Chapman Jouguet Research Articles

Air-breathing rotating detonation fueled by liquid kerosene in cavity-based annular combustor

This study experimentally demonstrates the practicality of air-breathing/ramjet rotating detonation engines fueled by liquid kerosene and air. Experiments are performed, via a direct-connect scheme, in an annular combustor with a specific air-heater for generating supersonic air with a total temperature of 860 K, which approximates the Mach-4 flight condition at an altitude of 20 km. To address the difficulty in stabilizing the liquid-kerosene-air fueled rotating detonations, an optimized cavity that mimics the functionality of a scramjet is adopted in the rotating detonation combustor. The results indicate that, while maintaining the mass flow rate of the supersonic air at approximately 1000 g/s, the kerosene-air detonations can be successfully obtained in a self-sustaining manner with the equivalence ratio located within a wide range of 0.77–1.47. To the best of the authors' knowledge, these are the first experimentally obtained liquid-kerosene-air rotating detonations operating in the air-breathing mode. The average propagation velocities of the rotating detonation waves are experimentally measured to be approximately 60% of the corresponding theoretical Chapman–Jouguet velocity. Such significant velocity deficits, typically reported for liquid-fueled detonations, are indicative of considerable non-ideal effects experienced by the rotating detonation. Additionally, both the maximum average propagation velocity and largest statistically averaged pressure peak are obtained when the equivalence ratio approaches 1.10. Moreover, owing to the high-speed air inflow and the characteristic distance required for the evaporation and mixing of liquid kerosene, the detonation wave is located significantly downstream of the cavity, rather than typically being attached directly or close to the combustor inlet. The findings of this study provide insights into rotating detonations fueled by liquid kerosene, as well as demonstrate the high potential of their application to air-breathing propulsion.

Chemical reaction zone measurements in pressed trinitrotoluene (TNT) and comparison with triaminotrinitrobenzene (TATB)

Photonic Doppler velocimetry and digital high-speed shadowgraphy have been used to characterize the chemical reaction zone parameters of pressed trinitrotoluene (TNT) samples with an initial density of 1.568 g cm−3. Comparison of the nanosecond time-resolved particle velocity histories of the free surfaces of detonating charges in air and light vacuum and of the interfaces between TNT detonation products and lithium fluoride or polymethyl methacrylate windows allow one to bracket the von Neumann spike pressure between 24.8 and 28.8 GPa. Our velocity waveforms confirm the two-step reaction pathway already observed in TNT, triaminotrinitrobenzene (TATB), and nitromethane, with a first fast energy release over 80 ns followed by a slower release over 250 additional ns. We consider the end of the first release zone as the locus of the Chapman–Jouguet (CJ) state, and the CJ pressure thus lies between 17.6 and 17.7 GPa. The energy release is not completed in this Jouguet plane but only after about ≈280 ns when the carbon cluster formation process ends. This corresponds to both the end of the slow release part of the interface velocity profiles and to the moment at which the free surface velocity profiles reach their maximum. Our shadowgraphy images confirm that carbon formation occurs very rapidly after the detonation breakout, in good agreement with previous time-resolved small-angle x-ray scattering measurements. The comparison with similar results previously obtained on TATB allows one to further highlight their similarities, which mainly result from their excess carbon production at late times.

Numerical simulation of similarities between rotating detonation and high-frequency combustion instability under two mixing schemes

This paper presents an experimental study on rotating detonations in a hollow combustor with the slit-orifice nozzle. The experimental results reveal that the propagation speed of detonation waves increases with the rise of mass flow rates and is greater than the Chapman–Jouguet detonation speed (VC−J). Furthermore, numerical simulations of rotating detonation in a non-premixed three-dimensional cylindrical combustor have been conducted based on a multispecies reacting code. The influence of two mixing schemes—that is, slit-orifice and coaxial injector—on detonation waves are studied to determine whether the characteristics of detonation waves tend toward high-frequency combustion instability due to changes in the mixing scheme. It is found that the slit-orifice scheme’s detonation speed, pressure, and temperature are significantly higher than those of the coaxial injector scheme. In particular, the detonation speed of the former reaches 124% of the VC−J, while that of the latter is only 80.5% of the theoretical value. The numerical results reveal that the low-speed detonation is caused by the deterioration of the hydrogen (H2)/air mixing conditions. Moreover, the flow-field structures of two mixing schemes were comparable, both containing transverse detonation waves, oblique shocks, contact surfaces, and wedge-shaped reactant regions. Furthermore, the Rayleigh index analysis showed that the unsteady heat release was in phase with the pressure fluctuations, amplifying the pressure. Therefore, it is suggested that high-frequency combustion instability may be a manifestation of rotating detonation waves under poor mixing conditions.

