Effects of nitrates on hydrocarbon-air flames and detonations

The subject of hydrocarbon sensitization by nitrates under conditions of a heterogeneous spray has been of interest due to its applicability in promot ing ignition. To gain insight into the mechanisms of the nitrate sensitizat ion effect: the present work was limited to vapour phase studies at elevate d temperatures in order to avoid the influence of heterogeneous factors. Th e experiments performed included studies of flammability, flame propagation , shock ignition and detonation. The mixtures used were composed of air, he xane, and isopropyl nitrate (IPN) with IPN concentrations ranging from 0 to 100 mole % in hydrocarbon-IPN. In addition, methane and propane were also included in the flame experiments. For the shock ignition and detonation ex periments, the measured ignition delay and detonation cell size had minimum values for IPN-air and maximum values for hexane-air. With increases in th e IPN concentration, the ignition delay and detonation cell size fell monot onically between the values for hexane and IPN. This monotonic behaviour wa s explained to he the result of mixing the hydrocarbon with the more sensit ive nitrate whose energetics are larger than or comparable to the hydrocarb on when mixed with air. For the slow combustion mode, the results also conf irmed the monotonic behavior and showed that the lean flammability limit an d the flame velocity fell between those of the hydrocarbon and IPN.