Do we artificially add a smell to jet fuel?
Aviation fuels are all hydrocarbons that have fairly strong natural odors, so no additives are necessary to give them a noticeable smell. Jet-A1 is refined kerosene, which has a distinctive smell which some find unpleasant and others not. Aviation Gasoline (AVGAS) has many "aromatic" hydrocarbons to boost octane which are called aromatic because of their distinctive odors. 

So you can smell a fuel spill or leak pretty easily, for at least AVGAS I know this from experience. I once had a fuel leak which filled the cockpit with avgas fumes, I got a lungful before I managed to ventilate the cockpit and it was very unpleasant!