(a) “Diesel fuel” means any liquid that is commonly or commercially known or sold as a fuel that is suitable for use in a diesel-powered highway vehicle. A liquid meets this requirement if, without further processing or blending, the liquid has practical and commercial fitness for use in the engine of a diesel-powered highway vehicle.

However, a liquid does not possess this practical and commercial fitness solely by reason of its possible or rare use as a fuel in the engine of a diesel-powered highway vehicle.

“Diesel fuel” does not include kerosene, gasoline, liquified petroleum gas, natural gas in liquid or gaseous form, or alcohol.