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The numerical and experimental research of rotating detonation engines is usually conducted in ground environmental conditions. Although many breakthroughs have been made, there are still deficiencies in understanding engines operating in real flight conditions. In order to reveal the effect of engine size and initial kerosene droplet size on the rotating detonation engines in flight conditions, the Eulerian-Lagrangian model is adopted, and a series of two-phase kerosene/air rotating detonation cases are simulated in the conditions of Mach 5 and 24 km altitude. When 5 μm and 10 μm droplets are adopted, the RDE behaves like gaseous rotating detonations with clear cellular structures. When the 20 μm and 30 μm droplets are adopted, the rotating detonation waves tend to be divided into two layers and form the λ-shaped shock structure. The results indicate that droplet size and engine size influence detonation wave propagation and flow field mainly through droplet heat absorption and evaporation height. Increasing the engine sizes can promote the two-phase rotating detonation and broaden the initial diameter range capable of obtaining rotating detonation waves. However, as droplet size increases, the fresh mixture layer becomes stratified, with an upper layer predominantly comprising fuel vapor and a lower layer of fuel droplets, which results in an λ-shaped shock structure at the detonation front. The flight operation condition brings in differences in features such as detonation wave height and velocity deficit. The detonation height in flight conditions is higher than that in ground conditions. The most velocity deficit in flight conditions observed in our study is below 15 %, which is lower than the results (22.5 %) in ground operating conditions. These results indicate that the optimal design of the rotating detonation engine must consider the real operation conditions and the effect of engine sizes and droplet sizes. • The propagation characteristics of two-phase rotating detonation waves in flight operation conditions are revealed. • The effects of engine sizes and droplet sizes are analyzed. • Detonation height and propagation velocity are increased in flight operation conditions, compared with the ground test. • The rotating detonation engine design should be based on the real operation conditions. [ABSTRACT FROM AUTHOR]

Experimental studies were conducted on the initiation characteristics of rotating detonation waves (RDW) using auto-initiation and pre-detonation methods with high-temperature hydrogen gas. The effects of the two initiation methods on the formation and propagation characteristics of rotating detonation waves were compared. The experimental results showed that the formation process of the RDW was different when using auto-initiation and pre-detonation initiation. However, the parameters of the stable propagation stage of the RDW were similar. The time required for the formation of the RDW by pre-detonation was relatively short. As the equivalence ratio increased, the rotating detonation chamber (RDC) exhibited five propagation modes: two-co rotating detonation waves (TRDW), two-counter rotating detonation waves (TCRDW), a mixed mode, intermittent single rotating detonation wave (ISRDW), and single rotating detonation wave (SRDW). It is worth noting that both initiation methods were capable of achieving rotating detonation within the equivalence ratio range of 0.68–1.96. The pre-detonation initiation can expand the range of stable SRDW modes and has some advantages in terms of RDW propagation stability. • The characteristics of RDW exhibited similarities between two initiation methods. • The time for the formation of the detonation wave by pre-detonation was short. • Detonation be achieved by both the initiation ways with the ER of 0.68–1.96. • Pre-detonation initiation can expand the range of stable single-wave modes. [ABSTRACT FROM AUTHOR]

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 d 0 = 5–15 μ m , 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 d 0 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. • Rotating detonation engines (RDEs) fueled by liquid ethanol are investigated by a numerical study. • A multi-stage interaction process between the evaporating droplets and the rotating detonation wave (RDW) is revealed. • The effects of inlet conditions on the phenomenon of wave multiplicity are analyzed. [ABSTRACT FROM AUTHOR]

In this study, numerical simulations based on an Eulerian-Lagrangian framework are conducted to investigate the liquid-fueled rotating detonation engine (RDE) with heterogeneous kerosene-hydrogen-air mixtures. The hydrogen addition is implemented for combustion enhancement of the liquid kerosene and helps to ignite and achieve a self-sustained two-phase rotating detonation wave (RDW). The effects of droplet evaporation at various initial droplet sizes and kerosene mass flow rates on the structure and propagation of the two-phase RDW are analyzed. Results suggest that with smaller droplet sizes, the structure of the RDW is analogous to that of a gaseous RDW, and a comparison with experimental data suggests that the estimated detonation speed and thrust performance (fuel-based specific impulse) are within the reasonable ranges. However, as the droplet size or the mass flow rate of kerosene increases, the two-phase RDW exhibits characteristic features such as the dual-front laminated structure, micro-explosions and secondary transverse waves. • Rotating detonation engines (RDEs) with a heterogenous kerosene-hydrogen-air mixture are investigated. • Numerical simulations based on an Eulerian-Lagrangian two-way coupled framework are conducted. • A dual-front rotating detonation wave (RDW) caused by droplet evaporation is explained. • Micro-explosions and secondary RDWs are captured at higher kerosene mass flow rates. [ABSTRACT FROM AUTHOR]

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. • Tesla valve inlet and bypass manifold are used to suppress feedback. • Two quantitative evaluation parameters of pressure feedback are established. • The degree of combustion product backflow is evaluated. • The optimized structure can effectively improve the propulsion performance. [ABSTRACT FROM AUTHOR]

Utilization of liquid fuels is crucial to enabling commercialization of rotating detonation engines (RDE) in the near future. In this study, Eulerian-Lagrangian simulations are conducted for rotating detonative combustion with dilute n -heptane sprays and preheated air. Two-dimensional flattened configuration is used and a skeletal chemical mechanism with 44 species and 112 elementary reactions for n -heptane combustion is adopted. The flow structure, droplet distribution, and thermochemical parameters in the refill zone are first analyzed. It is shown that the mixture in the refill zone is heterogeneous, including evaporating droplets, vapor, and air. When the total temperature is below 950 K, the average equivalence ratio increases with the total temperature. When it is higher than 950 K, the average equivalence ratio is almost constant. Subsequently, the chemical explosive mode analysis is applied to identify the controlling reactions and dominant combustion modes in the fuel refill zone and reaction fronts. Results demonstrate that the initiation reaction (R104: n -C 7 H 16 + O 2 → 2-C 7 H 15 + HO 2) and low-temperature reaction (R107: RO 2 → R'O 2 H) are dominant in the upstream and downstream of the refill zone, respectively. The intermediate species from low-temperature chemistry, R'O 2 H, is found to be important for the chemical explosive mode in the undetonated mixture. The influence of species diffusion and dispersed droplets is further analyzed. Results show that vapor autoignition facilitated by droplet evaporation occurs in the refill zone. Finally, the effects of the air total temperature on the detonation propagation speed and RDE propulsion performance are investigated. It is found that the detonation propagation speed and specific impulse increase with air total temperature. The total pressure ratio first increases and then decreases as the air total temperature increases. Moreover, when the total temperature of the preheated air is above 1,300 K, the effects of low-temperature chemistry are negligible. [ABSTRACT FROM AUTHOR]

In order to investigate the effects of gas mixture components on the combustion characteristics of rotating detonation wave, two-dimensional simulation is presented to simulate the propagation process of rotating detonation wave with different methane conversions. The results indicate that there are five propagation modes of rotating detonation wave with different components: single-wave mode, single wave with counter-rotating components mode, double-waves mode, triple-waves mode and quadruple-waves mode. The detonation wave propagates along the forward direction in all five modes. With the increase of methane conversion, multi-wave mode appears in the combustion chamber. The fuel component has a great influence on the heat release ratio of detonation combustion. The velocity of detonation wave decreases with the increase of methane conversion. With the increase of methane conversion, the chemical reaction rate gradually increases, which leads to the intensification of chemical reaction on the deflagration surface. The reaction on the deflagration surface develops to the unburned fuel zone, which eventually leads to the formation of compression waves and shock waves in the fuel refill zone. When the shock wave sweeps through the fresh premixed gas, the reactant is compressed to form a detonation point and then ignite the fuel. A new detonation wave is finally formed. The total pressure ratio decreases with the increasing methane conversion, and the uniformity of the total pressure of outlet decreases with increasing methane conversion. • Component change of multicomponent mixture dictate propagation mode. • The influence of component change on detonation wave velocity and pressure is revealed. • The effect of deflagration surface reaction on the characteristics of detonation wave is analyzed. • Pressure ratio of combustion chamber with mixture of different components is compared. [ABSTRACT FROM AUTHOR]

