Performance Of Scramjet Combustor Research Articles

Influence of the hydrogen transverse injection mode in a scramjet combustor performance

This paper focuses on the numerical investigation of the transverse hydrogen injection technique in the supersonic airflow on the combustor performance of a scramjet technological demonstrator developed at Universidade Federal do Rio Grande do Norte (UFRN). The UFRN's scramjet vehicle was designed to be fully operational at a hypersonic velocity of 2050 m/s (Mach number 6.8), at 30 km of altitude, which provided a temperature of 1156.95 K and supersonic velocity of 1414.39 m/s (Mach number 2.1), at the combustion chamber entrance. Hydrogen was transversally injected into supersonic airflow at a sonic speed of 1318.46 m/s. A set of 2D-RANS simulations of the reactive flow was performed in combination with a simplified chemical kinetics approach based on the finite-rate chemistry model, defined by a one-step global reaction based on Arrhenius expression to combustion modeling. The turbulence was modeled by the k-kl-ω transition model. Different transverse fuel injections with different dimensions and positioning of injectors were evaluated keeping the same inlet conditions: single-injection versus dual-injection modes. A detailed visualization of several flow phenomena, such as the formation of shock waves, and the performance combustion parameters on the combustor surface were discussed. The analyses indicated hydrogen combustion with a predominantly supersonic flow regime. The transversal injection caused the detachment of the boundary layer as indicated by the recirculation flow structures in the neighboring region next to the injectors. Flow analyses indicate that the purely oblique shock trains were established tending to redirect the airflow over the mixing layer and accelerate the hydrogen burning. Nevertheless, the results showed that this was a local effect since the downstream both mixing and combustion efficiency increased. The dual-injection mode proved to be a promising injection method due to the higher global fuel penetration, elevated from 27,9% to 33,8%, and higher combustion efficiency, increased from 10,33% to 21,99%, with reduced addition of total pressure loss, concerning the single-injection case. Additionally, the growth behavior of performance curves showed that an extension of the combustor downstream length can be indicated to maximize combustor performance.

The numerical investigation of combustion performance of scramjet combustor with variation in angle of attack

The present article involves computational investigation of parallel fuel injection based scramjet combustor. The wedge shaped strut face is used as a fuel injector. Selected geometry is first validated and then further investigation is performed. Steady-state, two dimensional, scramjet combustor model has been chosen to complete the numerical convergence through ANSYS Fluent software. Grid independence analysis has also been performed. Reynolds Average Navier Stokes equation in addition with k-epsilon turbulence modelling have been utilised to reach the convergence at a lower computational cost. Finite rate eddy-dissipation based Species transport modelling is chosen to solve the chemical kinetics between hydrogen and air. The incoming boundary condition of free-stream air has been optimized to improved combustion efficiency. There are three selected model is utilised for comparison i.e. zero degree, positive five and negative five degree air angle of attack model. To change the angle of attack of the incoming air, a Modified isolator is added ahead of the combustor with constant length. It is observed that the behaviour of shock waves and flow properties are dependent on the angle of attack. Comparative observation has been analysed with monitoring the combustion efficiency graph. Maximum combustion efficiency reaches up to 93% in negative five degree air angle of attack model moreover, mixing is also improved by 4%. It can be summarized that the scramjet combustor performance is primarily highly influenced by the geometry configuration and the nature of flow of incoming air.

Numerical investigation on the effect of variation of upper wall divergence angle of parallel fuel injection scramjet combustor performance

