimental analysis of detonation interaction with the supersonic regimes show that the detonation propagates freely in the ideally-expanded regime. Deflagration-to-detonation transition (DDT) occurs in the over-expanded regime. Based on the data collected, the DDT process favors supersonic flow with higher source pressures.

Experimental investigation on the propagation mode of rotating detonation wave in plane-radial combustor

A plane-radial rotating detonation engine (RDE) was tested to identify the impact of different injection conditions on the propagation mode and parameters of rotating detonation wave (RDW). Changing the mass flow rate and equivalence ratio, various propagation modes were obtained in experiments: one-wave mode, two-wave mode, three-wave mode and unstable propagation mode. The operating ranges of various propagation modes were acquired. Results indicate that, in this structure, under the condition of stoichiometric ratio, when mass flow rate is less than 122 g/s, the RDE operates in unstable mode, and the RDW propagation velocity is less than 1500 m/s at Ф102 mm. Low frequency oscillation occurs in unstable mode, and the oscillation frequency is approximately 300 Hz. When mass flow rate is greater than 122 g/s, with the increase of mass flow rate, the propagating mode is transformed from one-wave mode to two-wave mode, and then changes into three-wave mode. The propagation velocity in one-wave mode is higher than that in other modes, and varies from 1785 to 1900 m/s. The velocities in two-wave and three-wave mode have little difference, and vary from 1547 m/s to 1650 m/s in two-wave mode, and from 1525 m/s to 1578 m/s in three-wave mode. The mass flow rate has only a slight effect on the RDW propagation velocity, but a large effect on the pressure peak under the same mode. Furthermore, the variation of equivalence ratio will alter the propagation mode, and the RDE operating range of equivalence ratio widens as the mass flow rate increases.

Experimental investigation on delay time phenomenon in rotating detonation engine

This study explored the phenomenon of the detonation formation delay time in an RDE with an annular combustion chamber with an array of holes fueled with hydrogen. It was determined that the delay time increased when the combustor prefilling time increased. Due to the explosion, the interaction of the shock wave and the pressure wave in the combustor leads to an increase in pressure near the inlet wall surface, thereby impeding the gas feeding. The wavelet transformation was used to analyze the pressure time signal associated with the detonation wave, which was found to be better than the fast Fourier transform typically used. Moreover, the phenomenon of single–double–single wave transformation was observed, of which the underlying mechanism can be explained by an interactive-adjusting process. Also, the experiment captured the reinitiation phenomenon of detonations after a long period of time (around 300 ms) of extinction.

Performance Sensitivities of Rotating Detonation Engines Installed onto Waverider Forebodies

The installed performance of a rotating detonation engine in a waverider vehicle was investigated. An ideal parametric analysis was performed by combining a waverider forebody generated by the osculating flowfield method and a second-order performance model for a rotating detonation engine. The analysis examined the waverider forebody geometry and freestream conditions on engine performance, with emphasis on volumetric efficiency and vehicle range. Design cases were selected by considering the physical limitations of initiating and sustaining a detonation wave. The greatest pressure recovery, and therefore the greatest installed engine performance, was observed at small waverider cone angles and convex forebody profiles. Engine performance was found to improve with increasing Mach number, but propellant autoignition temperature limits might present a barrier to operation at freestream Mach numbers above 3.5. These limits were eased, and performance increased, at higher dynamic pressures of operation. Mass-independent range metrics were observed to be insensitive to freestream parameters.

Velocity behavior downstream of perforated plates with large blockage ratio for unstable and stable detonations

Due to the excellent thermal propulsion performances of detonation, it has been applied for the purpose of aerospace propulsion devices, e.g., pulse detonation engines (PDEs), rotating detonation engines (RDEs), and oblique detonation wave engines (ODWEs). However, it remains challenging for developing those new-concept propulsion devices, mainly because it is a formidable task to establish a steady and self-sustained detonation in the hypersonic flow and combustible mixture. One of the fundamental problems is to understand the interaction of diffractions and the detonation waves within the engines. In this study, perforated plates with various blockage ratios are seated at the beginning of the detonation propagation to explore the diffractions that generated from the plates on the detonation propagation mechanism. Two explosive mixtures of C2H2 + 5N2O and C2H2 + 2.5O2 + 70% Ar are studied to illustrate the difference in propagation velocity behavior of detonation after it suffers from large-scale diffractions. The results show that diffractions have less effect on the propagation of highly unstable mixture, and the effect becomes obvious as BR increases to 0.962; this phenomenon occurs because detonation has an irregular cellular pattern and sub-structures are characterized by highly unstable detonation, in which the detonation instabilities are amplified by the large perturbations of obstacles, leading to an augment in forming more cellular cells of detonation in its front that cover the weakening effects from diffractions. In contrast, the diffractions significantly affect the stable mixture, manifested by a remarkable increase of the critical pressure for a self-sustained detonation downstream of the obstacle with the augment of blockage ratio; this phenomenon can be attributed to the diffractions being distributed along the curvature over the detonation surface, thereby causing more excessive curvature of the entire detonation front, which in turn exacerbates the failure of detonation.