Rotating Detonation Engine Research Articles

RDE research and development in Poland

A very short survey of research conducted in Poland on the development of the rotating detonation engine (RDE) is presented. Initial studies conducted in cooperation with Japanese partners lead to development of a joint patent on RDE. Then, an intensive basic and applied research was started at the Institute of Heat Engineering of the Warsaw University of Technology. One of the first achievements was the demonstration of performance of the rocket engine with an aerospike nozzle utilizing continuously rotating detonation (CRD), and research was directed into development of a small turbofan engine utilizing such a combustion regime. These activities promoted international cooperation and stimulated RDE development not only in Poland but also in other countries. A research directed to measure and calculate flow parameters as well as to analyze the use of liquid fuels was conducted. In the Institute of Aviation in Warsaw, research on the application of the CRD to turbine engines as well as rocket, ramjet, and combined cycle engines was carried out. In the paper, a special emphasis is given to international cooperation in this area with partners from many countries engaged in the development of the pressure gain combustion to propulsion systems.

Effects of the dimensionless radius of an annulus on the detonation propagation characteristics in circular and non-circular rotating detonation engines

Effects of the dimensionless radius of an annulus on the detonation propagation characteristics in circular and non-circular rotating detonation engines

Torque Around Axial Direction on Rotating Detonation Engines

A rotating detonation engine (RDE) generates a continuous thrust with one or more rotating detonation waves. Because of the velocity on the order of kilometers/second, the reaction zone is relatively small. Therefore, the RDE realizes a short combustion chamber length. However, the detonation waves induce an azimuthal motion of propellant, resulting in torque around the thrust axis. Because the motion does not contribute to the thrust, the torque is important in terms of performance loss. Herein, we conducted combustion tests with a six-axis force sensor to simultaneously measure torque and thrust. A comparison of detonation waves captured by high-speed camera revealed that the torque followed the direction and was offset when the waves existed in both of two directions simultaneously, which indicates the possibility of controlling the torque. Under a mass flow rate at and an equivalence ratio at , when the azimuthal component of shear force was of the thrust, of the total kinetic energy of the exit flow was distributed to the azimuthal component of velocity and did not contribute to the thrust. We therefore concluded that the effect of the azimuthal motion on the RDE’s performance was small.

Numerical investigation on formation mechanism of low-frequency detonation instability

In recent years, rotating detonation engine (RDE) has been wisely studied in the world due to its inherent advantages. In the process of the application of RDE, the stable and reliable performance of the engine is always what researchers pursue. In the process of the research on RDE, a phenomenon called Low Frequency Instability (LFI) has been widely found. But so far, the exact mechanism behind LFI hasn’t been really revealed yet. In this paper, a numerical investigation of LFI was performed. In the numerical study, Euler equation with source terms was chosen as the governing equation, ignoring viscosity, thermal conduction, and mass diffusion. The Strang’s operator splitting method, the fifth order weighted essentially non-oscillatory scheme (WENO) and the second order total variation diminishing (TVD) Runge-Kutta method were used. With the methods mentioned above, the mechanism behind LFI and the whole detailed process of shock waves causing this phenomenon were finally revealed. It is shown that near the inlet wall there exist some reverse shock waves (propagating in the opposite direction to the rotating detonation waves), which will interact with the inlet wall and therefore generate some injet blocking point (IBP) in the fresh gas layer which will make the fresh gas layer periodically irregularly distributed. The irregular fresh gas layer will cause the distribute of the pressure on the detonation front changes periodically. With the positions where the IBPs are generated moving slowly along the inlet wall, the distance between the sampling point and the last IBP will gradually changes, and this will lead to that every time the rotating detonation wave meet the sampling point, the pressure of the place where the detonation front contacts with the inlet wall (and so contacts with the sampling point) is different from the last time. Therefore, the peak pressure at the sampling point oscillates at a low frequency and in another word, a so called low frequency instability is formed.

