Numerical analysis of laminar combustion of fuel gas clouds

• Published in: Combustion and flame 1999-09, Vol.118 (4), p.669-683
• Main Authors: Librovich, B.V., Makhviladze, G.M., Roberts, J.P., Yakush, S.E.
• Format: Article
• Language: English
• Subjects: Applied sciences; Combustion. Flame; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Theoretical studies; Theoretical studies. Data and constants. Metering
• ISSN: 0010-2180; 1556-2921
• DOI: 10.1016/S0010-2180(99)00054-1

Combustion of finite amounts of fuel gas in an oxidizer atmosphere is studied numerically using one-dimensional spherical geometry. Calculations are performed for nonpremixed octane fuel clouds ignited at the periphery and for premixed clouds ignited at the center or at the periphery, with the reaction rate described by a one-step global chemical kinetic scheme. Flame front coordinates are obtained as function of time for different initial fuel concentrations. The numerical results obtained are compared with the analytical solutions available. For initially unmixed fuel clouds the effects of variation of gas properties with the temperature are studied. Solutions obtained for constant density and transport coefficients are compared with the results obtained in the calculations where density and transport coefficient variations were alternatively taken into account. Gas expansion is shown to change the cloud size up to several times while increase in the transport coefficients results in higher burning rates. Both factors make the characteristics of cloud combustion different from those studied previously assuming constant gas properties. Combustion of fuel-rich premixed clouds is featured through the existence of two reaction zones, of which one propagates as a premixed flame, while the other one is a diffusion flame burning out the remaining fuel. The trajectories of both flames are studied in detail for the cases of central and peripheral ignition. The dependencies of the burnup time on the initial fuel concentration obtained for the unmixed and premixed clouds are compared.