Soot formation and temperature field structurein co-flow laminar methane–air diffusion flamesat pressures from 10 to 60 atm

摘要

The effects of pressure on soot formation and the structure of the temperature field were studied in coflowmethane–air laminar diffusion flames over a wide pressure range, from 10 to 60 atm in a high-pressurecombustion chamber. The selected fuel mass flow rate provided diffusion flames in which the soot was completelyoxidized within the visible flame envelope and the flame was stable at all pressures considered. Thespatially resolved soot volume fraction and soot temperature were measured by spectral soot emission as afunction of pressure. The visible (luminous) flame height remained almost unchanged from 10 to 100 atm.Peak soot concentrations showed a strong dependence on pressure at relatively lower pressures; but thisdependence got weaker as the pressure is increased. The maximum conversion of the fuel’s carbon to soot,12.6%, was observed at 60 atm at approximately the mid-height of the flame. Radial temperature gradientswithin the flame increased with pressure and decreased with flame height above the burner rim. Higherradial temperature gradients near the burner exit at higher pressures mean that the thermal diffusion fromthe hot regions of the flame towards the flame centerline is enhanced. This leads to higher fuel pyrolysisrates causing accelerated soot nucleation and growth as the pressure increases.