Effect of Synthetic Aviation Fuels on the Stochastic Ignition of Fuel Droplets on Hot Surfaces

When a flammable liquid is put in contact with a very hot surface, thermal ignition of fuel vapors can occur. In the event of a leak, this process, called hot surface ignition, can lead to fires in aircrafts, spacecrafts, vehicles, and machinery. In the aerospace industry, design practices and certification processes must ensure that this fire hazard is mitigated. In the present work, we performed experiments to assess whether sustainable aviation fuels have a different hot surface ignition behavior compared to petroleum-derived jet fuel. In a canonical configuration, 2.5mm fuel droplets were released onto a high temperature optically accessible surface. After a 150mm fall representative of a typical aircraft engine compartment, the droplets broke up upon impact and ignition occured if the surface temperature was sufficiently high. The temperature of ignition was quantified and we found that all investigated fuels had a similar or higher hot surface ignition temperature to jet-A in this configuration. The temperature of ignition spanned a 70K range for the 4 fuels investigated. High speed shadowgraphy revealed the effect of fuel surface tension on the droplet break-up process, and high speed chemiluminescence imaging revealed the multi-step ignition process that the droplet underwent.