Sooting propensities of novel cage hydrocarbon propellants

Abstract

The absolute sooting propensities of three bishomocubane-based cage hydrocarbon fuels– bis(nitratomethyl)-1–3-bishomocubane (DNMBHC), 1,3-Bishomocubane dimer (BHCD), and diazido-dimethyl-bishomocubane (DADMBHC) having potential for propulsive applications were estimated using the full field light extinction technique (LE). The results were compared against relative soot volume fraction measurements obtained using color-ratio pyrometry (CRP). The Rayleigh assumption used in this study was validated by TEM (transmission electron microscopy) measurements. The experiments were conducted using the tethered droplet combustion technique in ambient air under normal gravity conditions. The sooting propensities of 10% w/w blends of the novel BHC fuels with an RP-1 surrogate fuel (RP-1-s) were also studied along with other fuels, includingn-dodecane, methylcyclohexane, isocetane, and dicyclopentadiene (DCPD), which was the starting fuel for the synthesis of the novel BHC compounds. Results indicate an excellent match in the sooting propensities estimated using the two methods despite considerable differences in the estimation methodologies. The novel BHC fuels were extremely sooty compared to RP-1-s and its constituent components on account of their caged molecular structure that favoured the formation of polyaromatic hydrocarbons (PAHs). The assumption of a constant soot dispersion exponent in CRP was judged as having consequences similar to the assumption of a constant soot refractive index in the LE method. The LE technique was assessed as more robust in comparison to CRP as it could capture soot emissions outside the luminous flame zone and had significantly lower uncertainties than CRP for sooty fuels..