Spherically symmetric droplet combustion of three and four component miscible mixtures as surrogates for Jet-A

Abstract

This study examines the droplet combustion characteristics of three and four component miscible liquid mixtures and compares the results with an aviation fuel (Jet-A) burning under the same conditions. The configuration used in the comparison is the base case of spherical symmetry whereby the droplet and flame are spherical and concentric. Mixtures consisting of n-decane/iso-octane/toluene and n-dodecane/iso-octane/1,3,5-trimethylbenzene/n-propylbenzene in specific molar ratios of 42.67/33.02/24.31 and 40.41/29.48/7.28/22.83, respectively, were previously shown to replicate certain gas phase combustion properties of Jet-A. These specific blends are assessed here for their ability to replicate combustion properties derived from the spherically symmetric case. The data compared include the evolution of the droplet, flame and soot shell diameters. The initial droplet diameter was fixed at 0.56±0.04mm in the experiments and combustion was carried out in room temperature air under normal atmospheric pressure.It was found that both blends do replicate certain features of the droplet burning process of Jet-A, though the four component blend performs slightly better. In particular, the sooting propensity and soot standoff ratios are better replicated by the four component blend which is consistent with that blend having been formulated to match the molecular weight and threshold sooting index of Jet-A. Flame standoff ratios and burning rates show a conformance suggested by fuel property variations. The liquid density is identified as a potentially important property in developing liquid surrogate fuels. The results suggest the potential of combustion properties derived from spherically symmetric droplet combustion to assist with developing surrogates for complex transportation fuels.