Numerical investigation of Scramjet combustor is performed with the help of center lobed strut to act as a parallel fuel injector. The geometry of the combustor plays a major role to get the enhanced combustion performance in scramjet engine due to the absence of rotating parts. Keeping this idea, the behavioral impact of upper wall divergence angle inside the supersonic combustor and their outcome have been studied by allocating three models. The supersonic free stream air is used as an oxidizer and sonic speed hydrogen as a combustible fuel to complete the chemical reaction during the combustion. Experimental model has been selected for the purpose of comparison and validation. The grid independence analyze has also been done. Ansys 14.0 - Fluent solver is opted for numerical investigation. The computational results show substantial conclusions. The mixing behavior follow the similar pattern in all the models and reaches up to 100% but the behavior of mixing length is found lesser in case of one and two degree upper wall divergence angled combustor model. The mixing length is found 41 mm for both one and two degree angle model whereas 51 mm mixing length has been captured in case of three degree divergence angled model. Initially the rapid combustion is observed in one degree angle of divergence model among all cases. However, the maximum combustion efficiency reaches 95.3% in case of two degree angle of divergence at the upper wall. Which signifies the greater impact of combustor geometry on the scramjet engine performance.

Interplay of self-throttling and air throttling on combustion enhancement of the scramjet combustor

The present work discusses the effects of self-throttling in conjunction with air throttling on the scramjet combustor performance. Ethylene fueled cavity-strut based combustor is considered and LES simulations are performed to gain insight on influence of Mach number, inlet temperature, self-throttling and air throttling on combustion performance. Our study shows substantial improvement both in mixing and combustion efficiency of the combustor. This is evident from the flow characteristics like shock, vortices, recirculation zones, mixing length and penetration depth. It is found that pressure profile is distributed more uniformly across the combustor with minimum pressure losses. Complete mixing is attained relatively earlier as a result of intense shock-shear interactions. Furthermore, the enhancement in the combustion performance is greater at higher Mach number. The increase in static pressure is found to be a strong function of the inlet Mach number and temperature also. The separate study on effect of initial temperature indicates the mixing length is the shortest with the maximum fuel penetration at inlet temperature of 700 K beyond which the performance deteriorates. It is seen that air throttling is found to be more effective when self-throttling works in tandem alongside having a direct bearing on the combustor performance.

NUMERICAL INVESTIGATION OF COMBUSTION PERFORMANCE OF VARIOUS FUELS IN WEDGE-SHAPED STRUT-BASED SCRAMJET COMBUSTOR

NUMERICAL INVESTIGATION OF COMBUSTION PERFORMANCE OF VARIOUS FUELS IN WEDGE-SHAPED STRUT-BASED SCRAMJET COMBUSTOR

The Numerical Investigation of Combustion Performance of Scramjet Combustor with Variation in Angle of Attack

The Numerical Investigation of Combustion Performance of Scramjet Combustor with Variation in Angle of Attack

Numerical Investigation on the Effect of Variation of Upper Wall Divergence Angle of Parallel Fuel Injection Scramjet Combustor Performance

Numerical Investigation on the Effect of Variation of Upper Wall Divergence Angle of Parallel Fuel Injection Scramjet Combustor Performance

Numerical Investigation on Performance of Axisymmetric Variable Geometry Scramjet Combustor Equipped with Strut Flame Holder

ABSTRACT This manuscript designed an axisymmetric variable geometry scramjet combustor equipped with a strut flame holder to help the combustor work in a wide flight Mach numbers and conducted a series of numerical calculations and experiments to study the performance of the axisymmetric combustor. The characteristics of the combustor under the different flight Mach numbers (2, 4, 6) are discussed by the numerical calculations, and the results testify that the designed combustor can operate in a large range of the flight Mach number. Then the performances of the combustor in high Ma (4 and 6) are studied. The maximum pressure ratio of the combustor under Ma = 6 is about 6.5. With the divergence ratio increasing, the thermal chock of the combustor decreases under the flight Ma = 4. When the flight Ma is 2, and the divergence ratio is 3.2, the combustor can work well with the fuel injected by the center cone and the wall1. However part of the oxygen near the bottom wall can not be ignited, and the flame distribution is uneven. To solve this problem, the multi-wall fuel injected method is taken. With the wall2 fuel added, the mixing efficiency of the fuel increases, and the flame near the bottom wall is established. The results in this study are valuable for the future axisymmetric variable geometry scramjet combustor design and the optimization of combustion distribution uniformity.

