Continuous Rotating Detonation Wave Research Articles

Effect of the inlet spatial fluctuation on the gas–solid continuous rotating detonation flow field characteristics

Continuous rotating detonation engines have been extensively studied due to their high thermal efficiency. The utilization of solid particles as fuel can effectively reduce costs and enhance detonation performance. We have constructed a compressible gas–solid multimedium flow combustion numerical method, employing the double flux model coupled with fifth-order weighted essentially non-oscillatory and third-order total variation diminishing Runge–Kutta schemes to solve the unsteady multi-component chemical reaction Eulerian–Eulerian equations. Finite-rate methods and surface reaction models are used to simulate the combustion of gaseous mixtures and carbon particles. The effects of the inlet total pressure spatial fluctuations and particle diameter on the flow field characteristics of the continuous rotating detonation engine are investigated. The results indicate that changing the fluctuation period significantly affects the number, propagation direction, and intensity of gas–solid two-phase continuous rotating detonation waves (CRDW). The variation of fluctuation amplitude noticeably alters the combustion characteristics of the two-phase continuous rotating detonation wave, and excessively high amplitudes cannot form continuous rotating detonation waves. Introducing solid particles into fuel significantly mitigates the impact of inlet total pressure spatial fluctuation and promotes propagation stability on the detonation waves. Moreover, when solid particle diameters reach or exceed the micrometer scale, they contribute more favorably to generating a stable detonation flow field. However, excessive particle sizes result in a low surface reaction rate and inadequate contribution of heat released from particle combustion to the propagation of detonation waves.

Verification and characteristics of continuous rotating detonation waves in a novel rounded-rectangle hollow combustor

A noncircular cross-sectioned combustor holds the potential to facilitate the flexible design of continuous rotating detonation (CRD) engines, meeting the demands of airframe/engine integration. In this study, we propose and validate a novel rounded-rectangle hollow combustor comprising arc and straight segments. We conduct experimental and numerical investigations into the detailed propagation and combustion characteristics of the CRD wave in this combustor. The results demonstrate that a single hydrogen–air CRD wave can be achieved and sustained over a wide equivalence ratio (ER) range. As the ER increases from 0.71 to 1.25, the CRD wave's propagation velocity escalates from 1837.1 to 2190.8 m/s, with a substantial decrease in the relative standard deviation from 9.76% to 0.85%. The curvature variation along the combustor circumference influences the local propagation velocity, combustion intensity, shock wave strength, and shock wave system. Specifically, the constraints imposed by the arc segment significantly enhance combustion intensity and amplify shock wave strength. This is evident through a higher heat release rate fraction (fHRR), increased pressure peaks, and elevated propagation velocity. At the straight segment, the shock wave system comprises the CRD wave, leading, and trailing diffracted shock waves. However, the constraint from the arc segment leads to the formation of an additional reflected shock wave, altering the shock wave system to include the CRD wave, the reflected shock wave, and the leading diffracted shock wave. Thus, this study advances our understanding of CRD characteristics in noncircular cross-sectioned combustors, providing insight to the design theory for CRD engine combustors.

Effects of inner cone length on continuous rotating detonation in a variable cross-section combustor

A variable cross-section combustion chamber with different inner cone length L is designed, composing of an annular part with divergent width and a cylinder part without inner cone. Ethylene-air and hydrogen-air continuous rotating detonation (CRD) experimental tests are conducted. The results show that the ethylene-air CRD wave can be achieved in the variable cross-section combustor with the short inner cone. The propagation velocity of ethylene-air CRD wave can be 1661.37 m/s with the equivalence ratio of 0.91 and L of 10 mm. With L increasing from 0 mm to 30 mm, the combustion mode varies in the single wave mode, the sawtooth wave mode, and the hybrid mode. The combustor width is not the main factor leading to the failure of detonation in this study. The acceleration of propellent mixture caused by the expansion of the annulus channel, and the downstream movement and reduction of recirculation zone around the inner cone both increase the difficulty in CRD realization. While the hydrogen-air CRD can self-sustain with the intensive reaction zone in the annular part in the critical configuration of ethylene-air CRD. This study will contribute to the understandings of self-sustaining mechanism of CRD in the divergent combustor and the combustor design of the hollow chamber.

