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Original Articles

OH Concentration in an Atmospheric-Pressure Methane-Air Flame from Molecular-Beam Mass Spectrometry and Laser-Absorption Spectroscopy

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Pages 225-239 | Received 11 Aug 1981, Accepted 01 Feb 1982, Published online: 10 May 2007
 

Abstract

The concentration of lhe OH radical in a stoichiometric methane-air flat flame at atmospheric pressure was measured with both laser-absorption spectroscopy and molecular-beam mass spectrometry (MBMS). The nonequilibrium peak OH concentrations and the OH decay rate measured from the two techniques were in good agreement. The OH profile from the MBMS measurements, however, was shifted downstream from the absorption measurements by the MBMS sampling process. A comparison of temperature profiles from thermocouple measurements and from a molecular-beam time-of-flight technique exhibited a similar downstream shift. The MBMS measurements effectively sampled the gas properties approximately five orifice diameters ahead of the sampling-probe tip. Perturbation of the OH concentration profile using various sampling probes indicate the importance of minimizing the length of the sampling-orifice channel to reduce composition relaxation during sampling.

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