As this thread has moved onto the topic of "alternative" fuels, I hope no one minds if I post this regarding some of the terminology used. Unfortunatly I often find that use of the wrong terms can lead to confusion and create difficulties when trying to understand someones point. Can I also add that this is a genuine attempt to make this subject easier to understand and is certainly not a dig at anyone who may have used the terms differently.
Here are what I believe to be the generally accepted usages.
Biofuel:- A generic term that includes all non mineral derived fuels.
Biodiesel:- A specific type of Biofuel refered to as a F.A.M.E. Fatty Acid Methyl Ester. see here.
http://en.wikipedia.org/wiki/Fatty_acid_methyl_ester
Although usualy derived from vegtable oil can actualy also be made from animal fats and even algie, by using a process known as transesterification. Pump diesel now contains between 2 & 5% biodiesel as the need to reduce sulpher content, the lubricant in mineral diesel, means that an alternative lubricant was required, a function Biodiesel performs very well.
This I believe is the most missused term, often used when refering to Biofuels or Vegtable oils.
Vegtable oil:- This can be split into 2 catagories S.V.O. Straight Vegtable oil, the stuff you buy from Tesco Asda etc. and W.V.O. Waste Vegtable Oil, ex chip shop oil filtered and cleaned.
The main difference between V.O. and Biodiesel is that a component part of V.O. is Glycerin. It is this that causes the oil to become "sticky" when cold and generally causes the problems, W.V.O. is worse in this respect.
It is this that the transesterification process removes in order to make Biodiesel. This is why I believe that using the correct terminology is important as many of the so called problems caused by Biodiesel are actualy caused by using Vegtable Oil.
Having said that however many diesel engines will run quite happily on V.O. providing they are at opporating temperature and the oil is heated to around 80'c.
For anyone who has got this far without being bored silly here are a couple of sites you may find of interest.
http://en.wikipedia.org/wiki/Biodiesel
http://www.dieselveg.com/
http://journeytoforever.org/biofuel_...rofRapeOil.pdf