An experimental approach for estimating the detonation cell size for liquid hypergolic propellants is presented and applied for monomethylhydrazine (MMH) and a MON-3 variant of nitrogen tetroxide (NTO) in a non-premixed combustor. The method utilizes a correlation between cell size and reactant fill height in an annular combustor geometry. Reactant fill height is inferred using a control-volume analysis to relate the geometry of the reactant fill zone to the propellant flow rate, detonation wave-speeds and number, and annular gap size. High-speed videography is used to measure the number of waves and their speed over a range of quasi-steady continuous detonation conditions. The detonation criteria is also proven valid in the transient conditions as the decrease of the fill height below a critical value identified in this work matches modal transitions with decreasing number of waves. A power law relating the cell width with induction length further supports the validity of the present technique down to cell sizes of 1–10 µm, a scale not practically resolvable with conventional methods. [ABSTRACT FROM AUTHOR]

The objective of this study is to apply the finite difference method (FDM) scheme to generate profiles of velocity, vorticity, pressure, temperature, and density of the flow field inside the chamber of a rotating detonation engine. In addition, this study discusses the Kuo's algorithm used in the computation of Chapman-Jouguet (CJ) variables. A new computational algorithm is introduced to compute the CJ variables, the shock, and the post-shock conditions. Five different fuels are tested, H 2 –O 2 , H 2 -air, CH 4 -air, C 2 H 6 -air, and C 2 H 2 -air. The results show good performance for the FDM scheme, and the new algorithm is adopted in this study to perform all CJ calculations. The new algorithm's results are compared with the experimental data available for the tested fuels and show close results. Another important result is that the highest vorticity forms along the slip line of the combustion chamber, then it gradually shrinks along the path of the slip line. • Presenting a new algorithm to compute the Chapman-Jouguet variables. • Each detonation wave can achieve a different Chapman-Jouguet pressure. • CFD test cases fuels used: H 2 –O 2 , H 2 -air, CH 4 -air, C 2 H 6 -air, and C 2 H 2 -air. • The RDE detonation reactants mixture height varies with fuel type. • Vorticity is highest at the slip line and shrinks downstream the slip line. [ABSTRACT FROM AUTHOR]

In this study, the adaptive mode switching process of rotating detonation waves (RDWs) in response to the change of inlet conditions is numerically explored and analytically explained. Once a quasi-steady rotating detonation flow field is obtained, the inlet total pressure of the reservoir is decreased and maintained at different levels for a certain period of time in order to observe the feedback on the RDWs. It shows that instead of being quenched immediately, the RDWs can adapt to the change of inlet conditions by a mode switching adjustment; it decreases the number of detonation waves and begins to run in a new operating mode, a process that is found to occur swiftly and is corroborated by experimental observations; moreover, an analytical analysis indicates that for a stable RDW flow field, the characteristic parameters such as the number and height of detonation waves are related to the combustor geometry and inlet conditions, which determine whether the RDWs are required to switch into a new operating mode as a means to ensure stability. Additionally, the results indicate that the rotating detonation engine (RDE) can work in different operating modes at the same mass flow rate, or conversely, the RDE can remain in the same operating mode even if the mass flow rate varies. • Numerical simulations are conducted to investigate the operating modes of rotating detonation engines (RDEs). • The RDE can adapt to the changes of inlet conditions and switch its operating mode when necessary. • A quasi-steady analysis of the rotating detention waves is provided to explain the adaptive mode switching process. [ABSTRACT FROM AUTHOR]

For high-Mach-number incoming flow circumstances, a rotating detonation ramjet engine configuration is proposed in this research. By installing supporting blocks at the rear of the combustor, this configuration achieves continuous rotating detonation operation. Based on the Comparison of the flow structures obtained from the engine configuration with and without the supporting block before and after detonation ignition respectively, we obtain the intrinsic mechanism of detonation wave's propagation and re-initiation under the action of the supporting block. The supporting block creates a deflagration wave that is almost stationary before detonation ignition. In the detonation-ignited state, the deflagration wave is continually formed and traveling upstream under the influence of the supporting block, which is analogous to the periodical before detonation ignition of a transverse wave structure. The dynamic deflagration wave will cause the incomplete reactants behind the detonation wave to burn as the intensity of the detonation wave decreases. As a result, the incident shock wave is transformed into a Mach stem to achieve the re-initiation of the detonation wave. • The continuous spin detonation with kerosene as fuel is realized at flight Mach number M = 6. • Flow characteristics in the before and after detonation ignition states with and without supporting blocks are compared. • The supporting block may effectively contribute to maintaining the continuous propagation of the detonation wave. • The detonation wave's mechanism of propagation and re-initiation is examined under the influence of the supporting block. [ABSTRACT FROM AUTHOR]

Rotating detonation using ammonia as fuel may be a potential carbon free combustion technology for gas turbine. The detonation wave structure and flow field of a rotating detonation annular combustor are investigated by three-dimensional simulation with detailed chemistry of ammonia/hydrogen-air. The detonation properties, propagation mode, combustor performance and emission characteristics are studied by varying the equivalence ratios and hydrogen concentrations. Both the increases of the combustor pressure and the hydrogen concentration promote the chemical reaction rate of the ammonia burn and the detonation wave velocity gradually increases with increasing hydrogen proportion based on one-dimensional simulation. A stable single-rotating waves resulting in ammonia/hydrogen combustor are observed for a wide range of equivalent ratios only when the hydrogen concentration is at least 0.2. The steady run of the single rotating detonation had an optimal cycle efficiency when the hydrogen concentration is increased to a critical value of 0.3. NOx emissions are more dependent on equivalent ratios than hydrogen concentration in equivalence ratios ranging from 0.70 to 1.40. • Three-dimensional simulation of rotating detonations with detailed chemistry of NH4/H2-air. • The detonations propagate stably in premixed ammonia-oxygen-enriched air mixture with at least 20% hydrogen. • RDE has an optimal cycle efficiency when hydrogen concentration is at a critical value of 0.3. • NOx emissions are more dependent on equivalent ratios than hydrogen concentration. [ABSTRACT FROM AUTHOR]

To improve the propulsive performance, exhaust nozzles are desired for rotating detonation engines in practical applications. Therefore, their effects on the upstream behaviors inside the combustion chamber are required to be clarified. This study focuses on the characteristics of rotating detonation waves influenced by different outlet configurations. Three types of aerospike nozzle configurations are developed with different throat areas. Ethylene and oxygen-enriched air with an oxygen volume fraction of 50% are utilized in this study. When nozzles are employed, five wave propagation modes (i.e., the single-wave mode, the counter-rotating wave mode, the self-adjustive mode, the periodic oscillation mode, and the deflagration mode) are observed with the equivalence ratio ranging from 0.33 to 1.39, while only single-wave mode appears in the nozzle-less case under the same operating conditions. When increasing the equivalence ratio or reducing the nozzle throat area, those unstable propagation modes are more likely to happen and three boundaries of the equivalence ratio for the wave propagation transformation are clarified. On the contrary, the standard deviations of propagation velocities in the stable propagation process are smaller when employing nozzle configurations compared to the nozzle-less cases, which indicates a more stable state of the wave propagation although the stable propagation range is narrowed. Besides, the pressure rise and specific thrust are analyzed under different outlet configurations. • Five types of propagation modes were observed with different outlet configurations. • Propagation mode evolutions along with the equivalence ratio have been analyzed. • Nozzles enhance the propagation stability but narrowed stable mode operating range. • The propulsive performances of the rotating detonation engine were investigated. [ABSTRACT FROM AUTHOR]

