Momentum Flux Ratio Increases Research Articles

동축형 분사기의 연소 특성에 영향을 주는 인자에 관한 연구

Factors affecting the combustion characteristics of gas-centered swirl coaxial (GCSC) injectors are investigated numerically and experimentally. The factors are fuel volume flow rate (Qf), momentum flux ratio (MFR) and oxidizer/fuel (O/F) ratio. Firstly, the flame pattern becomes asymmetric as the fuel volume flow rate increases with a fixed momentum flux ratio. Then, the suitable fuel volume flow rate is selected according to the results. Next, the momentum flux ratio is increased by increasing the oxidizer volume flow rate (QSUBo/SUB) with a fixed fuel volume flow rate. Results show that the spreading angle decreases as momentum flux ratio increases, which agrees with our previous results. Finally, in order to check effects of oxidizer/fuel ratio, the QSUBf/SUB, QSUBo/SUB, and MFR are kept the same but the O₂ mole fraction of oxidizer is changed. From numerical and experimental results, it is found that flame pattern depends on oxidizer/fuel ratio and spreading angle increases as the O₂ mole fraction decreases.

RESPONSE OF LIQUID JET TO MODULATED CROSSFLOW

Experimental results on the response of spray formed by the liquid (Jet-A) jet injection into a crossflow (Air) is presented with a special emphasis on its response to the modulating crossflow. The pressure of the chamber is up to 3.5 atm and the corresponding Weber number is up to 510. The spray of a liquid jet for steady and oscillating crossflow is characterized. The flow field at the injector location in the crossflow direction is determined using PIV (Particle Image Velocimetry) for oscillating as well as steady crossflow case. Planar Mie-scattering measurement is used to characterize the response of spray formed under oscillating crossflow and supplementary phase-averaged PDPA measurements are used to understand the response behavior. The global response of spray to the oscillating crossflow is characterized using the planar Mie-scattering imaging. It shows that there exist very little differences in the heights of the maximum-pixel intensity trajectory for the non-oscillating and oscillating crossflow conditions and the trajectory under oscillating crossflow is lower than that of steady crossflow, suggesting the oscillating crossflow affects the atomization (i.e. the oscillating crossflow enhances atomization process, results in smaller droplets and penetrates less transversely). The response of spray to the oscillating crossflow characterized in terms of the spray transfer function (STF) shows that the gain of the STF increases linearly (at least monotonically) as the liquid-air momentum flux ratio increases but does not change as much with respect to the change of the Weber number for a fixed liquid-air momentum flux ratio. This also indicates that the liquid jet atomization under oscillating crossflow is enhanced much more with the increase of liquid-air momentum flux ratio than with the increase of Weber number. The phase-averaged PDPA measurements confirm that the oscillating crossflow indeed enhances the atomization process in that the oscillating crossflow results in relatively greater number of smaller droplets and the mean droplet size.Copyright © 2013 by ASME

Study on spray patterns of gas-centered swirl coaxial (GCSC) injectors in high pressure conditions

Recess ratio and momentum flux ratio are the key parameters in determining spray characteristics and mixing efficiency of the propellants in rocket injectors. In this study, effects of the recess ratio and momentum flux ratio on the spray patterns of gas-centered swirl coaxial (GCSC) injectors have been experimentally investigated through cold flow tests in a high pressure chamber, in which the liquid fuel and gaseous oxidizer are simulated by water and gaseous nitrogen, respectively. By elevating the chamber pressure, the cold flow test conditions are adjusted to match the ratios of momentum flux, density, and velocity between the gas and liquid flows to those of the actual hot-firing conditions. The results showed that the spray patterns change drastically from a wide hollow cone to a narrow solid cone as the gas to liquid momentum flux ratio increases. Also, the injector with the shorter recess needs a higher momentum flux ratio to have a similar spray pattern to that with the longer recess. Based on the measured spray contraction parameters, the critical momentum flux ratio, which determines the near-injector spray pattern as internal or external mixing, correlates with the recess ratio.

Cold modeling investigation of aerodynamic characteristics of an arch-fired boiler on particle image velocimetry (PIV): Influence of momentum flux ratio of arch air to secondary air and secondary air angle

To study the aerodynamic characteristics, experiments were carried out on a laboratory-scale model for an arch-fired boiler. The airflow velocity was measured by using a two-dimensional PIV. The results show that: (1) as the momentum flux ratio increases, the arch air becomes stronger and reaches deeper into the furnace; however, the velocity distribution was non-uniform in the lower furnace, and the recirculation region expanded slightly. The ideal value of the momentum flux ratio is 2.54. (2) As the low layer secondary air is injected with an inclination angle, its mixing with the arch air is postponed. So, the gas after mixing can reach the lower furnace and the residence time of fuel is prolonged. As the inclination angle increases from 0° to 20°, 30° and 40°, respectively, higher penetration depth and fullness degree of airflow can be obtained as well as the larger recirculation region. The ideal inclination angle is 30°; and (3) Compared with increasing the momentum flux ratio, adjusting the secondary air inclination angle is more beneficial to improving the distribution of the airflow within the furnace.

Characteristics of Dual Transverse Injection in Scramjet Combustor, Part 2: Combustion

The combustion characteristics of a dual transverse injection system in a scramjet combustor were studied with numerical methods. The effects of the jet-to-crossflow momentum flux ratio and the distance between injectors on combustion characteristics were investigated. It is shown that the dual injection system has very different combustion characteristics with respect to the single injection system; the burning process of the rear injection flow is strongly influenced not only by the blockage effects but also by the preheating effects due to the chemical reactions of the front injection flow. The dual injection system has a higher burning rate and a higher flame height but more loss of stagnation pressure than the single injection system. It is also shown that there is an optimal distance between injectors for combustion characteristics and that the optimal distance increases as the jet-to-crossflow momentum flux ratio increases.