Effect of combustor geometry and fuel injection scheme on the combustion process in a supersonic flow (original) (raw)
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INVESTIGATION OF SUPERSONIC COMBUSTION WITH CAVITY BASED INJECTION IN A SCRAMJET COMBUSTORDr.M.Y.Ali
CFD analysis of supersonic combustion of air with hydrogen fuel has been performed for a scramjet engine. As the combustion is taking place at supersonic speeds, the flow has very less residence time (milliseconds) in the combustor. The Primary objective of this analysis is to improve residence time, thereby increasing fuel-air mixing and combustion efficiency. The eddies or vortices generated in the cavity acts as a flameholder and increases the residence time of flow. The two-dimensional coupled implicit Navier Stokes equations, reailizable k-ε turbulence model and the finite-rate/eddy-dissipation reaction model have been applied to numerically simulate flow field of the hydrogen fueled scramjet combustor with a cavity flameholder under two different working conditions, namely, cold flow and engine ignition. Hydrogen and H 2 O mass fractions left at the outlet are considered as complete fuel-air mixing and combustion efficiency.
1992
Supersonic combustion was experimentally investigated in a strut-cavity based scramjet combustor with kerosene and pilot hydrogen as fuels. Strut-cavity is the space between two tandem struts in streamwise direction. The occurrence of cavity induced pressure oscillations in the strut-cavity was confirmed through cold flow experiments. The dominant modes of pressure oscillations were strongly influenced by the cavity aspect ratio. A ventilated rear wall (VRW), which is a new passive control device, was adopted in the strut-cavity. The strut-cavity with the VRW attenuated pressure oscillations better than the 'ramp rear wall' configuration. A scramjet combustor was realized with two strut-cavities in tandem for mixing enhancement and a strut-cavity with the VRW for flame stabilization. The combustor was tested at the following inlet conditions: total pressure of 4.89 bar, total temperature of 1517 K, and Mach number of 2. Supersonic combustion was observed. Steep increase in static pressure in the region of the strut-cavity with the VRW indicated that the flame was stabilized. The combustor was operated at a wide range of equivalence ratios (0.3-0.7) without inlet interactions. The total pressure at the combustor exit plane indicated that the flow was uniform, except at the central region. The total pressure loss and combustion efficiency of the combustor were evaluated for various equivalence ratios.
Numerical study on supersonic combustion with cavity-based fuel injection
International Journal of Heat and Mass Transfer, 2004
The present study describes the numerical investigations concerning the combustion enhancement when a cavity is used for the hydrogen fuel injection through a transverse slot nozzle into a supersonic hot air stream. The cavity is of interest because recirculation flow in cavity would provide a stable flame holding while enhancing the rate of mixing or combustion. Several inclined cavities with various aft wall angle, offset ratio and length are evaluated for reactive flow characteristics. The cavity effect is discussed from a viewpoint of total pressure loss and combustion efficiency. The combustor with cavity is found to enhance mixing and combustion while increasing the pressure loss, compared with the case without cavity. But it is noted that there exists an appropriate length of cavity regarding the combustion efficiency and total pressure loss.
Numerical Simulation of Wall Injection with Cavity in Supersonic Flows of Scramjet Combustion
International Journal of Soft Computing and Engineering
A supersonic combustion ramjet engine (scramjet) is one of the most promising air-breathing propulsive systems for future hypersonic vehicles, and it has drawn the attention of an ever increasing number of researchers. This work involves an application of computational fluid dynamics to a problem associated with the flow in the combustor region of a scramjet. A cavity wall injector is an integrated fuel injection approach, and it is a new concept for flame holding and stabilization in supersonic combustors. The presence of a cavity on an aerodynamic surface could have a large impact on the air flow surrounding it, and this makes a large difference to the performance of the engine, namely it may improve the combustion efficiency and increase the drag force. The objective of the work was to design the four wall injector model with cavity using gambit, study the combustion processes of air- fuel (h2) mixture for the wall injector models with inlet air at Mach number 2 and inlet fuel at Mach number 2 and compare the performance of the different wall injector models. There are several key issues that must be considered in the design of an efficient fuel injector. Of particular importance are the total pressure losses created by the injector and the injection processes that must be minimized since the losses reduce the thrust of the engine. In this analysis, the two-dimensional coupled implicit Reynolds averaged Navier-Stokes (RANS) equations, the standard k-ε Turbulence model, sst-kω Turbulence and the eddy-dissipation reaction model have been employed to investigate the flow field in a hydrogen-fuelled scramjet combustor with a cavity design and to analyze the combustion processes. Numerical results are obtained with the fluent solving sst-kω Turbulence model to have the best results of all models. The grid independent test was also carried out. The profiles of static pressure, static temperature, and two components of velocity and mole fraction of hydrogen at various locations of the flow field are presented. Computed values using sst-kω turbulence model are found to have good overall agreement with results obtained from literature reviews and some discrepancies were observed for static pressure and static temperature in the vicinity of the jets due to unsteadiness in the shock system.
Numerical Study of the Cavity Geometry on Supersonic Combustion with Transverse Fuel Injection
2017
The small residence time, in designing the engine of a supersonic aircraft, presumed to have a very important character in combustion. At hypersonic flight, the flow is supersonic while entering in the combustor to avoid excessive heating and fuel is essentially to be injected, mixed and combusted entirely within a short residence time of the order of millisecond. In order to resolve the restrictions given by short residence time, numerous studies have been carried out to suggest the concepts of injection, among which, the transverse fuel injection in a combustor with a cavity is being used in several engines. This paper describes the numerical study of the combustion enhancement with hydrogen fuel injection in a transverse aperture nozzle into a supersonic hot air stream. Several cavities with single and dual steps with different cavity wall angles are analyzed. Eddy dissipation concept model with detailed hydrogen-air combustion with 21 reactions and 9 species transport has been a...