The rotating detonation gas turbine boasts several advantageous characteristics, including self-pressurization, minimal entropy increase, high thermal efficiency, and a high thrust-to-weight ratio. These features make it a promising candidate for the next generation of aerospace power devices. This study investigates the flow characteristics and performance attributes of the supersonic turbine stage coupled with a rotating detonation chamber based on different rotational speeds, blade ratio of rotor and stator, and hub radius, and uses DMD (Dynamic Mode Decomposition) to analyze the main modes of the supersonic turbine. The research identifies distinct wave modes in both the stator and rotor blades of the supersonic turbine. In the stator blades, the modes include waveless contact modes, opposite side λ -wave oblique shock wave modes, and derived modes from opposite side λ -wave oblique shock waves. In the rotor blades, the modes encompass non-separation modes (waveless modes, asymmetric dual λ -wave modes, oblique cut wave modes, and single-side λ -wave modes on the pressure surface), leading-edge stator excitation single separation bubble modes, saddle-type separation modes, and dual separation bubble modes. The efficiency and power of the supersonic turbine stage increase with the rotational speed. The turbine efficiency is highest when the blade ratio is 10:7. Under multi-wave mode conditions, detonation waves demonstrate adaptive self-regulation abilities, ultimately achieving equilibrium in speed, detonation wave height, and spacing. The dominant modes in the stator blades and combustion chamber are governed by detonation waves and slip lines, while in rotor blades, the primary mode is the flow-directional vortex mode governed by detonation waves and slip lines at a frequency lower than their propagation frequency. This research holds certain reference significance for understanding the internal flow characteristics of rotating detonation gas turbines, as well as discussing the patterns of efficiency, power, and load characteristics, thereby offering valuable insights for the practical application of rotating detonation gas turbines. • Supersonic turbine stage with different parameters coupled with RDC. • DMD mode characteristics of supersonic turbine coupled with RDC. • Unsteady modes of wave system of interaction between TGVs and combustion chamber. • Unsteady modes of shock wave system of turbine rotor blade. • Performance characteristics of supersonic turbine stage under different parameter conditions. [ABSTRACT FROM AUTHOR]

• RDC passage area has a significant impact on operating range of rotating detonation gas turbine. • The increase of RDC passage area makes the operating range of gas turbine move to the higher power. • Equivalence ratio of RDC replaces turbine efficiency as the greatest influence factor on cycle efficiency increment with different combustor passage areas. • Qualitative analysis based on sensitivity analysis of component parameters is further optimized to announced the comprehensive reason for change of cycle efficiency increment. Application of rotating detonation combustion can significantly enhance gas turbine performance, but the limited flow capacity caused by normally aspirated characteristic of rotating detonation combustor (RDC) severely constrains the operating range of gas turbine. In this paper, the detailed investigation was carried out for the influence of RDC passage area on cycle characteristic parameters for a 25MW single shaft gas turbine. The results demonstrated that changes of RDC passage area had a significant impact on operating range of rotating detonation gas turbine. As RDC passage area increased, operating range of gas turbine moved to the higher power, with the slight increases for cycle efficiency, cycle efficiency increment and net power increment compared to traditional gas turbine at identical net power. For the process when RDC passage area decreased from 0.0272 m2 to 0.0240 m2, the lower working limit of rotating detonation gas turbine decreased to 53.3 % of rated power, in which equivalence ratio of RDC replaced turbine efficiency as the greatest influence factor on cycle efficiency increment. [ABSTRACT FROM AUTHOR]

• The gas generator is combined with the rota detonation engine. • Detonation waves are generated spontaneously without pre-detonator. • The gas generator is combined with the rotating detonation engine. • Low gas temperature is not conducive to the deflagration-to-detonation transformation. • High gas temperature will produce secondary detonation wave. • Rich gas at higher temperatures contains more proportion of highly active ingredients. In this study, the propagation characteristics of a rotating detonation wave (RDW) between ethylene-rich gas and ambient air were investigated experimentally. The traditional pre-detonator initiation method was abandoned in the experiment, but the spontaneous combustion of high-temperature ethylene-rich gas and air was adopted. The RDW auto-initiated through the deflagration-to-detonation transformation (DDT) process. With an increase in the ethylene-rich gas temperature, the modes of RDW propagation appeared as delayed initiation, dual-wave collision, and fluctuating dual-wave collision modes. When the gas temperature was too high, a secondary detonation wave was produced near the head of the rotating detonation chamber (RDC), which affected the propagation efficiency and stability of the RDW. The increase in gas temperature expanded the equivalence ratio range of auto-initiation, which was due to the higher gas temperature, and more highly active components were precipitated. [ABSTRACT FROM AUTHOR]

The combustion characteristics in annular rotating detonation combustors are experimentally investigated using 40% oxygen-enriched air and liquid aviation kerosene (RP-3) as reactants. Two types of wall cavity structures, embedded in the outer and the inner wall of the annular combustors, respectively, are employed to study their effects on detonation stability. The characteristics of typical combustion modes observed in the annular combustors are firstly analyzed. The regime of typical combustion modes is then examined in the phase diagram of mass flow rate and equivalence ratio. Results show that the single-wave mode regime can be affected by wall cavities. In comparison to the combustor without a wall cavity, the regime is expanded for the cavity in the inner wall but significantly reduced for the cavity in the outer wall. When the single-wave mode forms, the cavities embedded in the inner wall result in a significant increase of the apparent detonation wave velocity but a decrease in the velocity fluctuation rate, and the effects are changed with the axial location of the cavities. The axial location of the cavity can also influence the stable propagation location of the detonation wave. Additionally, the analysis of the high-frequency pressure signals indicates that the cavities do not affect the initiation process of the formation of the combustion modes. However, the variation of oxidizer mass flow rate and equivalence ratio can evidently influence the evolution time of different combustion modes after ignition. The study indicates that the wall cavity structure has a significant influence on the propagation behavior of rotating detonation waves in the combustors, and it can be utilized to enhance the stability of kerosene two-phase rotating detonation combustion. [ABSTRACT FROM AUTHOR]

Rotating detonation as a kind of pressure gain combustion is expected to greatly improve efficiency when applied to gas turbine engines. In this paper, the operation of rotating detonation combustor and turbine rotor blade was studied. Firstly, the analysis of the interaction between detonation wave and turbine blade shows that the compression of gas by detonation wave and reflected wave will lead to a sharp increase in the temperature at the wall of blade. When the detonation wave propagates, the oscillation amplitudes of pressure and temperature at the turbine inlet are 70% and 75% respectively, and the detonation oblique shock will change the flow trajectory of the air flow, resulting in the flow direction deviating from the incident angle. Then the comparison between detonation and deflagration shows that the total pressure of detonation is higher and will have greater work potential. The torque generated by the blades under detonation has the characteristics of high-frequency oscillation, which may be detrimental to the operation of the engine. [Display omitted] • Coupled operation of rotating detonation and turbine rotor blades. • Characteristics of interaction between detonation wave and turbine. • Variation of pressure and temperature in combustor under deflagration and detonation. • Torque value of turbine rotor under the influence of rotating detonation wave. [ABSTRACT FROM AUTHOR]

In order to investigate the structure and propagation characteristics of hydrogen-assisted kerosene (liquid phase)-air rotating detonation, a modified solver based on OpenFOAMⓇ was proposed and utilized to simulate detonation in the mixture of hydrogen, liquid kerosene and air. The obtained results show that evaporation waves exist in the discrete liquid mist detonation, and the coupled-waves structure formed by the evaporation wave (EW) and the incident shock wave (ISW) propagates upstream. By analyzing the overall and instantaneous propagation characteristics, it is found that the propagation speed of the detonation wave increases with the increase of the equivalence ratio at the fuel rich state. Increasing the droplet size will cause the evaporation wave to be further downstream relative to the ISW, resulting in lower evaporating pressure. The effect of EW on ISW is accomplished by the blast wave traveling upstream which is generated by droplet reaction, while EW is influenced by the ISW by modulating the droplet enthalpy and the pressure attenuation following ISW. Part of the droplet reaction energy is held in the gap between the EW and ISW, consequently the gap acts as an energy storage piston, regulating the ISW and EW propagation speeds. The combustion of droplets with smaller sizes imposes more positive feedback on their evaporation, and increasing the total temperature of the premixed gas promotes the interaction between the EW and the ISW, resulting in a more steady propagating overall structure. • The evaporation wave (EW)'s existence in two-phase rotating detonation is verified. • EW and incident shock wave (ISW) combine and propagate as a general structure. • Mechanism of two-phase detonation wave's propagation is extracted. • Influences of multiple factors on the propagation of EW and ISW are analyzed. [ABSTRACT FROM AUTHOR]