Experimental verification of cylindrical air-breathing continuous rotating detonation engine fueled by non-premixed ethylene

An especial air-breathing continuous rotating detonation engine without a centerbody is proposed to reduce energy loss and simplify the structure, which is analogous to a typical scramjet combustor with the cavity. Non-premixed ethylene/air rotating detonation experiments are performed in a direct-connect experimental facility with an air inflow of 860 K total temperature (Ma 2.02). Two combustion modes (continuous rotating detonation and deflagration mode) are discovered with varying equivalent ratio (ER). A proper accumulation layer of the combustible mixture in the cavity re-circulation region attaching the outer wall is critical for rotating detonation realization. The average propagation velocity of the detonation wave is 1297.1 m/s (78.5% C-J velocity) at ER = 0.64 with the combustor pressure of 230 kPa. Its motion of the reaction zone is quantitatively verified to be rotating through the integral of chemiluminescence intensity. Besides, it is confirmed by the optical observation that deflagration could also self-sustain in the short combustor with the axial-moving flame. The combustor pressure of deflagration mode can reach 220 kPa with ER = 0.56. Though the combustor pressure of detonation is slightly higher than that of deflagration, the impact of combustor high-pressure on the inflow of detonation mode is much stronger through the induced oblique shock wave.

Experimental study on the effect of equivalent ratio on working characteristics of gasoline fuel two-phase rotating detonation engine

To understand the effect of equivalent ratio on the working characteristics of gasoline fuel two-phase rotating detonation engine, a gas-liquid two-phase rotating detonation experimental study with high total temperature air as oxidant has been carried out in this work. The outer diameter, inner diameter and length of rotating detonation engine annular combustor are 202, 166 and 155 mm, respectively. Gasoline and high temperature air are injected into the combustor through a nozzle-gap impinging model constructed of high pressure atomizing nozzles and annular gap to improve the mixing effect and chemical activity of propellant. A pre-detonator tube is used as ignition device. In experiments, the equivalent ratio of propellant is controlled by changing the mass flow rate of gasoline with constant mass flow rate of air. Based on high frequency dynamic pressure signals and average static pressure measured in the combustor, the propagation mode and propagation characteristics of the gas-liquid two-phase rotating detonation wave and working characteristics of the engine were analyzed in details. Experimental results show that continuous self-sustained propagation of rotating detonation wave is realized in the combustor during the equivalent ratio ranging from 0.79 to 1.25. With the increase of the equivalent ratio, the propagation mode of detonation wave transforms from double wave collision/single wave mixed mode to single wave mode. By reducing the equivalent ratio to 0.61−0.66, the propagation stability of detonation wave becomes worse, and the propagation mode transforms to the intermittent detonation or sporadic detonation. When reducing the equivalent ratio to 0.52, the detonation initiation fails. In addition, with the increase of the equivalent ratio, both the average absolute pressure in the combustor and the average propagation frequency of detonation wave increase and then decrease, and the maximum value appears around the equivalent ratio of 1.19. Under this condition, the best experimental results are obtained. The average propagation frequency of detonation wave is 1 900.91 Hz, and corresponding average propagation speed is 1 110.8 m/s, which are consistent with the main frequency obtained from Fast Fourier Transform of high frequency pressure signal. There is a heavy velocity deficit existing during the propagation of detonation wave.

Data-driven surrogates of rotating detonation engine physics with neural ordinary differential equations and high-speed camera footage

Interacting multi-scale physics in the Rotating Detonation Engine (RDE) lead to diverse nonlinear dynamical behavior, including combustion wave mode-locking, modulation, and bifurcations. Here, surrogate models of the RDE physics, including combustion, injection, and mixing, are sought that can reproduce mode-locked combustion waves through their interactions. These surrogate models are constructed and trained within the context of neural ordinary differential equations evolving through the latent representation of the waves: the traveling wave coordinate ξ=x−ct+a. It is shown that the multi-scale nature of the physics can be successfully separated and analyzed separately, providing valuable insight into the fundamental physical processes of the RDE.

Multiscale physics of rotating detonation waves: Autosolitons and modulational instabilities.