Effect of Ramp-Cavity Injector in Supersonic Combustion
2013
A computational analysis has been carried out in a Scramjet engine combustor with the multiple ramp-cavity injectors which will enhance the fuel air mixing in a short flow residence time for both cold flow and reacting flows. Inclined injection of hydrogen is used for the combustion analysis. The analysis includes: 1. Study and analysis of multi cavity effect in flame holding enhancement at supersonic flows by cold flow. 2. Reacting flow analysis of multi ramp-cavity injectors with different fuel injection angels in the scramjet combustor. It is observed that the ramp-cavity injector in supersonic combustor helps to lift the fuel away from wall and enhances the mixing and flame holding capabilities in supersonic combustion which was identified by the increment in combustor exit temperature and combustion efficiency. The roles of the cavity, ramp, injection angle, and heat release in determining the flow dynamics are examined systematically.
Journal of Thermal Science, 2003
A numerical investigation has been performed on supersonic mixing of hydrogen with air in a Scramjet (Supersonic Combustion Ramjet) combustor and its flame holding capability by solving Two-Dimensional full Navier-Stokes equations. The main flow is air entering through a finite width of inlet and gaseous hydrogen is injected perpendicularly from the side wall. An explicit Harten-Yee Non-MUSCL Modified-flux-type TVD scheme has been used to solve the system of equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. In this study the enhancement of mixing and good flame holding capability of a supersonic combustor have been investigated by varying the distance of injector position from left boundary keeping constant the backward-facing step height and other calculation parameters. The results show that the configuration for small distance of injector position has high mixing efficiency but the upstream recirculation can not evolved properly which is an important factor for flame holding capability. On the other hand, the configuration for very long distance has lower mixing efficiency due to lower gradient of hydrogen mass concentration on the top of injector caused by the expansion of side jet in both upstream and downstream of injector. For moderate distance of injector position, large and elongated upstream recirculation can evolve which might be activated as a good flame holder.
The effect of injection angle on mixing and flame holding in supersonic combustor
Journal of Thermal Science, 2002
A numerical study on mixing of hydrogen injected into a supersonic air stream has been performed by solving two-dimensional full Navier-Stokes equations. An explicit Harten-Yee Non-MUSCL Modified-flux-type TVD scheme has been used to solve the system of equations, and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The main objectives of this study are to increase the mixing efficiency and flame holding capability of a supersonic combustor. The performance of combustor has been investigated by varying the hydrogen injection angle made with the direction of air stream considering anticlockwise direction as positive. The injector position from left boundary, backward-facing step height and the inlet width of air stream are kept constant. The results show that upstream of injector the mixing is dominated by recirculation and in downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60 ° and 90 °. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.
2014
This paper describes the numerical investigation of Supersonic combustion with Hydrogen as fuel injected with cavity of L/D ratio of 3 in two dimensional combustor at Mach number 4 using species transport model for combustion. In the present study the flow regime is simulated by using reailizable k(two equations) model with standard wall function. The hydrogen fuel is injected just upstream of the cavity. A cavity flame holder is provided which injects hydrogen fuel in a supersonic hot air stream that facilitates enhanced mixing and combustion efficiency. The cavity is of interest because recirculation flow in cavity would provide a stable flame holding while enhancing the rate of mixing or combustion. The combustor with cavity is found to enhance mixing and combustion while increasing the pressure loss, compared with the case without cavity. But it is noted that there exists an appropriate length of cavity regarding the combustion efficiency and total pressure loss.
International Journal of Energy Research, 2020
Supersonic combustion ramjet (scramjet) is a variant of ramjet in which the combustion takes place at supersonic velocity. The flow physics inside the scramjet combustor is quite complex due to the fact that the mixing and completion of the combustion take place in a short time, which is of the order of milliseconds. This study focuses on flow characteristics within the combustion chamber of the scramjet engine that is designed to improve energy efficiency by enhancing combustion efficiency. The effect on combustion performance and thereby the energy efficiency on using strut-based flame stabilizer is evaluated at different positions. Reynolds averaged Navier-Stokes equations are solved with the Shear Stress Transport k-ω turbulence model. Single strut configuration is used to validate with the experimental data. Single strut is then compared with three-strut configuration. In the three-strut configuration, the location of the primary strut is kept constant, and the secondary struts are relocated in x and y directions. Combustion performance was evaluated for the cases of flow from primary strut only and through three struts. It was found that the placement of secondary strut in a three-strut configuration plays a vital role in improving energy efficiency. A maximum of 33.86% improvement in combustion efficiency was observed in comparison to the single strut combustor. A reduction in unburned fuel was observed, making the system more energy efficient. If the struts are not placed optimally, the combustion performance of the combustor was observed to be lower than that of a single-strut configuration. The shock reflection and expansion fans within the primary combustion zone and the secondary strut region enhance the combustion efficiency. The wall static pressure was observed to increase with the addition of secondary struts. For certain strut configurations, flow separation was seen on the combustor walls. If the secondary strut was placed close to the primary strut, combustion efficiency was found to enhance. It was seen that