Rotating detonation combustors are prone to a wide range of off-design behaviors during both atmospheric and pressurized operation. The current manuscript deals with the transient mean pressure change seen in back-pressurized combustors after ignition. Using experimental high-speed pressure data acquired during this transience, we report two distinct, but overlapping, mechanisms that are well-known in deflagrative rocket combustors, but are not currently considered in rotating detonation combustors: DC shift and chugging. The former is characterized by sudden and seemingly random alterations of the time-averaged chamber pressure during operation, not unlike the same behavior observed in conventional rockets during instability onset. The latter is a low frequency instability that is inherently coupled to the reactants feed, causing significant oscillations of the mean chamber pressure. We show that these phenomena are strongly linked, where onset of chugging oscillations alter the frequency and pressure of the operating mode, which in turn produces a DC shift of the mean chamber pressure. To discern this complex interaction, we use multivariate polynomial curve-fitting, considering all the appropriate parameters to arrive at an empirical formulation that is seen to reasonably match the observed pressure transience after ignition. • The transient pressure increase after RDC ignition is studied. • The low frequency oscillations accompanying this transience is also investigated. • These two behaviors in RDCs are linked to DC shift and chugging instability in rocket engines. • These two phenomena are also interlinked between themselves. • An empirical correlation is proposed to discern the pressure evolution after ignition. [ABSTRACT FROM AUTHOR]

In order to investigate the relationship between high frequency tangential instability and continuous rotating detonation, series of H 2 /Air rotating detonations are experimentally achieved in the hollow chamber with double injection sections. In the center part, gaseous H 2 and air injected by co-axial injector. Near the outer wall, the same propellants are injected in the form of slit-orifice collision. By keeping the total air mass flow rate approximately constant, varying the mixture of the inner and outer injection, series experiments are conducted in the test model with or without Laval nozzle. The results verify the possibility of rotating detonation in the hollow chamber with co-axial injector. To clarify the relationship between continuous rotating detonation and high frequency tangential combustion instability, the intrinsic frequencies of the test model are captured to be compared with propagation frequencies of detonation waves. The results show that they are close to each other when enough propellant assembled near the outer wall. In the combustor, the flame direction in constant pressure mode can change itself into rotating direction spontaneously. The results indicate that rotating detonation is an implication to high frequency tangential instability. • The results verify the possibility of rotating detonation in the hollow chamber with co-axial injector. • The key factor to forming detonation wave with co-axial injector has been discussed. • The results indicate that rotating detonation is an implication to high frequency tangential instability. [ABSTRACT FROM AUTHOR]

• Ethylene and oxygen rich combustion to produce ethylene-rich gas as fuel. • Ethylene-rich gas and air generate rotating detonation wave spontaneously. • The collision of high temperature gas with the outer wall generates a "hot spot". • The rotating detonation wave was produced by the DDT process. This study investigates an experimental process of high-temperature ethylene-rich gas and air for rotating detonation. After abandoning the pre-detonator method, the high-temperature ethylene-rich gas was injected and collided with the outer wall to create a localized high temperature and pressure region that ignited the gas mixture to form the deflagration state. Whether it is a single deflagration flame or double deflagration flame, it is eventually transformed through the deflagration-to-detonation transition (DDT) process into a double detonation wave. With propagation and collision of the double waves, the injection pressure increases, which results in shortening the self-initiation delay time. The equivalence ratio, gas temperature, and mass flow rate affect the success ratio of self-initiation. Rotating detonation engine (RDE) can be successfully initiated in the equivalence ratio range of 0.82 to 1.69. Equivalence ratio and gas temperature increase the propagation velocity of rotating detonation wave (RDW), for maximum RDW velocity of 1324.61 m/s, the gas temperature is 1021.3 °C. At the double wave collision point, a new weak RDW appears that decreases the RDE operating stability and a periodic quenching and re-initiation of RDW phenomenon occurs at that point. [ABSTRACT FROM AUTHOR]

The rotating detonation combustor is investigated as a potential implementation of pressure-gain combustion. Achieving net pressure-gain has proven to be extremely challenging in most combustors reported in the literature, regardless of their operating parameters. The performance losses observed in rotating detonation, compared to ideal predictions, can be attributed to mechanisms such as vitiation by residual burnt gases, partial detonation, and pre-combustion of reactants. The literature frequently discusses the impact of these mechanisms on measurable properties such as thrust and wave speed, but their effects on the front structure have not been fully understood. This study proposes using the rotating detonation structure for the first time to evaluate the vitiation quantitatively. The front structure of a compressed natural gas — oxygen-fueled rotating detonation is characterized using broadband chemiluminescence, and properties such as oblique shock angle, expansion angle, and front height are reported. The experimental values are then compared to the ideal predictions derived based on mass flow rates. The experimental front heights are found to be much higher than their ideal predicted counterparts. Analytical calculations that include pre-burning and vitiation show an increase in front height and a reduction in expansion angle, consistent with the chemiluminescence levels observed. The vitiated mass fraction is then deduced from the experimental front height, and the remaining velocity deficit is then used to evaluate the partial detonation mass fraction. Vitiated front angles compare favorably to the predicted values. Novelty and Significance This study reports high-quality chemiluminescence imaging of natural gas/oxygen rotating detonation front enabling the measurement of critical geometrical front features such as the front height, oblique shock angle, and expansion angle. The conventional front mass flow rate balance is extended to account for the re-circulation of burnt gases effects and is used to estimate the experimental vitiation. Most notably, vitiation of the fresh mixture, which was already known to reduce front speed and pressure rise, is also shown to strongly decrease the expansion angle resulting in further losses of axial thrust. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tesla valve is effectively applied to mode control. • The rotating detonation wave propagates clockwise in the mode control combustor. • Guide channel inhibit the formation of multi-wave mode. The detonation mode has a significant impact on the operational characteristics and propulsion performance of the rotating detonation combustor (RDC). Controlling the combustion mode effectively is advantageous for improving the propulsion performance of the pressure gain combustor. A Tesla valve mode control combustion chamber (TVMC) was used for experimental research in this study. An equal-width annular combustion chamber (EWA) was used as a control test, with room temperature kerosene as the fuel, and oxygen-enriched air as an oxidizer. The experiment successfully validated the feasibility of mode control in TVMC along with its operational characteristics. Monitoring the pressure pulsation of detonation and guide channels in TVMC led to the unfolding of possible mode control mechanism. The results indicated that the rotating detonation wave (RDW) propagates clockwise in TVMC. After RDW propagating counterclockwise enters the guide channel, the width limitation of guide channel causes RDW decoupling. It changes the propagation direction of the leading shock wave, resulting in mode control. Because of the presence of a guide channel, the RDW is unstable at low equivalence ratios, and the operation range is also narrower. [ABSTRACT FROM AUTHOR]

• Experiments of Rotating Detonation Engine fueled by liquid kerosene in room temperature. • Clear modal change process of liquid RDE. • The modal transformation law was reproduced through numerical simulation method. • Quantitative analysis of combustion efficiency under different modes by statistical method. 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. [ABSTRACT FROM AUTHOR]

