Effects of nitrates on hydrocarbon-air flames and detonations

Abstract. The subject of hydrocarbon sensitization by nitrates under conditions of a heterogeneous spray has been of interest due to its applicability in promoting ignition. To gain insight into the mechanisms of the nitrate sensitization effect, the present work was limited to vapour phase studies at elevated temperatures in order to avoid the influence of heterogeneous factors. The experiments performed included studies of flammability, flame propagation, shock ignition and detonation. The mixtures used were composed of air, hexane, 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 experiments, the measured ignition delay and detonation cell size had minimum values for IPN-air and maximum values for hexane-air. With increases in the IPN concentration, the ignition delay and detonation cell size fell monotonically between the values for hexane and IPN. This monotonic behaviour was explained to be the result of mixing the hydrocarbon with the more sensitive nitrate whose energetics are larger than or comparable to the hydrocarbon when mixed with air. For the slow combustion mode, the results also confirmed the monotonic behavior and showed that the lean flammability limit and the flame velocity fell between those of the hydrocarbon and IPN.