Explosion behavior predictions of syngas/air mixtures with dilutions at elevated pressures: Explosion and intrinsic flame instability parameters

Explosion processes of H₂/CO/air mixtures with diluents are experimentally investigated with a confined vessel. Explosion pressure and maximum rate of pressure rise are obtained and results show that explosion pressure increases firstly and then decreases with increasing equivalence ratios. The maximum rate of pressure rise increases all the time when the combustible mixture becomes richer. When CO₂ and H₂O are added into the mixture, both explosion pressure and maximum rate of pressure rise decrease and CO₂ addition has a stronger effect. Except for the explosion parameters, intrinsic flame instability parameters are also needed in order to evaluate the deflagration index of full-scale cases at higher pressure from lab-scale experiment. When CO₂ and H₂O are added into the mixture, both Markstein length and critical Peclet number decrease and the effect of CO₂ is stronger. For critical radius, it is always decreasing with the addition of diluents but H₂O addition may lead to the postponing of the onset of self-acceleration when CO/H₂ ratio is higher. Linear instability theory could predict the critical radius quantitatively, but it is not accurate enough. The acceleration exponent increases firstly after the flame radius is larger than a critical value and then reaches a constant value of around 1.18, which is quite different from theoretical one, 1.5. In addition, the average cell sizes are obtained by theoretical calculation and results show CO₂ and H₂O have the similar effect on the cellular structure and intrinsic flame instability of syngas mixture and the effect of CO₂ is relatively stronger.