Proposed is a phenomenological modeling framework that is capable of reproducing the diverse experimental observations of the nonlinear, combustion wave propagation in a rotating detonation engine (RDE), specifically the nucleation and formation of combustion pulses, the soliton-like interactions between these combustion fronts, and the fundamental, underlying Hopf bifurcation to time-periodic modulation of the waves. In this framework, the mode-locked structures are classified as autosolitons or stably propagating nonlinear waves where the local physics of nonlinearity, gain, and dissipation exactly balance. We find that the global dominant balance physics in the RDE combustion chamber are dissipative and multiscale in nature: The fast combustion physics provide the energy input to form the fundamental mode-locked autosoliton state, while the slow physics of exhaust and propellant recovery shape the waveform and dictate the number of autosolitons. In this manner, the global multiscale balance physics give rise to the stable structures-not exclusively the frontal dynamics prescribed by classical detonation theory. Experimental observations and numerical models of the RDE combustion chamber are in strong qualitative agreement. Moreover, numerical continuation (computational bifurcation tracking) of the RDE analog system indicates that a Hopf bifurcation of the steadily propagating pulse train leads to the fundamental instability of the RDE, or time-periodic modulation of the waves. Along branches of Hopf orbits in parameter space exist a continuum of wave-pair interactions that exhibit solitonic interactions of varying strength.

Numerical investigation of pre-detonator in rotating detonation engine

Pre-detonators are commonly used in rotating detonation engine (RDE) experiments. Current experimental studies focus on the performance of pre-detonator while ignoring the influence of pre-detonator on the flow field. In numerical simulations one-dimensional detonation wave is usually used to ignite the fresh gas in RDE. This is a simplification of the pre-detonator used in practical hotfire tests. But the coupling between the pre-detonator and the combustor is ignored. The aim of the present study is to study the influence of pre-detonator on the flow field in the RDE. A model of RDE with a pre-detonator is built, in which three-dimensional numerical simulations fueled with hydrogen/air is performed. The influence of pre-detonator on the combustor in different stages is studied. After initiation, detonation wave from the pre-detonator forms two counter-rotating detonation waves. The tangential installation of pre-detonator fails in directional initiation of detonation wave. The coupling effect is shown as the reflection and expulsion of shock wave. Detonation wave or oblique shock wave in the combustion chamber enters the pre-detonator and turns into shock wave before colliding with the end and re-entering the combustion chamber. Under some circumstances, the reflected shock wave will initiate a detonation wave and affect the wave structure in the combustion chamber. In the stable stage, the reflected shock wave has no effect on the flow field. However, periodic collision of reflected shock wave with detonation wave at the junction causes ablation in long-time experiments. Increasing the axial distance between pre-detonator and injection wall is expected to be a solution for the ablation problem.

Shock dynamics and expansion characteristics of an aerospike nozzle and its interaction with the rotating detonation combustor

The flow of products through the aft-end of a detonation combustor is intrinsically unsteady, ultimately resulting in periodic and nonuniform flow parameters at the exit plane of a rotating detonation combustor. Therefore, the integrated design of the nozzle and combustion chamber is an important challenge in rotating detonation engines (RDEs). This paper describes a thorough three-dimensional numerical simulation of a hydrogen–air rotating detonation combustor with/without an aerospike nozzle and investigates the nozzle flow without a combustor. The simulation results allow us to analyze the coupling characteristics of the rotating detonation combustor and the aerospike nozzle. The new features of the shock wave dynamics and expansion characteristics in the nozzle with/without an integrated RDE combustor are compared. For the same rotating detonation combustor exit, the propagation mode of the detonation wave and backpressure in the RDE combustor exit are affected by the aerospike nozzle. The intensity of the shock wave and the angle with respect to the direction of the air flow are lower with the aerospike nozzle than in the nozzleless model, which is consistent with the effect of backpressure increase on the shock dynamics. Regardless of whether the nozzle is connected to the combustor, the nozzle affects the dynamic alternation of the design point state to over-expansion and under-expansion along the circumferential direction. The shock wave intensity and total pressure recovery inside the nozzle with the combustor are slightly stronger than those in the nozzle without the combustor. Consequently, the thrust and total pressure recovery of the nozzle integrated with the RDE combustor are enhanced by 7% and 5.6%, respectively. Thus, decoupling the nozzle from the rotating detonation combustor is feasible for testing the design performance of the unsteady nozzle.

