Propagation characteristics of hydrogen-air deflagration need to be understood for an accurate risk assessment. Especially, flame propagation velocity is most important factor. Propagation velocity of spherical flame has been estimated based upon the propagation velocity of flat flame; however, existing method is not enough to estimate the actual propagation velocity because cellular flame front is formed in hydrogen-air premixed flame. In this study, we investigated the propagation characteristics of hydrogen-air deflagration in explosion tests using a closed chamber which has large windows, 300mm in diameter. Explosion tests were conducted at atmospheric pressure and room temperature and in the range of equivalent ratio from 0.3 to 1.0. By using Schlieren photography, flame propagation phenomena were observed, and flame radius and flame propagation velocity were measured. These results showed that the flame propagation velocity of hydrogen-air mixture is accelerated owing to developing of cellular flame in a huge space. Based upon these results, an estimation method of flame propagation characteristics was proposed.
