Flammability limits and explosion characteristics of toluene-nitrous oxide mixtures

Flammability limits and explosion characteristics of toluene-nitrous oxide mixtures are experimentally determined in an 8 l spherical vessel, and are compared with corresponding values of toluene-air mixtures. The experiments, performed at atmospheric pressure and at an initial temperature of 70 °C, show that the flammable range of toluene in nitrous oxide (0.25-22.5 mol%) is about three times as wide as the corresponding range of toluene in air (1.3-7.1 mol%). Maximum values of the explosion pressure ratio and the deflagration index, KG, are clearly higher when nitrous oxide is applied as an oxidizer. This can be attributed to the increased flame temperature and burning velocity of toluene-nitrous oxide flames. Moreover, extremely high values of KG for near-stoichiometric mixtures in combination with strong acoustic oscillations in the pressure signals of these mixtures indicate the existence of a flame accelerating mechanism. These phenomena are enhanced when an initial pressure of 6 bara is applied. Finally, when evaluating the lower flammability limit, it was found that pure nitrous oxide decomposes at pressures above 4.5 bara when applying an ignition energy of about 10 J.