LPG vs Liquid Fuels

On last week’s show I was extolling the virtues of diesel (modern turbo diesels) over petrol.

Someone called up off air and said “you convinced me of diesel, but what about LPG?”

It’s a good question.  LPG of course stands for liquefied petroleum gas, and is actually a mixture of butane and propane.  When it’s pressurised it turns into a liquid, and that’s the liquid you see sloshing around inside a cigarette lighter.

There are several advantages of LPG over both petrol and diesel.  The most obvious one, of course, is that its much cheaper.  But there are other advantages.

Most notable, of course, is the fact that the motors run so clean.  The reason for this is quite straightforward.  Simply put, as soon as it leaves the fuel tank it is already a gas.  Both petrol and diesel, on the other hand, are of course liquids, and the fuel delivery system on your car, whether it be a carburettor or fuel injectors, has the job of doing its level best to turn that liquid into a gas.

Unfortunately, this process is less than perfect, particularly on the older type diesels, and the consequence of this is that your engine gets some liquid fuel that doesn’t burn and runs down into the sump.

Now, as we have seen, the combustion of fuels is less than perfect, with one of the products being carbon.  The most likely place for this to form is on the surface of one of the liquid fuel droplets, as the inside of the drop would not contain any oxygen, so it’s the right conditions for the oxygen starvation that’s will result in carbon, instead of CO2.

Because it forms in the drop, it then falls into your sump and hence the dirty oil.

But with LPG since it is a gas, the tiny particles of carbon that may form just get blown out of the engine..

So LPG is a great choice from that standpoint.  The only disadvantage it has, is that if you run out of fuel, it’s a towing job to refill.  If you’re going for a drive in the country, a second problem emerges – it’s not that easy to find service stations that sell it.

But one of the things that puzzles me most about LPG is that so few car manufacturers make it as a factory option.  The only attempt at a dedicated LPG vehicle of course is the Falcon, but it was a pretty poor attempt.  But I don’t understand why other manufacturers paint make dedicated LPG vehicles – I reckon they’d sell like hotcakes.

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