Rotating Detonation Engine Research Articles

A Short Review on Efficiency of Rotating Detonation Engine

The rotating detonation engine (RDE) is a revolutionary propulsion technology with the potential to significantly enhance the efficiency of propulsion systems. This paper provides an in-depth review of the RDE's efficiency, its advantages over pulse detonation engines (PDEs) and deflagration concepts, as well as its applications in rocketry. The historical development of detonation engines, specifically RDE, is discussed, along with various research methodologies applied in both atmospheric and vacuum conditions. The challenges and potential solutions for utilizing RDE in space missions are also explained in this paper.

Critical Decay Time Model for Direct Detonation Initiation Energy in Gaseous Mixtures

A critical decay time (CDT) model is developed to predict the critical energy of direct detonation initiation in gaseous mixtures. It is based on the global initiation criterion that the energy deposit should allow the decaying shock speed to stay in a specific range below the Chapman–Jouguet (CJ) speed at least for a critical decay time. The speed range is estimated with the sub-CJ Zel’dovich–von Neumann–Döring (ZND) simulations. The critical decay time is calculated as the minimum time to reach unity Mach number in the sub-CJ ZND simulations. The lower-speed bound is taken as a characteristic extinction speed below (which means the lower-speed bound) which the direct initiation should fail. This speed is calibrated using one-dimensional simulations for hydrogen (H2)–oxygen (O2)–argon (Ar) mixtures. The calibrated CDT model is then applied to estimate the critical initiation energy with the point-blast theory. The model yields better agreement with experimental data for hydrogen-fueled mixtures such as H2─O2─Ar and H2─air mixtures than the well-known critical decay rate model. For small hydrocarbon-fueled mixtures such as acetylene (C2H2)─O2─Ar, methane (CH4)–air, ethylene (C2H4)–air, and ethane (C2H6)─air mixtures, the predicted critical energies also agree well with experimental results. The CDT model provides an efficient tool to evaluate the detonability of fuel–oxidizer mixtures, which could be beneficial for ignition initiation in propulsion and power devices such as rotating detonation engines.

Investigation of multi-stage evaporation and wave multiplicity of two-phase rotating detonation waves fueled by ethanol

In this study, a numerical investigation based on the Eulerian-Lagrangian model is conducted to explore a rotating detonation engine (RDE) fueled by liquid ethanol. The focus is on examining the characteristic phenomena of the two-phase rotating detonation wave (RDW) caused by droplet evaporation and varying inlet conditions. To enhance the evaporation of liquid fuel, pre-heated air is used, and both liquid and pre-vaporized ethanol are simultaneously injected. The distribution of ethanol droplets reveals an initial concentration near the injection surface and accumulation in the fuel-refill zone. Here, liquid droplets gradually evaporate after absorbing latent heat from the surrounding gas. The subsequent interactions between the evaporating droplets and the RDW vary with the droplet size. For droplets with diameters of d0 = 5–15 μm, after being swept by the RDW, a secondary evaporation process occurs, leading to an enlargement of the width of the reaction zone. However, the chemical reactions still predominantly take place in close proximity to the detonation front. As d0 further increases, droplet evaporation persists in the post-detonation expansion zone over a long distance until the remaining droplets are fully evaporated and eventually burned in this region. The study also analyzes the extinction of rotating detonations and the emergence of new detonation waves resulting from local explosions and consequent shock collisions. It is demonstrated that variations in the diameter of injected droplets and inlet temperature can lead to different operating modes with varying numbers of RDWs.

Numerical study on the effect of carbon particles on flow field characteristics of rotating detonation engine

Rotating detonation engines have high thermal efficiency and thus have been extensively studied. Using solid particles as fuel can reduce costs, and experiments have demonstrated the feasibility of gas-solid two-phase rotating detonation. However, numerical simulation research is required that examines the flow field characteristics of a rotating detonation engine. In order to explore the role of carbon particle fuel in a gas-solid two-phase rotating detonation wave, the weighted essentially non-oscillating scheme and third-order total variation diminishing Runge-Kutta scheme are used to solve the gas-solid unsteady Eulerian–Eulerian equations. Finite rate chemical and surface reaction models are used to simulate the combustion of gaseous substances and carbon particles. The influence of the proportion of carbon particles in the fuel and the diameter of the carbon particles on the rotating detonation flow field characteristics is analyzed. The results indicate that when the size of carbon particles is in the micrometer scale or below, the two-phase rotating detonation waves exhibit double-front or single-front detonation structures, respectively. Adding carbon particles to the fuel enables the rotating detonation engine to achieve a total pressure gain.