Initiation process of non-premixed continuous rotating detonation wave through Schlieren visualization

High-speed schlieren visualization on the initiation process of non-premixed air and hydrogen continuous rotating detonation (CRD) is carried out in a well-designed rounded-rectangle hollow combustor in this study. The CRD initiation processes of pre-detonator ignition and spark plug ignition are comprehensively revealed by synchronous high-speed schlieren images and high-frequency dynamic pressure results. The results show that the CRD undergoes three processes after ignition, including initiation process, adjustment process and stable propagation process. The CRD initiation process of pre-detonator ignition involves the upstream-propagation phase of leading shock wave and reaction zone and the coupling phase of circumferentially-propagating shock wave and reaction zone, while that of spark plug ignition includes the upstream-propagation phase of reaction zone, and the coupling phase of circumferentially-propagating pressure wave and reaction zone. The formation of deflagration combustion flowfield and re-establishment of combustible mixture layer after ignition are important prerequisites for CRD initiation. The strong interaction between circumferentially-propagating shock wave and post-shock wave reaction conduces to the rapid initiation of CRD by pre-detonator ignition, while the pressure wave gradually interacts with reaction leading to the detonation initiation by spark plug ignition. The CRD initiation time and adjustment time of pre-detonator ignition are shorter than those of spark plug ignition. This study provides detailed insight into the physics of CRD initiation process of pre-detonator and spark plug ignition, which can deepen the understanding of the initiation mechanism and provide practical guidance for the optimal design of CRDE ignitor.

Propagation characteristics of rotating detonation with high-temperature hydrogen gas

The rotating detonation characteristics of high-temperature hydrogen-rich gas were studied. Hydrogen-rich gas was generated by the pre-combustion of hydrogen, and a rotating detonation experiment of hydrogen-rich gas and air was subsequently performed. The auto-initiation of high-temperature hydrogen-rich gas was observed in the experiment, and the influence of pre-detonation tube ignition on the steady propagation of the detonation wave was analyzed. The results show that high-temperature hydrogen-rich gas and air have the ability to spontaneously form rotating detonation waves. The operation of the pre-detonation tube has a significant influence on the propagation mode and propagation velocity of the continuous rotating detonation wave after auto-initiation. The rotational detonation wave formed by the auto-initiation of hydrogen-rich gas and air has a short instability in the propagation process. The propagation velocity of the detonation wave before and after the unstable state is 1345.4 m/s and 1425.3 m/s, respectively, the unstable state is 1345.4 m/s and 1425.3 m/s, respectively.

Characteristics of ethylene–air continuous rotating detonation in the cavity-based annular combustor

Characteristics of continuous rotating detonation (CRD) in a cavity-based annular combustor are studied through three-dimensional simulations, which are solved in OpenFOAM with a skeletal chemical kinetics mechanism. The results show that the continuous rotating detonation wave (CRDW) attaches to the outer wall and detaches from the inner wall in the cavity-based annular combustor. A high-temperature recirculation zone is found in the cavity with reactive intermediate species in the cavity-based annular combustor. The cavity is identified as a high-temperature ignition source, which provides heat and active intermediate radicals enhancing the detonability of the combustible gases in front of the CRDW. Consequently, the propagation performance, the propulsive performance, and the detonation combustion intensity are promoted in the cavity-based annular combustor. The propagation mode of the CRDW transforms from an unstable mode to a single-wave mode with the application of cavity. As the cavity deepens from 0 to 15 mm, the propagation velocity significantly increases from 923.21 to 1662.81 m/s and the fuel-based specific impulse increases from 941.91 to 1044.48 s as the cavity depth varies from 0 to 15 mm. Furthermore, the detonation-dominant combustion fraction remarkably improves from 27.21% to 62.29%.