The emerging new generation of RAM engines – rotating detonation engines – placed the problem of numerical forecasts of its effectiveness and reliability on top of current research needs. The paper presents the results of 3D numerical modeling of an engine with a rotating detonation wave (RDE) fed with hydrogen-oxygen mixture. An engine using rotating detonation waves is a new approach to increase of thrust characteristics of power facilities. The research studied the influence of a combustion chamber shape parameters on the RDE performance. Different internal body lengths were considered; the internal body was a cylinder with a conic top. The body could extend out of the nozzle of the engine. A 3 cases were studied: 1) the inner body length 6 cm, 2) 9 cm, 3) 9.75 cm. Besides, the chamber channel could hold inclusions: rings partially blocking it, near the inflow end of the combustion chamber. The influence of those rings was also studied. Stable modes of rotating detonation were obtained with one, or two waves. For all the cases, thrust characteristics were obtained and analyzed. • The process of switching to a rotating detonation wave mode was investigated. • Different internal body lengths were considered. • The influence of internal compression rings was considered. • For all the cases, thrust characteristics were obtained and analyzed. [ABSTRACT FROM AUTHOR]

The wall effect on the flow structures of the three-dimensional rotating detonation wave in an annular chamber is investigated by utilizing premixed hydrogen/air at a stoichiometric ratio as the reactant and a 7-species-8-reaction finite-rate chemical reaction model for evaluating the chemical source term. Three cases are constructed with different flow solvers, i.e. , Euler, Navier-Stokes and filtered Navier-Stokes with Improved Delayed Detached-Eddy Simulation to identify the wall effects. Both slip and non-slip wall boundary conditions are considered to quantify the viscous effect near the wall. It is found that the flow structures of the rotating detonation wave change notably when the effect of the viscous wall is taken into consideration, resulting in the extension of the deflagration zone to the upstream along the wall, the severe deformation of the detonation front at the unbounded side, and the formation of the reactant deficit. The mechanism of such alteration in the flow structures is analyzed, and the formation procedure of the reactant deficit zone is proposed. The comparison of specific impulse shows that our simulation is about 10% lower than the ideal two-dimensional rotating detonation engine model, and the practical experiment model is about 5.8% lower than our simulation. The wall effect, the three-dimensional effect and the turbulent mixing would lead to the performance losses. • The wall effect causes the changes of flow structures in the 3-D RDW. • The formation mechanism of the reactant deficit zone is proposed. • The wall molecular viscosity is the dominant factor and turbulence effect is minor. [ABSTRACT FROM AUTHOR]

Rotating detonation combustor (RDC) operation is investigated under the main composition of the coal and supercritical water gasification process (a methane–hydrogen–carbon dioxide mixture), and air is selected as an oxidizer. Experiments are performed under four flow rates (79.1, 101.2, 125.8, and 158.2 g/s), and the equivalence ratio (ER) ranges from 0.23 to 0.87. The detonation delay time and propagation characteristics of the rotating detonation wave (RDW) are investigated, and the nonlinear time series analysis method is applied to the pressure signal using the wavelet entropy algorithm and phase space reconstruction. It is demonstrated that a decrease in the flow rate can increase the detonation delay time near the lean fuel boundary; however, the detonation delay time is affected only slightly when the ER is greater than 0.4. The ER significantly affects the wave velocity but is affected only slightly by the flow rate. Contrary to the wave velocity performance, the pressure of the RDW increases with the flow rate. The lean fuel boundary becomes wider when the flow rate increases. Five combustion modes are investigated: failure, fast deflagration, sawtooth wave, single-wave, and two-counter rotating wave modes. The fast deflagration and sawtooth wave modes may occur near the detonation operating boundary, and a higher flow rate tends to increase the occurrence probability of a multiwave mode. The phase space pattern and distribution of wavelet entropy can be used to distinguish the combustion modes intuitively. • Rotating detonation fueled by a methane–hydrogen–carbon dioxide mixture. • Detonation delay time is decreased with the higher equivalence ratio. • Acoustic mode tends to occur near lean fuel conditions. • Nonlinear time series analysis would distinguish the combustion modes intuitively. [ABSTRACT FROM AUTHOR]

This work investigates the stabilization mechanisms of two types of longitudinal pulsations in rotating detonation combustors. The first type is linked to operating modes with two counter-rotating waves in combustors with open outlets and appears as a minor peak in the pressure spectrum. The second type is observed as pulsed operation of the combustor when the outlet is restricted. Different combustor lengths are studied and the susceptibility to these longitudinal pulsations is investigated. Pressure measurements along the length of the combustor and around the perimeter are used to identify the operating mode and to describe the propagation and stabilization mechanisms of the two longitudinal modes. The results show that both modes are linked to the longitudinal acoustic resonance of the combustor. The length-to-perimeter ratio and the mass flux are identified as the driving parameters for the existence of these longitudinal modes. The first mode is shown to be an acoustic resonance supported by the intersections of counter-rotating waves. The second mode is controlled by the reflection of an explosion induced shock wave propagating through a high velocity bulk flow. [ABSTRACT FROM AUTHOR]

In this work, the effect of different injector geometries and different outlet restrictions on the operating modes of a hydrogen-air Rotating Detonation Combustor (RDC) is investigated. The different operating modes are identified based on pressure measurements in the combustor annulus and the reactant supply, combined with high-speed video from the aft end of the combustor. The pressure frequency spectra are analyzed to determine the global operating mode in terms of number, direction, and speed of waves. The results explore the ability of the RDC to establish rotating, counter-rotating, and longitudinal waves, as well as their superpositions. A good agreement between longitudinal modes and the acoustic resonance frequencies of the RDC annulus was found. Overall, operation was found to be highly injector and outlet restriction dependent. Adding an outlet restriction helped to suppress counter-rotating waves, which is a prerequisite to stabilize single detonation waves. However, it was also shown to prompt high frequency pulsed operation. Apart from the total reactant supply pressure, the relative strength of the injectors was identified as a key factor for stable RDC operation. Pressure feedback into the reactant supply was observed to be dependent on the reactant supply pressure and the RDC operating mode. The study further revealed the presence of transverse resonance modes in the fuel plenum, however these oscillations were weak relative to the injector pressures and do not appear to influence the combustion. [ABSTRACT FROM AUTHOR]

In order to investigate the formation process and propagation characteristics of detonation wave, developing process of detonation wave from initiation to stable detonation formation under non-premixed conditions has been studied by experiments and numerical simulation. The results show that when mass flow rates of air and hydrogen are 158.957 g/s and 2.728 g/s respectively, stable detonation can be formed in the combustor. Due to the lower inlet pressure, there is an unstable stage in combustor before the stable detonation is formed. Reducing the air pressure will increase the lowest detonation limit of combustor and lead to flame-out and re-initiation in the combustor. The propagation direction of detonation wave may change after re-initiation. Non-premixed intake structure lead to the inconsistency of rotating detonation combustion fluid in the radial direction. Moreover, peak pressure appears near the outer wall, while peak temperature appears near the inner wall. • Hydrogen-air rotating detonations under low total air pressure were obtained. • Low total air pressure disturbs rotating detonation. • Re-initiations of RDWs were discovered. • The propagation direction of RDW changes randomly after re-initiations. • Differences of temperature and pressure on the inner and outer wall were discovered. [ABSTRACT FROM AUTHOR]

Perforated walls are potentially applied in rotating detonation combustors (RDCs) to stabilize combustion and perform transpiration cooling. This study involves an experimental investigation on the rotating detonation in perforated-wall combustors for the first time. Five types of walls with different hole sizes and perforated area ratios that range from 0 to 3.5% are examined to analyze acoustics and combustion characteristics, and performance of the RDC. The stable and unstable rotating detonation are both observed in the experiments, and the unstable phenomena mainly correspond to the counter two-wave rotating detonation that co-exists with the acoustic modes of the combustor. The acoustic modes are effectively suppressed by the perforated wall with area ratios over 1.75%, and the stability of rotating detonation significantly improves. The perforated walls significantly weaken the measured detonation pressure peaks and mitigate the impact of rotating detonation on the H 2 plenum, while they do not evidently reduce the specific impulse. It is proposed that the acoustic modes are excited by local high-pressure spots generated by the collision of two detonation waves, and they induce the fluctuating pressure peaks and wave velocity by affecting the H 2 injection. The perforated holes dissipate high-pressure spots, and thereby suppress the acoustic modes. [ABSTRACT FROM AUTHOR]

