Flame heights and fraction of stoichiometric air entrained for rectangular turbulent jet fires in a sub-atmospheric pressure

Abstract

This paper investigates the flame height and the fraction of stoichiometric air entrained (n, the basic parameter in flame heights correlation) for rectangular turbulent jet fires at sub-atmospheric pressure, for which no data are available in the literature. Comprehensive experiments are carried out in a naturally sub-atmospheric pressure (Lhasa city, 64kPa) by rectangular nozzles whose aspect ratio varied from 1:1 to 1:71. The flame heights are measured and correlated by the unified formula suggested by Quintiere and Grove which was obtained at standard atmospheric pressure, meanwhile the change of the important parameter, n or Cf (reflecting air entrainment into flame and thus being basic in flame height correlation) in the sub-atmospheric pressure is addressed. It is found that: (a) the flame height in the sub-atmospheric pressure can be well approached by the unified formula suggested by Quintiere and Grove; however (b) the correlation parameter Cf is larger (1.6 times that in standard pressure) or the value of n is smaller (73% of that in standard pressure) in the sub-atmospheric pressure than that in the standard pressure. The relative change of n at the sub-atmospheric pressure is then theoretically deduced from the change of entrainment strength (C1) and flame envelope along with pressure drop. The theoretically deduced ratio of n (or Cf) between these two pressures agrees with the experimentally correlated results. Then, by accounting for the changes of the correlation parameters, a proposed explicit model can generally predict the flame heights in both pressures.