Propagation and flow field analysis of wall-detached continuous rotating detonation wave in a hollow combustor

Wall-detached continuous rotating detonation (CRD) was experimentally and numerically achieved in the designed hollow chamber. For this novel CRD wave, the pressure signals measured at the chamber wall showed lower peak pressure but much higher frequency when compared with typical wall-attached CRD. Meanwhile, the high-speed photographs showed that the luminous area (i.e. coupled reaction zone) of this CRD wave always varied within a “wall-detached” cylindrical zone. Experimental results with different ribs further proved that the CRD wave propagated within a cylinder whose diameter was about 44 mm, and the corresponding propagation velocity was very close to that of C-J detonation. A model was proposed to illustrate the flow field structure of this special CRD. According to the annular injection position of propellants, the hollow chamber was divided into two parts, namely, central CRD zone and outer shock wave zone. The detonation wave propagated within the former zone and the induced oblique shock waves stretched in both of the two zones. These two waves rotated synchronously to form the basic flow field structure of this wall-detached CRD. This model was further verified by a premixed numerical simulation case. The wall-detached propellants injection was believed to contribute to the formation and self-sustaining of the detonation wave in the center, and the oblique shock waves were induced on both sides due to the lateral expansion effect. This study shows that the detonation wave could rotate spontaneously and continuously without the support of chamber wall. The analyses on the propagation characteristics as well as the flow field structure of wall-detached CRD contribute to the understanding of self-sustaining mechanism of CRD wave in the hollow chamber.

The nature of sawtooth wave and its distinction from continuous rotating detonation wave

To pinpoint the nature of the sawtooth wave, extensive experiments of methane-air continuous rotating detonation (CRD) are conducted in a hollow chamber around the boundary of the operating range. The time occupancy ratio and the increasing ratio of pressure rise (Δti/ΔTi and ΔPi/Δti) derived from high-frequency pressure data, and the integral of chemiluminescence intensity (ICI) based on self-luminescence images are proposed as quantitative parameters to distinguish the detonation wave and the sawtooth wave. The results show that the sawtooth wave is a critical unstable mode between conventional isobaric combustion and CRD, propagating with high Δti/ΔTi and low ΔPi/Δti. Meanwhile, the reaction zone of sawtooth wave is verified to be stabilized in the center of combustor through the self-luminescence observation. Especially, the multiple transition processes from the sawtooth wave to the CRD wave are accurately captured, and simultaneously represented as the change from single-peak waveform to double-peak waveform on ICI, the rise of ΔPi/Δti, and the reduction of Δti/ΔTi. The significant distinction of the sawtooth wave and the CRD wave in the coupling characteristics is confirmed through Short-Time Fourier Transform processes on ICI and high-frequency pressure. For the CRD wave, the propagation frequency of the reaction zone matches that of the pressure wave, whereas not for the sawtooth wave. It is ascertained that the reaction zone is decoupled with the pressure wave for the sawtooth wave, and the nature of the sawtooth wave is deflagration combined with a weak pressure wave.

Study on the Influencing Factors of Modal Transformation of Continuous Rotating Detonation Wave Propagation

In order to study the propagation mode of rotating detonation wave, the detailed reaction mechanism of hydrogen-oxygen with 9 components and 19 steps is used, and the finite rate chemical reaction model is used for numerical calculation. After ignition, there is a stable collision period in the flow field for a certain period, and the collision extinguishing and new detonation wave generation occur during the mode conversion. By adding nitrogen or argon to the hydrogen-oxygen mixture for dilution, when the dilution ratio increases, the activity of the gas mixture decreases, the height of the combustible gas layer increases, and the temperature of the combustion product after the detonation wave decreases away from the head of the detonation wave, which will reduce the mixture that is burned in advance. There are different degrees of reflected shock at the outlet of the combustion chamber, and the upward detonation wave will cause the height change of the detonation wave head and the instability of the flow.

