h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

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I don't see what the problem is. Some bus companies in Europe have been running buses on rape seed oil for almost 20 years, and it doesn't seem to have done them much harm. Sure, there's a costly engine conversion to get them to run efficiently, but the benefits are paid back in the long run. That's one of the reasons why public transport is cheaper on the continent compared to in the UK, another being that public transport is still public owned but that's another story.

I think the problem he was referring to applied to using diesel made from reacting waste vegetable oil and and NaOH in common diesel engines that already exist in many vehicles today, not to using vegetable oil (waste or otherwise) itself as a fuel. I've not heard of any IC engines burning vegetable oils for fuel. I find it quite a novel concept - why are such oils more beneficial than more traditional fossil fuels like diesel and gasoline? I can't imagine that complete combustion is more easily attained with such relatively high weight organic compounds. Not only that, but I'm nearly positive that even crudely produced rapeseed oil is far more expensive to produce per liter than gasoline or diesel (note I said produce, not sell or buy - taxes, economics, laws, embargos, etc. can all affect the price as well as the production costs of the fuels, but I would still be surprised to learn of any advantages in production costs of vegetable oil over other fossil fuels). Besides that, I'm interested to know how such an engine achieves complete combustion, how it achieves fewer pollutants than the burning of a fossil fuel like gasoline and diesel. From a strictly chemical and mechanical engineering standpoint I find it hard to accept - but then I could be merely just out of touch! So, enlighten me!

Diesel engines at the 1900 World Fair were demonstrated running on peanut oil by Rudolf Diesel.
The problem with running diesel engines on vegetable oils (or animal fats) is that their viscosity is far higher at ambient temperatures than mineral diesel oil. The biodiesel methods overcome this by removing the most viscous portion of the oils. However clean, dry Straight Vegetable Oil (SVO) can be used simply by heating the oil to around 60deg C at which temperature its viscosity matches that of normal diesel. This has the advantage of leaving in the chemicals that provide the best lubrication, a desirable element in diesel fuel. The lubricity of SVO exceeds that of both diesel oil and biodiesel.

The environmental benefits of SVO are: low levels of heavy metals and low levels of sulphur giving lower levels of exhaust pollutants (excepting oxides of nitrogen), and carbon neutrality in that the CO2 released by the exhaust is equal to the amount of CO2 taken up by the growing plant to produce the oil.
The last point becomes problematical when the energy inputs and CO2 outputs for fertilizer, transport, processing and packaging are considered.
However for Waste Vegetable Oil (WVO) these inputs occur irrespective of the final use, and so can be ignored when looking at the environmental cost.

Some diesel injector pumps are able to cope with the high viscosity of room temperature vegetable oils. There are numerous reports of German drivers of unmodified diesel Mercedes fuelling their cars with salad oil. And motoring happily. For some, however, injection pump failure and coking of injectors have occurred.