I agree with traumadog. I can see more and more people being busted for running a ‘refinery’ or ‘chemical processing plant’ in a residential area. I can also see costly permits being required. The government wants your money so they can waste it to make well connected people rich cough KBR cough but whatever they want they money. In NY IIRC about 69 cents per gallon of diesel is tax. You pay state and federal fuel tax per gallon then you pay sales tax on the price of the fuel WITH the fuel tax. Thus you pay sales tax on tax.
My feeling is that whatever happens it will not cost you less to drive XXX miles per year. Whether we drive WVO, propane, LNG, CNG, fuel cell, hybrid whatever we will pay no less. How we will pay more will remain to be seen. It could be mileage tax, higher tolls, higher registration fees, etc. Rest assured you will still pay. If the new CAFE rules reduce fuel consumption by 25% how are the government and big oil going to keep making the same money? Simple. Higher profit margins on fuel and higher marginal taxes.
Good for the governement, good for big oil, and good for the politicians as it is sold under the guise of environmental responsibility.
Back to grease. It gets cold around here. If you aren’t under a rock you should know that at 25 degrees F fryer oil is like a slippery brick. If you try to start your engine with that in the injection pump you will break something. Thus you need to start and stop the engine on diesel. I think it would be a PITA to wait five minutes whenever you need to shut the engine off. A very good engine heater would also be a necessity here. That can be a little costly to run.
I also think many people gloss over the labor. I think if you put a cost on your labor to mess with the handling the per gallon cost would be much higher.
I think grease is much more suited to stationary applications like pumps and generators. These engines don’t start and stop often nor do they move far from their fuel production station. They are also exempt from motor fuel tax so you won’t get in so much trouble in that regard.