Does an additive exist to decrease the freezing point of jet fuel? I have found an additive that decrease the freezing point generated by drops of water (appears between 0 and -10°C), but I'm needing to reduce the freezing of the fuel (-45°C).
There is an additive known as a Fuel System Icing Inhibitor (FSII), it is designed to be mixed with the fuel of non-fuel heated aircraft i.e military. Mixed in at about 0.10-0.15% is optimal to reduce the formation of ice crystals, which will stop it freezing.
Alternatively, Jet A-1 fuel has a freezing point of -47°C, which is below your threshold and could be useful. Or if Jet A-1 is unavailable you could try Jet B which has a lower freezing point of -60°C, but is more dangerous to handle, and is less prevalent and hence unavailable at many locations.
Question to Wehrner von Braun: "Why did you name it Saturn?". Answer: "It was the one after Jupiter!"
The lower freezing jet fuel is Jet B.
Jet fuel (kerosene) is taken from a higher boiling fraction than "naphtha" (gasoline) when refining crude oil. A mixture of kerosene and naphtha will lower the freezing point. This is how Jet B is made.
Before doing this in your garage, make sure there is no water in the mix, as frozen ice crystals will be present at much higher temperatures.