We carried out the numerical simulation of methane-oxygen coaxial turbulent nonpremixed flames and of non-combusting flows at high pressures. The main objectives of this research were to assess the potential of several turbulence models and combustion models for their abilities to predict the characteristics of high pressure combustion. Four combinations of numerical models were studied: (1) a PDF model with k-ε model, (2) a flamelet model with k-ε model, (3) a PDF model with Reynolds stress model (RSM), and (4) a flamelet model with RSM. Comparison of the numerical results with measurement data under high pressure conditions revealed: (a) good agreement of the k-ε model for corresponding cold jets with increasing pressure; (b) a greater effect of the k-ε model and RSM on flow field characteristics than combustion models at high pressure; (c) good predictions, with the exception of turbulent energy, with the RSM/PDF model.
We investigated the influence of the spherical aberration on ignition performance owing to laser beam focusing. Although ideal optical elements can produce a perfectly converging spherical wave-front, the spherical aberration of actual optical system results in a complicated intensity distribution around the focal point, which should significantly affect the laser-induced ignition of a combustible mixture. To clarify this, laser-induced breakdown in air with actual lenses was studied experimentally and numerically. Variations in the breakdown threshold and focusing profiles of the laser beam were investigated under various focusing conditions. We found that considerable influence due to spherical aberration existed in conventional laser-induced breakdown experiments. As a result, the focusing optics should be taken into consideration to minimize the effect of the spherical aberration in performing precise laser ignition experiments.
Basic experiments were carried out using the THT-IV 1-kW-class Hall-effect plasma accelerator to examine influences of magnetic field shape and strength, and acceleration channel length on performance characteristics for space propulsion. Thrusts were measured with varying magnetic field and channel structure. Exhaust plasma diagnostic measurement was also made to evaluate plume divergent angles and voltage utilization efficiencies. Ion current spatial profiles were measured with a Faraday cup, and ion energy distribution functions were estimated from data with a retarding potential analyzer. The Hall thruster was stably operated with the highest performance under an optimum acceleration channel length of 20 mm and an optimum magnetic field with a maximum strength of about 150 Gauss (0.015 Tesla) near the channel exit and with some shape considering ion acceleration directions. The optimum operational feature was discussed with measured plasma plume characteristics.
Hard surfacing layers of WC-Co/Ni-base self-fluxing alloy were successfully formed on a steel substrate using an electron beam cladding method. The WC particles were densely and homogenously dispersed within the Ni-base self-fluxing alloy without porosity. The effect of the electron beam conditions on layer formation was investigated, and the cladding layer properties were examined by hardness tests, abrasive wear tests and immersion corrosion tests. It was found that the cladding layers showed higher hardness and abrasion resistance with increasing WC-Co mixing ratio, however, corrosion resistance decreased with WC-Co mixing ratio. A coating layer having high abrasive and corrosion resistance simultaneously was achieved by multiple cladding of high WC-Co mixing ratio layers after low WC-Co mixing ratio layers.