The data-driven intelligent reconstruction of a flow field in a supersonic combustor aids the real-time monitoring of wave system evolution in a scramjet flow field structure, allowing the determination of the combustion state for active flow control. In this paper, a deep learning architecture based on a multi-branch fusion convolutional neural network (MBFCNN) is proposed to reconstruct the flow field in a supersonic combustor. Experiments on hydrogen-fueled scramjets with different equivalence ratios were carried out in a direct-connected supersonic pulse combustion wind tunnel with an inflow Mach number of 2.5 to establish a dataset for MBFCNN network training and testing. The trained model successfully reconstructed the flow field structure from measured wall pressure data. The flow field reconstruction model provided a rich information source for the evolution of the wave system structure under the self-ignition conditions of the hydrogen-fueled scramjet, greatly improving the detection accuracy. The proposed deep learning architecture method was compared with basic convolutional neural network and symmetric convolutional neural network methods. The three methods all accurately reconstructed the flow field of the supersonic combustor. However, the proposed MBFCNN provided the best reconstruction results, and its average linear correlation coefficient in the test set was 0.952. The proposed MBFCNN had a lower mean square error and higher peak signal-to-noise ratio than the other two methods, which verified that the proposed model is eminently able to reconstruct and predict the flow field of a supersonic combustor.

This paper describes a numerical and experimental investigation of the combustion process in an ethylene-fueled scramjet combustor. The combustion process could be divided into six parts. Part 1 consists of a nonreacting flow before the hydrogen was injected. In part 2, hydrogen injection led to the generation of a shock wave, resulting in an increase in the monitor pressure. Part 3 involved hydrogen combustion, including ignition and flame stabilization. The ignition time of the pilot hydrogen was about 26 ms, and the shock train generated by hydrogen combustion moved at about 20 m/s. In part 4, with the injection of ethylene, there was a hydrogen and ethylene combustion flow, the combustion became more intense, and the shock waves were pushed into the isolator and disappeared from the schlieren images. In part 5, with the cessation of hydrogen injection, the combustion involved ethylene alone, and the ethylene flame moved from the front of the cavity to the back. The combustion mode changed from subsonic to supersonic, and the flame stabilization mode changed from cavity recirculation to cavity shear layer combustion. In part 6, the flame was blown out and combustion ceased.

The effects of pulsed injection on the flow structure and flame development in a scramjet were investigated experimentally with a pilot hydrogen equivalence ratio (ER) of 0.1 and a kerosene ER of 0.3; the pilot hydrogen was used to enhance the kerosene combustion. In the steady injection flow, the non-reacting flow structure changed periodically, and the monitor pressure built up rapidly when the pilot hydrogen self-ignited at t = 0.0096 s, increasing from 0.03 to 0.037 MPa. The pilot flame was stable and filled the whole cavity until the kerosene began to be injected into the combustor at t = 0.05 s; the kerosene combustion occurred only in the cavity shear layer. After a very short time, the pilot flame was blown off by the kerosene. In the pulsed injection flow, the kerosene kept burning with the help of the pilot flame, and the monitor pressure remained at a high value that was about six times that in the non-reacting flow. The mixture of pilot hydrogen and kerosene flame could propagate into the isolator, which was discontinuous and a distinct fault could be seen in the flame images. The kerosene combustion under pulsed injection was very intense, and even when the pilot hydrogen was removed, the cold room-temperature kerosene could still burn steadily for some time. Comparing with the flame development process under steady injection conditions, it is concluded that pulsed injection helps greatly to realize kerosene ignition and stable combustion.

The atomization process of liquid fuels is vital in scramjet engines. The level of atomization directly impacts the subsequent evaporation, mixing, and combustion processes. Therefore, understanding the atomization mechanism of liquid jets in crossflow is necessary to promote the mixing process of scramjet engines and improve the combustion efficiency. This article overviews the atomization process of liquid jets in transverse airflow based on the breakup mechanism, atomization characteristics, and factors affecting atomization. The deformation and fragmentation of droplets are influenced primarily by the Weber number and have little correlation with the Reynolds number. There are similarities in the properties between the primary fragmentation of liquid jets and the breakup of liquid droplets in crossflow. The primary breakup of liquid jets in crossflow is characterized primarily by continuous jet column breakup. The Rayleigh–Taylor instability causes columnar breakup, while the Kelvin–Helmholtz instability causes surface breakup in the jet. The size distribution of droplets follows C-, I-, or S-shaped distributions, while the velocity distribution of droplets follows an inverse C-shape. Finally, the shortcomings of current research are pointed out, namely, the lack of research on the jet breakup mechanism in crossflow under actual scramjet engine configurations and inflow conditions. In the future, it can be combined with artificial intelligence to reveal the jet breakup mechanism under actual working conditions and establish a wide range of theoretical prediction models.

Pilot hydrogen is used for the ignition of gaseous ethylene to improve combustion efficiency at low flight Mach numbers. The process of dynamic flame stabilization has been investigated experimentally in a scramjet equipped with a cavity by using a variety of fuel injection strategies involving the injection of pure hydrogen, pure ethylene, and combinations of fuels to understand the effects of pilot hydrogen on supersonic combustion. This study reports experiments conducted in a direct-connected facility that simulated flight conditions at a Mach number of 4, a total temperature of 953 K, and a total pressure of 0.82 MPa. The data were collected by using hydroxyl planar laser-induced fluorescence (OH-PLIF), methylene (CH), luminosity images, and 10-kHz static pressure transducers. The results show that the internal flow oscillated at a dominant frequency of approximately 450 Hz without fuel injection. Oscillation in internal flow was suppressed when pilot hydrogen was injected into the cavity, whereas the influence of other injection strategies was minor. The OH-PLIF images indicate that the pilot flame was unstable, with different locations and occupying different areas. The normalized pressure was apparently higher when pilot hydrogen was injected ahead of the cavity step. The pure ethylene flame was difficult to stabilize without the application of pilot hydrogen. Once the pilot hydrogen had been turned off, the ethylene flame moved toward the cavity ramp and its area expanded. Thus, pilot hydrogen is a precondition for the stabilization of the ethylene flame.