Utilizing Liquified-Petroleum-Gas (LPG) Fuels and Liquid-H 2 to Improve the Thermal-Lift-Capacity of Aerospace Platforms

This paper studies the increase of thermal-management-system (TMS) cooling-capacity achieved by cooling petroleum-based hydrocarbon or liquid-H2 fuels to near their cryogenic liquid freezing points of ~ 14 K to 92 K. This cooling provides an ~ 4-10x increase of delta-T and therefore TMS cooling capacity for exhaust temperatures of ~ 100 °C, compared to JP8 or kerosene-based fuels at ambient temperatures. And even higher cooling capacities are achieved ~ 10-100x for liquid-H2 warmed from 20 K to 1950 K for combustion. Hydrocarbon fuels studied include alkane compositions (CxH2x+2) with x = 1-4; a.k.a. methane (M, CH4,), ethane (E, C2H6), propane (P, C3H8), butane (B, C4H10) and complex mixtures of (M+E, M+P, and M+E+P), and also liquid-H2. The paper demonstrates that significant increases of volume density ~ 15-20% are also achieved for all hydrocarbon fuels cooled to cryogenic temperatures, and the cryo-liquid volume densities reach within ~ 10-20% of JP8 fuel at ambient temperatures (-10 °C to 20 °C). The density increase to near that of JP8 does not occur for liquid-methane, however is observed for other hydrocarbon cryo-liquids including ethane, propane, and butane and mixtures of methane-ethane-propane (M+P, M+E, or M+E+P). All hydrocarbon fuels studied have ~ 15-30 % higher heats of combustion density than JP8, so for constant fuel energies the cryo-cooled fuels can have reduced vessel volumes or increases ranged compared to JP8. Finally it is demonstrated for a 1 MW aircraft, that cooling capacities of ~ 100-120 kW can be achieved with either liquid-hydrocarbon or liquid-H2 fuels, which is ~ 4x higher than the public-known TMS limits for fighter jet aircraft.