Effects of the perturbation inlet on the evolution and oscillation characteristics of multiple rotating detonation waves

A numerical simulation using the open-source platform OpenFOAM is conducted to investigate the effect of periodic perturbations at the inlet on the evolution and oscillation characteristics of multiple rotating detonation waves (RDWs). The study uses a two-step chemical reaction mechanism of C2H4/Air. The results reveal that periodic perturbations have a significant effect on the pressure, detonation wave height, heat release rate, thrust, and specific impulse of the rotating detonation engine. The oscillation pattern of these parameters is found to be highly correlated with the form of the inlet perturbations. The study also examines the evolution mechanism of multiple detonation waves and identifies three primary propagation stages under inlet perturbations: chaotic propagation, self-adjustment, and oscillatory propagation. The multiple detonation waves originate from the chaotic propagation and are mainly adjusted in terms of the number and direction of detonation waves through the double-wave collision. The results demonstrate that increasing the amplitude of perturbations poses a significant risk to the survival of the RDW, while high-frequency perturbations may disrupt the three primary propagation stages, leading to predominantly the chaotic propagation. Furthermore, an analysis of the fast Fourier transform of the thrust and specific impulse shows that the oscillation forms of the specific impulse and thrust differ in the chaotic propagation stage.

Effect of Combustor Outlet Geometry on Operating Characteristics of Disk-Shaped Rotating Detonation Engine

A disk-shaped rotating detonation engine with H2/air mixture was tested to identify the impact of combustor outlet geometry on the engine’s operating characteristics. Three combustor outlet diameters and five outlet lengths are employed in the experiments. Results show that with the increase of combustor convergent ratio, the propagation stability of the rotating detonation wave decreases, and the propagation velocity and pressure peak decrease slightly. When the convergent ratio increases to a certain value (1.70 in this study), a “platform zone” with a lower pressure value appears before the sharp rise of the dynamic pressure curve. The propagation mode varies with the increase of mass flow rate at different convergent ratios. As the mass flow rate increases, the wave head number in the combustor increases. But the change rule of propagation mode with mass flow rate is greatly affected by convergent ratio. Increasing the convergent ratio is conducive to the formation of multi-wave modes, and the critical mass flow rate for mode transition drops sharply. When the convergent ratio increases to 1.70, the unstable asymmetric dual-wave mode is obtained. With the increase in the convergent ratio, the engine’s operating range and operating stability decrease significantly. Finally, changing the combustor outlet length has little influence on the engine’s operating characteristics and detonation-wave parameters.

Study of the characteristics and combustion efficiency of liquid kerosene/oxygen-enriched air rotating detonation wave with different modes

In a liquid kerosene rotating detonation engine (RDE), detonation waves often exhibit different propagation modes. The propagation characteristics with different modes are worthy of further study. To further investigate the propagation characteristics, a series of experiments was conducted, and the flow field characteristics under different modes were comparatively studied using high-speed photography and pressure sensors. The modal features and mode change trends obtained in the experiments were simulated using numerical methods. Based on this, the combustion efficiencies of the different modes were quantitatively characterized. The results showed that with increasing propellant mass flux, the detonation wave gradually changes from the two-counter wave mode to the single-wave mode, and the interim mode is a hybrid mode. Compared with the two-counter wave mode, the velocity deficit of a single wave is smaller, and the reaction zone is more compact. Numerical simulations show that a higher proportion of fuel is consumed by more violent chemical reactions in the single-wave mode; that is, the combustion efficiency in the single-wave mode is higher than that in the two-wave mode. The results provide a reference for further understanding the liquid fuel detonation phenomenon and improving fuel combustion efficiency.

