Rotating Detonation Wave Research Articles

Two-dimensional numerical study of two-phase rotating detonation wave with different injections

Two-dimensional numerical simulations on the two-phase rotating detonation wave of a stoichiometric ratio of the air-octane mixture by the discrete phase model are performed. The propagation process and stable flow field of the rotating detonation wave under nonpremixed and nonuniform injection conditions are analyzed. The effects of air injection total temperature and fuel injection inhomogeneity on the gas-liquid two-phase rotating detonation wave are investigated. The results show that under the same conditions, with the increase in the total temperature of air injection, the peak temperature, height, and propagation velocity of the detonation wave increase, but the peak pressure of the detonation wave decreases. The larger the jet spacing, the more pronounced the detonation wave is disturbed by the fuel jet. As the fuel jet spacing increases, the detonation wave propagation velocity decreases, but the peak temperature and peak pressure of the detonation wave increase. For the case of a jet spacing of 10 mm, the detonation wave cannot propagate when the air total temperature is 300 K, but the detonation wave can be stably propagated when the air total temperature is increased to 600 K. The stable propagation boundary of the rotating detonation wave with the combined action of the air total temperature and the jet spacing is obtained.

Investigation of rotating detonation fueled by the pre-combustion cracked kerosene

In this study, a method of pre-combustion cracking is adopted in the investigation of the rotating detonation fueled by kerosene. The basic characteristics of the rotating detonation wave (RDW) including the wave speed, pressure, and propagating modes are researched. The wave speed increases when the equivalence ratio is near the stoichiometric ratio, but it is little affected by the flow rates. Different to the wave speed performance, the pressure of the RDW tends to increase when the flow rates rise but show weak relation with the ER. Features and transition of the five rotating detonation modes including the two-co rotating waves, two-counter rotating waves, single-wave, pop-out and failure mode are investigated. The lean fuel boundary of the RDW is broadened with the increase of the flow rates. Also, the effect of the oxygen ratio (50% and 30%) of the oxidizer (oxygen-enriched air) on the characteristics of the RDW is investigated. The rotating detonation using oxidizer with the higher oxygen ratio has a better speed performance than with the lower oxygen ratio.

Effects of Diverging Nozzle Downstream on Flow Field Parameters of Rotating Detonation Combustor

In this study, three-dimensional numerical studies have been performed to investigate the performance of a rotating detonation combustor with a diverging nozzle downstream. The effects of a diverging nozzle on the formation and propagation process of a detonation wave and typical flow field parameters in a rotating detonation combustor are mainly discussed. The results indicate that the diverging nozzle downstream is an important factor affecting the performance and design of a rotating detonation combustor. The diverging nozzle does not affect the formation and propagation process of the rotating detonation wave, while the time of two key wave collisions are delayed during the formation process of the detonation wave. With increases of the diverging angle, the rotating detonation combustor with the diverging nozzle can still maintain a certain pressure gain performance. Both the diverging nozzle and diverging angle have great influence on the flow field parameters of the rotating detonation combustor, including reducing the high pressure and temperature load, making the distribution of the outlet parameters uniform, and changing the local supersonic flow at the outlet. Among them, the outlet static pressure is reduced by up to 88.32%, and the outlet static temperature is reduced by up to 32.12%. This evidently improves the working environment of the combustor while reducing the thermodynamic and aerodynamic loads at the outlet. In particular, the diverging nozzle does not affect the supersonic characteristics of the outlet airflow, and on this basis, the Mach number becomes coincident and enhanced.

Interaction between rotating detonation wave propagation and reactant mixing

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

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

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

A numerical study of rotating detonation wave with different numbers of fuel holes

In this paper, three-dimensional numerical investigations are conducted to characterize the slot-hole rotating detonation combustor under various numbers of fuel holes (40, 60, 90 and 120). The effects of fuel holes number on detonation wave are discussed according to three typical stages which are non-reacting stage, detonation formation stage and detonation stable stage respectively. Numerical results show that the number of fuel holes has a significant impact on the formation and propagation characteristics of rotating detonation wave. On detonation formation stage, the general formation processes of detonation wave are similar under different holes numbers, which mainly includes the collision of transmit pressure waves and reactant re-initiation phenomenon. Within the scope of this study, as the increase of holes number, shorter axial length is taken to close to the global equivalence ratio on non-reacting stage. For 90-hole case, it takes the shortest time to establish self-sustained detonation wave and has the highest propagating stability. Additionally, dual-wave mode is obtained when the holes number is 90, while single-wave mode occurs when the holes numbers are 40, 60 and 120. The propagating direction of RDW is reversal when the holes number is 60 and 120, the reason is related to the collision spot of pressure wave and distributions of equivalence ratio. Besides, the establishment of new detonation wave is dependent on the intensity of accumulated pressure wave and the distribution of equivalence ratio.

