D-limonene is a non-toxic, non-flammable, non-carcinogenic, biodegradable, renewable hydrocarbon commercially derived from citrus rinds, with a flash point around 120, a kauri-butanol value around 67,(twice that of Stoddard solvent, but half methylene chloride), boiling point around 349f. The problem with using it for tire prep is the latent heat of vaporization. It is hydrophobic, and completely miscible in most common used chemicals except PG. If used in a solution with variables that fill in its shortcomings, a very well rounded prep can be had. Like other terpenes, it will very easily impart stickiness to a tire when heated, and will most definitely swell a tire if used in too high of concentration or in contact for too long.