Characteristics of outwardly propagating spherical flames of R134a(C2H2F4)/CH4/O-2/N-2 mixtures in a constant volume combustion chamber

摘要

The characteristics of the outwardly propagating premixed flames of stoichiometric mixtures of R134a/CH4/O-2/N-2 have been experimentally investigated in a constant volume combustion chamber. Three regimes of the expanding flames were categorized based on the flame behavior. In the typical regime, a conventional outwardly propagating spherical flame was observed. The laminar burning velocity was correlated reasonably well as a function of the concentrations of oxygen and methane. When the concentration of R134a was relatively high, the buoyancy-induced regime, where the flame rises vertically while propagating outwardly, was observed. Phenomenological analysis in which the Richardson number and the Froude number were used to characterize the rising flames confirmed that the main cause of this phenomenon was buoyancy resulting from the difference between the densities of unburned and burned gases. The dimensionless velocity, which is based on the concept of the Damkohler number, explained the mechanism controlling the characteristic of the flame behavior. In addition, an intermediate transition regime existed between the two regimes. (C) 2015 Elsevier Ltd. All rights reserved.