Increasing Oxygen Balance Leads to Enhanced Performance in Environmentally Acceptable High-Energy Density Materials: Predictions from First-Principles Molecular Dynamics Simulations.

Environmental concerns have stimulated the development of green alternatives to environmentally pollutive nitramine compounds used for high-energy density materials (HEDMs). The excellent energetic properties of CL20 make it a promising candidate, but its negative oxygen balance limits its efficiency for industrial and military applications. We predict here that CL20-EO formed by introducing ether links into the CC bonds of the original CL20 structure to attain balanced CO2 and H2O production leads to improved performance while minimizing the formation of carbonaceous clusters and toxic gases. To test this concept, we predicted the detonation properties at the Chapman-Jouguet (CJ) state using reactive molecular dynamics simulations with the ReaxFF force field combined with quantum mechanics based moleculear dynamics. We predict that CL20-EO enhances energetic performance compared to CL20 with a 6.0% increase in the CJ pressure and a 1.1% increase in the detonation velocity, which we attribute to achieving the correct oxygen balance to produce fully oxidized gaseous products. After expansion to normal conditions from the CJ state, CL20-EO leads only to nontoxic fully oxidized gases instead of forming the carbonaceous clusters and toxic gases found with CL-20. Thus, CL20-EO is predicted to be environmentally green. These results indicate that oxygen balance plays an important role in both energy availability and end-product toxicity and that balanced CO2 and H2O production systems provide promising candidates for the next generation of environmentally acceptable alternatives to toxic HEDMs while also enhancing the detonation performance.

Spontaneous runaway of fast turbulent flames for turbulence-induced deflagration-to-detonation transition

One of the fundamental mechanisms for detonation initiation is deflagration-to-detonation transition (DDT). This research experimentally explores the runaway condition for highly turbulent fast flames before DDT, which are characterized by extremely high turbulent flame speeds. Such fast turbulent flames experience increased effects of compressibility and may develop a runaway acceleration combined with a pressure buildup that leads to a turbulence-induced DDT (tDDT) mechanism that has been recently reported. The flame dynamics and the associated reacting flow field are characterized using simultaneous high-speed particle image velocimetry, OH* chemiluminescence, pressure measurements, and schlieren imaging. We study the flow-field conditions for runaway acceleration of fast turbulent flames and effects of compressibility on the evolution of these flames. The locally measured turbulent flame speed is found to be greater than that of a Chapman–Jouguet deflagration speed, which places the flame in the runaway transition regime that would eventually lead to a detonation.

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.

Numerical study of direct initiation for one-dimensional Chapman–Jouguet detonations by reactive Riemann problems

Numerical study of direct initiation for one-dimensional Chapman–Jouguet detonations by reactive Riemann problems

Numerical investigation of free oblique detonation wave induced by non-intrusive energy deposition

To validate the concept of free oblique detonation waves (ODWs) induced by non-intrusive energy deposition applied in ODW engines (ODWEs), numerical simulations are performed by modeling the laser spark as a high-temperature and high-pressure zone embedding in the high-speed incoming flow and by solving the non-dimensional reactive Euler equations with one-step chemistry. The initiation process, flow structures, and self-adapted characteristics of such kinds of free ODWs in an open space are discussed with varying dimensionless source energy and inflow Mach number. The results show that free ODWs can be initiated successfully by local non-intrusive energy deposition. In particular, four ignition regimes, namely, the subcritical regime, the critical I regime, the critical II regime, and the supercritical regime, which are analogous to the one-dimensional direct initiation of detonation, are distinguished by varying the dimensionless source energy. However, the typical energy required by each ignition regime is higher than that in the one-dimensional case due to multi-dimensional energy transmission and instabilities. Moreover, the dimensionless source energy should be moderate to obtain a stable free ODW flow field because extremely low source energy leads to ignition failure, while extremely high source energy causes premature ignition. When the inflow Mach number varies, it is found that free ODWs can adjust automatically to a nearly Chapman–Jouguet state, indicating the self-sustaining nature of free detonation waves. Due to this feature, ODWE performance will be relatively stable despite the change in inflow Mach numbers if free ODWs are utilized in the combustor.

