Basic study for developing supercritical spray combustion simulator

点击翻译按钮获取中文摘要

Numerical simulations were performed to examine the vaporization/cobustion characteristics for a liquid fuel droplet which was suddenly placed in an otherwise quiescent, inert/oxidizing gas at various status beyond the critical point of the fues. The vaporization/combustion characteristics were fully disclosed, together with their underlying physics. For a given ambient gas temperature, the minimum gasification/combustion time is achieved at such a pressure that the surface temperature which the droplet assumes immediately after its exposure to the hot inert gas or ignition coincides with the 'mixture' critical temperature. This pressure is far above the fuel critical pressure for a droplet gasifying in the ambient gas at a relatively low temperature, whereas the presence of flame shifts it very cose to the fuel critical pressure. Three modes of droplet vaporization were identified in the parameter space of ambient gas temperature and pressure ; (1) In the subcritical vaporization regi … More me, the droplet has the surface throughout its lifetime. (2) In the supercritical gasification regime, spatially continuous phase change occurs from the beginning. (3) Between them, there is the transient vaporization regime in which the transition from the sub-to-supercritical vaporization mode takes place.A generalized asymptotic theory was constructed to gain insight into the interactive droplet vaporization and combustion property in spray. At high pressures, a spray can be regarded as an ensemble of independent droplets pressures because the range of influence of each droplet is restricted within a short distance. A new numerical calculation method which incorporates the inherently unsteady droplet vaporization and combustion property was developed in order to transform a low-pressure spray combustion simulator at hand to a high-pressure one, in which the movements of a great number of droplets can be pursued in a Lagrangian way. Dynamic phenomena which would appear when the surface tension of droplet diminishes or vanishes were examined to approach the masked dynamic behaviors of sprays in supercritical conditions. Less