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In this study a flush wall scramjet combustor is tested in a supersonic incoming air flow with the Mach number of 3 which is generated by an air vitiation heater producing the stagnation temperature of 1505 K. Using liquid kerosene as the fuel, the flame is stabilized by means of a centrally mounted O2 pilot strut after being ignited by a plasma torch. During experimental measurements, the fuel is injected with a constant equivalence ratio of 0.8 according to specified strut/wall injection ratios, i.e., a portion of the fuel amount is injected from the strut while the rest is injected from the wall. The strut and wall injectors are arranged at the same axial position. The combustion performance and wall temperature gradients are evaluated with various fuel feeding ratios between the wall and the strut. Experimental results show, when the equivalence ratio is constant and the axial injection position is fixed, the combustion characteristics vary significantly with the strut/wall fuel feeding ratio, especially when this ratio is close to its lowest and highest limits. Among the four fuel feeding ratios examined, the strut only injection mode and the average distributed strut/wall injection mode show the best combustion performance. However, the strut/wall injection mode produces a smaller wall temperature gradient compared to the strut only injection mode, which is due to the significant film cooling effect caused by the wall injected liquid kerosene. 相似文献
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HRM code for the simulation of N2O/HTPB hybrid rocket motor operation and scale effect analysis has been developed. This code can be used to calculate motor thrust and distributions of physical properties inside the combustion chamber and nozzle during the operational phase by solving the unsteady Navier–Stokes equations using a corrected compressible difference scheme and a two-step, five species combustion model. A dynamic fuel surface regression technique and a two-step calculation method together with the gas–solid coupling are applied in the calculation of fuel regression and the determination of combustion chamber wall profile as fuel regresses. Both the calculated motor thrust from start-up to shut-down mode and the combustion chamber wall profile after motor operation are in good agreements with experimental data. The fuel regression rate equation and the relation between fuel regression rate and axial distance have been derived. Analysis of results suggests improvements in combustion performance to the current hybrid rocket motor design and explains scale effects in the variation of fuel regression rate with combustion chamber diameter. 相似文献
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《Acta Astronautica》2014,93(2):463-475
The influences of miscellaneous combustor structures for solid fuel scramjet combustion on the performance are investigated, including a detailed interaction analysis between shocks/waves and combustion. Hydroxyl-terminated polybutadiene is chosen as the solid fuel with the non-premixed equilibrium probability density function combustion model. The results show combustion enhancement when structure of combustor is modified. The radical emphasis is to examine the sensitivity of the properties due to variations on the length-to-depth ratio of cavity, aft wall angle, and offset ratio. It is noted that there is an appropriate structure of cavity (L/D=4, θ=45°, and Dd/Du=1.25–1.5) regarding the combustion efficiency, total pressure loss and specific impulse. The observation of function for combustor components provides instructional insight into the design considerations for a combustor of a solid-fuel scramjet. 相似文献
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In the present study we investigate steady-state combustion of a liquid fuel droplet in the atmosphere of oxidizer under the condition of non-equilibrium evaporation from the surface.Utilizing the fact that chemical interactions of fuel with oxidizer involve a chain mechanism or several reaction stages, we transform the Shvab-Zel'dovich method so as to obtain exact analytical solution accounting for the possibility of several chain reactions.The obtained results show that this method is effective for solving the combustion problem and allow to define the values of parameters in gas around the droplet more accurately than the original method having taken into account one brutto-reaction. 相似文献
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A comparison between two analytical models of a free turbulent mixing of reacting streams with finite chemical reaction rates is presented and the results of calculations compared with experimental data. The substance is a mixture of the inert non-dissociated nitrogen and oxygen that dissociates and reacts with hydrogen.For the first model the local values of flow parameters along the streamlines were provided by the numerical solution of the conservation equations in the boundary layer form for a multicomponent mixture of perfect gases in the von Mises coordinate system. In the course of this analysis the problem was treated by dividing the flowfield into a large number of regions and by solving the Cauchy problem of the conservation equations for each region.The second analytical model was based on the ignition delay to describe the chemistry in the region of pre-ignition. The external air stream was heated by combustion and the influence of the water vapor and the intermediate species on the reaction kinetics in the mixing zone was numerically investigated.The results of calculation are compared with the experimental data with respect to the location of a visible flame edge under combustion of hydrogen jet in the co-current flow. 相似文献
