Most Jet engine fuel systems have means to heat the fuel to prevent it from freezing. Typical heat exchange methods followed are by employing hot air or hot oil taken from the engine.

Reference: FAA [Aviation Maintenance Technician Handbook, Chapter 14: Aircraft Fuel System][1]


  [1]: https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/amt_airframe_hb_vol_1.pdf