Global characteristics of hydrogen-hydrocarbon blended fuels turbulent diffusion flames

Abstract

The global performance of a series of attached turbulent diffusion flames using different hydrogen-ethylene fuel blends is reported for H2 volume fractions varying from 33 to 100%. The parameters assessed are the flame length, radiant fraction and emission indices of NOx and CO. For blended flames with constant exit strain rate, a transition regime was found for H2 fractions in the range 50%-65%. Below this range the flames are ethylene dominated while above this they are hydrogen dominated. The normalized flame length, Lf/dj, decreases with an increasing H2/mix ratio and this relationship becomes approximately linear as H2 fraction is varied from 70% to 100%. The NOx emission index for blended fuels tends to increase with H2 fraction, although for lower strain rate the trend is reversed for H2 fractions above 70%. The CO emission index also generally increases with H2 fraction for ethylene-hydrogen flames, except for very high H2 fractions, especially for flames with lower strain rate.