A rotating detonation engine using methane-ethylene mixture and air

Most of hydrocarbon fuels often have larger methane numbers than hydrogen. It is more difficult to detonate the mixture of hydrocarbon fuels and air at room temperatures in non-premixed engines since the mixing is slower than hydrogen-air mixing and the mixing is slower at lower temperatures. Ethylene–air rotating detonation operations have been successful, but methane-ethylene-air mixture at room temperatures is more difficult to detonate for rotating detonation engines since methane is more chemically stable. The hollow combustor channel here had an outer diameter of 220 mm and a length of 163 mm. Methane-ethylene mixture was injected axially into the combustor from cylindrical orifices in a diameter of 0.8 mm, and air was injected radially through a convergent-divergent circular channel with a throat width of 0.8 mm. Non-premixed rotating detonation waves were obtained for methane-ethylene-air mixture at total temperatures of 280–285 K in the present study. Both high-speed images and pressure traces show that three-wave mode has a higher detonation speed than five-wave mode. The rotating detonation speed is increased with the increased detonation height.

Carbon-Based Multi-Phase Rotating Detonation Engine

Abstract This article focuses on extending an H2/air rotating detonation engine's detonability limits by introducing solid carbon particles into the combustor. Carbon black particles consisting of 1% volatility and a carbon concentration of 99% were used as a solid-phase mixing agent for enhanced reaction wave dynamics. Carbon black was found to sustain detonations over multiple operational regimes formerly unattainable without carbon particles. The experiments confirm that detonations were attainable over a wide range of operational parameters, including the total mass flux flowing through the annulus (≅120–270 kg/s m2), the hydrogen/air equivalence ratios (0.65–1.0), and carbon additions (0–20 g). Chemiluminescence imaging was used to visualize the detonation wave within the annulus, quantify detonation wave velocities, and define a detonability map. The detonability map demonstrates the advantage of carbon addition, shows that detonation-based combustion can be sustained at leaner equivalence ratios, reduces hydrogen consumption dependency. The detonation wave velocities decreased as the H2/air equivalence ratio was reduced, where, in general, the detonation wave velocities decreased with respect to the Chapman–Jouguet velocity, suggesting a decrease in the detonation waves efficiency with reduced H2 concentrations. However, an extraordinary phenomenon was witnessed at very lean H2/air equivalence ratios and low mass flux conditions, where the detonation wave velocity increased upward of 100 m/s. This variation is a direct effect of the carbon particles, which drive the detonation wave. Thus, the results demonstrate that carbon particles’ addition provides an economically feasible solution to sustain high-efficiency energy production.

Flow and performance analysis of a natural gas-air rotating detonation engine with high-speed velocimetry

An experimental investigation of a high pressure, natural gas-air rotating detonation engine is presented. Simultaneous high-speed measurements of combustion chamber pressure, axially-integrated chamber chemiluminescence, and particle image velocimetry at the combustor exit plane were used to qualitatively and quantitatively analyze the exhaust flow of two test conditions with distinct wave dynamics. A single detonation wave with an intermittent counter-rotating wave was characterized in the first test case, while a steady counter-rotating mode was studied in the second. Analysis using the continuous wavelet transform informs the coupled shift in the frequency and amplitude of pressure and velocity fluctuations observed in the raw timeseries. The high-speed measurements are used to reconstruct the wave structure for each case over the course of a cycle, revealing the canonical rotating detonation engine exhaust flow structure with a trailing oblique shock sweeping through the products for the single wave case. Interactions between counter-propagating detonation fronts result in a flowfield that varies with cycle phase angle, in contrast to the self-similar field of the single propagating wave. The axial velocity profile around the circumference of the combustor is independent of wave location, while azimuthal velocity fluctuations from the trailing oblique shocks are observed to track the detonation fronts and destructively interfere at wave intersections. The total pressure and temperature of flow exiting the combustor are computed using the phase-resolved velocity measurements along with the measured reactant flowrate and thrust to close the global balance of mass and momentum. The case with counter-rotating waves delivers 5% higher performance than the single-wave case. The application of simultaneous high-speed diagnostics helps elucidate the flow structure in a rotating detonation engine and provides a connection between the local flow structure and global combustor performance.

