Abstract
The effect of air throttling on flame stabilization of an ethylene fueled scramjet combustor was investigated by numerical simulation and experiments in this paper. The results were obtained under the inflow condition with Mach number of 2.0, total temperature of 900 K, total pressure of 0.8 MPa, and total equivalence ratio of 0.5. The shock train generated by air throttling had a big effect on the flow structure of the scramjet combustor. Compared with the combustor without air throttling, the flow field with air throttling had a lower velocity and higher pressure, temperature, and vortices intensity. Air throttling was an effective way to achieve flame stabilization; the combustion in the combustor without air throttling was nearly blowout. In the experiment, the combustion was nearly blowout with air throttling location of 745 mm, and the fuel/air mixture in the combustor with air throttling location of 875 mm was burned intensively. It was important to choose the location and time sequence of air throttling for fuel ignition and flame stabilization. The numerical simulation results agreed well with experimental measurements.
Highlights
When the flight Mach number is bigger than 6, the air flow remains completely supersonic throughout the scramjet combustor in a few milliseconds
Control and optimization of ignition transient and flame development in a scramjet engine using air throttling were studied by Li et al [2], the locations and operation timing of air throttling and fuel injection on the engine start-up transient characteristics were examined systematically, and a dynamic optimization scheme based on the genetic algorithm (GA) was developed to maximize the performance of air throttling
Temperature contours of the scramjet combustor at different cross section were shown in Figure 5; the temperature of the scramjet combustor with air throttling was much higher than that of the scramjet without air throttling from the exit of the isolator, especially between cross sections “A” and “B.” The temperature of the scramjet with air throttling was higher than 700 K but that of the scramjet without air throttling was about 500 K; the influencing zone of the shock train produced by air throttling in the scramjet combustor was from the exit of the isolator to the exit of the combustor
Summary
When the flight Mach number is bigger than 6, the air flow remains completely supersonic throughout the scramjet combustor in a few milliseconds. Air throttling was an effective method to achieve ignition and combustion establishment. A proper shock train is generated by air throttling, and the velocity decreases and the pressure increases in the combustor section which can effectively enhance the ignition and flame stabilization. The transient process of flow establishment and combustion process were studied for an ethylene fueled direct-connect dual mode scramjet combustor with air throttling by Choi et al [3]. Experiment results showed that successful ignition could be achieved by the air throttling method. Their research showed that air throttling could generate a precombustion shock train in the isolator, the resultant decrease in the flow velocity and increases in the temperature and pressure in the combustor section to improve the ignition characteristics and the flame stabilization process.
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