The use of detailed kinetics for modeling aerospace propulsion devices

A three-dimensional numerical simulation of a combustion chamber with a continuous rotating detonation wave was studied. A nozzle-type main system feeding was located at the end part of the chamber, and an additional feeding from the inner and outer walls of the annular channel was considered. A hydrogen-oxygen mixture was considered as a fuel. A detailed kinetic mechanism by Z. Hong (2010) consisting of 20 reactions with 9 components was used to simulate chemical processes. Various relations of the fuel were considered: lean mixture [H2]:[O2] = 1:1, stoichiometric mixture [H2]:[O2] = 2:1, and rich mixture [H2]:[O2] = 3:1. Besides, either the same mixture, or additional oxygen, or air was supplied from the side-wall feeding system. For all the considered feeding options, a detonation mode was obtained, and the traction characteristics were calculated.

Characteristics of rotating detonation waves in a hollow chamber with different fuel injection positions

Ethylene-air continuous rotating detonation (CRD) was achieved in the hollow chamber with different fuel injection positions. As the injection position moved downstream, the propagation mode of CRD waves appeared in the order of single-wave mode, co-rotating two-waves mode, and lifted-single-wave mode. The axial heat release rate of the former two modes were rapid, indicating that CRD waves propagated near the ethylene orifices. Typically, for CRD wave of single-wave mode, a high peak pressure (about 0.7 MPa) led to a local backflow of propellants in the head recirculation zone. The lifted-single-wave mode was a new propagation mode where the CRD wave was ‘lifted’ from the ethylene orifices. For this mode, the CRD wave propagated with little velocity deficit (8 %) but lower peak pressure (about 0.2 MPa). Besides, the axial heat release rate was much slower in this mode, indicating that the detonation wave propagated in the unburned propellants and the intermediate products of the upstream deflagration. The achieved propagation modes were significantly affected by the ethylene injection position, which was supposed to be related to the variations of matter and energy exchanges between the main stream and the combustion products in the central recirculation zone.

Experimental investigation on propagation characteristics of liquid-fuel/preheated-air rotating detonation wave

The rotating detonation combustor can be applied to the turbine engine to develop into a new power device, and the liquid-fuel/air rotating denotation has important research significance for engine applications. In this research, the propagation characteristics of liquid-fuel/air rotating detonation wave were experimentally investigated. A hydrocarbon mixture—liquid gasoline was employed for the fuel, the oxidizer was high-temperature air preheated by a hydrogen-oxygen heater, and the rotating detonation wave was initiated via a hydrogen-oxygen pre-detonator. The effects of the equivalence ratio, ignition pressure, and air total temperature on the propagation characteristics of the liquid-fuel rotating detonation wave were analyzed. The liquid-fuel/air continuous rotating detonation wave can be successfully obtained with a single-wave mode, and the velocity and peak pressure of the rotating detonation waves increase as the equivalence ratio increases. As the detonation-wave pressures at the outlet of the pre-detonator increase, the establishment time of the rotating detonation wave gradually decreases, and the average establishment time is 4.01 ms. Stable rotating detonation waves are obtained with the air total temperature of 600–800 K, but the intensity of the detonation wave has a large deficit due to some instabilities.

Continuous rotating detonation engine fueled by ammonia

As a carbon-free fuel, ammonia has attracted increasing interests while the corresponding utilizations are still limited. In this paper, ammonia-oxygen continuous rotating detonation (CRD) was firstly proposed and realized in the hollow chamber with Laval nozzle. The formation process and propagation characteristics were investigated through pressure measurement and optical observation. The CRD wave formation time increased with the nozzle contraction ratio, which was mainly attributed to the slower injection recovery process under the higher chamber pressure. The operation range was large, and the CRD wave propagated in single-wave mode with the velocity of 1806 m/s in the chosen test. The propagation velocity did not increase continuously as the equivalence ratio increased, which could be attributed to the changeable reaction mechanisms and the slow heat release of ammonia. The coupling of ammonia injection and CRD wave propagation was analyzed under both supersonic and subsonic injection conditions. The synchronous fluctuations of the pressure in ammonia plenum and the intensity of detonation waves proved that the coupling was very tight under subsonic injection condition. This paper was beneficial to the improvement of the detonation theory, and it provided an efficient approach to the utilization of ammonia.

