COMBUSTION OF HYDROGEN-AIR-STEAM MIXTURES IN THE PRESENCE OF REPEATEDOBSTACLES IN A CONFINED VOLUME

Flame acceleration experiments were performed in hydrogen-air and hydr ogen-air-steam mixtures in a 1.5 m-diameter, 5.7 m-high cylindrical ve ssel, fitted with repeated obstacles, to investigate the effects of ob stacles on combustion behaviour. The obstacles were made of 16.5 cm-ou ter-diameter aluminum pipes. The study included a hydrogen concentrati on range of 10 to 20%, steam concentrations of up to 40%, obstacle spa cing of 0.55 m to 1.1 m, and flow area blockages of 10% and 28%. The e xperiments were performed at an initial temperature of 128 degrees C a nd an initial pressure of 100 kPa. For all mixtures investigated the f lame speed in the vessel increased rapidly, reached a peak value at ap proximately midheight, and then decreased. The flame speed increased a s the hydrogen concentration increased. Addition of steam had a signif icant mitigating effect on combustion; the extent of mitigation, howev er, depended on steam concentration and obstacle configuration. Wherea s steam was highly effective in reducing the flame speed in a one-colu mn obstacle configuration (similar to 10% blockage), its effect. was s mall in the presence of three columns of obstacles (similar to 28% blo ckage). The flame speed increased as the blockage increased. An increa se in the obstacle spacing caused a reduction in the flame speed. Over the range of investigations, the effect of initial pressure on flame speed was small.