Hongbin Gu

Simultaneous measurements of multiple flow parameters for scramjet characterization using tunable diode-laser sensors

This paper reports the simultaneous measurements of multiple flow parameters in a scramjet facility operating at a nominal Mach number of 2.5 using a sensing system based on tunable diode-laser absorption spectroscopy (TDLAS). The TDLAS system measures velocity, temperature, and water vapor partial pressure at three different locations of the scramjet: the inlet, the combustion region near the flame stabilization cavity, and the exit of the combustor. These measurements enable the determination of the variation of the Mach number and the combustion mode in the scramjet engine, which are critical for evaluating the combustion efficiency and optimizing engine performance. The results obtained in this work clearly demonstrated the applicability of TDLAS sensors in harsh and high-speed environments. The TDLAS system, due to its unique virtues, is expected to play an important role in the development of scramjet engines.

Measurement of temperature, velocity and water vapor concentration in a scramjet combustor based on near-infrared diode laser absorption

A multi-channel Tunable Diode Laser Absorption Spectroscopy (TDLAS) system was designed and constructed for flow parameters diagnostics in a scramjet combustor. Two fiber coupled distributed feedback (DFB) lasers with narrow line width were used to probe two H2O absorption features (7185.597cm-1,7444.35cm-1+7444.37cm-1(c ombined)) by using direct absorption Time-Division-Multiplexing (TDM) strategy at a 4-kHz repetition rate. Laser light was split into five beams and transmitted across the test region. Two motorized precision translation stages were used to move the collimators during the test, so that the three beams located near the cavity and at the exit of the combustor can scan the cross sections respectively. Flow parameters could be obtained simultaneous which included average temperature, water vapor concentration and velocity at the entrance of the combustor, the distribution of temperature, water vapor concentration at a cross section near the cavity, the distribution of temperature, water vapor concentration and velocity at the exit cross section of the combustor. The parameters of the flow entering and exiting the combustor could be used to evaluate the performance of the direct-connected scramjet facility and the combustion efficiency of the combustor. The parameters at the cross section in the combustor could also be used to analysis combustion characteristics in the combustor.

Thrust and drag of a scramjet model with different combustor geometries

Many efforts have been made to improve performance of scramjets (1-4). For this purpose cavities and struts were frequently used as the functions of mixing enhancement and flame stabilization. The present work focused on the effects of different strut and cavities on the thrust and drag of a side-wall compression scramjet model. This model consisting of a side-wall compression inlet, a combustor and a thrust nozzle and fueled by kerosene was tested in a propulsion tunnel that typically provides the testing flow with Mach number of 5.8, total temperature of 1800K, total pressure of 4.5MPa and mass flow rate of 4kg/s(5). A strut was used to increase the contraction ratio and to inject fuels, as well as a mixing enhancement device. Several wall cavities were also employed for flame-holder. The experimental results show that the cavities do not produce significant drag, but improve thrust performance well. It is found that the strut functions as an isolator and also helps the mixing enhancement, resulting in the improvement of the thrust performance. However the strut causes big drag to the scramjet model. Copyright

Flow-field of the Excited Jet and Mixing in the Supersonic Flow

The planar laser scattering and gas sampling were used to investigate the mixing of the excited CO2 jet into the supersonic flow in this article. The jet was from the HartmannSprenger tube, which was put into the traditional jet device. The jet was excited at three different frequencies and compared with the base case without excitation. The results shown that the better mixing with less total pressure loss could be obtained in the excited cases. The penetration was the deepest for 900Hz-excited jet while the number of the large-scale structures was the most in the 5 kHz-excited case. The excited jet didn’t only take effects on the jet shear layer, but also in fluenced the boundary layer.

Performance of the fuel injector in supersonic combustor

Enhancing the fuel-air mixing is critical for scramjet combustor performance. The performance of four different aerodynamic ramp injectors was reported in this paper. The experiments were conducted in a direct-connected scramjet test facility. The concentration profiles were obtained by gas sampling and chromatogram analysis. The pictures of the flow field were obtained by using laser scatter. It would be used to analyze the flow field generated by the aerodynamic ramp, then optimize the layout of the injectors. The results would offer some useful information for engine design.

