Detonation structure and detonability of C2H4-O-2 mixtures at elevated initial temperature

We have studied the influence of initial pressure (P-0 = 0.05-1 bar) and te mperature (T-0 = 300 500 K) on the detonation structure of three: acetylene -oxygen based mixtures. Two were stoichiometric, C2H2 + 2.5 O-2 and C2H2 2.5 O-2 + 3.5 Ar and one was lean, C2H2 + 10 O-2 The gaseous mixtures were heated by the detonation tube itself which was electrically heated by Joule effect at a rate of about 100 K per minute. Experimental results show that the detonation cell size lambda of the stoichiometric mixtures increases w ith To and is nearly independent of this parameter for the lean one. The ev olution of the cell size with respect to the initial temperature and pressu re is reasonably well predicted through the ZND model using global or detai led kinetics. Calculations show that the influence of To on cell size depen ds strongly on the value of the reduced global activation energy Ea/RTZND o f the given mixture. The critical diameter de of detonation transmission from a tube into a larg e volume and the critical radius of curvature Re of spherical detonation in itiation have been studied using the two stoichiometric mixtures at elevate d initial temperature. Results indicate that the classical relationships d( C) congruent to 13 lambda (CJ) and R-C congruent to 20 lambda (CJ) hold als o in these conditions. As a consequence, because of increasing lambda with T-0, the detonability of the stoichiometric mixtures drops at elevated temp erature.