TEMPERATURE AND CO CONCENTRATION MEASUREMENTS IN A PARTIALLY PREMIXED CH₄/AIR COFLOWING JET FLAME USING COHERENT ANTI-STOKES RAMAN SCATTERING

Abstract

In a partially premixed methane/air flame, temperature and CO concentration measurements were conducted using coherent anti-Stokes Raman spectroscopy. Additionally, qualitative two-dimensional OH laser-induced fluorescence imaging was applied. Measurements were performed at different positions downstream of the burner's exit for equivalence ratios (φ) between 1.7 and 4.0. A distinct double-flame structure was observed. Accurate temperature and CO concentration results were achieved, even under sooting conditions. Temperature measurements close to the burner (5 mm downstream) indicated a temperature peak of 2000 K while further downstream at 10 and 20 mm a high-temperature plateau could be found. The CO concentration increases with decreasing φ starting below a particular threshold value. It was a maximum at the inner flame due to the formation of CO as a result of partial combustion. The maximum CO is found to be greater than that in a diffusion flame. The maximum CO concentration has been found for φ = 1.7, the upper ignition limit for CH₄/air mixtures. OH measurements indicate that OH is mainly formed in the outer flame and is consumed there by reactions with CO and H₂ diffusing from the inner flame.

Keywords:

• partially premixed flame
• temperature
• CO concentration
• CARS

The authors gratefully acknowledge financial support of parts of this work by Deutsche Forschungsgemeinschaft and by Volkswagen-Stiftung. Alexander von Humboldt Stiftung, Germany, supported A. Datta for his research stay at LTT-Erlangen where this work was conducted. The LIF measurements were performed by Volker Wagner.