How is my vehicle powered – how does petrol make my engine work? Part 1 0

engine mechanismIn a nutshell, the fuel our car uses is a specific ‘fraction’ extracted from the refining of crude oil, which is a naturally occurring liquid, formed from the remains of animals and plants that lived millions of years ago, and were compressed by billions of gallons of sea water. Imagine crude oil is a box of coloured sweets…well, refining sorts all the colours out, so all the red ones are separated from the green ones, and the blue ones etc. Rather than by colour, the fractions of crude oil are differentiated by the size of their hydrocarbon molecules. So we have petrol – made up of molecules of roughly the same size, and similarly diesel is made up of slightly larger molecules, and there are also other fractions – tar, aircraft fuel and fuel oil amongst others…lots of different coloured sweets.

Once the oil companies have got crude oil out of the ground, a wonderful network of pipelines through the frozen Russian steppes, and huge oil tankers ploughing the oceans, deliver the black gold to oil refineries. The UK has a number of such refineries. When those oil refineries have finished their refining – sorting their sweets – petrol lorries deliver the prize sweets; highly flammable petrol and diesel to your local petrol station. Its quite amazing really, the logistics involved. You can then pump the fuel into your vehicle’s petrol tank at a per-litre price, less than it costs to buy spring water…and all they have to do to get that is put a bucket in a stream (probably somewhat naive ).

So, you have filled your fuel tank…and spent your hard earned cash. What happens then?

Petrol, or diesel, in its liquid form is as we all know highly flammable. Holding a lighter to a puddle of petrol would leave you with a hot burning fire but probably not a great deal more. It might even leave you with severe burns on your hand, so don’t try at home, ‘eh?  Fuel burns (you may remember from chemistry in school) consuming oxygen in the air, and produces heat together with exhaust gases – carbon dioxide and steam predominantly, and smaller amounts of (mostly nasty) other gases.

Importantly, the space taken up by the exhaust gases is much much greater than the space that the original petrol and oxygen took up to start with. This is due to the gases produced, and a lot of heat. If liquid petrol is combusting in the open air this extra volume and heat just dissipates into the atmosphere, most probably to the good of no one.

In an internal combustion engine…like the one in your car…a couple of special things happen to get something much more useful from the burning fuel – what physicists would call useful ‘work’…….

Part 2, Part 3

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