Experimental and numerical investigation of micro scale hydrogen diffusion flames

The characteristics of microscale hydrogen diffusion flames produced from sub-millimeter diameter (d = 0.2 and 0.48 mm) tubes were studied using non-intrusive UV Raman scattering coupled with LIPF technique. Qualitative two-dimensional OH imaging indicated that a spherical flame was formed with a radius of about 1 mm as the tube diameter was reduced to 0.2 mm. The coupled effect of ambient air leakage and pre-heating enhanced thermal diffusion of H₂ led to lean-burn conditions for the flame. The calculated characteristic features and properties indicated that the buoyancy effect is minor while the flames are in the convectiondiffusion controlled regime because of low Peclet number. The effect of Peclet number on the flame shape was minor as the flame was in the convection diffusion controlled regime. Comparisons between the predicted and measured data indicated that the trends of temperature, major species, and OH distributions are properly modeled. However, the code did not properly predict the air entrainment and pre-heating enhanced thermal-diffusive effects. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).