- Author
-
Smyth, K. C.
|
Tjossem, P. J. H.
- Title
- Radical Concentration Measurements in Hydrocarbon Diffusion Flames.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Journal
-
Applied Physics B,
Vol. 50,
499-511,
1990
- Keywords
-
diffusion flames
|
lasers
|
radical concentrations
|
absorptivity
- Identifiers
- methane/air diffusion flame
- Abstract
- Absolute OH concentrations and relative H-atom and O-atom profiles have been measured in a laminar, co-flowing methane/air diffusion flame burning at atmospheric pressure. Laser absorption and laser-induced fluorescence methods were used to probe the [equation] transition in OH. The maximum OH concentration is found to be 1.8 ±0.2 x 10(16)cm(-3) (mole fraction =5.0x10(-3)) at a temperature of 2080 K, which is twice the value calculated assuming local total equlibrium but less than half that predicted from partial equilibrium [equation]. Multiphoton ionization has been used to detect H atoms, while laser-induced fluorescence 845 nm excited by two photon absorption at 226 nm was employed to observe O atoms. In both cases it was found that low photon intensities and a retroreflected beam, Doppler-free geometry was required in order to avoid the photolytic production of the species of interest. For all of the concentration profile data it is necessary to correct the raw signals for variations in collisional quenching. In the case of the multiphoton ionization measurements the variation in electron detection sensitivity as a function of flame position must be accounted for as well. Establishing absolute H-atom and O-atom concentrations is discussed in terms of partial equilibrium considerations and detailed flame structure calculations.