The wavelet features of rotating detonation waves (RDWs) are numerically investigated using Euler equations and a two-step induction-reaction model. The effects of the inflow stagnation temperature T st and the heat release rate k R on the number, height and intensity of the RDWs are discussed in this study. An increase in the stagnation temperature results in more detonation waves in a combustion chamber, which indicates the number of RDWs is sensitivity to the thermodynamic state of the reactants. As the heat release rate decreases, the number of detonation wave decreases and an unstable wavelet pattern is observed. This is represented as the oscillation in height and intensity of the detonation. In addition, some numerical cases are performed to determine the effects of ignition patterns on the number of RDWs. The features of the flow fields are analyzed using varied inflow stagnation temperature and initiation patterns, identifying the co-existence of different wavelet configurations. • An increase in the stagnation temperature generates more rotating detonations. • The variation of heat release rate also changes the wavelet number. • The height and pressure of the detonation front oscillates periodically. • The wavelet features in rotating detonation is sensitive to the ignition patterns. [ABSTRACT FROM AUTHOR]

In the study, the propagation behaviors of rotating detonation are investigated in an obround slit-channel combustor which has four curvature transition sections by employing a H 2 O 2 N 2 mixture with different oxygen volume fractions (α) and equivalence ratios (ERs). High-frequency pressure sensors are circumferentially mounted into the outer wall to obtain pressure temporal variations. Statistical indexes related to wave velocities are adopted to characterize the behaviors of rotating detonation based on which the experiment data are divided into stable and unstable regions. The stable rotating detonation is obtained within wide-range ERs for α = 40% and 35% in which the detonation velocity fluctuation ratio is approximately 1%. The pressure histories indicate that the instability of the detonation front is induced by the curvature transition for α = 30% and 21%. Complicated unstable phenomena associated with the detonation propagation are observed in which the acoustic modes can be identified. With respect to α = 21%, the unstable propagation of rotating detonation and the intensity of the first longitudinal acoustic mode are heightened when the oxidizer flow rate increases and even lead to detonation quenching. It is proposed that the unstable propagation of rotating detonation results from the coupling of acoustic modes and the curvature transition induced instability of detonation front. The stabilization of rotating detonation is affected by the curvature transition and requires smaller equivalent detonation cell size, i.e. higher activity reactants, in the obround combustor when compared to that in annular combustors. [ABSTRACT FROM AUTHOR]

In this study, the effect of the channel and oxidizer injection slot width on the rotating detonation fueled by the pre-combustion cracked kerosene was researched. Three channel widths of 15, 25, 40 mm and two slot widths of 0.4, 1 mm were examined in the implemented experiments using cracked kerosene and oxygen-enriched air (oxygen ratio of 30%). The time for the formation of the RDW is extended with the wider channel and shortened with the narrower slot. While the wave speed increases with the increasing channel width, the wave speed is little influenced by the change of the slot width. The lean fuel operating boundary becomes narrower when the channel width increases. The narrower slot tends to increase the occurring probability of the two-counter rotating waves mode while the wider channel has a contrary effect on the rotating detonation. When the flow rate is set at a relatively low level, the acoustic mode may occur near the detonation operating boundary. • Rotating detonation fueled by pre-combustion cracked kerosene. • Wave speed is increased with the wider channel. • Narrower oxidizer slot promotes the occur of the two-counter rotating waves mode. • Acoustic mode tends to occur at low flow rate near the detonation boundary. [ABSTRACT FROM AUTHOR]

The extraordinary complexity of real Rotating Detonation Combustors (RDC) demands a deep knowledge of each phenomenon involved in the wave development and propagation. Since the reactants are typically injected separately, a key element for the combustor design optimization is understanding the refilling process and the reactants mixing. However, due to the harsh environment and high working frequencies of RDCs, the experimental diagnostics is usually limited, so high-fidelity simulations represent an essential tool to complement the measurements with detailed insights into the flow. In the present work, the non-premixed RDC installed at TU Berlin is simulated with the AVBP code by solving the fully-compressible, spatially-filtered reactive Navier-Stokes equations. The complete hydrogen and air injection system is included in the numerical model to accurately describe both the reactants mixing and the complex turbulent flow field in the resulting refill region. This study shows how both the injection system configuration and its transient interaction with the wave are fundamental for the reactants mixing, as they directly influence the refilled gas properties. Limiting the imbalances between the blockage dynamics of the fuel and oxidizer ducts and optimizing the fuel injectors can improve considerably the homogeneity of the fresh mixture, and consequently the leading shock strength and reasonably the pressure gain. In fact, the detailed analysis of the detonation front speed shown a higher instability near the chamber base for the periodic presence of unmixed reactants. Nevertheless, the unstable root of the front does not affect the whole wave speed, and remaining part propagates steadily thanks to the tangential mixture uniformity. Moreover, the local speed distribution does not appear directly related to the small-scale mixture properties, indicating a higher sensibility to the annulus curvature rather than to the local gas state. [ABSTRACT FROM AUTHOR]

Series of experiments have been conducted in a hollow chamber with pintle injector to investigate the relationship between continuous rotating detonation (CRD) and tangential instability. The results show that the insertion length of pintle has great influence on the operation range of CRD. When it exceeds 10 mm, the CRD will be unrealizable. The influence of pintle diameter is finite. The deflagration in head recirculation zone and mixing delay lead to a poor quality of detonation waves. Three different propagation modes are presented. Most of the successful CRD in this work are single-wave mode. The highest frequency and velocity are 6.55 kHz and 2010.40 m/s, respectively. Two dominant peak one-wave mode (TDPO) has been observed and it is a fairly new one which has not been sufficiently studied. Sawtooth-wave mode is a critical mode which always shows around the lean limit. The intrinsic frequency of the combustion chamber has been calculated and compared with the experiment results. It shows great agreement with the frequencies of TDPO with the error less than 5%. This work shows the effects of the pintle injector on H 2 /air CRD wave in a hollow chamber. And it will contribute to a better understanding of the relationship between CRD and tangential instability. • Realizing rotating detonation in a hollow chamber with pintle injector. • Analyzing the effects of pintle configurations on rotating detonation. • Introducing three propagation modes of rotating detonation. • Comparing intrinsic frequency with experiment frequencies. [ABSTRACT FROM AUTHOR]

Highlights • An experimental study of single and counter-rotating waves in an RDC is conducted. • The pressure and natural luminosity of the detonation wave is characterized. • Counter-rotating waves interact and stabilize the combustion. Abstract Various operating modes have been observed in the rotating detonation combustor (RDC) studied here, as well as by others. These modes can be generally categorized into two groups: one or more co-rotating waves and counter-rotating waves. The combustor is able to stabilize both types of operation, however the stabilization mechanism remains unclear. In order to better understand these cases, these operational modes are investigated with high-speed pressure transducers installed in the combustor annulus combined with simultaneous high-speed video imaging of the natural luminosity of the detonation wave from the aft end of the RDC. These results confirm the operation in both the steady single wave mode as well as the counter-rotating waves mode. The presence of this mode further demonstrates the complex dynamics inherent in the stabilization of the detonation wave. As each wave propagates, they initially begin to weaken followed by re-strengthening after collision which serves to stabilize the mode. Differences in the velocities of the waves was also observed to result in a beating phenomenon expressed as an amplitude modulation of the pressure traces. High-speed video imaging of the high-temperature emission from H 2 O in the RDC annulus was used in conjunction with the pressure traces for a range of flow rates and equivalence ratios. Processing of the images into the wave frame of reference allowed for the identification of the average luminosity profile, characterized by a steep increase in natural luminosity near the wave front, followed by a trailing tail extending approximately half the annulus perimeter. [ABSTRACT FROM AUTHOR]

