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 of vaporized kerosene injection holds the potential of enhancing fuelair 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.

The heat transfer characteristics of China no. 3 kerosene were investigated experimentally and analytically under conditions relevant to a regenerative cooling system for scramjet applications. A test facility developed for the present study can handle kerosene in a temperature range of 300-1000 K, a pressure range of 2.6-5 MPa, and a mass flow rate range of 10-100 g=s. In addition, the test section was uniquely designed such that both the wall temperature and the bulk fuel temperature were measured at the same location along the flowpath. The measured temperature distributions were then used to analytically deduce the local heat transfer characteristics. A 10-component kerosene surrogate was proposed and employed to calculate the fuel thermodynamic and transport properties that were required in the heat transfer analysis. Results revealed drastic changes in the fuel flow properties and heat transfer characteristics when kerosene approached its critical state. Convective heat transfer enhancement was also found as kerosene became supercritical. The heat transfer correlation in the relatively low-fuel-temperature region yielded a similar result to other commonly used jet fuels, such as JP-7 and JP-8, at compressed liquid states. In the high-fuel-temperature region, near and beyond the critical temperature, heat transfer enhancement was observed; hence, the associated correlation showed a more significant Reynolds number dependency.

High-pressure jet injection into quiescent air is a challenging fluid dynamics problem in the field of aerospace engineering. Although plenty of experimental, theoretical, and numerical studies have been conducted to explore this flow, there is a dearth of literature detailing the flow evolution and instability characteristics, which is vital to the mixing enhancement design and jet noise reduction. In this paper, a density-based solver for compressible supersonic flow, astroFoam, is developed based on the OpenFOAM library. Large-eddy simulations of highly underexpanded jets with nozzle pressure ratios from 5.60 to 11.21 at a Reynolds number around 10 5 are carried out with a highresolution grid. A grid-convergence study has been conducted to confirm the fidelity of the large-eddy simulation results. The large-eddy simulation results have also been validated against available literature data in terms of the time-averaged near-field properties of underexpanded jets. The turbulent transition processes are revealed based on the instantaneous flow features and are quantitatively resolved according to the jet penetration and maximum width. The vorticity analysis is conducted to understand the turbulent transition mechanism, and it is found that the vortex stretching term plays a leading role on the distortion of the vortex rings in the near field of the jets. The dominant instability modes of jets, visualized by helicity, are quantitatively revealed based on the spectrum and relative phase of pressure fluctuation. The single helical modes corresponding to a phase angle close to 180 deg with the 1 1 helices are dominant for nozzle pressure ratios of 5.60 and 7.47, whereas the complex and multiple helices for the other two higher nozzle pressure ratios are due to the superposition of the single and double helical modes. In addition, the performance of the coarse mesh and different subgrid-scale models on capturing the dominant instability characteristics in large-eddy simulation of underexpanded jets is investigated.

The p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and subsequently Mn+ ions implanted. The properties of Mn+ ions-implanted GaN epilayers were investigated by optical and magnetic measurements. The results of photoluminescence measurement show that optical transitions related to Mn apparently appear at 2.5 eV and around 3.0 eV. It is confirmed that the photoluminescence peak at 2.5 eV is a donor–Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature-dependent magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.

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As one of the major short chain hydrocarbons resulting from the cracking process, ethylene is often used as a surrogate for cracked kerosene. In this study, a skeletal mechanism of ethylene was developed under the typical working conditions of scramjet combustors. The skeletal mechanism was reduced from a fully verified detailed mechanism under the desired working conditions. An integrated reducing method containing directed relation graph with error propagation method (DRGEP), sensitivity analysis (SA), and computational singular perturbation (CSP) was employed to obtain three skeletal mechanisms. A three-level fidelity validation of the skeletal mechanisms respectively comparing the kinetic properties, the global combustor performance, and the detailed flame structure was proposed to comprehensively evaluate the skeletal mechanisms. In the first-level fidelity validation, the three skeletal mechanisms all show good agreement with the detailed one in the autoignition delay and laminar flame speed over a wide range of working conditions. Then in the second-level fidelity validation, the smallest mechanism consisting of 24 species and 86 reactions (24S/86R) was further validated through incorporating with the large eddy simulation of a realistic scramjet combustor. Comparisons with the experimental data and the predictions by the detailed mechanism show that the global combustor performance (e.g., pressure, Mach number, and combustion efficiency) was accurately predicted by the 24S/86R mechanism. In the third-level fidelity evaluation, the flame structure characterized by the distribution of CO, OH, and heat release rate was analyzed through comparing the predictions by the 24S/86R mechanism with those by the detailed one during which the insufficiency of the skeletal mechanism was also recognized.

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a b s t r a c tRegenerative cooling of aviation kerosene plays an important role for thermal protection of scramjet engines. Since the thermophysical properties of kerosene change acutely near the pseudo-critical point, heat convective in kerosene pipe flow is complicated. Here the convective heat transfer characteristics of China RP-3 aviation kerosene at a supercritical pressure are numerically studied using the finite volume method. The RNG k-e two-equation turbulence model with enhanced wall treatment is considered. The heat transfer with different constant wall heat fluxes is analyzed, and a correlation of heat transfer enhancement is obtained. The effect of mass flow rate on the convective heat transfer with a varying wall heat flux condition at the supercritical pressure is also investigated. Because of the special thermophysical properties of the kerosene at supercritical pressure, the Nussult number is only related to the Reynolds number after the heat transfer is enhanced. The simulation results are compared with the empirical formulas in the literature.