Ammonia/oxygen-enriched air continuous rotating detonation in the hollow chamber

As a carbon-free and renewable energy source, ammonia can help to mitigate global warming. However, the utilization of ammonia is currently limited by its low chemical reactivity and flame consumption velocity. In contrast to deflagration, detonation has the inherent advantage of a faster heat release rate, which makes it a promising approach for ammonia utilization. In this study, the ammonia/oxygen-enriched air continuous rotating detonation (CRD) was first realized in a hollow chamber. The ammonia CRD wave propagated in single-wave mode with a velocity of 1753 m/s, which accounts for 77.16% of the theoretical Chapman–Jouguet (C-J) velocity. An analysis of the integral of chemiluminescence (ICI) was conducted based on images obtained using high-speed photography to reconfirm the stable propagation of the CRD wave. In the experiment, the ammonia CRD could be realized when the oxygen mass fraction (OMF) was at least 43%. The operating range clearly decreased as the OMF decreased from 83% to 43%. The axial ICI peak gradually moved downstream with reductions in OMF and equivalence ratio, indicating afterburning of the ammonia CRD. The enhanced combustion downstream led to a circumferential excess of the CRD wave structure downstream, which was verified through CRD flow-field reconstruction.

Characteristics of methane-air continuous rotating detonation wave in hollow chambers with different diameters

Due to the low chemical activity and large detonation cell size, methane-air continuous rotating detonation (CRD) is hard to be realized in a traditional small annular chamber without extra additives. In order to investigate the characteristics of methane-air CRD wave in a small chamber, three hollow chambers with Laval nozzles are adopted in this research. The methane-air CRD can be realized in a quite small chamber (diameter of 80 mm) under very particular condition. The operating range enlarges with the increase of chamber diameter. The CRD wave propagation frequencies vary apparently with chamber diameter while the propagation velocities stay in a quite narrow range of 1744–1812 m/s, and the relative deviation is within 4%. The CRD wave propagation process is very stable, and the propagation velocity accounts for 99% of the theoretical C-J velocity in the chosen test. Optical observation results illustrate that the reduction in chamber diameter or increase in nozzle contraction ratio will lead to CRD deterioration. By comparing the frequencies of high-frequency pressure and optical observations, the coupling of inducing shock wave and combustion flame is proved quantitatively.

The competitive relationship between detonation and deflagration in the inner cylinder-variable continuous rotating detonation combustor

To investigate the impact of the competitive relationship between detonation and deflagration on continuous rotating detonation, a series of ethylene-air and hydrogen-air rotating detonation tests are conducted by varying the inner cylinder length. In the experiments, ethylene-air detonation wave self-sustains in the hollow chamber part closely following the terminal of inner cylinder, instead of in the 5 mm-wide annulus. The deflagration in the upstream annulus combined with the deflagration prior to continuous rotating detonation wave in the hollow chamber part is supposed to be parasitic combustion, which destroys the accumulation of combustible mixture. The increase of intensity and longitudinal range of parasitic combustion makes the operating range, propagation frequency, and stability decrease. In contrast, hydrogen-air detonation wave can self-sustain in the 5 mm-wide annulus. However, the short annulus cannot hold the integrated detonation wave, and the separated structures of detonation wave make the ratio of commensal combustion increase. It is suggested that continuous rotating detonation should be quickly initiated within the short distance to reduce the impact of parasitic combustion, and the structural integrity of detonation wave should be maintained to reduce the ratio of commensal combustion. Besides, longitudinal pulsed deflagration mode is discovered and analyzed.