Effect of losses on hydrogen–oxygen–argon detonation cell sizes

This work revisits the effect of losses on detonation characteristic length scales. Low-pressure experiments of the very regular hydrogen–oxygen–argon detonations in the straight narrow channel and along the exponentially diverging ramp were reported, demonstrating the significant role of losses in increasing detonation velocity deficits and cell sizes. Both the theoretically established and experimentally obtained relationships show the exponential sensitivity of detonation cell sizes to losses in terms of flow divergence, which is controlled by the global activation energy. The presence of losses modulates the lengthening of the characteristic detonation reaction zones and thus results in larger cell sizes, as indicated by the linear correlation characterizing the amplification of cell sizes and induction length. Moreover, the present work proposed an effective method for calibrating the ideal Chapman–Jouguet (CJ) detonation cell size from experiments, by adopting a revised formulism of Mirels' laminar-boundary-layer theory and also the generalized Zeldovich–von Neumann–Doering (ZND) model in the presence of flow divergence. Comparisons of the ZND-model calibrated ideal CJ detonation cell sizes from experiments with those from detailed numerical simulations show that, while differences still exist for the relatively high pressure cases, accounting for wall losses could excellently reconcile the discrepancy for the lower pressure cases, which appears to suggest no evident influence of the vibrational non-equilibrium effects for the hydrogen–oxygen–argon reactive system.

Numerical investigation of three deflagration-to-detonation transition conditions related to the velocity of the spontaneous reaction wave

In this work, the deflagration-to-detonation transition (DDT) process in a tube filled with quiescent and stoichiometric hydrogen/oxygen mixture is numerically simulated by a detailed chemical reaction model together with a high-resolution adaptive mesh refinement (AMR) mesh system. Then the flow field is analyzed in detail. It is found that for the onset of detonation in a DDT process there are three essential conditions related to the velocity of the spontaneous reaction wave DSpRW. The first condition is that on a hot spot the DSpRW should be slower than the speed of the Chapman–Jouguet (CJ) detonation wave DCJ to make sure that a spontaneous shock wave could arise originating from the spontaneous reaction wave. The spontaneous shock wave and the spontaneous reaction wave have conspicuous positive correlation to accelerate the spontaneous reaction wave to be faster than the local sound speed, which is the second DDT condition. With this condition the spontaneous reaction wave could catch up with its associated spontaneous shock wave and implement a coupling of the gasdynamics and the chemical energy release. This process is in line with Lee's SWACER idea, while throughout the process the spontaneous reaction wave propagates mainly through the Zel'dovich's reactivity gradients mechanism. Meanwhile, the gas velocity Vg is also essential to maintain the above two conditions and the resultant velocity meets the relation ∥DSpRW+Vg∥≥DCJ, which is the third condition. Distinctly this settles the wave speed gap between deflagration and detonation. More importantly, gas velocity plays an important role especially for the pressure build-up. The most important expressive differences between CJ deflagration and CJ detonation are the gas velocities of both the reactants and products as well as the pressure build-up. When these three relations successfully trigger a DDT and get a detonation wave, they still hold in the resulting detonation wave. They are delicately inherited as the inherent characters of the (detonation) wave. Formerly they are preconditioning-sustaining in the DDT process, and now they become self-sustaining in the detonation wave. Besides, the important role of the progress ratio of the induction period ε is emphasized for a spontaneous propagation.