LES study on the effect of cavity configuration on combustion characteristics of a scramjet combustor with air-throttling

Three-dimensional Large Eddy Simulation (LES) is performed to numerically investigate the implication of air throttling on the combustion performance of ethylene fueled dual-cavity scramjet combustor. The augmentation of combustion performance with the conjunction of throttling and dual cavity being established, the effects of L/D ratio and interspacing distance between the cavities is discussed. Our results indicate that combustion efficiency is enhanced owing to the pre-combustion shock train generated because of the introduction of air throttling for different configurations of cavity. Further, the combination of air-throttling with dual cavity improves combustion performance in comparison with dual cavity without air throttling. Also, dual cavity with L/D = 7 and spacing S = 12 mm displays intense and larger recirculation zones in comparison with other configurations being considered. It is found that for dual cavity with L/D = 7 and S = 12 mm, shorter mixing length and higher penetration height is attained.

Implication of geometrical configuration of cavity on combustion performance in a strut-based scramjet combustor

The present work describes the numerical investigation on the implication of the geometrical configuration of a cavity with a strut-based scramjet combustor. Firstly, the combustion characteristics of a combustor with a cavity and the combustor without a cavity are compared and evaluated to portray the effect of a cavity. On the other hand, a separate study is performed to investigate the interplay of cavity parameters namely, length to depth (L/D) ratio of a cavity and angle of a cavity (α) on the performance of a strut-based scramjet combustor. Our study reveals the formation of a strong recirculation zone in the cavity region which improves the mixing and combustion efficiency in the case of a cavity-based combustor. It is observed that the combustion commences relatively earlier in the case of a cavity-based combustor and reaches to its peak value of around 80%. Further, the size of a recirculation region depends on the distance between the strut injector and the length of a cavity. Moreover, the shear layer is observed in the cavity region inducing a weak shock at the trailing edge of a cavity which deteriorates the performance of a scramjet combustor particularly for a higher angle of a cavity(α) and lowers L/D ratio of a cavity. Also, the combustion efficiency is found to be optimal with moderate pressure losses at L/D = 4 and α = 300.

Influence of the vortex generator on the performance of solid rocket scramjet combustor

In this paper, the influence of vortex generator on the performance of solid scramjet was investigated by means of direct-connected fire tests. The experiments simulated a flight Mach number 5.5 at 23 km. Hydrocarbon fuel was used as the fuel-rich solid propellant. The experimental results show that compared with the benchmark configuration, where no vortex generator was employed, the configurations with vortex generator can promote significantly the ignition and stable combustion of the primary fuel-rich mixture produced in the gas generator. The combustion efficiency of the test no.3 (with a strut) in the supersonic combustor reaches 0.60, while it is only 0.11 in the benchmark test. The vortex generators (ramp or strut) can promote the ignition of the primary fuel-rich mixture and therefore decrease significantly the ignition delay time in the supersonic combustor. And the ignition delay time in the test no.3 (a strut) is shorter than that of in test no.2 (a ramp). In summary, the vortex generators in these experiments play an important role in ignition, and flame stabilization of the fuel-rich mixture in the supersonic combustor of the solid rocket scramjet.

Numerical investigation on the performance of scramjet combustor with a novel strut configuration

The design of the strut fuel injector plays an important role in the performance of the strut-based scramjet combustor. The current study numerically investigates the flow and combustion characteristics of a scramjet combustor. An in-house code was developed to compute the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model and the one-step reaction finite-rate/eddy-dissipation model. In order to enhance the mixing and combustion efficiency, we develop a novel double-strut concept with backward-facing steps in the scramjet combustor. Firstly, the numerical methods are validated by the available experimental data in open literature. Then we compare the mixing and combustion performance between the single strut and the double-strut. Finally, the effects of the perpendicular distance between the two struts on the mixing and combustion efficiency are also reported. The numerical results show an acceptable agreement with the experimental results. The presence of the double-strut with backward facing steps has a remarkable enhancement on the mixing degree and combustion efficiency in the scramjet combustor when compared with the original single-strut. Further, the combustion efficiency for the perpendicular distance of 4 mm is the highest one among the six cases, and the total pressure loss is relatively low. Therefore, the new configuration with the perpendicular distance of 4 mm is the optimal one within the range considered in this study.