Small-size rotating detonation engine: scaling and minimum mass flow rate

Rotating detonation engines (RDEs) have been observed to exhibit several operating modes and instabilities under different operation conditions (reactant mixture, injection pressure, engine geometry, injection mass flow rate, etc.). We develop the simplest model possible describing the operation of an RDE. This model takes into account the dependence of detonation properties on engine conditions, the injection process, and the geometric constraints. Using this model, we predict the lowest allowable reactant injection rates that allow an RDE to operate with a single detonation wave propagating in the annular combustion chamber. This model is compared with experimental results of engines running on H $${}_2$$ /O $${}_2$$ and C $${}_2$$ H $${}_4$$ /O $${}_2$$ .

Experimental and theoretical analysis of carbon driven detonation waves in a heterogeneously premixed Rotating Detonation Engine

Coal dust explosions can be hazardous; however, they can also generate a significant rise in stagnation pressure if adequately harnessed. Rotating detonation combustors seek to take advantage of the stagnation pressure rise phenomenon in a more sustained and controlled manner via confinement to a physical annulus, leading to increased overall thermodynamic efficiency. This investigation presents an analysis of detonations fueled by Carbon Black, a solid particulate consisting of virtually pure carbon molecules and lean Hydrogen-Air mixtures. It is realized that with the addition of Carbon Black, an increase of lean mixture detonability and detonation velocities extending the operating limit over that of a pure hydrogen-air mixture is experienced. For all testing conditions, the total equivalence ratio is held at φ = 1, while the fuel mixture's carbon mass fraction is increased from 0 to 0.7 while the hydrogen is decreased. Detonation wave velocities are extracted from high-speed imaging through applying a Discrete Fourier Transform algorithm to determine changes to the wave speed as Carbon Black particles are introduced. As a result, due to the addition of Carbon Black as an auxiliary fuel source, detonations were formed instead of deflagrations in operating conditions where one would expect deflagrations at the same hydrogen-air equivalence ratios without Carbon Black addition. The detonation formation provides evidence that the coal particles are reacting within the detonation wave in a large enough capacity to support a detonation wave within the annulus. Furthermore, the wave speed is shown to increase with the additional of carbon particles. At a constant global equivalence ratio, the detonation wave velocities were found to decrease with hydrogen's incremental replacement with coal particles. Whereby, through a theoretical comparison of the heat of combustion as computed from the experimentally derived detonation wave velocities, a linear relationship of the two was shown to exist. Therefore, the heat of combustion has the potential to describe an operational limit to sustaining a detonation wave.

Computational and Experimental Study of Nozzle Performance for Rotating Detonation Rocket Engines

A computational and experimental study was conducted on nozzle geometries for rocket application rotating detonation engines (RDEs). Three geometries, including a nozzleless blunt body typically employed in RDE combustor hot-fire testing and two aerospike nozzles, were investigated. Simulations of the exhaust flow of a rotating high-frequency, high-pressure ratio wave based on rocket RDE test results were related to comparable constant-pressure conditions. Computational and experimental results showed the high momentum added by the highest-pressure detonation products influences the exhaust plume differently than a comparable steady flowfield fed by the same average product gas flow rate. In particular, the RDE exhaust flow tended to enhance entrainment on the nozzleless blunt body recirculation region and delay flow separation on nozzle expansion surfaces due to overexpansion compared to a constant-pressure engine. Results have important ramifications for isolating RDE combustor performance from nozzle effects and must be considered for future design of nozzle geometries to exploit the high-frequency, high-pressure ratio outflow of an RDE.

Data-driven modeling of rotating detonation waves

A rotating detonation engine displays complex nonlinear shock front propagation dynamics which impede effective dimensionality reduction. A novel optimization is used to discover separate low-rank modes and interpretable dynamics for each front's propagation. Koopman autoencoders similarly enable separation and forecasting of shock wave interactions.

