Effect of injection scheme on asymmetric phenomenon in rectangular and circular scramjets

The asymmetric separation has a crucial effect on the performance of the scramjet. In this study, the asymmetric separation and combustion in both rectangular and circular scramjets are investigated numerically, and the effect of injection scheme is analyzed. The characteristics of the flow field are analyzed based on sufficient code verification. In the rectangular scramjet, the separation tends to occur in the corner due to the corner boundary-layer effect. The separation is asymmetric and only two corners have serious separation. The fuel penetration depth in the separation zone increases and the combustion is intensified. When the injection scheme is uniform, both the combustion and separation become weak. In the circular scramjet, the separation and combustion are basically axisymmetric in the scramjet with one-row injection scheme. The asymmetric combustion becomes obvious in cases with multi-row injection scheme. When the injection orifices distribute intensively on the top and bottom sides, the strongest and weakest separations occur near these two sides respectively. When the distribution of orifices becomes uniform, the direction of separation cannot be predicted. For multi-row cases, the nonuniform injection scheme could result in violent combustion and asymmetric flow structures compared with the uniform injection scheme.     

进气道出口截面形式对补燃室掺混性能的影响研究

为研究进气道出口截面形式对补燃室掺混气动特性和燃烧性能的影响，本文对双下侧布局形式的固冲发动机内流场进行数值模拟，对比分析了补燃室相同压比下两种不同进气道出口截面形式在不考虑燃气的混合和反应时掺混段的气动特性和考虑燃气反应时补燃室的燃烧性能。结果表明：两股空气掺混过程中，研究的两种进气道出口截面方案的整体总压损失大致相同，但进气道圆形出口截面的掺混段内流线表现为不稳定的螺旋点形态，相比于方形出口截面的掺混段，其使气流掺混更剧烈，短距离内掺混已经很均匀，且旋流强度小；在考虑燃烧时，进气道圆形出口截面对应的补燃室出口总压恢复系数比方形截面的高约2%，方形进气道出口截面的补燃室出口截面总燃烧效率为95.58%，而圆形截面的达到99.86%。     

Mixing and combustion characteristics in a scramjet combustor with different distances between cavity and backward-facing step

The mixing and combustion characteristics in a cavity flameholding combustor under inlet Mach number 2.92 are numerically investigated with ethylene injection. Dimensionless distance is defined as the ratio of the actual distance to the height of the combustor entrance. The cavity shear-layer mode, the lifted cavity shear-layer mode, and jet wake mode with upstream separation are observed respectively with dimensionless distance equals to 1.5, 4.5, and 7.5. In both non-reacting and reacting flow...     

Promotional effect of silica on the combustion of nano-sized aluminum powder in carbon dioxide

This paper presents how the combustion performance of nano-sized aluminum(nAl)powder in carbon dioxide are affected by silica. The ignition and combustion performance of nAl powder with silica addition were studied by a high-temperature tube furnace. An s-type thermocouple and a high-speed motion acquisition instrument were performed to evaluate the ignition temperature, maximum combustion temperature, maximum change of rate of temperature, and combustion propagation speed. The combustion effici...     

Numerical study on combustion efficiency of aluminum particles in solid rocket motor

The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size, while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.