Hydrogen Fueled Scramjet Combustor Research Articles

Intelligent reconstruction algorithm of hydrogen-fueled scramjet combustor flow based on knowledge distillation model compression

The real-time perception of the combustion flow of a scramjet can help to quickly evaluate the working state and provide a new opportunity for the intelligent reconstruction of the data-driven combustion flow field. However, the working process of supersonic combustors is extremely short, usually of the order of milliseconds, and the inference speed is slow due to the large number of parameters of traditional deep learning flow field reconstruction models within a very short time. Currently, knowledge distillation is known as an effective model compression method. In this paper, a neural network model based on symmetric structure cascade (NNSSC1) is proposed. By means of symmetric structure cascade, features of different levels are spliced and fused, which can effectively improve the reconstruction performance of the model. Secondly, to accelerate the application of the neural network model in the flight test, a student model with a simple structure is constructed. By distillation learning, the NNSSC model is used as the teacher model, combining the high performance of the teacher model and the high efficiency of the student model, and the combustion flow field is reconstructed with high speed and high precision based on the supersonic combustor wall pressure. In a direct connected supersonic pulse combustion wind tunnel with an inflowing Mach number of 2.5, the model was trained and tested on a dataset constructed in a hydrogen fuel scramjet experiment with different equivalent ratios. This method achieves high-precision and efficient reconstruction of complex flow fields in the combustor based on sparse wall pressure, providing more reliable data for accurately evaluating the flow and combustion status of the combustor of a scramjet.

Reactive Flow Dynamics of Low-Frequency Instability in a Scramjet Combustor

This study numerically investigated the combustion instability and characteristics of a laboratory-scale gaseous hydrogen-fueled scramjet combustor. For this purpose, a numerical simulation with an improved detached eddy simulation and a detailed hydrogen/oxygen reaction mechanism was performed. The numerical framework used high-resolution schemes with high-order accuracy to ensure high resolution and fidelity. A total of five fuel injection pressures were considered to characterize the combustion instability as a function of the equivalence ratio. A sampling time of up to 100 ms was considered to sufficiently accumulate several cycles of low-frequency combustion instability dynamics with a period in the order of 100 Hz. Numerical results revealed the repetitive formation/dissipation dynamics of the upstream-traveling shock wave, and it acts as a key factor of combustion instability. The period and derived principal frequency of these upstream-traveling shock waves is several ms. The frequency analysis showed that the instability frequency increased in the low-frequency range as the combustion mode transitioned from the cavity shear-layer to the jet-wake type. This characteristic was derived from the transition in combustion mode at the same equivalence ratio. Therefore, it suggests that the instability frequency shifting is governed by the combustion mode rather than the equivalence ratio. These comprehensive numerical results demonstrated not only the effect of the equivalence ratio but also the important role of the combustion mode on the low-frequency combustion instability.

Application of hydrogen mechanisms in combustion simulation of DLR scramjet combustor and their effect on combustion performance

In view of the promising application of hydrogen in scramjet combustor and the rapid development of hydrogen kinetic mechanisms, present work applies representative mechanisms with good kinetic performance to the combustion simulation of DLR scramjet combustor with a customized solver based on OpenFOAM platform. Different Reynolds-Averaged Navier Stokes (RANS) turbulence models including standard k-ε, SST k-ω and their corresponding modified versions for turbulent round jets, are utilized to simulate the non-reactive and reactive flow fields. Compared with the detailed experimental measurements of schlieren image, streamwise velocity, pressure etc., the modified k-ω SST turbulence model shows good performance and improves the simulation results near hydrogen jet. In combination with partially stirred reactor (PaSR) combustion model, three representative detailed hydrogen mechanisms (marked with Ó Conaire-2004, Varga-2015 and Konnov-2019) are adopted to evaluate their effect on combustion performance under scramjet combustion condition. And their effects on the combustion performance are quantified based on combustion efficiency, net thrust, total pressure loss, etc. All of them can well characterize the thermal combustion characteristics of hydrogen in the combustor. Among them, Ó Conaire-2004 slightly overestimates flame temperature, combustion efficiency and net thrust, and underestimates total pressure loss. Whereas Varga-2015 and Konnov-2019 provide nearly identical results on these performance parameters and give temperature profiles coinciding well with experimental data. Although the newly added excited states in Varga-2015 and Konnov-2019 deepen the understanding of hydrogen combustion processes and can served for optical combustion diagnostics, their effects on thermal combustion characteristics are negligible under present combustion condition, judging from their low content and the analysis on the performance parameters. Present work is conducive to the selection of hydrogen mechanisms for the combustion simulation of hydrogen-fueled scramjet combustor, and facilitates to obtain reliable simulation results for scramjet with turbulent round jets by employing the modified SST k-ω turbulence model.

