This discussion is running in circles and reappears over and over again.
We had started a pilot project on Bio diesel by converting a Mercedes UNIMOG truck in our logistic sector for the use of different types and blends of bio diesel. We did that in cooperation with and permission of Mercedes because it was a brand new truck. After 8 month, the injection pump died. Guess what happened.
Mercedes did not pay for the repair because the producer of that injection pump, Bosch, never cleared that pump for the use with bio diesel. After 6 more month, the engine needed new piston rings, valve seals and cylinder liners, meaning a complete overhaul.
The next tests were about long term storage of bio diesel (when being used for the emergency generator on ships for example). That stuff went bad after about six month, became totally unusable and caused some expensive tank and line cleaning.
We are done with that type of fuel for propulsion and heating. Vegetable oil or alcohol distillate type of fluids belong in the kitchen for cooking or in a bottle as rum or whiskey but not in an engine unless in an emergency situation.
A lot of public services in Germany like fire departments, road services and public transport services converted their diesel trucks, busses and special vehicles for the use of bio diesel, both as blended fuels and up to pure vegetable oil. This was not because of the reduction of costs, it was more for political correctness, for a more green image. Most of those services have come back to normal road diesel after some expensive and painfull repairs.
For sure, we have to look for alternative fuels, both due to shortage of mineral oil and due to ever rising costs. But converting human and animal food into fuel for propelling cars, ships and planes can not the way to go.
The only real alternative and green type of bio fuel are IMO the algea type bio reactor fuels that are produced with the help of sun energy. But I have no idea how much of that fuel can be produced in a mass production scenario. Up to now it seems those reactors only exist in a type of laboratory scale and environment.
Again, my personal favorite way of producing fuel for diesel engines would be converting natural gas into diesel fuel (called GTL diesel). This is the cleanest diesel fuel possible, has no disadvantages, can be produced in greatest quantities, does not require modifications on the engines or fuel lines / tanks and NG will be available for hundreds of years to come.
That will give us the time to invent the Flux Compensator or find the Delitium cristals
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