Naphtha, or more precisely, Varnish Makers and Painters Naphtha, VM&P Naphtha, is a mixture of fairly volatile solvents, mostly parafins, a few olefins and aromatics. That's what's used to thin oil based paints. It dries without residue and can be used in different applications besides paint thinning. Example, as a lubricant for Teflon paste extrusion. It has even been used in certain medical applications because of its residue free finish.

It burns clean having similar power potential to isooctane. Hence the reports of how well it does in plane engines. Octane is rather low but our engines are not compressed enough to cause pre or post ignition or detonation. Nevertheless, in very hot conditions it could cause some vapor locking.x

It's very volatile, more so than gasoline. It has a flash point lower than 100 degrees which means there are enough vapors around to support ignition at relatively low temp (around 60F)