NUMERICAL INVESTIGATION ON THE SPACE-TIME CORRELATION BETWEEN OBLIQUE DETONATION AND NORMAL DETONATION PROPAGATION

The propagation theory of one-dimensional detonation is complete and accurate, while prediction of two-dimensional oblique detonation propagation with large scale and high accuracy is still difficult primarily due to the treatment of wedge wall during the calculation and the modelling of viscosity. In this paper, the space-time correlation between two-dimensional steady oblique detonation induced by finite wedge and one-dimensional unsteady detonation supported by piston is investigated by numerical simulations of multi-species Euler equations with H2-Air detailed chemical kinetics. The initiation and propagation process of detonation wave, together with its interaction with rarefaction waves are numerically analyzed from the perspective of both space and time. The results show that under the same overdriven degree, the wave structure, wall parameters and profile variation calculated from one-dimensional case fit well both qualitatively and quantitatively with two-dimensional case after a certain space-time transformation, which validates the space-time correlation between one- and two-dimensional detonation waves. The difference mainly lies in the transition process between different stages of detonation development, such as the transition from over-driven oblique detonation wave to near Chapman-Jouguet (CJ) oblique detonation wave under the effect of rarefaction waves. Since most features of oblique detonation waves over finite wedge can be obtained efficiently by one-dimensional numerical calculation of piston-driven detonation and space-time transformation, the present work provides a feasible way to understand the spatial structure of oblique detonations waves, including detonation initiation, formation of over-driven oblique detonation and cellular structure downstream. Besides, this paper also provides a novel method to distinguish the effect of wall compression and boundary layer by comparing one- and two-dimensional numerical results. Moreover, the results imply that two-dimensional flow field over wedges of different shapes can be obtained with satisfying accuracy by altering the velocity of piston, which greatly reduces the time, cost and complexity of numerical simulation during the design of combustion chamber in an oblique detonation wave engine.

Evaluation of the two-γ model and the energy balance process of a Chapman-Jouguet detonation

Two issues related to the application of Chapman-Jouguet (C-J) theory have been investigated in this study. Firstly, the solution of the two-γ analytical model cannot agree with the exact solution calculated from the Chemical Equilibrium Compositions and Applications (CEA) code even all the required parameters are substituted with the exact ones. To root the source, the original derivation has been reviewed. It is believed that the perfect gas approximation induces the discrepancy, which will result in a huge discrepancy in the heat release at C-J state. Hence, a four-γ model for ideal gases has been derived, whose results are consistent with those from the CEA code though it requires more input parameters. Sensitive analysis implies that the accuracy of the four-γ model is greatly impacted by γ2‾ and qCJ. Besides, a parabola function that can describe the heat release and the lower heating value correlation has been proposed. Using this function, about ±5% relative error of estimated MS can be achieved when γ2‾ is equal to 9/7 for most selected stoichiometric gas mixtures. Secondly, the energy distribution in a C-J detonation process is found quite different when attaching the reference frame to the ground or the detonation wave front. Hence, regarding the C-J state as the equivalent burned state at the exit of a detonation combustor is questionable. Accordingly, a four-step thermodynamic process for a closed system has been developed, which can quantitatively analyze the energy balance process of a C-J detonation. Discussion is made by comparing the process with a traditional steady thermodynamic process as well as constant-volume combustion.

Near-optimal combination of high performance and insensitivity in a shock compressed high explosive single crystal

Achieving the desired combination of superior detonation performance and insensitivity to shock initiation has been a long-standing goal in high explosive (HE) science and technology. Having previously established the shock insensitivity of 1,1-diamino-2,2-dinitroethene (also known as DADNE or FOX-7) single crystals to 20 GPa (extended to 25 GPa in this work), the FOX-7 detonation response was determined through wave profile measurements in ∼250 μm thick single crystals shock compressed to 64 GPa. Quite unexpectedly, FOX-7 demonstrated the classic Chapman–Jouguet (C–J) detonation response—reaction completion in the detonation front (<0.7 ns) at pressures of 44 GPa and higher—not observed in other insensitive high explosives. The experimentally determined C–J pressure (35 GPa), detonation wave velocities and the detonation products equation of state—together with shock insensitivity to 25 GPa—demonstrate that FOX-7 single crystals display a near-optimal combination of high performance and shock insensitivity, not observed in another HE crystal.

