Flammability limits of alternative aviation fuels
Alternative aviation fuels are being developed recently to partially replace the limited resources of traditional liquid fuels in the aviation industry. The fire-safety properties of these fuels, however, are unknown. Especially, the flammability limit of a fuel is a crucial parameter. The present work focuses on measurements of concentration and temperature flammability limits of four pure hydrocarbon fuels, as well as traditional and alternative aviation fuels, including Jet-A, HEFA, SIP, and FT-S8. The lower and upper concentration flammability limits of these selected fuels were determined under specific temperatures and pressures. An experiment including a customized power supply system to generate sufficient spark energy for ignition near the flammability limits was built to measure the lower and upper limits. The temperature flammability limits were also measured using a different experimental apparatus for the four selected aviation fuels. As the initial temperature increases, the lower concentration flammability limit decreases. In terms of the fuel-air mass ratio, the limit is within the range of 0.032-0.04 for all four aviation fuels. The upper flammability limit increases with temperature within a range of 0.21-0.23 except for SIP. Unlike temperature, pressure has minor influence on the lower concentration flammability limit for all fuels. Among the four aviation fuels, Jet-A and HEFA have similar results, and FT-S8 is considered to be least sensitive with temperature variation. Three correlations and models were used to predict the lower concentration flammability limits of the four pure fuels. The predictions were compared to the measurements. As for temperature flammability limits, SIP has the highest lower temperature flammability limit. From this perspective, SIP can be considered a better choice for alternative aviation fuels for safer storage and transportation during ground operations. HEFA has similar results as Jet-A, while FT-S8 has smaller lower temperature flammability limit than Jet-A and HEFA.^
Li Qiao, Purdue University.