Experimental investigation on the performance of the variable cross section rotating detonation engine

Optimizing the structure of the rotating detonation engine (RDE) is an effective way of improving its performance. In this paper, a variable cross section RDE with convergent-channel combustor (CC-RDE) is designed and compared with annular-channel combustor (AC-RDE). The operation range, propagation characteristics of rotating detonation waves (RDWs), and working performance were analyzed. In this study, the combustor outlet blockage ratios of both RDEs were equal, both being 0.35. The results show that the CC-RDE increased the propellant flow velocity, thus increasing the chemical reaction rate, and led to a comparative increase in RDW intensity of up to 185.4%. However, the higher the RDW intensity, the more likely the air plenum and the combustor were to be coupled, which shortened the range of stable operation. The RDW position under two RDEs were approximately 100 mm away from the combustor inlet. The percentages of pressure feedback and pressure pulsation in the air plenum were defined to evaluate the extent of pressure feedback. The results show that a higher RDW intensity in the CC-RDE led to a greater pressure pulsation in the air plenum. When the unstable mode appeared, the pressure feedback further increased. The heat flux of the combustor was also measured to assess the thermal environment of the RDE. The rates of chemical reaction and energy release were higher when the CC-RDE was used, and the average heat flux increased by 40.2% compared with that of the AC-RDE. Moreover, the specific thrust of the CC-RDE was increased by 40.3%.

Experimental Study on the Propagation Characteristics of Rotating Detonation Wave with Liquid Hydrocarbon/High-Enthalpy Air Mixture

Rotating detonation engines (RDEs) are a promising propulsion technology featuring high thermal efficiency and a simple structure. To adapt the practical engineering applications of ramjet RDEs, rotating detonation combustion using a liquid hydrocarbon and pure air mixture will be required. This paper presents an experimental study on the propagation characteristics of rotating detonation waves with a liquid hydrocarbon and high-enthalpy air mixture in a hollow cylindrical chamber. The parameters, such as the equivalence ratio and inlet mass flux, are considered in this experiment. The frequency and the propagation velocity of rotating detonation combustion are analyzed under typical operations. The experimental results show that the peak pressure and propagation velocity of the rotating detonation wave are close to the C-J theoretical values under the inlet mass flux of 400 kg/(m2s). Both the propagation velocity and peak pressure of the rotating detonation wave decrease as the mass flux and equivalence ratio are reduced while the number of detonation wavefronts increases. Detonation wave instability tends to occur when the inlet mass flux decreases. There is a transition progress from thermo-acoustic combustion to rotating detonation combustion in the experiment under the condition of mass flux 350 kg/(m2s) and the equivalent ratio 0.8. The static pressure in the chamber is higher during detonation combustion than during thermo-acoustic combustion. These experimental results provide evidence that rotating detonation waves have the potential to significantly improve propulsion performance. The findings can serve as a valuable reference for the practical engineering application of rotating detonation engines.

Experimental investigation on rotating detonation engine with full/half inner cylinder

To lucubrate the velocity deficit of rotating detonation wave (RDW) fueled by hydrocarbon fuel, experiments are conducted in an elaborate combustor with full/half inner cylinder. The results show that the introduction of half hollow section alters the RDW propagation mode from counter-rotating two-wave mode to single-wave mode, accompanied by an obvious increase in the propagation velocity. In the combustor with half inner cylinder, the promotion effect of hollow part on the propagation velocity has been proved with segmented calculation method. Deflagrations in the form of “reverse flame” are observed to spread in the annular part, consuming the propellants ahead of the RDW. This pre-detonation combustion is believed to reduce the propagation velocity and the pressure ratio of RDW. Besides, some weak pressure perturbations can also be captured along with the “reverse flame”, indicating that there is a weak pressure wave propagating against the RDW. To some extent, this weak pressure wave can be seen as the precursor or the limit of a counter rotating detonation wave.