Carbon-Based Multi-Phase Rotating Detonation Engine

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

First principles reactive simulation for equation of state prediction.

The high cost of density functional theory (DFT) has hitherto limited the ab initio prediction of the equation of state (EOS). In this article, we employ a combination of large scale computing, advanced simulation techniques, and smart data science strategies to provide an unprecedented ab initio performance analysis of the high explosive pentaerythritol tetranitrate (PETN). Comparison to both experiment and thermochemical predictions reveals important quantitative limitations of DFT for EOS prediction and thus the assessment of high explosives. In particular, we find that DFT predicts the energy of PETN detonation products to be systematically too high relative to the unreacted neat crystalline material, resulting in an underprediction of the detonation velocity, pressure, and temperature at the Chapman-Jouguet state. The energetic bias can be partially accounted for by high-level electronic structure calculations of the product molecules. We also demonstrate a modeling strategy for mapping chemical composition across a wide parameter space with limited numerical data, the results of which suggest additional molecular species to consider in thermochemical modeling.

South Africa: platinum companies earn well and invest

An experimental investigation was performed to study the pressure limits and mechanism of the detonation re-initiation behind the perforated plate with various thicknesses and hole diameters in H2–O2-Ar mixture by schlieren and soot track measurement. The Chapman-Jouguet (CJ) detonation and overdriven detonation were used to collide with the perforated plate. For the CJ detonation transmission, the detonation re-initiation distance is larger than 3.9 times the tube hydraulic diameter. Both the thickness and the hole size have significant effects on the critical pressure and the re-initiation distance. The ratios of the hole hydraulic diameter and the critical cell size (dH/λc) are less than 1. The cellular structure can be observed near the perforated plate on the smoked foils due to the collision of the arc-sharp shock waves via multi-jet structure. For the overdriven detonation transmission, the detonation can be re-initiated quickly, and the re-initiation distances are all less than twice the tube hydraulic diameter. The re-initiation distance increases with the hole size while the thickness has little effect on the re-initiation distance. The “abrupt” mode of the detonation re-initiation is transformed into the “gradual” mode with the increase of the initial pressure. The pressure limit of the re-initiation mode transformation also increases with the decrease of the hole size. Two mechanisms of the multi-jet initiation: rapid turbulent mixing initiation and the induction by the collisions of transverse waves were verified experimentally, corresponding to the “abrupt” and “gradual” modes, respectively. The critical condition of detonation propagation can be quantified as dH/λ∗ > 3.37 and 3.77 for the 3 mm-hole and 2 mm-hole perforated plates, respectively, where dH is the hydraulic diameter and λ is the detonation cell size.

Effect of perforated plate with high blockage rate on detonation re-initiation in H2–O2-Ar mixture

An experimental investigation was performed to study the pressure limits and mechanism of the detonation re-initiation behind the perforated plate with various thicknesses and hole diameters in H2–O2-Ar mixture by schlieren and soot track measurement. The Chapman-Jouguet (CJ) detonation and overdriven detonation were used to collide with the perforated plate. For the CJ detonation transmission, the detonation re-initiation distance is larger than 3.9 times the tube hydraulic diameter. Both the thickness and the hole size have significant effects on the critical pressure and the re-initiation distance. The ratios of the hole hydraulic diameter and the critical cell size (dH/λc) are less than 1. The cellular structure can be observed near the perforated plate on the smoked foils due to the collision of the arc-sharp shock waves via multi-jet structure. For the overdriven detonation transmission, the detonation can be re-initiated quickly, and the re-initiation distances are all less than twice the tube hydraulic diameter. The re-initiation distance increases with the hole size while the thickness has little effect on the re-initiation distance. The “abrupt” mode of the detonation re-initiation is transformed into the “gradual” mode with the increase of the initial pressure. The pressure limit of the re-initiation mode transformation also increases with the decrease of the hole size. Two mechanisms of the multi-jet initiation: rapid turbulent mixing initiation and the induction by the collisions of transverse waves were verified experimentally, corresponding to the “abrupt” and “gradual” modes, respectively. The critical condition of detonation propagation can be quantified as dH/λ∗ > 3.37 and 3.77 for the 3 mm-hole and 2 mm-hole perforated plates, respectively, where dH is the hydraulic diameter and λ is the detonation cell size.

