Investigations on supersonic combustion in a combustion-driven shock tunnel

This article reports experimental results on supersonic combustion in a new facility. The facility is a combustion-driven shock tunnel, which is cheaper to build than the facilities in which such experiments are carried out conventionally. The observation region is a zone between two parallel flat plates with a 33 degrees wedge attached to the upstream end of the bottom plate. Gaseous hydrogen is injected at an angle of 45 degrees into an oncoming supersonic flow of Mach 2 (approximate) from a port on the bottom plate. The resulting flow field is visualized by a high speed camera in a dark background. Three different test gases, namely nitrogen, air, and oxygen-rich air are used, and the results are compared. A distinct luminosity due to combustion for oxygen-containing test gases is observed. Heat-transfer rates on a probe placed at the downstream end of the observation region and midway between the parallel plates are measured and compared for the three cases. Wall static pressure at 28 mm downstream of the injection port on the bottom plate is also presented.

超临界煤油超声速燃烧特性实验 Experiments on Supersonic Combustion of Supercritical Kerosene

针对各种温度、压力下，马赫数2．5流场中超临界煤油的超声速燃烧性能进行了实验研究。研制并测试了一个新型二级煤油加热系统，该系统能够把0．8kg的煤油在5．5MPa压力下加热至至950K而不产生严重的结碳。超声速燃烧试验表明，在相同的来流和燃料当量比条件下，超临界煤油的燃烧效率比室温煤油提高10％～15％，与氢气泡雾化的燃烧效率相当。

Experimental studies on self-ignition of hydrogen/air supersonic combustion

Self-ignition tests of a model scramjet combustor were conducted by using parallel sonic injection of gaseous hydrogen from the base of a blade-like strut into a supersonic airstream, The vitiated air was produced by burning H-2, O-2, and air to a stagnation temperature of 1000-2100 K and a stagnation pressure of 0.8-1.6 MPa, The effects of different parameters on the self-ignition limits were analyzed, In addition, the effects of the combustor's different wall configurations on self-ignition limits were specifically studied. It was found that the wall configurations of the combustor had a significant effect on self-ignition limits, which might have variations of 420-840 K deg in stagnation temperature; however, the local static temperature in the recirculation zones for different wall configurations remained the same at approximately 1100 K, It was found that self-ignition could initiate at the exit of the combustor and this can be considered as a weak self-ignition characteristic.

Investigation of Vaporized Kerosene Injection and Combustion in a Supersonic Model Combustor

Injection and combustion of vaporized kerosene was experimentally investigated in a Mach 2.5 model combustor at various fuel temperatures and injection pressures. A unique kerosene heating and delivery system, which can prepare heated kerosene up to 820 K at a pressure of 5.5 MPa with negligible fuel coking, was developed. A three-species surrogate was employed to simulate the thermophysical properties of kerosene. The calculated thermophysical properties of surrogate provided insight into the fuel flow control in experiments. Kerosene jet structures at various preheat temperatures injecting into both quiescent environment and a Mach 2.5 crossflow were characterized. It was shown that the use ofvaporized kerosene injection holds the potential of enhancing fuel-air mixing and promoting overall burning. Supersonic combustion tests further confirmed the preceding conjecture by comparing the combustor performances of supercritical kerosene with those of liquid kerosene and effervescent atomization with hydrogen barbotage. Under the similar flow conditions and overall kerosene equivalence ratios, experimental results illustrated that the combustion efficiency of supercritical kerosene increased approximately 10-15% over that of liquid kerosene, which was comparable to that of effervescent atomization.

Investigation of Vaporized Kerosene Injection and Combustion in a Supersonic Model Combustor

Injection and combustion of vaporized kerosene was experimentally investigated in a Mach 2.5 model combustor at various fuel temperatures and injection pressures. A unique kerosene heating and delivery system, which can prepare heated kerosene up to 820 K at a pressure of 5.5 MPa with negligible fuel coking, was developed. A three-species surrogate was employed to simulate the thermophysical properties of kerosene. The calculated thermophysical properties of surrogate provided insight into the fuel flow control in experiments. Kerosene jet structures at various preheat temperatures injecting into both quiescent environment and a Mach 2.5 crossflow were characterized. It was shown that the use ofvaporized kerosene injection holds the potential of enhancing fuel-air mixing and promoting overall burning. Supersonic combustion tests further confirmed the preceding conjecture by comparing the combustor performances of supercritical kerosene with those of liquid kerosene and effervescent atomization with hydrogen barbotage. Under the similar flow conditions and overall kerosene equivalence ratios, experimental results illustrated that the combustion efficiency of supercritical kerosene increased approximately 10-15% over that of liquid kerosene, which was comparable to that of effervescent atomization.

Chemiluminescence imaging in supersonic combustors operating in radical-farming mode

Emission spectroscopy was used to investigate ignition and combustion characteristics of supersonic combustion ramjet engines. Two-dimensional scramjet models with inlet injection, fuelled with hydrogen gas, were used in the study. The scramjet engines were configured to operate in radical farming mode, where combustion radicals are formed behind shock waves reflected at the walls. The chemiluminescence emission signals were recorded in a two-dimensional, time-integrated fashion to give information on the location and distribution of the radical farms in the combustors. High signal levels were detected in localised regions immediately downstream of shock reflections, an indication of localised hydroxyl formation supporting the concept of radical farming. Results are presented for a symmetric as well as an asymmetric scramjet geometry. These data represent the first successful visualisation of radical farms in the hot pockets of a supersonic combustor. Spectrally resolved measurements have been obtained in the ultraviolet wavelength range between 300 and 400 nm. This data shows that the OH! chemiluminescence signal around 306nm is not the most dominant source of radiation observed in the radical farms.

