Influence of gellant and drag-reducing agent on the ignition characteristics of typical liquid hydrocarbon fuels

This experimental research studies the ignition of fuel particles (droplets) in a high-temperature air medium. Two groups of fuel compositions are considered: the first one is based on kerosene, the second one is based on diesel fuel, with gellant (silicon dioxide) and drag-reducing agent (polyhexene) added to them, respectively. The following compositions were used: K-100 (100% kerosene), K-99 (1 wt% silicon dioxide), K-95 (5 wt% silicon dioxide), K-90 (10 wt% silicon dioxide), K-85 (15 wt% silicon dioxide), D-100 (100% diesel fuel), D-FTA (0.04 wt% ForeFTA drag-reducing agent according to TU 2458-002-10022,712-2015), and D-FTA02 (0.04 wt% ForeFTA-02 drag-reducing agent according to TU 20.59.42-015-10022,712-2018). Fuels K-100, D-100, D-FTA, and D-FTA02 behave like Newtonian fluids with constant viscosity vs. shear rate. Kerosene gels K-99 and K-95 behave like non-Newtonian fluids, exhibiting a shear-thinning property, and decrease in viscosity with an increase in the shear rate. Kerosene gels K-90 and K-85 are incapable of flowing and appear to be “solids”. Single fuel particles (droplets) were ignited in a heated air medium at temperatures 873–1273 K. Using a system of high-speed video recording, we established that at various initial temperatures of the compositions, different in the concentrations and appearance of fuel components, an identical set of physical and chemical processes occurs during the induction period, whose duration corresponds to the ignition delay time. These are roughly the same as the processes, occurring when liquid fuels are ignited in a normal state (without gellants or agents). The lowest temperature of heated air, at which fuel compositions are ignited, is 873 K. This value can be notionally referred to as the auto-ignition temperature of fuel when conducting the experiments under the said conditions. The ignition delay times for K-100 and K-99 droplets are identical, whereas for K-95, K-90, and K-85, they are 10–30% longer than the induction period for liquid fuel droplets in a normal state. Compositions based on diesel fuel with 0.04% of drag-reducing agent feature puffing of droplets, when heated, though this process does not affect ignition delay times as the main process characteristic.