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.

Automated image processing method to quantify rotating detonation wave behavior.

An image processing technique is developed to automatically determine both average and instantaneous detonation wave properties within a rotating detonation rocket engine (RDRE) using high-speed imaging. This method entails segmenting the imaged RDRE annulus into 200 azimuthal bins and tracking integrated pixel intensity in each bin. By combining individual pixel intensity temporal histories across the azimuthal bins, this provides what is termed a detonation surface that visualizes the propagation of the individual detonation fronts azimuthally around the annulus. Average detonation modal properties including wave speed Ūwv, operational frequency fdet, and the number of waves m are determined automatically through a two-dimensional Fourier analysis of the detonation surface data. Also, instantaneous wave speeds Uwv for each individual detonation are determined by taking the numerical derivative of each waves' angular position temporal history from the detonation surface. This provides useful insight into wave-to-wave variability for an operating condition, as well as denoting modal transitions and mode stability. For the flow conditions investigated, the number of waves ranges from 2 to 14, with Ūwv varying between 900 and 1700 m/s, corresponding to 33%-71% of the ideal Chapman-Jouguet detonation speed; these modes exhibit an operational frequency of 20-45 kHz, with an average of 40 kHz. Overall, these measurements advance the understanding of RDRE's and may lead to performance gains above those achievable from constant pressure engines.

Numerical investigation of a non-premixed hollow rotating detonation engine

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

Numerical research of rotating detonation initiation processes with different injection patterns

Three-dimensional numerical simulations are performed to study the initiation process of the rotating detonation combustor initiated by a pre-detonator. Navier-Stokes equations are solved with a 7-species and 8-steps H2/Air chemical reaction mechanism. Three different injection patterns are considered, including the inner-slit injection, outer-slit injection and mid-slit injection. A single stable rotating detonation wave is established finally for all three injection patterns. Firstly, the initiator dynamics of the pre-detonator is discussed. The initial detonation wave spreads into the combustor from the pre-detonator and two oppositely propagating detonation waves are formed in the combustor in all cases, causing wave collisions. Similar fresh gas injection disturbance is seen, suggesting the little effect of different injection patterns at the beginning. After the recovery of the injection, ‘L-form’ fresh mixture layers are formed in the inner-slit/outer-slit injection patterns, leading to a rapid establishment of stable propagation mode. While in the mid-injection pattern, transition of fresh mixture layer structure is seen from ‘I-form’ to ‘L-form’. Severe lateral expansion exists during this period, resulting in a long-term wave initiation.

On the response of annular injectors to rotating detonation waves

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

Effects of the pintle injector on H2/air continuous rotating detonation wave in a hollow chamber

Abstract 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 H2/air CRD wave in a hollow chamber. And it will contribute to a better understanding of the relationship between CRD and tangential instability.

Investigation on propagation characteristics of rotating detonation wave in a radial-flow turbine engine combustor model

In this experiment, the propagation characteristics of rotating detonation waves in a radial-flow turbine engine combustor model were investigated. An annular combustor, with an inner diameter of 94 mm and an outer diameter of 106 mm was used as the rotating detonation combustor, and the H2 and air were separately injected into the combustor. The stability of the detonation wave propagation with and without a guide vane at the exit of the combustor was analyzed. The velocity of the detonation wave for the guide vane tests is higher than that of no guide vane tests, and the guide vane has a significant effect on the oscillating pressure. For the no guide vane tests, only the two-wave collision mode of detonation wave is obtained for all the equivalence ratios, and there is an unstable phenomenon of the collision point displacement. For the guide vane tests, the detonation-wave gradually stabilizes with the increase of the equivalence ratio, and then the stability gradually weakens. The phenomenon of the low-frequency pressure fluctuation occurs with the equivalence ratio larger than 1, and the fluctuation frequency is lower than 400 Hz.

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

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

Three-dimensional modeling of rotating detonation in a ramjet engine

A 3D numerical model of a combustion chamber with continuous rotating detonation wave was performed. The ignition, onset and stabilization of a rotating detonation wave in combustion chambers of different shapes was investigated. The effect of additional oxygen injection on the onset of rotating detonation wave was studied. Formation of a stable detonation wave was investigated against different factors: internal body diameter, injectors number and diameter, pressure at the fuel and oxidizer orifices. The calculations were performed using specialized computer code designed by the Authors at the APK-5 super-computer system.