Effects of entry conditions on cracked kerosene-fueled supersonic combustor performance

Supersonic combustion of thermally cracked kerosene was experimentally investigated in two model supersonic combustors with different entry cross-section areas. Effects of entry static pressure, entry Mach number, combustor entry geometry, and injection scheme on combustor performance were systematically investigated and discussed based on the measured static pressure distribution and specific thrust increment due to combustion. In addition, the methodology for characterizing flow rate and composition of cracked kerosene was detailed. Using a pulsed Schlieren system, the interaction of supercritical and cracked kerosene jet plumes with a Mach 2.5 crossflow was also visualized at different injection temperatures. The present experimental results suggest that the use of a higher combustor entry Mach number as well as a larger combustor duct height would suppress the boundary layer separation near the combustor entrance and avoid the problem of inlet un- start.

Performance of a Supersonic Model Combustor using Vaporized Kerosene Injection

Characteristics of supersonic combustion by injecting kerosene vapor into a Mach 2.5 crossflow at various preheat temperatures and pressures were investigated experimentally. A two-stage heating system has been designed and tested, which can prepare heated kerosene of 0.8 kg up to 820 K at pressure of 5.5 Mpa with minimum/negligible fuel coking. In order to simulate the thermophysical properties of kerosene over a wide range of thermodynamic conditions, a three-component surrogate that matches the compound class of the parent fuel was employed. The flow rate of kerosene vapor was calibrated using a sonic nozzle. Computed flow rates using the surrogate fuel are in agreement with the experimental data. Kerosene jets at various preheat temperatures injecting into both quiescent environment and Mach 2.5 crossflow were visualized. It was found that at injection pressure of 4 Mpa and preheat temperature of 550 K the kerosene jet was completely in vapor phase, while keeping almost the same penetration depth as compared to the liquid kerosene injection. Supersonic combustion tests were also carried out to compare the combustor performance for the cases of vaporized kerosene injection, liquid kerosene injection, and effervescent atomization with hydrogen barbotage, under the similar stagnation conditions. Experimental results demonstrated that the use of vaporized kerosene injection leads to better combustor performance. Further parametric study on vaporized kerosene injection in a supersonic model combustor is needed to assess the combustion efficiency as well as to identify the controlling mechanism for the overall combustion enhancement.

Performance of supersonic model combustors with staged injections of supercritical aviation kerosene

Supersonic model combustors using two-stage injections of supercritical kerosene were experimentally investigated in both Mach 2.5 and 3.0 model combustors with stagnation temperatures of approximately 1,750 K. Supercritical kerosene of approximately 760 K was prepared and injected in the overall equivalence ratio range of 0.5-1.46. Two pairs of integrated injector/flameholder cavity modules in tandem were used to facilitate fuel-air mixing and stable combustion. For single-stage fuel injection at an upstream location, it was found that the boundary layer separation could propagate into the isolator with increasing fuel equivalence ratio due to excessive local heat release, which in turns changed the entry airflow conditions. Moving the fuel injection to a further downstream location could alleviate the problem, while it would result in a decrease in combustion efficiency due to shorter fuel residence time. With two-stage fuel injections the overall combustor performance was shown to be improved and kerosene injections at fuel rich conditions could be reached without the upstream propagation of the boundary layer separation into the isolator. Furthermore, effects of the entry Mach number and pilot hydrogen on combustion performance were also studied.

乙烯超声速燃烧的数值模拟研究

利用Fluent软件、ISAT算法与由CARM(Computer Assisted Reduction Method)简化而来的11组分、7步反应的乙烯简化机理对碳氢燃料/空气的超声速燃烧问题进行数值模拟.研究结果表明这种方法是可利用的.计算得到的压力数据与试验压力值可以比较.

超燃燃烧室一维流场分析模型的研究

对公开发表的用于超声速燃烧流场分析的几种一维模型进行了研究，指出了其中存在的问题，研究结果表明：基于实验静压数据的一维模型，若不借助必要的流场测量数据或分析结果，或借助于经验性的处理方法，单靠一维假设，无法获得较为完整的一维流场分析结果。改进后的一维模型降低了数据处理过程中的不确定性，提高了对一般情况的适应能力。用编制的计算程序SSC-2对两组典型的超燃燃烧室壁面静压实验数据进行了演算，取得了燃烧室出口总压恢复系数的计算值与测量值基本一致的好结果。

煤油-空气预混气流超声速燃烧数值研究

对以高温燃气作为引导火焰的煤油．空气预混气流超声速燃烧进行了数值模拟，系统研究了预混气流的温度、压力、当量比，以及预混气流与高温燃气的压力匹配关系等多种重要因素对超声速燃烧的影响。结果表明：随着预混气流静温、静压的升高，着火点诱导的压缩波增强，最高燃烧温度升高，火焰传播角相应增大；预混气流的当量比为化学恰当比时，燃烧温度最高；与静压匹配的情况相比，静压不匹配情况下的火焰传播角增大，当预混气流的静压高于高温燃气的静压时，着火点前移，反之，着火点则后移；此外，在多种情况下，燃烧室下壁面边界层都出现了自燃现象。

超声速燃烧的湍流流场数值模拟

选择了6个有代表性的湍流模型，对超声速燃烧湍流流场开展了数值模拟。采用的模型包括5个线性涡粘性模型和1个非线性模型，在非线性模型中同时引入了可压缩修正。数值结果表明，本文发展的数值方法可以成功地应用于求解可压缩、含化学反应的多组分N—S方程。同时引入可压缩性修正的二阶涡粘性模型给出的结果较好。