Assessment of the Parameters of a Shock Wave on the Wall of an Explosion Cavity with the Refraction of a Detonation Wave of Emulsion Explosives

At present, studying the parameters of shock waves at pressures up to 20 GPa entails a number of practical difficulties. In order to describe the propagation of shock waves, their initial parameters on the wall of the explosion cavity need to be known. With the determination of initial parameters, pressures in the near zone of the explosion can be calculated, and the choice of explosives can be substantiated. Therefore, developing a method for estimating shock wave parameters on an explosion cavity wall during the refraction of a detonation wave is an important problem in blast mining. This article proposes a method based on the theory of breakdown of an arbitrary discontinuity (the Riemann problem) to determine the shock wave parameters on the wall of the explosion cavity. Two possible variants of detonation wave refraction on the explosion cavity wall are described. This manuscript compares the parameters on the explosion cavity wall when using emulsion explosives with those obtained using cheap granular ANFO explosives. The detonative decomposition of emulsion explosives is also considered, and an equation of state for gaseous explosion products is proposed, which enables the estimation of detonation parameters while accounting for the incompressible volume of molecules (covolume) at the Chapman–Jouguet point.

Wave Mode Dynamics in an Ethylene-Air Rotating Detonation Combustor

This experimental study focuses on investigating the wave mode dynamics in an ethylene–air rotating detonation combustor. The experiments were conducted at various equivalence ratios from to and at three testing mass flow rates of , , and . Fast-response wall pressure measurements, high-speed gas luminosity imaging, and heat flux measurements were employed simultaneously to evaluate the dynamics of the detonation waves among various testing conditions. Wave mode transition from two pairs of counter-rotating waves at fuel lean conditions to a single dominant wave at fuel-rich conditions has been observed. Four different wave modes in this transition are identified and discussed in the views of the wave dynamics, the pressure rise magnitude, and the thermal effect. Spectral analyses on the combustor pressure and the flame intensity present good consistency, showing the dynamics of the multiple detonation wave components from two different measuring techniques. The results suggest multiple wave components (namely, a single wave component, a primary wave pair, and a secondary wave pair) can coexist in the current rotating detonation combustor. The wave dynamics at different equivalence ratios follow the tendency of the wave evolution at ideal Chapman–Jouguet conditions. The wave mode transition is found to be a fact of the change of the dominant wave component in the combustor. The sudden growth of the single wave component is observed in the wave mode transition, which greatly changes the combustor environment. The wave mode is inferred to be correlated to the fuel–oxidant mixing configuration, suggesting the fuel–oxidant blowing ratio and the combustor geometry could be significant parameters in the formation of the wave mode.

Experimental Investigation of Detonation Propagation Modes and Thrust Performance in a Small Rotating Detonation Engine Using C2H4/O2 Propellant

A small rotating detonation engine (RDE) model and the corresponding experimental setup were constructed for the experimental investigation of the detonation propagation characteristics and thrust performance of a circular RDE. Experiments were conducted at a range of 0.3–2.5 equivalence ratio with a total mass flow rate of less than 180.0 g/s using a C2H4/O2 mixture. Irregularly unstable detonative combustion occurs immediately after the detonation initiation, which includes initiation, propagation, decaying, and the merging of detonation waves. Following this, periodically unsteady detonative combustion occurs in the circular channel, resulting in the stable operation of the RDE. During stable operation, two detonation waves are predominant, rotating along the wall at a speed lower than the Chapman–Jouguet (CJ) detonation speed. The characteristic velocity efficiency is approximately 73% on average. The low characteristic velocity efficiency is presumed to be caused by the unoptimized combustion channel and the poor mixing efficiency owing to the two-dimensional injector configuration. The effect of the RDE component design and the RDE flow field characteristics need to be further investigated for improving the performance of the RDE.