Fuel distillation affects spray flame blowout thresholds

Emulation of prevaporized real fuel combustion behaviors through use of surrogates has been widely demonstrated in the literature. However, many combustion applications utilize atomized fuel sprays, and for these configurations, the prevaporized combustion assumption of fuel property homogeneity becomes tenuous. Our previous work uses a simplified ASTM D86-relevant distilling droplet model to demonstrate the real potential for vaporization-coupled deviations from single-valued surrogate fuel combustion properties that are characteristic of prevaporized combustion. Further, simulations reveal surrogate-to-surrogate differences in one or more of the combustion properties (such as ignitibility, H/C/O atomic ratios, average molecular weight, and sooting propensity) among sets of effectively equivalent prevaporized surrogates as each similar fuel distills. The present experimental work supports these model-based observations with flame blowout measurements from a custom-built annular spray burner rig. Initial measurements demonstrate the sensitivity of the new experimental setup by comparing chemistry-driven blowout behavior of 1) fully linear and fully branched alkanes of nearly equal chain length (nC7, iC8) and with otherwise similar physical properties, and 2) spray-coupled blowout in the chemically similar homologous family of n-alkanes (nC7, nC10, nC12). Subsequently, sets of essentially equivalent prevaporized jet fuel and gasoline surrogates suggested in the literature are tested to examine blowout threshold variations driven by distillation behavior. The noted variations in blowout limits (and also allowing for other limiting combustion behaviors not studied here) highlights the need to consider the coupling between distillation and prevaporized combustion properties when formulating and evaluating surrogate fuels.