Combustion of hydrogen–air mixtures in a tube with annular ignition

The combustion dynamics for hydrogen–air mixtures with a hydrogen content of $15$ and $20$ vol $\%$ in tubes with an annular cross section and central and annular ignition was studied experimentally. In studying annular ignition, the width of the ring gap was varied. The dynamics and structure of the flame front were determined by shadow imaging and high-speed video recording. The optimal value of the size of the ring gap, which provides the maximum velocity of the flame front at the initial stage of propagation, was established. The slowing of the flame before transition to a quasi-plane front was also obtained. The results can be used in developing advanced power plants using both combustion and detonation of hydrogen–air mixtures.