Role of overdriven state of ignition wave in pre-detonators on detonation transition modes in a flat chamber

Using the small-diameter pre-detonator is an important method to provide reliable and fast detonation to the denotation engines (i.e., pulse detonation engines or rotating detonation engines). This work examines the role of the overdriven state of ignition waves generated in pre-detonators on detonation transition modes in a flat chamber. For this purpose, a series of experiments are performed using different lengths of pre-detonators (Lp) with different mixtures to initiate the detonation in the main chamber. Results show that maintaining an overdriven state at the pre-detonator exit can significantly enhance the probability of fast detonation initiation (i.e., supercritical/critical mode) in the main chamber. Especially for the high nitrogen diluting ratio (β) mixtures, forming the overdriven detonation at the pre-detonator exit becomes a necessary condition for the fast initiation. As a result, the fast detonation initiation mode distributes in an upper-right shrinking ‘canyon’ in the Lp-β map. It is illustrated that the increased overdriven degree required for transitioning detonation wave under the higher β cases is responsible for this observation.

Application of a Convolutional Neural Network for Wave Mode Identification in a Rotating Detonation Combustor Using High-Speed Imaging

Abstract Utilizing a neural network, individual down-axis images of combustion waves in the rotating detonation engine (RDE) can be classified according to the number of detonation waves present and their directional behavior. While the ability to identify the number of waves present within individual images might be intuitive, the further classification of wave rotational direction is a result of the detonation wave’s profile, which suggests its angular direction of movement. The application of deep learning is highly adaptive and, therefore, can be trained for a variety of image collection methods across RDE study platforms. In this study, a supervised approach is employed where a series of manually classified images is provided to a neural network for the purpose of optimizing the classification performance of the network. These images, referred to as the training set, are individually labeled as one of ten modes present in an experimental RDE. Possible classifications include deflagration, clockwise and counterclockwise variants of co-rotational detonation waves with quantities ranging from one to three waves, as well as single, double, and triple counter-rotating detonation waves. After training the network, a second set of manually classified images, referred to as the validation set, is used to evaluate the performance of the model. The ability to predict the detonation wave mode in a single image using a trained neural network substantially reduces computational complexity by circumnavigating the need to evaluate the temporal behavior of individual pixel regions throughout time. Results suggest that while image quality is critical, it is possible to accurately identify the modal behavior of detonation waves based on only a single image rather than a sequence of images or signal processing. Successful identification of wave behavior using image classification serves as a steppingstone for further machine learning integration in RDE research and development of comprehensive real-time diagnostics.

Multidimensional Numerical Modeling of Combustion Dynamics in a Non-Premixed Rotating Detonation Engine With Adaptive Mesh Refinement

Abstract In the present work, a novel computational fluid dynamics (CFD) methodology was developed to simulate full-scale non-premixed rotating detonation engines (RDEs). A unique feature of the modeling approach was the incorporation of adaptive mesh refinement (AMR) to achieve a good trade-off between model accuracy and computational expense. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations were performed for an Air Force Research Laboratory (AFRL) non-premixed RDE configuration with hydrogen as fuel and air as the oxidizer. The finite-rate chemistry model, along with a ten-species detailed kinetic mechanism, was employed to describe the H2-Air combustion chemistry. Three distinct operating conditions were simulated, corresponding to the same global equivalence ratio of unity but different fuel/air mass flowrates. For all conditions, the capability of the model to capture essential detonation wave dynamics was assessed. An exhaustive verification and validation study was performed against experimental data in terms of a number of waves, wave frequency, wave height, reactant fill height, oblique shock angle, axial pressure distribution in the channel, and fuel/air plenum pressure. The CFD model was demonstrated to accurately predict the sensitivity of these wave characteristics to the operating conditions, both qualitatively and quantitatively. A comprehensive heat release analysis was also conducted to quantify detonative versus deflagrative burning for the three simulated cases. The present CFD model offers a potential capability to perform rapid design space exploration and/or performance optimization studies for realistic full-scale RDE configurations.