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

Sometimes I hear people saying oh you can run your diesel vehicle on vegetable oil. I know that there are people around who are quite able to produce biodiesel from vege oil at home (as opposed to it being something only specialist businesses can do), but it annoys me when people talk about it in a way that makes it seem much easier than it is. I want some simple answers I can give to that assertion. So just to be sure:

1. Is it possible to run a diesel vehicle on vegetable oil without first converting it? Why not?

2. What's the simplest, one paragraph explanation of the conversion process? Something that explains what the oil has to convert to and how.


kea.

There´s an episode of Mythbusters where you see them running a diesel car on nothing but filtered, used vegetable oil. The mileage was apparently not too bad either.

Yes, you can run a diesel engine on pure vegetable oil...

My ex father did it quite often with the last car he owned (Renault - with a 1.9 litre Turbo diesel engine)

I don't think his mileage was too bad, but what I've no idea about is whether or not he was doing any long-term damage to the engine... (other bits of the car fell to pieces before the engine did so he ended up scrapping it and buying a petrol engined car

What was noticable however is that the car smelt like a McDonald's when it was running on oil.

Whoops - for "ex father" read "ex father in law" - I got divorced, I didn't commit patricide

I assume you´d have to somehow empty all the diesel out before pouring vegetable oil into the tank.

He didn't - in fact, he started off with about 20% vegetable oil in a tank and slowly built up the percentages until he was running the thing on oil alone.

That´s suprising. I can imagine an engine running on one thing or the other, but I would have thought mixing them would mess things up.

So how come we're all using diesel and not oil?

What was his source of oil do you know, Whisky? Was it used oil?

Did it smell inside the car, or just outside?

>What was his source of oil do you know, Whisky?<

I think there's a clue in his description of the smell

WHat's the price of vegetable oil? I can get Diesel for about 99 cents a litre.

Why are we using diesel instead of oil?

Various reasons:
1) Who knows what it'll do to your engine over the long term
2) Certainly in the UK, if you happen to be stopped by HM Customs & Excise because your car smells like a chip shop, you'll get done for not paying excise duty on your fuel (you should theoretically declare the fuel you're using to your local customs office and pay some kind of duty on it - even if its old chip fat).

What oil was he using?

He was actually using brand new oil, bought from a cash & carry in 25 litre drums.

How much did it cost?

Not a great deal less than filling up with normal diesel - but his reasoning was that at least cooking oil is theoretically carbon-neutral and a more renewable energy source than fossil fuels.

It would be considerably cheaper if you were to use 'used' oil, but you've got to filter it carefully... Black Crunchy Bits getting into your cylinders would make a hell of a mess of the engine.


And, as far as I'm aware, to do it properly, you're supposed to add something to the cooking oil to adjust its chemical properties to stop it ruining your engine - but engines will run on the stuff without any additives.

About filtering used oil - there's a company here in Sweden (the only one of its kind in this country as far as I know) that collects used fat in tank trucks from the restaurants, whether it be oil, butter or margarine that has been used for frying (the fat is stored in big thanks in the basement of the establishments until collection). The purified fat is then used to make soaps etc. - I wonder if it might be used as fuel as well?

I´ve been in places where large areas of jungle have been cut down to grow palm oil for biofuel. It does not seem very ecological to me.

That's what worries me about biofuel. I don't really know that much - but have heard that it hasn't been thought through. Food has become more expensive because large areas have been turned into fuel production and palm oil is environmentally destructive. Are these real fears or scare stories - one hardly knows whether to believe the media?

Yep, it's true. Biodiesel is at best a short term transition tool to post-peak oil society, but swapping food for oil is completely insane. Not surprise there.


>>1) Who knows what it'll do to your engine over the long term<<

So, we have a cheap source of fuel (used fat) and no-one's done the science yet on how it works in practice?


>>And, as far as I'm aware, to do it properly, you're supposed to add something to the cooking oil to adjust its chemical properties to stop it ruining your engine - but engines will run on the stuff without any additives.<<

I think you have to do a conversion, so you add chemicals, repeatedly, and you end up with biodiesel and a waste product. It kind of sounded a bit like soap making last time I looked at it


Re the filtering, wouldn't the fuel filter make sure nothing untoward got through?

Xan, there's no reason why we can't use used oil, but we cut down the jungle for all sorts of stupid reasons

Well, there´s not enough used oil to run that many cars. I´d just like us to avoid cutting down jungle for this extra reason.

I am old enough to remember when a household only had one car at the most - and people walked or caught the bus. It was true to say that obesity was not a common then either. Society is so addicted to personal cars - my neighbours have 5 cars!! (and motorbikes for fun as well)

When I was young, Dublin had about 500,000 people, all living within about four miles of the centre. The public transport was adequate. Now it's a city of a million people, with many people as far as 10 miles from the centre, and people commuting from other towns as far as 80 miles away as well, and the public transport is no better than it was. So one car is no longer enough per family. If we are to do without cars, the city will have to be redesigned. This is one of the big challenges, and applies even more so to American cities.

Link to EG entry on biodiesel: A460667