Abstract
In this work, the dynamic combustion characteristics in a scramjet engine were investigated using three diagnostic data analysis methods: DMD (Dynamic Mode Decomposition), STFT (Short-Time Fourier Transform), and CEMA (Chemical Explosive Mode Analysis). The data for the analyses were obtained through a 2D numerical experiment using a DDES (Delayed Detached Eddy Simulation) turbulence model, the UCSD (University of California at San Diego) hydrogen/oxygen chemical reaction mechanism, and high-resolution schemes. The STFT was able to detect that oscillations above 50 kHz identified as dominant in FFT results were not the dominant frequencies in a channel-type combustor. In the analysis using DMD, it was confirmed that the critical point that induced a complete change of mixing characteristics existed between an injection pressure of 0.75 MPa and 1.0 MPa. A combined diagnostic analysis that included a CEMA was performed to investigate the dynamic combustion characteristics. The differences in the reaction steps forming the flame structure under each combustor condition were identified, and, through this, it was confirmed that the pressure distribution upstream of the combustor dominated the dynamic combustion characteristics of this scramjet engine. From these processes, it was confirmed that the combined analysis method used in this paper is an effective approach to diagnose the combustion characteristics of a supersonic combustor.
Highlights
In a supersonic combustor, which sustains highly turbulent, compressible, and non-premixed reacting flows, combustion is mostly held at the fuel/air mixing layer
The differences in the reaction steps forming the flame structure under each combustor condition were identified, and, through this, it was confirmed that the pressure distribution upstream of the combustor dominated the dynamic combustion characteristics of this scramjet engine
Before describing the results of the combined diagnostic analysis, the numerical experiment is briefly discussed
Summary
In a supersonic combustor, which sustains highly turbulent, compressible, and non-premixed reacting flows, combustion is mostly held at the fuel/air mixing layer. Supersonic combustion is essentially an unsteady combustion with ignition, extinction, and re-ignition occurring repeatedly. The flow-residence time of a supersonic combustor with the abovementioned features is very short, in the order of 1 ms. This implies that all the processes of mixing, ignition, and combustion after the fuel is injected must take place within an extremely short time span. Flame holding, which avoids extinction and propellant mixing, is recognized as one of the most important mechanisms in supersonic combustion. As with all other combustors, supersonic engines exhibit different combustion characteristics depending on the shape of the cavity and the combustor, the working fluid, and the operating environment
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