Effect of H2/O2 concentration gradient on detonation re-initiation behind the pre-detonator tube

A numerical study on the effect of H2/O2 concentration gradient on detonation re-initiation behind the pre-detonator tube was carried out using an OpenFOAM based solver DCRFoam. Simulations of the processes rely on solving the Navier-Stokes equations. The results indicate that the cellular size increases with the increase of hydrogen volume fraction. And the decoupled degree of detonation is higher in the rich fuel region. The decoupled shock propagates faster but exhibit lower intensity in the rich fuel region. When the concentration gradient increases to 2.22 m-1 and 4.44 m-1, the unburned mixture is ignited to form a transverse detonation. When the concentration gradient increases to 5.55 m-1 and 6.66 m-1, the triple point in the rich fuel region is decoupled. The decoupled triple point collides with the rich fuel wall to generate a hot spot. The energy of the hot spot is too small to ignite the unburned mixture to form a transverse detonation. The diffraction, re-initiation, and self-sustained detonation processes behind the pre-detonator tube are similar under different concentration gradients. The key to the detonation re-initiation is to form a hot spot. And the formation of a transverse wave is essential to the development of self-sustained detonation. Transverse waves originate from the poor fuel region and exhibit higher intensity in the rich fuel region. © 2025