Numerical investigation of low-frequency instability and frequency shifting in a scramjet combustor

The combustion instability in a laboratory-scale direct-connect hydrogen-fueled scramjet combustor is investigated numerically. The numerical simulation has been carried out using a delayed detached eddy simulation (DDES) with a detailed reaction mechanism. The computational framework has high fidelity by applying multi-dimensional high order accurate schemes for handling convective and viscous fluxes. The field data were accumulated up to 100 milliseconds on each case to capture sufficiently the repetitive behavior of low-frequency instability of order of 100 Hz. The numerical results exhibit the formation/dissipation of pressure and shock wave induced by continuous heat release in the combustor. This motion of pressure/shock wave, so-called upstream-traveling shock wave, presents repeated dynamics between isolator and combustor with a period of several milliseconds. With this periodic hydrodynamic characteristic, the upstream-traveling shock wave interacts with the boundary layer and injected fuel stream affecting fuel/air mixing and burning, and finally inducing the combustion instability in a scramjet combustor. Frequency analysis derived major instability frequencies of 190 Hz and 450 Hz in the isolator and combustor for low and high equivalence ratios, respectively. Current numerical results present the underlying flow physics on the shifting of the instability frequency by changing the equivalence ratio observed by the previous experimental studies. The fact that an instability frequency exists homogeneously from isolator to combustor informs that the combustion instability of scramjet engine is the fully coupled flow/combustion dynamics throughout the engine on a macroscopic scale.

Effect of inclined fuel injection in the strut wake region for a hydrogen fueled scramjet combustor

The supersonic airflow and injected fuel stream mixing process is complicated for a scramjet combustor because of little supersonic air resident time and high airflow stream momentum. The direction of fuel injection into a supersonic airflow stream plays a significant role in mixing enhancement with turbulence generation. This study investigates the effect of strut-based parallel (primary) and inclined fuel injection in the strut flame holder wake region. The primary strut with parallel injection is derived from the open literature. The base model strut consists of parallel injection, whereas in the new models, the fuel is injected at an angle of θ for both the upward and downward directions. By computing the Reynolds averaged Navier-Stokes equations, finite-rate eddy dissipation turbulence chemistry, and SST k-ω turbulence models, the mixing and combustion behavior for various fuel injections were investigated. The impact of different fuel injections on the downstream wake region is assessed by evaluating the distribution of H2 and H2O species in the radial and axial directions. The turbulence intensity and turbulent kinetic energy are also considered to evaluate the cross-impact of the air stream and fuel stream for inclined fuel injection. Numerical results found that inclined injection significantly impacts the mixing phenomenon with the development of enriched re-circulation zones in the vicinity of the flame keeper. The mixing and combustion efficiencies performance parameters are evaluated for different fuel injection schemes and found the average increased mixing efficiency of 13% and combustion efficiency of 12%, respectively, for inclined fuel injection. From the analysis of mixing efficiency, it is observed that complete mixing has been found after 235 mm, whereas for inclined injection, the complete mixing happened within a 175 mm distance. The maximum of 75% and 62% combustion efficiency has been observed at a 225 mm and 285 mm distance for inclined and parallel fuel injection, respectively.

Suppression of combustion mode transitions in a hydrogen-fueled scramjet combustor by a multi-channel gliding arc plasma

A multi-channel gliding arc (MCGA) plasma was utilized to suppress combustion mode transition in a hydrogen-fueled cavity-based scramjet combustor with an inflow speed of Ma2.92. Several optical and electrical techniques, including OH* chemiluminescence, optical emission spectrum, discharge waveform acquisition, and pressure measurements, were employed to show the characteristics of the MCGA discharge and the processes of the combustion mode transitions. When the MCGA is off, the flame frequently oscillates between a cavity shear-layer mode and a cavity-stabilized mode at a low global equivalence ratio, whereas the flame is more likely to be kept in the cavity-stabilized mode when the MCGA is on. The ratio of the cavity-stabilized mode increases from 28.2% to 93% when the plasma is on. The combustion frequently oscillates between a cavity-stabilized mode and a jet-wake stabilized mode at a high global equivalence ratio, but the mode transitions can be suppressed significantly in the presence of the MCGA. The ratio of the jet-wake stabilized increases from 21.9% to 48.8% when the MCGA is on. The Proper Orthogonal Decomposition (POD) method is employed to analyze the oscillation, and it is found that the mean energy content of the large-scale oscillation across the different modes can be significantly suppressed by the MCGA. A plausible explanation can be mainly related to the reactions of N2* species with O generated by the MCGA, which increases the temperature in the vicinity of the plasma. The temperature rises spread to the entire cavity with higher backpressure, and results in better mixing and more intense combustion, leading to the suppression of the combustion mode transitions.

