Soot formation, spray characteristics, and structure of jet spray flames under high pressure

Coaxial jet spray flames of kerosene and oxygen are experimentally studied over a pressure range of 0.1–1.0 MPa to determine the relationship between flame structure, droplet behavior, and soot formation region, which varies with changes in pressure. The direct images and chemiluminescence spectra show that the spray flames have three regions: the blue flame region, which has a peak of CH* and C₂* radical chemiluminescence, luminous flame region caused by soot emission, and blue emission region caused by CO₂ emission. With increase in ambient pressure, the flame length shortens drastically, the luminous flame region envelopes the blue flame region, and the blue emission becomes more intense. The result of phase-Doppler anemometry shows that a large number of small droplets evaporate and disappear near the burner, and the evaporation of large droplets also occurs rapidly under high pressure. The result of temperature measurements shows that high-temperature regions appear near the burner. The flame temperature drastically decreases along the central axis, and a minimum temperature point appears. This point moves upstream with increase in ambient pressure because evaporation of the droplets occurs further upstream. A laser-induced incandescence measurement shows that the soot volume fraction does not monotonously increase or decrease with increase in ambient pressure. The soot volume fraction at the central axis becomes low upstream and high downstream. As pressure increases, the vertical position at which the peak of soot volume fraction appears at the central axis moves upstream.