Critical energy of direct detonation initiation in gaseous fuel-oxygen mixtures

The critical energy of some gaseous fuels and oxygen mixtures at different initial pressure and equivalence ratios are measured based on an experiment system we developed. The determination of direct initiation of detonation is based on the overpressure signal from a pressure transducer. The effective energy responsible for the direct initiation is considered as the first quarter cycle of the current discharge. The effect of initial pressure and equivalence ratio on the critical energy of direct initiation is firstly investigated in some typical gaseous fuel (i.e., C₂H₂, C₂H₄, C₃H₈, H₂) and oxygen mixtures. It shows that the relationship between critical energy and initial pressure is inversely exponential and it is 'U' shaped between critical energy and equivalence ratio. The study of the effect of different oxygen concentration and argon dilution on the critical energy of stoichiometric acetylene and oxygen is carried out, the results indicate that oxygen concentration significantly affects the critical energy, and the critical energy increases with increasing amount of argon dilution. This study finally quantitatively research on the detonation hazard parameter (D_H) of each stoichiometric mixture. The value of D_H in increasing order for the mixtures are as following: C₂H₂-O₂, C₂H₂-O₂-50%Ar, C₂H₄-O₂, C₂H₂-O₂-65%Ar, C₂H₂-O₂-70%Ar, C₃H₈-O₂ and H₂-O₂, the results also indicate the critical energy is different by orders of magnitude if fuels do not belong to the same group.