Now for those who don't know, propane is the mother of diesel tuning.
Essentially, Propane acts as a catalyst when combined with diesel fuel. When propane is added to diesel fuel, almost 100% of the fuel is burned (as opposed to approximately 75% without propane injection) which is what gives you the "powershot" of torque, horsepower and fuel economy.
Normally (especially with older diesel cars that you see smoking alot), a large proportion of diesel fuel is unburnt in the combustion chamber as the temperature around the outside is not high enough for the diesel to combust. The remaining fuel is wasted and expelled through exhaust.
It is cheap, usually easy to install, and unlike N2O thanks to its nature, it improves fuel economy rather than ruining it. And another massive plus, it breaks down any carbon build up in your engine.
I did a quick search and nothing came up here. I know the BMW engine bays are fairly full as a rule, so obviously this makes things difficult. But has anyone heard of anyone doing it in a relatively new BMW (E36+) before? Google brings up nothing and I'm sure alot of people have never even heard of it, but I thought it'd be worth a try.