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Hydrogen is one of the most promising fuels for the airbreathing hypersonic propulsion system, and it attracts an increasing attention of the researchers worldwide. In this study, a typical hydrogen-fueled supersonic combustor was investigated numerically, and the predicted results were compared with the available experimental data in the open literature. Two different chemical reaction mechanisms were employed to evaluate their effects on the combustion of H2–O2, namely the two-step and the seven-step mechanisms, and the vitiation effect was analyzed by varying the H2O mass fraction. The obtained results show that the predicted mole fraction profiles for different components show very good agreement with the available experimental data under the supersonic mixing and combustion conditions, and the chemical reaction mechanism has only a slight impact on the overall performance of the turbulent diffusion combustion. The simple mechanism of H2–O2 can be employed to evaluate the performance of the combustor in order to reduce the computational cost. The H2O flow vitiation makes a great difference to the combustion of H2–O2, and there is an optimal H2O mass fraction existing to enhance the intensity of the turbulent combustion. In the range considered in this paper, its optimal value is 0.15. The initiated location of the reaction appears far away from the bottom wall with the increase of the H2O mass fraction, and the H2O flow vitiation quickens the transition from subsonic to supersonic mode at the exit of the combustor. 相似文献
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《Acta Astronautica》2014,93(1):298-310
Numerical simulations were employed to analyze the flowfield of a scramjet with three-dimensional (3D) sidewall compression inlet, and the effect of inlet distortion on the mixing and combustion process was examined. The numerical approach solved the compressible Reynolds Averaged Navier–Stokes (RANS) equations supplemented with a finite rate chemical reacting model for the combustion of hydrogen fuel and air. Turbulence closure was achieved using Menter shear-stress transport (SST) model. To verify the accuracy of the simulation, the computed wall pressure was compared with the experimental data of the direct-connect combustor test. The metrics employed in the simulations included qualitative assessments related to flow structure as well as quantitative values of fuel mixing efficiency, combustion efficiency and static pressure distribution. Intake sidewalls were found to strongly affect the inlet flow structure, which became more complex in the nonuniform flowfield. The shock train system affected the combustion region located upstream of the injection and led to pairs of asymmetric separation bubbles. Nevertheless, the shock train system dissipated due to the reactions, the combustion patterns of each fuel jets in downstream region were nearly identical, and the degree of improvement of mixing and combustion efficiency near the downstream injectors was less than that near the upstream injectors. 相似文献
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凝胶燃料单滴燃烧的建模、实验及应用 总被引:2,自引:0,他引:2
讨论了凝胶燃料单个液滴燃烧的建模、实验研究和应用问题。单滴燃烧建模的关键在于依据凝胶燃料的胶凝结构和组份物性,确定燃烧过程的关键步骤,提炼主要影响因素。单滴燃烧实验研究的水平主要依赖于微小液滴的生成技术,高分辨率和高速成像技术,燃气成份的准确快速测量技术等光学测试技术的发展。单滴燃烧研究的主要应用在于揭示燃料的燃烧机理,分析燃料的燃烧特性,提高燃烧装置的设计水平。 相似文献
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A two-dimensional axis symmetrical model for multi-phase turbulent combustion simulation has been developed in a magnesium-based fuel ramjet, the stochastic model is applied to track the motion and transportation of discrete phase in the whole flow field in Lagrangian frame. Firstly, the flow field parameters distribution including temperature, velocity, Mg particle burning rate, main components are obtained to describe the basic operating characteristics, and the thermoacoustic oscillation during the combustion process is predicted due to the observed vortex. Then combined with the developed thermodynamic calculation program, the influencing rules of water/fuel ratio and magnesium-based fuel composition ratio on ramjet operating characteristics are analyzed. The results obtained show that the distribution of two water/fuel ratios exerts a direct impact on the temperature fluctuations in combustor, further influences the combustion stability, as for theoretical specific impulse, a maximal value is observed along with the total water/fuel ratio, while the monotonous trends for thermal efficiency and propulsive efficiency are achieved respectively. Moreover, the magnesium-based fuel composition ratio is a dominant factor to influence the operating characteristics, and it is proved that the high-proportion Mg in fuel is beneficial to specific impulse augment through validation of both simulation results and thermodynamic calculation results. 相似文献
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This paper models the combustion of a turbulent homogeneous mixture of propane and air within a duct having a stationary one-dimensional mean flow. The Bray-Moss model is applied to the closure of the chemical production terms, using a probability density function (pdf) of the temperature which is chosen as the characteristic variable. Under the conditions chosen for the study, chemical kinetic factors are important and the conventional assumption, that heat release is controlled by turbulent mixing, is not valid. The chemical model of Edelman and Fortune for the combustion of hydrocarbons is used and simplifying assumptions are made which reduce the systems of unknowns to that of the temperature alone. This leads to the introduction of two chemical production terms which are defined respectively in a “delay zone”, where the heat release is modest, and a “combustion zone”. The required equations for the Favre-averaged temperature, turbulence kinetic energy and the mean square fluctuation of the temperature are solved numerically. In the delay zone, a comparison is made between a second order Borghi type closure and the pdf closure. Good agreement is found in the case of relatively small turbulence intensity. It is shown that the pdf formulation does not require the two zones to be spatially distinct. Differing chemical source terms can be discriminated instantaneously by the reaction progress variable and contributions to the average production terms appropriately apportioned by its pdf. Predictions are made of the profiles of mean temperature and mean square fluctuation under different initial turbulence levels. 相似文献
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对带长深比为10的凹腔结构的燃烧室二维氢燃烧流场进行数值模拟,燃料喷注方式采用凹腔上游喷注加辅加凹腔前壁、底壁、后壁喷注。采用三阶MUSCL格式求解二维含组分守恒N-S方程组,湍流模型采用剪切修正的RNGk-ε湍流模型,对喷氢燃烧工况进行了计算研究,并分别分析了凹腔中不同燃料喷注方式对燃烧特性的影响。结果表明:凹腔是火焰驻留的主要区域;凹腔上游喷注氢,可以使燃料在凹腔中混合燃烧,辅加凹腔中喷氢的三种方式对燃烧状况产生一定的影响。在凹腔前壁、底面辅加喷氢,没有增强凹腔的稳焰特性,对整个燃烧状态影响不大;在凹腔后壁喷氢,能够增加凹腔中的燃料含量,加强了回流效果,对燃烧状态影响较大。三种喷注方式都没有从根本上改变凹腔燃烧流场的特性。 相似文献
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