Distribution of Enthalpy in Rotating Detonation Engine

In Rotating Detonation Engine (RDE), the detonation wave rotates inside the annulus of thecombustor. After initiation by a pre-detonator, this detonation wave can be sustained by thecontinuous supply of fuel and oxidiser. The frequency of rotation is reported to be of the orderof 5-10 KHz indicating a near continuous operation which can be used in rocket andairbreathing propulsion systems. An experimental study on the RDE is being carried out atNational Centre for Combustion Research and Development (NCCRD), Indian Institute ofTechnology (IIT), Madras using hydrogen and air system. In addition,N2H4 - N2O4 hypergolicsystemreported in literature is considered for comparative study. In order to understand thevarious processes undergone by the flow through the RDE, a detailed thermodynamic analysisis performed. The procedure is explained in greater detail for the better understanding of thevarious state properties in the entire flow field. The flow field comprises of detonation wave,trailing oblique shock wave and Prandtl- Mayer expansion waves. There are two slip lines,one separating the fresh reactants and inert combustion products of the previous cycle ofdetonation wave propagation and another separating the products of detonation combustionand the shocked inert products. Though all the state properties will be evaluated, the enthalpydistribution is considered in the entire flow field of RDE and discussed. This provides theknowledge of the energy availability in various flow regimes and the extent of energyconversion due to detonative combustion, flow expansion, shock compression, and axial flowexciting through the combustor outlet. Propulsion parameters such as axial specific thrust andspecific impulse are computed to show the capability of this modelling approach.

Experimental study on tesla valve and bypass manifold to suppress feedback of rotating detonation engine fuel by kerosene

In this paper, the effects of the Tesla valve intake structure with or without bypass manifold on suppressing pressure feedback and combustion product backflow in rotating detonation engine fueled by kerosene and enriched air with 29% oxygen content are investigated, with the configuration of convergent–divergent intake without bypass manifold being used for comparison. The working range, detonation wave propagation characteristics, and propulsion performance for the three configurations are evaluated. It is found that the Tesla valve intake structure can effectively improve the suppression of pressure feedback and combustion product backflow through the diversion function of the Tesla valve bypass channel and that the addition of the bypass manifold further improves the suppression of pressure feedback. The Tesla valve intake with bypass manifold configuration has the best ability to suppress pressure feedback, with a minimum value of pressure feedback percentage of about 6.5% and a minimum value of air plenum pressure fluctuation percentage of about 6.7%. By comparison, the minimum value of pressure feedback percentage of the convergent–divergent intake without bypass manifold configuration is about 29.8%, and its minimum value of pressure feedback percentage is about 7.8%. The Tesla valve intake without bypass manifold configuration is most effective in suppressing combustion product backflow, with the effective inlet area ratio of about 95.7%. Under the same conditions, the minimum effective inlet area ratio of the convergent–divergent intake without bypass manifold configuration is about 90.2%. Ultimately, optimizing the engine structure leads to a broader working range and higher propulsion performance. The Tesla valve intake structure broadens the working range by suppressing the generation of the longitudinal pulsed detonation mode. When the bypass manifold is incorporated, some combustible reactants directly enter the rear of the combustion chamber from the head of the chamber, and the working range is reduced. Compared with the convergent–divergent intake without bypass manifold configuration, the working range of the Tesla valve intake with bypass manifold configuration is widened by 383.3%, and that of the without bypass manifold configuration by 700%. Both the Tesla valve intake and bypass manifold increase the strength of detonation waves and improve propulsion performance. The Tesla valve intake with bypass manifold configuration has the highest specific thrust, at about 90.1 N s3/(kg·m). This is increased by an average of 10% compared with the Tesla valve intake without bypass manifold configuration, and by an average of 30.1% compared with the convergent–divergent intake configuration.

Experimental study on suppressing pressure feedback and combustion product backflow of the rotating detonation engine

To further improve the feedback suppression effect of rotating detonation engines (RDEs), an optimized Tesla valve inlet structure (TVI-II) was designed on the basis of the previous research of our research group. Taking kerosene and 29% oxygen-enriched air as the reactants, the operation characteristics, the feedback suppression effect, and the feedback suppression mechanism were obtained through a series of experiments. It is found that due to the existence of bypass channel, TVI-RDE can effectively suppress the occurrence of longitudinal pulsed detonation and broaden the working boundary of the engine. The working range of the TVI-I-RDE was broadened by 183.3%, and that of the TVI-II-RDE was broadened by 700%. The TVI-II-RDE is more effective in suppressing pressure feedback and combustion product backflow. When the pressure feedback phenomenon occurs, the rotating detonation wave mainly decoupled and attenuated in the converging section of bypass channel. The minimum pressure feedback percentage (PFdw) of TVI-II-RDE was 11.4%, as compared to about 40% for the TVI-I-RDE. The change law of the air plenum pressure fluctuation percentage (PFap) was similar to that of PFdw, and the minimum PFap of the TVI-II-RDE was about 7.7%. Narrower bypass channel width would lead to longer residence time of combustion products. The effective inlet area ratio (EA) of the TVI-II-RDE was at least 95.7%, which is at least 6.1% higher than that of the CDI structure. The results show that the TVI-II-RDE has great potential in suppressing feedback, which promotes the engineering application of RDE.

