A composite-fuel additive design method for n-decane low-temperature ignition enhancement

It is challenging to efficiently ignite traditional liquid hydrocarbons when they are applied in extreme combustion conditions, e.g., scramjet combustor. In this study, the low-temperature ignition enhancement performance of fuel additives of various properties and concentrations in n-decane were investigated theoretically and experimentally. The theoretical results indicate that there exists an optimized relationship between the effective activation energy and vaporization rate. Based on the optimization study, a novel design method for composite fuel additives was proposed. With this method, a metallic organic compound blended with a low-boiling-point auxiliary, methoxydiethylborane/tetrahydrofuran (MDEB/THF) solution, was employed to modify the ignition performance of n-decane. Thermogravimetry analysis and droplet-hot plate impinging experiment were performed to characterize the vaporization rate, ignition temperature, and ignition delay time of n-decane-based hybrid fuels. The experimental results suggest that, at a high concentration of MDEB/THF fuel droplets, the minimal ignition surface temperature is reduced to 160 °C, which is approximately 500 °C lower than that of pure n-decane. The ignition delay time of the fuel droplet is diminished from 353 ms to 45 ms at a surface temperature of 500 °C. Moreover, controlling the low-temperature ignition performance of an n-decane-based hybrid fuels by mixing various proportions of the additive was confirmed to be feasible. The results obtained from this study are of great significance in jet propellant design.