Gaseous nitromethane and nitromethane-oxygen mixtures: A new detonation structure

Detonation in gaseous nitromethane (NM) and mixed with O-2 has been studied. Experiments were performed in a preheated steel tube at an initial temperature T-0 congruent to 390 K for different initial pressures P-0 (1.7 greater than or equal to P-0 greater than or equal to 5 10(-2) bar). Different selfsustained detonation regimes were obtained, from multiheaded mode to spinning and galloping mode in marginal conditions. These chemical systems were characterized by a specific detonation cellular structure very different from that currently observed with classical gaseous CnHm/O-2/N-2 mixtures. All modes of detonation propagation in rich NM/O-2 mixtures exhibit a double scale cellular structure. The pattern of this double scale structure is particularly clear in the case of spinning mode.