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

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

Experimental investigation on propagation characteristics of rotating detonation wave with a hydrogen-ethylene-acetylene fuel

It is attracting much attention that the hydrocarbon mixtures are used as the fuel of rotating detonation engine when the oxidizer is air. In this study, a hydrogen-ethylene-acetylene mixture was used as the fuel of rotating detonation combustor to investigate the propagation characteristics of rotating detonation wave. An annular combustor, with an inner diameter of 124 mm and an outer diameter of 152 mm, was used in this research. The air and fuel were separately injected into the combustor through a slot-orifice injection structure. High-frequency pressure sensors and ionization probes were used to measure the detonation characteristics. Experiments could obtain a stable detonation wave whose velocity was about 65% of the C-J value, showing that there was a large velocity loss compared to hydrogen fuel, which reached a C-J velocity value of 94%. The detonation intensity for the hydrogen-ethylene-acetylene mixture is weaker than that of hydrogen. The equivalence-ratio range of forming a detonation wave with hydrogen-ethylene-acetylene mixture was narrower than that of hydrogen fuel with the same mass flow rate. The detonation-wave height of hydrogen-ethylene-acetylene mixture had similar results with hydrogen fuel.

Enhancement of continuously rotating detonation in hydrogen and oxygen-enriched air

The enhancement of continuously rotating detonation in oxygen-enriched air was demonstrated in an annular rotating detonation combustor (RDC) under a diffusive supply of hydrogen and an oxidizer. Experimental tests were performed to reveal the effects of oxygen volume fraction, mass flow rate, and equivalent ratio on the propagation of continuously rotating detonation wave (CRDW). It is observed that an increase in the air mass flow rate from 25 g/s to 225 g/s causes an increase in the propagation velocity of the stable CRDW in the RDC. For an oxygen volume fraction up to 35%, the difference between the propagation velocity of detonation and the theoretical Chapman–Jouguet value is less than 5%. Under the chemical stoichiometric ratio condition for air, the CRDW is stabilized when the air mass flow rate reaches 185 g/s. However, stabilized CRDW is observed even when the air flow rate is only 45 g/s under the presence of 30% or 35% oxygen. Increase in the oxygen volume fraction leads to an extension of the rich/lean limit for generating a stable CRDW. This study aims to provide guidance for the modulation of continuously rotating detonation.

Experimental investigation on the temperature and heat-transfer characteristics of rotating-detonation-combustor outer wall

The thermal management on rotating detonation engine is attracting much attention in recent years. In this study, the experiments were performed on a rotating detonation combustor to study the temperature and heat-transfer characteristics of the outer wall. Hydrogen, which was used as fuel, was injected into chamber through 120 orifices uniformly distributed in front of combustor, and air, which was functioned as an oxidiser, was injected into combustion chamber through an annular slot. An infrared thermal imaging was used to measure the temperature of outer wall. All the experimental test cases could obtain a stable rotating detonation wave, and the hot-gas temperature decreased with the increase of axial-direction length. The temperature initially increased and then decreased from the head of the wall towards the back. The heat which transferred from the hot gas to the outer wall was further large than the value of losing during the combustor operation, resulting in an approximately linear relationship for the temperature rise. There was a similar distribution trend for the outer-wall heat flux under the conditions of different equivalence ratios, and the location of 20% distance, relative to combustor length, had a biggest heat flux.

The effect of the throat width of plug nozzles on the combustion mode in rotating detonation engines

Rotating detonation engines have been studied due to their better theoretical propulsion performance than that of deflagration-based engines. In this experimental study, the Laval nozzle throat width was varied to study combustion features in rotating detonation engines with different air flow rates and equivalence ratios. The detonation channel had an outer diameter of 100 mm and an inner diameter of 80 mm. Air and hydrogen were injected into the combustor from 60 cylindrical orifices each of 2 mm in diameter and a circular channel with a width of 1 mm, respectively. Four different widths of the plug nozzle were used: 2, 4, 6, and 8 mm. Three dynamic pressure sensors were used to obtain the detonation pressure. A standard speed camera was used to observe the exhaust from the combustion process. The results show that rotating detonation never occurred for a throat width of 4 mm. Rotating detonation waves with high speeds above 2300 m/s were obtained for a throat width of 2 mm. The mode of combustion in the engine was highly dependent on equivalence ratio and throat width. Probabilities of occurrences of longitudinal pulsed detonation increased first and then decreased with the decreased throat width.