COMBUSTION AND MICRO-EXPLOSION OF MULTICOMPONENT DROPLETS.

摘要

The present study is an experimental investigation of the gasification, combustion, and micro-explosion of droplets of miscible multicomponent fuel mixtures and water/oil emulsions in hot, oxidizing, pressurized environments. The experiment involves generating a stream of droplets of uniform and controllable size, spacing, and velocity by the ink-jet printing technique, injecting them into the continuously flowing combustion environment produced by a flat-flame burner, and examining the subsequent combustion processes using high-speed photography.;Micro-explosion of miscible multicomponent droplets is found to be favored with an unstable droplet generation mode, with increasing the system pressure, and with light alcohol addition. Specifically, micro-explosion under atmospheric pressure is not significant either for conventional fuel blends or if alkanes are the volatile components or additives. The internal bubble growth process is a relatively slow one, occupying about 10% of the droplet lifetime.;Micro-explosion of water/oil emulsion droplets occurs under both normal and high pressure environments. The oil's boiling point, however, has to exceed approximately that of undecane. Results also show that prior to the onset of micro-explosion the nominally opaque droplet becomes transparent, indicating deterioration of the emulsion structure.;Results and insights on the ignition, extinction, and soot formation characteristics are also documented.;Results show that the gasification mechanism of miscible multicomponent droplets consist of an initial phase of transient adjustment of the droplet surface layer such that it becomes more concentrated with the less volatile component, and a second phase of liquid-phase-diffusion-limited steady-state combustion with the fractional gasification rate of the constituents being equal to their respective initial mass fractions in the mixture.