Study on the Atomization Gasification, Mixing and Combustuin Processes of Liquid fuel Jets in Supercritical Enironments

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Analyzes were made of characteristic processes involved in the combustion of sprays which are formed when liquid fuel is injected into the air whose thermodynamic state exceeds the critical point of the fuel. The following were found. ( 1) Despite the convectional belief that droplet auto-ignition delay time shortens monotonically with increasing pressure, it was found that the droplet auto-ignition delay time takes a peak at the ambient states near to the fuel critical point. This secular behavior is due to the influence of the phase equilibrium condition at droplet surface. Considering that current diesel engines operate at such condition, this knowledge addresses an interesting problem of finding an optimum spray condition for fast combustion. (2) Atomization is a keytechnology to spray combustion. However, the understanding of atomization mechanism involved in high-pressure sprays used in liquid rocket engines and diesel engines are very poor because optical observation is very difficult at high pressures. The current concept is based on the knowledge obtained from the experiments of water jet atomization at standard pressure. We examined the instability of jets with near-critical mixing surface and found a new instability mode with growth rate proportional to jet speed, which can make the liquid jetbroken into droplets with short spacing with the aids of hydrodynamic action. This finding theoretically bases the formation of dense sprays constituting of fine droplets at high pressures, if we regard a low-speed liquid jet as one of the liquid ligaments formed in the turbulent atomization process of an injected liquid. Furthermore, we studies (3) the mechanism of rapid flame propagation through combustible vortices formed in the process of turbulent mixing and (4) the modes of flame spreading between droplets for a various kind of sprays.