LES of Reacting Flow in a Hydrogen Jet into Supersonic Crossflow Combustor Using a New Turbulent Combustion Model

Modelling the complete flow physics and chemical kinetics of supersonic combustion is a particularly complex and daunting task that requires significant computational resources. To foster performance evaluation tools for future hypersonic vehicles, developing accurate yet computationally efficient solution methods is of great importance. In this work, a new subgrid combustion model for large eddy simulations is derived and used in a three-dimensional in-house flow solver to provide simulations of experimental scramjet ground tests. In particular, this paper introduces a hybrid model closure with the reaction-rate approach to close the filtered chemical source terms in the governing equations for species mass fractions and total energy. The model developed here makes use of a linear bridging function, depending on the segregation rate of the mixture fraction, between a resolved contribution issued from a perfectly stirred reactor (PSR) estimation, and a subgrid-scale (SGS) contribution where a closure that approximates the Lagrangian trajectory in the composition space is retained. The new model considers the effect of fluctuations of compositions and can be extended to take into account, for example, the fluctuations of temperature. The new approach is tested using a hydrogen-fueled scramjet combustor from circular injector into a Mach 2 vitiated airflow for total pressure and temperature of 0.40 MPa and 1695 K, respectively. The selected operating conditions are representative of the LAPCAT-II dual-mode ramjet/scramjet combustion. Chemistry is described using a four-step reduced mechanism. The results obtained with the present modelling proposal are compared to those issued from numerical simulations performed with the quasi-laminar chemistry or PSR approach. These results do show that, even for a highly resolved computational mesh, the effects of composition fluctuations remain significant, especially in the vicinity of the injection where the SGS fluctuations of the scalar field are non-negligible.

Hydrogen fueled scramjet combustor with a wavy-wall double strut fuel injector

The demand for the enhancement of scramjet performance is increasing worldwide due to its tremendous and upcoming applications. The major challenge in scramjet engines is the mixing of fuel and air and succeeding combustion at supersonic speed. In a scramjet combustor flow field, the development of high turbulence (flow disturbance), shear-mixing layer, and oblique shock waves are the key factors to magnify the mixing efficiency of fuel and air at the significantly less resident time of air in the combustion chamber. Based on these techniques, an innovative strut fuel injector with a wavy wall surface and double strut has been investigated for possible mixing enhancement of fuel and air. These results are compared with the basic single wedge strut available in the open literature to identify the performance improvement. The computational geometries are modeled with Reynolds-averaged Navier Stokes equations, SST k-ω model, and global one-step reaction mechanism. All the flow modeling has been solved with finite volume and a second ordered upwind discretization scheme. The evaluation of scramjet internal flow structure and numerical results found that the double strut with a wavy-wall shape improved the mixing efficiency and combustion phenomenon significantly. The mixing and combustion profiles reveal that wavy-wall double strut generates an early complete mixing within a distance of 0.17 m with increased mixing and combustion efficiency of 18% and 20%, respectively.

Investigation of combustion characteristics in a hydrogen-fueled scramjet combustor

The combustion characteristics of a hydrogen-fueled scramjet combustor were investigated experimentally and numerically. One nonreacting case (case 1), and two different equivalence ratio (ER) reacting cases (cases 2 and 3) were compared. The combustion process of each reacting case was divided into three phases. In the first phase, the monitor pressure in case 2 (ER = 0.1) reached a higher level due to the fuel injected before the hydrogen was ignited, whereas the change in case 3 (ER = 0.3) was the opposite, being less than that in the nonreacting flow. Almost all of the hydrogen in case 2 was in the front of the cavity, and that in case 3 was both throughout the whole cavity and near the top wall behind the cavity. In the second phase, the ignition times were about 0.010 s in case 2 and about 0.022 in case 3; a larger ER of hydrogen might be difficult to ignite. Finally, in the last phase, the hydrogen combustion was stable. The shock train in case 3 was pushed into the isolator, and the disturbing distance was about 0.08 m, in accordance with the wall pressure distribution. The higher static temperature in case 2 was mainly in the back of the cavity and that in case 3 was in the cavity shear layer, in line with the hydroxyl planner laser-induced fluorescence (OH-PLIF) results. The combustion mode in case 2 was supersonic combustion and that in case 3 was subsonic combustion.