Effects of Annular Combustor Width on the Ethylene-Air Continuous Rotating Detonation

The realization and stable operation of Continuous Rotating Detonation (CRD) in the annular combustor fueled by hydrocarbon-air are still challenging. For further investigation of this issue, a series of ethylene-air CRD tests with the variation of combustor width is conducted, and the effects of combustor width are well analyzed based on high-frequency pressure and high-speed photograph images. The results show that the combustor width plays a significant role in the realization and sustainability of the ethylene-air CRD. In this paper, the critical combustor width for the CRD realization and stable single wave are 20 mm and 25 mm, respectively. In wide combustors, the backward-facing step at the combustor forepart makes the main flow slow down, and thus, the mixing quality is promoted. Besides, the pilot flame at the recirculation zone contributes to sustaining the CRD wave. As the width increases, the propagation mode changes from counter-rotating two-wave mode to single wave mode with higher propagation velocity and stability. The highest propagation velocity reaches 1325.56 m/s in the 40 mm wide combustor, accounting for 71.51% of the corresponding Chapman-Jouguet velocity. Despite large combustor volume, high combustor pressure is obtained in detonation combustion mode indicating that a better propulsive performance could be achieved by CRD.

Hydrogen-air, ethylene-air, and methane-air continuous rotating detonation in the hollow chamber

A series of hydrogen-air, ethylene-air, and methane-air continuous rotating detonation (CRD) tests are performed in the hollow chamber with the variations on nozzle contraction ratio and equivalence ratio. Hydrogen-air, ethylene-air, and methane-air CRDs are achieved with low velocity deficit and high stability in the same laboratory hollow chamber. Larger combustor width, flame stabilization and mixing quality promotion benefited from the hollow chamber, and the prolongation of residence time impacted by the hollow chamber and nozzle are key factors for significant enhancement. Generally, the operating range, propagation frequency, propagationvelocityC−Jdetonationvelocity, and stability increase with the fuel detonability increasing. The quantitative analysis approaches, the integral of chemiluminescence intensity and axial distribution of chemiluminescence intensity ratio on high-speed photography images, and flowfield reconstruction based on the time difference calculation method, are proposed and applied. Multiple analysis approaches all show that the length of CRD wave increases with the fuel detonability decreasing, which is mainly attributed to that the hydrocarbon fuels release heat in longer axial distance with relatively lower intensity. In addition, two dominant peak one-wave mode is verified as the single wave coupled with the reflected shock wave, which propagates upstream from nozzle to combustor forepart.

Flowfield Analysis and Reconstruction of Ethylene–Air Continuous Rotating Detonation Wave

The time difference calculation method, using the pressure peak rise time difference of high-frequency dynamic pressure signals to demonstrate the motion track of continuous rotating detonation wave (CRDW), is presented and verified. With the calculation method, the flowfield of CRDW has been reconstructed precisely. The angle of upstream oblique shock wave is defined for representing the influence of CRDW on the air inflow, which is impacted by the detonation combustion intensity and nozzle choking effect. The increase of combustor pressure makes the angle of upstream oblique shock wave decrease, indicating that the influence of detonation on air inflow strengthens. The angle of downstream oblique shock wave is mainly influenced by the contraction geometry of nozzle in the contraction ratio range of 2–10. The heights of CRDWs scatter around mm (), mm (, single wave), and mm (, two waves), respectively. The detonation wave height of single wave is higher than that of two waves in homo-rotating, and the height of ethylene–air CRDW is higher than that of hydrogen–air CRDW. This study will enrich the understanding and analysis method of CRDW flowfield structure.

Realization of methane-air continuous rotating detonation wave

Methane-air Continuous Rotating Detonation (CRD) has been firstly achieved in this paper in the hollow chamber with a Laval nozzle, and the diameter of the chamber is just 100 mm. The contraction ratio of the Laval nozzle is a key factor for the CRD realization. CRD can only be obtained when the contraction ratio is no less than 4, but its ER operating range decreases in the increase of contraction ratio from 4 to 10. For all the success cases, the average propagation frequency and velocity are in the ranges of 5.32–5.65 kHz and 1670.48–1774.10 m/s, respectively, and the velocity deficits are less than 10%. Based on the high-speed photography images, the approach of chemiluminescence intensity integral is proposed in this paper, and the propagation characteristics of the flame are analyzed quantitatively. The propagation velocities of the flame and shock wave are agreed well with each other, indicating that the typical feature of detonation wave, i.e., the coupling of the flame and the shock wave, is verified quantitatively.