Recent advances in cavity-based scramjet engine- a brief review

Abstract At present, the critical issue related to design of scramjet engine is to achieve efficient mixing between the air and fuel. Among the several fuel injection strategies, cavity flame holder is identified as a well-organized method for supporting the ignition zone. In this review, some mixing enhancement approaches based on well-known cavity based injection scheme proposed in latest research works, are summarized in detailed. The influence of cavity on the performance of scramjet combustor is recapitulated from three aspects, namely variation of shape/geometry of cavity flame holder; location of fuel/air injection scheme; and recent progresses in dual/double cavity. This review reveals that the cavity rear wall-expansion is an innovative kind of cavity flame holder which has a great impact on the efficiency of scramjet combustor whereas the presence of micro air jets have improved the flame holding mechanism of scramjet engine. Additionally, the performance of scramjet is significantly improved by dual cavity indicating that the dual cavity flame holder would be a feasible preference for the future growth of scramjet engine.

Effect of different strut + wall injection techniques on the performance of two-strut scramjet combustor

The two-dimensional Reynolds-Averaged Navier–Stokes (RANS) equations coupled with the two equation Shear stress transport k–ω turbulence model as well as the finite-rate/eddy–dissipation reaction model have been employed to numerically simulate the flow field structures in a typical two-strut based scramjet combustor. Here all the computations have been performed by using ANSYS 14-FLUENT code. Additionally, validation has been completed for the single strut scramjet engine by comparing its outcome with the open, experimental data. The computational results show reasonable agreement with the experimental schlieren image, and the velocity, pressure and temperature variation graph available in the open literature. The introduction of two-strut improves the combustion and mixing efficiency of the combustor appreciably when compared with single strut engine. Further, investigations have been carried out on the effect of different strut + wall injector on the combustion as well mixing performance of two-strut scramjet combustor. The obtained results show that the combination of two-strut + wall 1+wall 2 injectors provide better air–H2 mixing as they lead to a higher penetration depth out of the other strut + wall injection techniques. Thus the combustion as well as mixing efficiency of two-strut + wall 1+wall 2 injection technique is found to be higher as compared to remaining strut + wall injection techniques but lower than that of the two-strut injection.

Numerical analysis of passive techniques for optimizing the performance of scramjet combustor

In this research paper numerical analysis of scramjet combustor has been carried out with different passive techniques to improve the mixing efficiency of supersonic airstream and hydrogen fuel. The actual mixing rate of air and hydrogen is very less because of the less resident time of supersonic air in the combustion chamber. The mixing of hydrogen fuel with supersonic airstream is greatly affected by the development of shock waves, streamline vortices and shear layer of mixing in the flow filed of the combustor. The experimental DLR scramjet model has been considered as a reference and standard model to compare and validate the numerical results. In this research article three different passive techniques are considered and defined as a uniform zigzag surface, small parabola shape cavities and bumps at lower wall of the combustion chamber. The computational scramjet domains are modeled as modified versions of DLR scramjet by the implementation of passive techniques. Two dimensional numerical analyses are carried out by solving Favre-averaged Navier–Stokes governing equations and SST k−ω turbulence model along with finite rate/eddy dissipation combustion chemistry turbulence model is also considered for accurate analysis of streamline vortices, shear layer development and shock waves. From the numerical results of various passive techniques it is found that the development or creation of gradient fluxes of flow property are increased. By incorporating these types of surfaces at combustor bottom wall it is identified that the growth rate of mixing layer has been increased along the flow field of combustor. Hence the more amount of hydrogen fuel being carried out by streamline vortices and velocity gradients or shock waves and this phenomenon improve the mixing efficiency of scramjet combustor and also it leads to increase in combustion efficiency. From the numerical analysis results and discussion it is to be concluded that highest mixing and combustion efficiency is identified with a uniform zigzag (wavy wall) surface combustor wall design.