Effect of a revolved wedge strut induced mixing enhancement for a hydrogen fueled scramjet combustor

The mixing concept of fuel and air is the burning issue for hypersonic vehicles (scramjet) due to the less resident time of supersonic air in the combustion chamber. So far, significant research has been done for mixing enhancement and introduced different technologies; still, there is a lack of research for mixing improvement. Shock wave and shear mixing layer are the main parameters for investigating mixing criteria at supersonic speed. In this research, an innovative fuel injection strut has been designed to develop mixing enhancement by elevating multiple interactions between the shock wave and shear mixing layer. This new strut has been designed with the reference of the DLR scramjet combustor. From the reference of a wedge-shaped strut, a revolved (wedge shape – circular 3D) wedge strut has been modeled with the same fuel injection base points. This new strut's performance has been analyzed for mixing enhancement by visualizing the development of shock wave, shear-mixing layer, and their interactions. Three-dimensional numerical analysis has been carried out by solving the Reynolds-Averaged and Navier-Stokes (RANS) equations. A comparison of results has been made for the basic wedge and new strut and identified the increase in multiple interactions of the shock wave and shear layer, which leads to an increase in mixing enhancement. For the new strut, complete mixing has been achieved within a distance of 0.180 m with an average increase in mixing efficiency of 9% and increased pressure losses of 12%.

Continuous 500-Hz OH-PLIF Measurements in a Hydrogen-Fueled Scramjet Combustor

In recent years, significant research attention has focused on scramjet bench-testing using optical measurement techniques to obtain significant experimental data. The work aims to verify the environmental reliability of high-speed planar laser-induced fluorescence (PLIF) technique and satisfy bench-test requirements. A high-speed OH-PLIF system with ~1.8 mJ/pulse at 500 Hz is developed, and conducted tests at a direct-connect supersonic combustion facility. In this paper, OH-PLIF signals and pressure were measured simultaneously, and flame dynamics during pressure buildup were investigated, with a special focus on the ignition and flameout processes. In addition, the flame trajectory of the ignition process is depicted. The results show that the time scale of flame development is consistent with that of pressure stability, whereas the pressure change lags the change in flame intensity. The flame structure is discussed in both scramjet and ramjet modes. An unstable flame structure develops in ramjet mode, and the flame area decreases similarly in both combustion modes. Flame oscillations are captured for three hydrogen equivalence ratios.

Analysis of combustion instability of hydrogen fueled scramjet combustor on high-speed OH-PLIF measurements and dynamic mode decomposition

This paper investigated the combustion instability of spanwise positions in a hydrogen fueled scramjet combustor with a cavity flame holder. High-speed OH-PLIF technique was performed on a direct-connect supersonic combustion facility, and dynamic mode decomposition (DMD) as postprocessing. Combustion instability was investigated by characterizing the dominant frequencies and growth factors. By changing the equivalence ratio of hydrogen, the peak frequencies of scramjet mode and ramjet mode were obtained. Scramjet mode tended to have small oscillation at 150–200 Hz reflected by negative growth factors due to the stable flame structure. At ram-to-scram transition, oscillations at 80–120 Hz were remarkably enhanced due to the positive growth factors. In ramjet mode, the large differences of frequency characteristics in spanwise positions were observed. The dominant DMD modes near the cavity wall appeared to have negative growth factors leading to a stable flame with small oscillations. Besides, the characteristics of frequency-shift were affected by the positions of injector.

