要約

This work presents an extended analysis of the external structure of multi-phase and -component fuel counterflow diffusion flame. The model assumes the main fuel in gaseous and liquid phases with addition of secondary gaseous fuel. The spray-flamelet is described by means of the Schvab−Zel'dovich−Liñán formulation. The droplets are described by a uniform mono-sized distribution and vaporize completely before the flame, working as an extra source of gaseous fuel. No relative velocity between droplets and gaseous phase is considered. The model exhibits a general spray combustion parameter combining chemical reaction, flow field, and spray properties. The aim of the analysis is to identify how the external structure of the spray-flamelet is affected by addition of methane or hydrogen in a spray of ethanol or n-heptane. The results point out that by substituting the gaseous part of the main fuel by methane does not affect significantly the spray flame structure. The same occurs for small gaseous injection of hydrogen. The negligible differences are due to non-unity Lewis number. For these cases, a quasi-universal behavior of the spray-flamelet is identified. For larger amounts of hydrogen, higher flame temperatures are obtained compared to the earlier cases. For a given dimensionless incoming condition and changing the liquid main fuel, the combustion characteristics and the flame structure are very similar. Consequently, independent of the spray fuel considered by injecting the same secondary fuel, the dimensionless temperature, species mass fraction, mixture fraction and excess of enthalpy, show a quasi-universal behavior for the external structure of the spray-flamelet.