Derek Bradley, Tawfiq Abdul-Aziz-Al-Mughanam, Adriana Palacios

Abstract:

The paper compares and contrasts heat release and flame quenching in both jet and premixed flames. Atmospheric jet flame heat release rates of a variety of fuels at blow-off are first discussed. It also reports burning data on less reactive fuels in a small 3 mm diameter pipe. Further analysis of an atmospheric methane jet flame reveals it to require a significantly greater volume for a given heat release rate than a stoichiometric premixed atmospheric methane-air flame. It is also shown that H2 and C2H2 exhibit high reactivity in both types of flame, and the heavier hydrocarbons exhibit low reactivity. A generalised, dimensionless, correlation of atmospheric flame blow-off data, covering many fuels, is the source of data for the derivation of practical values of heat release rates, at different such velocities on the 3 mm diameter pipe. This mathematical modelling and the experiments explore the differences between fuel jet and premixed combustion, and enable volumetric heat release rates to be evaluated and compared. The greater control that is possible with premixed flames makes for more compact combustion. It was found that the volumetric heat release rate of a methane atmospheric jet flame was 8.2 MW/m3, whilst an optimal design of a more compact premixed burner design resulted in a significantly higher value of 416 MW/m3. There are, nevertheless, strong underlying similarities in flame structures between jet and premixed flames, revealed through the propagation parameters, Ub* and K, and the quenching parameters, Db/δk and dk/δk. A Quench Diagram shows quench lines for different fuels, below which flame quenching occurs, and above which flames can propagate.

Keywords: Blow-off, Jet flames, Premixed flames, Volumetric heat release rate, Quenching of flames.

Date Published: May 8, 2025
DOI: 10.11159/jffhmt.2025.018

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