Numerical Studies on the Performance of Scramjet Combustor with Alternating Wedge-Shaped Strut Injector

AbstractNumerical analysis of the supersonic combustion and flow structure through a scramjet engine at Mach 7 with alternating wedge fuel injection and with three angle of attack (

CH* Luminance Distribution Application and a One-Dimensional Model of the Supersonic Combustor Heat Release Quantization

Abstract One-dimensional model is an important way to evaluate the performance and flow characteristics of dual-mode scramjet combustor. Current work is based on a modified one-dimensional model assisted by measurements acquired on a direct-connected scramjet facility. CH* images and gas-sampling facility have been employed to quantify heat release for optimizing one-dimensional model. The results show that modified one-dimensional model gives a better evaluation of axis parameters distribution, especially for Mach number, which is the standard parameter to evaluate combustion mode. The ram/scram mode derived by the analytical results has been investigated. Intensive heat release is beneficial to obtain more stable pre-combustion shock and subsonic flow in the recirculation zone.

Investigation on the effects of operating variables on the performance of two-strut scramjet combustor

The two equation SST k−ω turbulence model and the two-dimensional compressible Reynolds-Averaged Navier–Stokes (RANS) equations along with single-step chemical reaction mechanism have been applied to analyze the effect of divergence angle, radius of the strut tip and the half angle of the strut on the combustion enhancement of two-strut scramjet combustor. Here all the simulations are carried out by using ANSYS 14-FLUENT code. Simultaneously, the validation of the present computational simulation for single strut injection has been completed by comparing its result with the available DLR experimental data which is available in the literature. The results are in satisfactory agreement with the experimental schlieren image and pressure, velocity and temperature distribution curve obtained experimentally for the case of single strut combustor. The presence of two struts enhances the mixing and combustion efficiency significantly compared to single strut and the variation of divergence angle, radius of the strut tip and the half angle of the strut also have a great impact on the performance of two-strut scramjet combustor. The present results show that there is an optimal divergence angle for which the performance of the two-strut combustor particularly increases and effective combustion phenomena occur within the combustion region. Again on increasing the radius of the strut tip, the formation of separation region takes place on both the walls of two-strut scramjet combustor which may deteriorate the performance of combustor. Further, combustion phenomena are also affected by the variation of half angle of the strut from 5° to 8°.

Effect of variation of length-to-depth ratio and Mach number on the performance of a typical double cavity scramjet combustor

The two equation standard k–ɛ turbulence model and the two-dimensional compressible Reynolds-Averaged Navier–Stokes (RANS) equations have been used to computationally simulate the double cavity scramjet combustor. Here all the simulations are performed by using ANSYS 14-FLUENT code. At the same time, the validation of the present numerical simulation for double cavity has been performed by comparing its result with the available experimental data which is in accordance with the literature. The results are in good agreement with the schlieren image and the pressure distribution curve obtained experimentally. However, the pressure distribution curve obtained numerically is under-predicted in 5 locations by numerical calculation. Further, investigations on the variations of the effects of the length-to-depth ratio of cavity and Mach number on the combustion characteristics has been carried out. The present results show that there is an optimal length-to-depth ratio for the cavity for which the performance of combustor significantly improves and also efficient combustion takes place within the combustor region. Also, the shifting of the location of incident oblique shock took place in the downstream of the H2 inlet when the Mach number value increases. But after achieving a critical Mach number range of 2–2.5, the further increase in Mach number results in lower combustion efficiency which may deteriorate the performance of combustor.

Computational simulation of multi-strut central lobed injection of hydrogen in a scramjet combustor

Summary Multi-strut injection is an approach to increase the overall performance of Scramjet while reducing the risk of thermal choking in a supersonic combustor. Hence computational simulation of Scramjet combustor at Mach 2.5 through multiple central lobed struts (three struts) have been presented and discussed in the present research article. The geometry and model used here is slight modification of the DLR (German Aerospace Center) scramjet model. Present results show that the presence of three struts injector improves the performance of scramjet combustor as compared to single strut injector. The combustion efficiency is also found to be highest in case of three strut fuel injection system. In order to validate the results, the numerical data for single strut injection is compared with experimental result which is taken from the literature.