Abstract This work describes an experimental study on the transition dynamics in a hydrogen-air RDC as the operating mode transitions from two steadily propagating, equally-fast counter-rotating waves to a single wave depending on the operating condition. The operating mode for a range of equivalence ratios and mass flow rates is investigated based on time-resolved measurements of the pressure in the combustor annulus at multiple azimuthal locations, as well as based on simultaneous measurements of the natural flame luminosity from the aft end of the RDC. Overall reactant mass flow and equivalence ratio, coupled with the plenum pressures, were confirmed as the driving parameters for wave mode transition. Further experimentation is necessary to decouple these effects, however the results illustrate complex transition dynamics, yielding an acceleration of the primary wave and the simultaneous deceleration of the secondary wave(s). At the same time the secondary wave number is observed to increase up to a triplet of counter-rotating waves. A non-dimensional wave dominance parameter is proposed, which links the relative wave speeds of the waves to thermodynamic properties of the combustor. It indicates regimes of constant wave mode that are independent of changing operating conditions and that extend far into the operating map for the given RDC geometry. The results further indicate a correlation between the operating mode with two counter-rotating waves and choked flames, as well as quasi-detonations observed in generic detonation experiments in the literature. Highlights • An experimental study of different wave modes observed in an H2-air RDC. • Results show distinct regimes of operation. • CR waves transition to a single wave and are quantified by wave dominance. • CR waves propagate at the speed of sound in the products. • Sporadic transitions into pairs or triplets of counter-rotating waves. [ABSTRACT FROM AUTHOR]

In this study, the stable operating range and basic characteristics including the pressure and speed of a rotating detonation are researched. The fuel is an “ethylene–acetylene–hydrogen” mixture, examined at three mixing ratios of 2:1:4, 2.2:1:4, and 1.8:1:4 (ethylene:acetylene:hydrogen). The pressure of the rotating detonation wave (RDW) increases when the equivalence ratio (ER) is near the stoichiometric ratio, but it is little affected by the flow rate. The detonation wave speed maintains at 1200–1400 m/s, approximately 70% of the Chapman-Jouguet (C-J) speed, which is hardly impacted by the ER and flow rate. The speed of the RDW in the long-duration tests is higher than in the short-duration tests, and the time taken for the formation of a stable RDW is longer. The stable operating range is broadened and speed is increased with the increase in the acetylene and hydrogen in the mixture. The instabilities in the RDW are found to be correlated with the planar acoustic waves, whereas the mechanisms of the decoupling and re-ignition of the RDW are explained from the perspective of thermoacoustic coupling. [ABSTRACT FROM AUTHOR]

Experiments are performed to investigate the combustion characterization and operating diagram under the lean fuel condition in a laboratory-scale H 2 /air rotating detonation combustor (RDC). Pressure signals are obtained at different circumferential and axial positions on the RDC. Equivalence ratios ranging from 0.6 to 1.0 and air mass flow rates ranging from 25 to 225 g/s are used in the experiments. The operating diagram includes fast deflagration (FD), unstable detonation (UD), quasi-stable detonation, and stable detonation sub-regions characterized by the combustion mode. The results indicate that the occurrence of fast deflagration is mainly determined by the fuel-injection conditions and the acoustic properties of the annular combustor. The alternating occurrence of FD and detonation is typically observed in the UD region; therefore, the speed fluctuation of the wave propagation is very high, usually changed from 65% to 75% of its mean speed. In the quasi-stable detonation region, the FD completely disappears, but single/double-detonation wave inversion occurs. The statistical probability of the inversion of the single-detonation wave is approximately 10% of the 100 test runs conducted in the quasi-stable detonation region. In the stable-detonation region, a stable-detonation wave is formed and propagates stably without wave inversion or splitting. The speed and pressure fluctuations of the stable detonation wave are less than 15% of the mean ones. The present results serve as a guide for the design and practical application of rotating detonation engines. [ABSTRACT FROM AUTHOR]

This paper presents numerical results for a Rotating Detonation (RD) propagating in a layer of combustible mixture, created by injection of gaseous hydrogen and oxygen. 3D Large Eddy Simulations (LES) of a reacting flow have been performed in a domain of planar geometry in order to eliminate possible effects of the chamber curvature. First, the results for a 2D case with uniformly distributed premixed injection are presented to characterize the RD propagation under the most idealized conditions. Then a 3D concept is introduced for the injector composed of a series of injection elements. The RD propagation is simulated under the conditions of premixed and separate injection of the propellants at globally stoichiometric proportions. The case of separate propellant injection is the most realistic one. The computational results, represented by instantaneous and averaged flowfields, are analyzed to characterize the flowfield and the conditions of RD propagation. This analysis allows identifying the effects due to two major factors: the injection through discrete holes with respect to the distributed one and the separate propellant feeding with respect to the premixed one. Macroscopic quantities, such as the RD propagation speed, mean chamber pressure, average parameters of the mixture, and mixing efficiency are evaluated and compared in order to characterize the studied effects. [ABSTRACT FROM AUTHOR]

This article presents a numerical study on the rotating detonation engine (RDE). The simulation explores the phenomenon of the reinitiation of detonations in the RDE with a cylindrical combustion chamber. The process is modelled by the three-dimensional reactive Euler equations with an Arrhenius form of the reaction rate for the premixed stoichiometric hydrogen-air mixture. The detonation flow goes through three stages: initiation, quenching, and spontaneous reinitiation. The detonation fronts collide with each other and also have frequent collisions with the outer wall after initiation. While there is a possibility of generating new detonation fronts from the explosion, it is also likely that the explosion will burn out the surrounding reactive mixtures and snuff out the detonation waves. The simulation shows that a strong collision between two detonation wave fronts extinguishes the detonation flow and consequently renders the engine inoperative for an extended period until a spontaneous reinitiation occurs in the flow. The reinitiation is found to be triggered by a rapid and sharp increase of pressure near the chamber wall. [ABSTRACT FROM AUTHOR]

The operating behavior of a rotating detonation combustor is experimentally explored for stoichiometric H 2 –O 2 –N 2 mixtures for four combustor geometries to determine the role of cell width ( λ ) and combustor channel width ( w ch ) on the existence of detonation and number of waves. The ratio of nitrogen dilution ratio ( β = N 2 :O 2 ) of the oxidizer is varied from β = 3.76 (air) to β = 2, yielding a reduction in the cell width by a factor of two. The regime of successful detonation is bounded by a minimum normalized channel width of w ch / λ > 0.5, which agrees with the limit for classical detonation propagation in a rectangular channel. The number of detonation waves within the combustor ranges from n = 1–3, and increases in a predictable fashion when the normalized perimeter of a detonation front exceeds p / λ > 7.4. From the present work, it appears feasible to predict the existence and multiplicity of rotating detonations from the combustor geometry and mixture cell width. [ABSTRACT FROM AUTHOR]

To investigate the relationship of the rotating detonation and tangential instability, series of experiments have been done in a hollow chamber with Laval nozzle. In the present paper, two different ignition methods, named hot-jet and constant-pressure respectively, are adopted to compare the tangential instability and rotating detonation. The results show that, comparing with hot-jet method, when the contraction ratio of the nozzle is small, the realization of rotating detonation by constant pressure method is impossible. Three different combustion patterns have been found and characteristics of pressure oscillations have been discussed. When the contraction ratio is 10 and 12, the intrinsic frequencies of the test mode have been computed. Based on the pressure oscillations and the dominant frequency, the results are compared with the intrinsic frequency of combustion instability. The results show a good coincidence with each other. The non-linear tangential instabilities observed in rocket engines may actually be a manifestation of this rotating detonation wave mechanics in the hollow chamber with Laval nozzle. The work shows the possibility of detonation in a hollow chamber with Laval nozzle. It will enrich detonation wave theory and make a contribution to connecting the detonation and tangential instability. [ABSTRACT FROM AUTHOR]

