Critical energy for direct initiation of C ₂H ₄-O ₂ mixture

The detonation cell size for the C ₂H ₄-O ₂ mixture was predicted by chemical kinetics and Ng's model. And together with Lee's surface energy model, the critical energy was estimated for the direct initiation of spherical detonation in the C ₂H ₄-O ₂ mixture under different initial pressures and at different equivalence ratios. The direct initiation was performed via a high voltage capacitor spark discharge and the critical energy was accurately determined from the current output analysis. Good a-greement was found between the theoretical prediction and the experimental measurement. Through steady ZND analyses based on a comprehensive kinetic mechanism and by using the improved semi-empirical correlation by Ng, the factor in the relation between the cell size and its ZND induction zone length, i.e., non-dimensional parameter A, was determined at different initial pressures and equivalence ratios as following: A=43.815(1+p/p ₀)-0.12371 and A=8.531 exp (φ/3.135)+28.644, respectively. The cell size can be calculated ultimately from these correlations, and the experimentally measured cell sizes agree well with the theoretical prediction data. The cell size is considered as an input intermediate characteristic parameter and used to estimate the critical energy for direct initiation based on Lee's surface energy model. The combination of chemical kinetics and theoretical models may form a quantitative theory to predict the critical energy for direct initiation. The theoretical curve fit of the parametric relationship between the critical initiation energy and the initial pressure as well as the equivalence ratio is E _c=0.332 (p/p ₀)-2.017 and E _c=exp[3.951 (φ-1.401) 2-1.9], respectively.