Experimental research on the detonation behavior in annular combustors utilizing liquid hypergolic propellants

The development of rotating detonation engine utilizing hypergolic propellants is necessary for practical application of detonation-based rocket engines, but this liquid-liquid rotating detonation has been rarely researched due to its difficulty of well atomization and mixing in very short time. This study aims to experimentally investigate the propagation characteristics of rotating detonations using non-premixed hypergolic propellants in annular combustors. Here the monomethyl hydrazine (MMH) and nitrogen tetroxide (NTO) have been used as oxidizer and fuel, respectively. Twenty-four unlike impinging elements have been used for injection and mixing of liquid propellants. The orifice diameter is 0.4 mm for oxidizer and 0.3 mm for fuel. Three typical combustion modes such as deflagration mode, one-wave rotating detonation mode and two-wave collision mode have been captured by dynamic pressure transducers and the high-speed camera. The influence of many factors, such as mass flow rate, mixing ratio, annular combustor width and chamber throat, on rotating detonation behaviors have been investigated. The propagation velocity of rotating detonations is around 1328 m/s∼1405 m/s, including one-wave rotating detonation mode and two-wave collision mode. When the mass flow rate and mixing ratio is not appropriate, the hypergolic combustion becomes obviously unstable and combustion modes vary very quickly, especially at the start-up stage. The chamber throat plays a negative role on rotating detonation which suppresses the detonation propagation and can lead to detonation fail. Besides, the wider annular combustor width is beneficial for rotating detonation propagating, which can eliminate the negative influence of the chamber throat on the detonation propagation. In addition, increasing mass flow rate would lead to higher injection velocity and thus better impinging injection, atomization and mixing, which is positive for increasing the stable operation range of mixing ratio for rotating detonations.

Predicting combustion behavior in rotating detonation engines using an interpretable deep learning method

As rotating detonation engine (RDE) is maturing toward engineering implementation, it is a crucial step in developing real-time diagnostics capable of monitoring the combustion state therein to prevent combustion instability, such as detonation quenching, re-initiation, and mode switch. However, previous studies rarely consider monitoring combustion behavior in RDEs, let alone predicting the impending combustion instabilities based on the warning signals. Given active control requirements, a novel Transformer-based neural network, RDE-Transformer, is proposed for monitoring and predicting the combustion states in advance. RDE-Transformer is a multi-horizon forecasting model fed by univariate or multivariate time series data including pressure signals and aft-end photographs. Model hyper-parameters, namely, the number of encoder and decoder layers, the number of attention heads, implementation of positional encoding, and prediction length, are investigated for performance improvements. The results show that the optimal architecture can reliably predict pressures up to 5 detonation periods ahead of the current time, with a mean squared error of 0.0057 and 0.0231 for the training and validation set, respectively. Moreover, the feasibility of predicting combustion instability is validated, and the decision-making process through the attention mechanism is visualized by attention maps, making the model interpretable and superior to other “black-box” deep learning methods. In summary, the high performance and high interpretability of RDE-Transformer make it a promising diagnostics functional component for RDEs toward applied technology.

Flow-field reconstruction in rotating detonation combustor based on physics-informed neural network

The flow-field reconstruction of a rotating detonation combustor (RDC) is essential to understand the stability mechanism and performance of rotating detonation engines. This study embeds a reduced-order model of an RDC into a neural network (NN) to construct a physics-informed neural network (PINN) to achieve the full-dimensional high-resolution reconstruction of the combustor flow field based on partially observed data. Additionally, the unobserved physical fields are extrapolated through the NN-embedded physical model. The influence of the residual point sampling strategy and observation point spatial-temporal sampling resolution on the reconstruction results are studied. As a surrogate model of the RDC, the PINN fills the gap that traditional computational fluid dynamics methods have difficulty solving, such as inverse problems, and has engineering value for the flow-field reconstruction of RDCs.