As cycle efficiency of gas turbine can be significantly improved due to the pressure gain characteristic of rotating detonation combustion, a cycle calculation model of rotating detonation gas turbine based on component characteristic curves of a single shaft gas turbine of 25 MW and limited maximum flow capacity of rotating detonation combustor was established to investigate the variations of cycle performance and component characteristics under design and off-design conditions. Thereafter, sensitivity analysis of component parameters was conducted to explore the comprehensive reason for change of cycle efficiency increment. The results demonstrated that compared with those of traditional gas turbine, higher cycle performance and lower compressor pressure ratio were gained in rotating detonation gas turbine. Increment of cycle efficiency and cycle net power increment significantly increased with the drop of load, which reached to 0.0248 and 3.261 MW when turbine inlet total temperature was 1450 K and increased to 0.0539 and 4.008 MW when turbine inlet total temperature was 1279 K. Cycle performance was significantly affected by the changes of compressor pressure ratio, compressor efficiency, equivalence ratio of RDC and turbine efficiency, among which turbine efficiency rather than compressor outlet total temperature had the most significant effect on cycle efficiency increment under the calculated conditions. • A new calculation model of rotating detonation gas turbine cycle is built. • Sensitivity analysis of component parameters is carried out. • Higher performance and lower compressor pressure ratio are gained in the new cycle. • Turbine efficiency has the most significant effect on cycle efficiency increment. [ABSTRACT FROM AUTHOR]

To achieve the positive total pressure gain of the aerospace propulsion system is one of the critical issues for the application of rotating detonation. This study conducts a theoretical analysis on the total pressure gain (PG) of a rotating detonation system (RDS) composed of the isolator, anti-backflow zone and detonation combustor, with the system inlet Mach number of Ma 2. The impact of the reverse oblique shock wave (ROSW) on the system performance is emphasized. The definition of PG is based on the mass-weighted average pressure (MAP). An estimation method for PG is proposed, which is related to the inlet parameters and system anti-backflow capability. The approximate range of PG for the typical RDS and the parameter influence law are thus obtained. Results show that there is no guarantee that a positive PG can be achieved for the RDS. The theoretical upper limit PG max is obtained when the ideal detonation cycle is realized, and its value mainly depends the reactant activity. The theoretical lower limit PG min is mainly related to Ma 2 and the area ratio of system inlet and outlet, and a specific range of Ma 2 exists so that PG min ≥ 0. When the ideal check valve (ICV) is employed, which can completely suppress the ROSW and cause no total pressure loss in the anti-backflow zone, the PG ICV first increases and then decreases with the increase of Ma 2 , and reaches a maximum value when Ma 2 approaches 1. For a general RDS, PG is always less than PG ICV. The calculation example shows that for the stoichiometric C 10 H 20 /air mixture, the range of PG is ranged in (-1, 3). Eventually, two key approaches are needed to realize the positive PG of RDS, namely employing the ideal check valve, and making Ma 2 approach 1 that is achieving the maximum inlet mass flux. The present study is guidable for the RDS design in practice. [ABSTRACT FROM AUTHOR]

A 3D numerical simulation of a rotating detonation ramjet engine (RDRE) with isolator and combustor was performed under flight Mach number 2.5 conditions. Factors that influence the stable operation of isolator, such as equivalence ratio, length and expansion ratio of the isolator, were systematically investigated. The structure and stability mechanism of shock wave in the isolator wave were also investigated. Results show that the shock waves in the isolator are mainly composed of the spiral shock wave band (SSWB) and the leading shock wave (LSW), which are induced by the detonation wave and the strong disturbance of SSWB in the supersonic incoming flow, respectively. The airflow behind the LSW obtains the total pressure gain caused by the work of SSWB, when SSWB moves toward the isolator inlet. The speed of LSW is mainly affected by the pressure of detonation wave. The greater the pressure of the detonation wave, the faster the speed of LSW. When the total pressure at the leading edge of SSWB is lower than that of the incoming flow, LSW will stabilize in the isolator. A concept of critical pressure ratio was proposed in the present study, which is the ratio of the average total pressure of the rotating detonation wave to the total pressure at the isolator inlet. In the research configuration and working conditions of this paper, the critical pressure ratio is slightly smaller than 6 when the equivalence ratio of H2/Air premixed mixture is 0.7, below which the isolator can work continuously and stably. [ABSTRACT FROM AUTHOR]

• Experiments of a ramjet RDE fueled by kerosene with high total temperature air. • Effects of cavity length on the performance of two-phase kerosene/air RDWs. • Combustion distribution in cavity-based combustor of a liquid-fueled ramjet RDE. Our very recent work has experimentally demonstrated the successful operation of a liquid-kerosene-fueled ramjet/air-breathing rotating detonation engine with a cavity-based annular combustor. As a follow-up study, the present work aims to further reveal the effects of cavities on the initiation and propagation characteristics of detonation, and various cavity lengths ranging from 30 mm to 90 mm were employed in the combustor. An air-heater was designed to provide an incoming flow at a total temperature of 860 K, which resembles the specific flight Mach number of 4 at an altitude of 20 km. The total mass flow rate of the incoming air flow was kept at 1.0 kg/s. The results indicate that a sufficient cavity length, which is found to be around 45 mm in minimum, is necessary to achieve the successful initiation of the rotating detonation waves. By increasing the cavity length to 75 mm and 90 mm, the fuel-lean detonation limits in terms of equivalence ratios (ER) can be extended from 0.8 to 0.7. The maximum propagation stability and minimum velocity deficit of 39.1 % (with respect to the ideal Chapman-Jouguet velocity) were achieved when the cavity length was 75 mm with the ER of 0.95. The optical observation indicates that detonation mainly occurs downstream of the cavity. The detonability of the kerosene/air mixture can be enhanced by the preheating of the permanent flame, and better enhancement is provided by larger cavity lengths. However, when the cavity length reaches 90 mm, part of the mixture is pre-ignited and consumed by deflagration. Therefore, the propagation velocity and stability of the rotating detonation wave increase as the cavity is lengthened from 45 mm to 75 mm, while showing a decrease when the cavity length reaches 90 mm. It is suggested that better detonation performance can be achieved by placing the permanent flame in a proper axial position through changing the cavity length. In addition, the increase of the cavity length is beneficial to alleviate the disturbance of the upstream oblique shock wave on the incoming flow in the isolator. [ABSTRACT FROM AUTHOR]

The peculiar phenomenon of longitudinal pulsed detonation (LPD) in a rotating detonation combustor (RDC) is studied using hydrogen–air mixtures, by utilizing: (i) two air injection schemes having different inlet areas, and (ii) a convergent nozzle assembly with different spacers that affixes to the RDC exit. By varying the air injection pressure ratio and the backpressure, the regime of occurrence and the mechanism of this pulsed detonation instability are investigated. Immense evidence to suggest that LPD is caused by a peculiar detonation initiation mechanism enabled by a reflected shock wave from the RDC exit is discovered through an ensemble axial pressure profile analysis. Distance–time plots show that a single cycle of the pulsed detonation has two components: a fast-moving axial forward decaying detonation wave (with 75% of the ideal detonation speed) and a slower reflected detached shock wave (with 30% of the ideal speed). When the weak reflected wave comes in contact with the fresh reactants at the RDC headwall, another strong axial detonation is produced, thereby continuing the cycle without external ignition. LPD is also found to have three diverse facets, namely, inception, sustenance and operating frequency. For similar backpressures, the two air injection schemes have completely different operating regimes, leading to the inference that while backpressure is necessary for the onset of the pulsed detonation instability, by virtue of enabling reflected shock waves from the exit, lower air injection pressure ratio dictates the sustenance of the instability. A narrow band of injection pressure ratios, between 1.4 and 1.85, under back-pressurized RDC operation has high proclivity to produce sustained periodic longitudinal pulsed detonations in the combustor. Above this range, stable rotating detonation is preferred, and below this range, the operation is distinguished by the mixed presence of both rotating and pulsed detonations for a given test point, finally breaking down into chaotic instability for lower pressure ratios. The frequency of the pulsed detonation operation is found to depend on the initial combustor pressure and equivalence ratio, with higher frequency observed with an increase in backpressure and equivalence ratio. [ABSTRACT FROM AUTHOR]