A quasi-adiabatic laminar flat flame burner for high temperature calibration

Abstract

Flat flame burners were developed for many purposes. In this study, a new flat flame burner for the high temperature calibration of combustion product species and temperature is presented. The burner is operated on methane/air mixtures. Equivalence ratios can be varied from ϕ = 0.65 to ϕ = 1.5. A flat, laminar, premixed flame stabilizes above the flame holder that is manufactured from porous material and differently to other designs is not water cooled. Unlike most other realizations, the flame burns detached by 1.5–2.5 mm from the flame holder. This is realized by adjusting the exit speed to a value very close to the burning velocity of the corresponding equivalence ratio. As the control range between flame blow-off and attachment to the flame holder is very narrow, this strategy requires spatially very uniform porous materials and a precise mass flow control. Heat losses to the flame holder necessary for flame stabilization are minimized furthermost by these detached flames. This becomes manifested by a temperature rise of the flame holder by less than 10 K and an almost homogeneous temperature distribution within the flame holder. In consequence, flame temperatures measured by Rayleigh thermometry are observed to be close to adiabatic flame temperatures. Differences between adiabatic and measured temperatures depend on the equivalence ratio and range from 35 K to 50 K. By comparison with 1D-flame simulations with and without radiation models, it is shown that these temperature losses are mainly due to radiation but not to heat conduction to the flame holder. For this reason, flames stabilized on this burner are termed quasi-adiabatic as they exhibit exhaust gas temperatures very similar to freely propagating flames.