Combustion modes periodical transition in a hydrogen-fueled scramjet combustor with rear-wall-expansion cavity flameholder

Cavity-stabilized combustion modes periodical transition in a laboratory hydrogen-fueled scramjet combustor were captured by high speed imaging. Experiments were performed with an isolator entrance Mach number of 2.92, and a sonic transverse fuel jet upstream of the cavity was employed. The reproducibility of the results had been tested in several repeated experiments. It is observed that, under a fixed combustor entry flow parameters and fuel equivalence ratio, after the flame has been fully developed, the flame structure may periodically transform between two different combustion modes. Specifically, under a moderate equivalence ratio, the flame structure switches between the cavity shear-layer stabilized mode and the combined shear-layer/recirculation stabilized mode, which shows an apparent periodicity with a period of about 7.5 ms. The formation mechanism for this novel phenomena is analyzed and some suppositions are given. When increasing the equivalence ratio to a high level, the flame structure shows a quasi-periodic low-frequency oscillation and the combustion mode changes between the combined shear-layer/recirculation stabilized mode and the cavity-assisted jet wake stabilized mode. At last, the formation mechanism and characteristics of the combined shear-layer/recirculation stabilized mode are detailed analyzed.

Numerical investigation of wavy wall strut fuel injector for hydrogen fueled scramjet combustor

Mixing and combustion of a fuel with supersonic airstream in a scramjet combustor is a complex phenomenon because of very less resident time of the air in the combustion chamber. Mixing of fuel and air at supersonic speed and the subsequent combustion are greatly affected by the disturbance of the flow field in the form of shock waves, vortices and recirculation regions. In this research paper, the same concept has been considered by introducing an innovative strut fuel injector for the development of more shock waves and streamline vortices. The basic or standard computational domain of the scramjet combustor is considered from the reference of DLR experimental scramjet. The basic scramjet model consists of the wedge-shaped strut fuel injector. In this research, the strut injector has been re-designed such a way that to generate more oblique shock waves. Numerical analysis of the scramjet internal flow field has been performed with basic and innovative strut by solving the Reynolds-averaged Navier-Stokes equations with the help of computational fluid dynamics tool defined as ANSYS-FLUENT 16.0. The internal flow field of scramjet combustor with basic and innovative strut fuel injectors has been visualized from the analysis of pressure, temperature and velocity along with the analysis of flow structure, shock waves, and streamlines vortices. From the analysis of numerical results, it is identified that multiple numbers of oblique shock waves are being generated from the leading curved edge of the newly introduced strut. Both the pressure and temperature of airstream at the entrance of the combustion chamber are higher in the case of the wavy wall strut and it reduces the ignition delay time as compared to the basic strut model.

Experimental Investigation of Reacting Flow Characteristics in a Dual-Mode Scramjet Combustor

Abstract In this work, a hydrogen fueled dual-mode scramjet combustor was investigated experimentally. Clean and dry air was supplied to the combustor through a Mach 2 Nozzle with a total temperature of 800 K and a total pressure of 800 kPa. The high enthalpy air was provided by an electricity resistance heater. Room temperature hydrogen was injected with sonic speed from injector orifices vertically, and downstream the injector a tandem cavity flame holder was mounted. Except wall pressure profiles, velocity and temperature profiles in and at exit of the combustor were also measured using hydroxyl tagging velocimetry (HTV) and tunable diode laser absorption spectroscopy (TDLAS) respectively. Results showed that combustion occurred mainly at the bottom side of the combustor. And there were also an extreme disparity of the velocity and temperature profiles along the Y direction, i.e. the transverse direction.

Experimental study on the effect of equivalence ratio and injector position on flow structure and flame development in the scramjet combustor

In order to understand the combustion characteristic clearly in the scramjet combustor, the effect of equivalence ratio and injector position on flow structure and flame development in a hydrogen fueled scramjet combustor was investigated experimentally in the present paper, various measurements included schlieren, shadow, differential interferometry, flame emission and OH*-PLIF were made during the experiments in an attempt to better understand the combustion flow field. The results were obtained under the inflow condition of Ma2.0, total temperature and total pressure were 950 K and 0.82 MPa, respectively. The combustion induced backpressure had not spread into the isolator when the equivalence ratio was 0.1, the flow structure was stable and the flame was located in the cavity shear layer in a line shape. But the backpressure of the cases when the equivalence ratio was 0.3 had spread into the isolator, the flow structure was unstable and the flame existed both in the cavity and in the core flow in a shredded paper shape. The hydrogen injected from the upstream injector burnt more intensively than that injected from the downstream injector under the same equivalence ratio condition. The above mentioned non-intrusive measuring methods had their own limitations, but the synchronous measurement method could well show a more comprehensive coupling information of the flow structure and combustion characteristics.

