Generalized state relationships for scalar properties in nonpremixed hydrocarbon/air flames

Abstract

Generalized state-relationship correlations giving the mass fractions of major gas species (N 2, O 2, fuel, CO 2, H 2O, CO, and H 2) and temperature as functions of local fuel-equivalence ratios were studied for hydrocarbonair diffusion flames. The data base included existing measurements in laminar methane, propane, n-heptane, acetylene, and ethylene flames burning in air (or N 2 O 2 mixtures) with burner configurations involving porous cylinders in crossflow, coflowing round jet flames, and flat-laminar diffusion flames. Reasonably good generalized state-relationship correlations were found for major gas species over the available data base, which included molar fuel H C ratios in the range 1–4 and fuel-equivalence ratios in the range 10 −2–10 2. Typical of state relationships for particular fuels, the generalized state relationships approximated thermodynamic equilibrium for fuel-lean conditions and departed from equilibrium in a relatively universal manner for near-stoichiometric and fuel-rich conditions. Temperature state-relationship correlations were also reasonably good, over the more limited available data base, in view of uncertainties concerning radiative heat losses from the test flames and thermocouples. The results should be useful for estimating the scalar properties and the infrared gas-band radiation properties of laminar and turbulent hydrocarbon/air diffusion flames—the latter in conjunction with the laminar flamelet concept.