Highly-scalable GPU-accelerated compressible reacting flow solver for modeling high-speed flows

Emerging supercomputing systems utilize a combination of central processing units (CPUs) and graphics processing units (GPUs) in an effort to reach exascale capabilities while minimizing the energy footprint of operating such systems. Such heterogeneous machines introduce new challenges for fluids solvers because the hardware architecture and operation of a GPU are fundamentally different from conventional CPUs. In this work, a general approach for efficient implementation of finite-volume based reacting flow solvers on such heterogeneous systems is presented. Three main challenges, namely, data access pattern, thread divergence, and thread safety, are addressed. Since compressible reacting flows require special methods to deal with chemical reactions, hyperbolic and nonlinear convection terms, and the presence of turbulence, specific algorithms that ensure GPU-based efficiency are developed. The approach is demonstrated on the widely available OpenFOAM open source software by modifying core algorithms for GPU accessibility. The scalability of the resulting solver, is demonstrated using practical test cases, including flow through a scramjet engine and the dynamics of a rotating detonation engine. The solver provides near-ideal scaleup on a large number of GPUs (>3000), and extremely efficient use of the GPUs, with throughput nearly a constant even when processing a large number of control volumes.

Experimental study on propagation, quenching, and re-initiation characteristics of rotating detonation wave with liquid kerosene–oxygen-enriched air

In a rotating detonation engine (RDE), specifically a low-activity liquid fuel RDE, ensuring the continuous and stable propagation of detonation waves is important. In the RDE experiment with oxygen-enriched air as the oxidant and liquid kerosene as the fuel at room temperature, the stability of the rotating detonation wave (RDW) is found to be extremely inadequate. This inadequacy is manifested by more than 10 times of quenching and re-initiation within 500 ms. This frequent quenching and re-initiation phenomena considerably differ from those of the gaseous fuel RDE. Consequently, the velocity deficit of the detonation wave increased and the propulsion performance of the RDE was affected. In a further study using pressure sensors and high-speed cameras, the quenching phenomenon was found to be related to the supply state of the propellant, and the re-initiation phenomenon was related to the chemical reaction zone in the combustion chamber. To verify the foregoing, a special control test was performed. After improving the supply state of the corresponding propellant, the unstable characteristic of liquid fuel was effectively suppressed and a stable RDW with a velocity of 1321 m/s was obtained. The results of this study reveal the mechanism of liquid fuel quenching and re-initiation. This mechanism significantly restrains the instability of liquid fuel detonation waves.

Walking Droplets as a Damped-Driven System

We consider the dynamics of a droplet on a vibrating fluid bath. This hydrodynamic quantum analogue system is shown to elicit the canonical behavior of damped-driven systems, including a period doubling route to chaos. By approximating the system as a compositional map between the gain and loss dynamics, the underlying nonlinear dynamics can be shown to be driven by energy balances in the systems. The gain-loss iterative mapping is similar to a normal form encoding for the pattern forming instabilities generated in such spatially extended systems. Similar to mode-locked lasers and rotating detonation engines, the underlying bifurcations persist for general forms of the loss and gain, both of which admit explicit representations in our approximation. Moreover, the resulting geometrical description of the particle-wave interaction completely characterizes the instabilities observed in experiments.

Analysis on Propulsive Performance of Hollow Rotating Detonation Engine with Laval Nozzle

In the present study, an experimental performance analysis of hollow rotating detonation engines (RDEs) with Laval nozzles is carried out for the first time. Experiments of a hollow rotating detonation engine with a Laval nozzle were performed with a modular RDE at a backpressure condition of 1 atm. Two configurations with area ratios of the outlet throat to the inlet of and 2.7 have been tested with gaseous methane/oxygen as propellants. Three normalized metrics, usually used for evaluating the performance of conventional rocket engines, are introduced to analyze the performance deficit between the measured value of an RDE and the ideal value of an isobaric-combustion-based engine. These metrics allow for assessing the entire engine and each component separately. The metric analysis suggests a small outlet-to-inlet area ratio () is detrimental to the propulsive performance. To explain the mechanism, a gas-stratification flowfield model is further proposed. It is found that the unchoked region in the combustible gas layer, which is caused by unchoked injection on the injecting plate, is responsible for the performance deficit of the combustion chamber. This model is then validated by one-dimensional numerical simulations and experimental data. In addition, we also focus on the global performance, including the gross thrust, the specific impulse, and the utilization of the supplied stagnation pressure. The result implies a tradeoff space when choosing an appropriate .