Combustion stabilization modes in a hydrogen-fueled scramjet combustor at high stagnation temperature

Combustion stabilization modes were studied experimentally under a Mach 2.52 supersonic inflow at a high stagnation temperature of 1629 K. Optical observations including the high-speed flame luminosity and schlieren images were utilized to capture the combustion stabilization characteristics. Effects of the equivalence ratio and the injection distance on the combustion stabilization mode transition were discussed. Two supersonic combustion stabilization modes are identified clearly in the scramjet combustor, as the cavity stabilized mode and the jet-wake stabilized mode. At a relatively low equivalence ratio, the flame is stabilized in the cavity stabilized mode, and it will transfer to the jet-wake stabilized mode with the increase of the equivalence ratio. The flame stabilization mode is also affected by the injection distance. The critical equivalence ratio for mode transition reduces with the decrease of the injection distance. In the cavity stabilized mode, the shear layer of the cavity stabilizes the flame. In the jet-wake stabilized mode, the intense combustion induces high pressure, and leads to a large boundary-layer separation zone that exists in front of the flame. It contributes to the flame stabilization. In addition, a triple-reaction-zone mechanism is proposed to further explain the transition process from the cavity stabilized mode to the jet-wake stabilized mode, and the large boundary-layer separation zone also contributes to the transition process.

Numerical analysis of hydrogen fueled scramjet combustor with innovative designs of strut injector

In this research paper, passive method has been considered to improve the mixing and combustion efficiency of scramjet combustor. Modified and innovative strut injector designs have been developed from the reference of DLR scramjet. Strut is the mechanical component which is placed in the flow stream of supersonic airflow and used to inject the fuel. The newly introduced strut injector models are named as rocket and double arrow shape strut injectors. Numerical analysis of computational domains with innovative strut injectors has been carried out by considering the ANSYS – FLUENT 15.0, which is a numerical simulation tool. Shear stress transport model (SST k−ω model) has been considered for turbulence modeling under high speed flows. From the numerical results, it is observed that the compressed air entered into the combustion chamber is at higher pressure than the basic DLR scramjet model and it reduces the ignition delay. It is also found that both the rocket and double arrow strut models increases the boundary layer separation and vortex formation and therefore it enhances the better mixing of fuel and air and finally it improves the combustion efficiency.

Zonal Hybrid Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation of a Hydrogen-Fueled Scramjet Combustor

A zonal hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation framework is implemented to investigate the diffusion combustion of hydrogen–air in a model scramjet combustor. The computational domain is segregated into Reynolds-averaged Navier–Stokes and large-eddy simulation regions. An upwind convective flux discretization method and shear-stress transport turbulence models are applied to the Reynolds-averaged Navier–Stokes region, and the low-dissipative convective flux discretization method and improved delayed detached-eddy simulation are applied to the large-eddy simulation region. To generate turbulence at the Reynolds-averaged Navier–Stokes/large-eddy simulation interface, a synthetic-eddy method is employed. The geometries and boundary conditions of the model scramjet combustor are based on an experiment conducted at German Aerospace Center. The turbulent hydrogen diffusion flame is modeled using the steady flamelet approach. A total of nine computation cases are examined to analyze the influence of the numerical methods. As a result, the zonal hybrid method using the low-dissipative convective flux discretization method and synthetic-eddy method shows the best agreement with the experimental data in terms of quantitative temperature and rms velocity fluctuation profiles.

Experiments on flame stabilization in a scramjet combustor with a rear-wall-expansion cavity

The current study investigated the characteristics of the flame stabilization in a hydrogen fueled scramjet combustor with a rear-wall-expansion cavity at the inflow condition of Mach 2.92 with stagnation pressure 2.6 MPa and stagnation temperature 1530 K. Effects of four representative fuel injection schemes on the combustion process had been compared. The experimental results show that the injection schemes with two parallel injectors (30 mm upstream the cavity) and with single injector (10 mm upstream the cavity) achieve slightly heat release increment when increasing the equivalence ratio. While the injection schemes with two cascaded injectors (30 mm and 10 mm upstream the cavity) and with two parallel injectors (10 mm upstream the cavity) would perform obviously more intense and stable combustion in the combustor at the same equivalence ratio. For the injection scheme with two cascaded injectors (30 mm and 10 mm upstream the cavity), although there would be less intense combustion above the cavity, there exist wider heat release zones downstream the cavity compared to the injection scheme with two parallel injectors (10 mm upstream the cavity). It is also demonstrated that the injection scheme with two cascaded injectors (30 mm and 10 mm upstream the cavity) is a favorable fuel injection scheme for the rear-wall-expansion cavity during the flame stabilization process, and a robust and stable flame would be achieved in the combustor.