Experimental study of combustion oscillations in a dual-mode scramjet

Characteristics of combustion oscillations were studied experimentally in a direct-connected supersonic combustion test facility with a cavity flameholder and transverse fuel injection from the wall. Static pressures were obtained by using high-frequency dynamic pressure transducers. The effects of inlet Mach number and fuel injection were examined. The frequency spectrum of wall pressures shows that combustion oscillations are different between the ramjet mode and the scramjet mode. In the ramjet mode, the high frequency combustion oscillations are on the same order of frequency as cavity oscillations. The low frequencies increase as inlet Mach number increase and fall in a range of 200-450Hz. In the scramjet mode, the high frequency combustion oscillations exist in trailing edge of the cavity, the frequencies are about 4 kHz and the occurrence is related with transverse injection momentum ratio.

Experimental Study of Strut Parameters Effects on Performances of Scramjet Combustor

An experimental investigation of strut parameters for enhancing supersonic mixing and combustion had been carried out on direct-connect supersonic combustion test facility. The wall static pressure, gas sampling analysis system, CH* chemiluminescence imaging and the schlieren system were used to research the effect of different strut parameters. This paper uses the method of orthogonal experimental method, parametric modeling of strut configurations was performed by the orthogonal design with 5 factors at 3 levels. Undisturbed length and combustion efficiency were set as objective functions of combustion performance of scramjet combustor. The results are as follows: For combustion efficiency of scramjet, the order of significance levels of the strut factors in turn decreases on jet, height, distance, equivalence ratios and thickness of strut respectively. For undisturbed length of scramjet, the order of significance levels of the strut factors in turn decreases on respectively equivalence ratios, jet, height, thickness, and distances of strut. The higher the strut is, the deeper fuel mixing and combustion area are in the mainstream, the shorter and narrower the flames are, the greater the intensity and efficiency of combustion are. As the height of strut increases from 10mm to 30mm, the combustion efficiency increased accordingly by 15.1%. Meanwhile, moderate distance between strut and cavity can help to improve combustion performance of strut.

Interaction between Combustion and Shock Wave in Supersonic Combustor

Interaction between shock wave and combustion is very important for supersonic combustion. For scramjet, isolator is a key element to withstand the high pressure due to combustion and to avoid the unstart of the inlet. Therefore, the flow is very complex in isolator and combustor because of the interaction between combustion and shock wave. Usually, there are two modes of combustion in scramjet: supersonic mode and subsonic mode. Many researches have already shown how to achieve dual-mode scramjet to obtain better engine performance [1] [2] [3].

Experimental Study of Ignition and Flame Characteristics of Surrogate of Cracked Hydrocarbon Fuels in Supersonic Crossflow

The ignition and flame characteristics of ethylene and blend fuel (surrogate of thermal cracked kerosene) are studied experimentally on a direct-connect supersonic combustor facility. The blend fuel consists of H2, CH4, C2H4, C2H6, C3H6and C3H8with molar fractions according to the result of gaseous compositions of thermal cracked kerosene. CH* luminance in the combustion is filmed by a high-speed camera, and unsteady process of ignition as well as flame formation and proportion is captured. Meanwhile the image of CH* luminance is one-dimensional treated along the axis of combustor and the relative amount of heat release rate of combustion is obtained. The experimental results show that with equivalence ratio increasing the flame of ethylene is changed from the cavity stabilization mode to the jet-wake stabilization mode and the combustion efficiency increases. In contrast, the total heat release and combustion efficiency of the blended fuel decrease. 漏 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

CH* Luminance Distribution Application and a One-Dimensional Model of the Supersonic Combustor Heat Release Quantization

Abstract One-dimensional model is an important way to evaluate the performance and flow characteristics of dual-mode scramjet combustor. Current work is based on a modified one-dimensional model assisted by measurements acquired on a direct-connected scramjet facility. CH* images and gas-sampling facility have been employed to quantify heat release for optimizing one-dimensional model. The results show that modified one-dimensional model gives a better evaluation of axis parameters distribution, especially for Mach number, which is the standard parameter to evaluate combustion mode. The ram/scram mode derived by the analytical results has been investigated. Intensive heat release is beneficial to obtain more stable pre-combustion shock and subsonic flow in the recirculation zone.