Can you put it in numbers? Like what's the cost of 100km worth of LPG vs Gasoline for your car? I'm just curious how the numbers stack up. I don't see much of a benefit to it being cleaner burning, so you'll get a little less carbon deposit on your pistons and combustion chamber, that doesn't affect the life of the engine anyway except in extreme cases usually, caused by a poorly tuned carburetor or an issue causing the engine to run overly rich. Now lack of fuel dilution of the oil is a little more beneficial since you might get more life out of your oil, but that's minimal savings unless your engine is really known for fuel dilution like my wankel engines which reek of fuel at every oil change.
LPG is a little hard to quantify because you use more of it per kilometre, at least on some systems. I’ve heard that with liquid injection systems the economy is actually better than petrol, but either way it works out cheaper because it’s a much cheaper fuel. On Venturi setups like mine, there’s a roughly 30% efficiency penalty. My car uses a Venturi style setup, which is basically a carburettor with all the guts taken out and jammed into the side of the intake.
The LPG must be in a vapour form, but it’s liquid in the tank. This is achieved using a heat exchanger. Engine coolant is used to heat up the liquid LPG which converts it into a gas which then goes to the Venturi. More advanced injection systems have fuel injectors, which squirt the LPG into the combustion chamber as a liquid. The injector atomises the LPG like it does for petrol. It’s a simpler system in a way, because you don’t need a gas converter.
As for price, LPG can be anything from 80 cents to $1.20 or more per litre, and petrol tends to be $1.50 up to $2.30 per litre for 91, which is all my car needs.
Here are two tests I did, on the highway coming home from mum’s. Same route, both at night, both with air con on the whole way. The lower figure is petrol. As a reminder, it’s a Buick 3800 Series II with a 4L60-E box.
Also, my car has a bunch of nice little features I don’t really see in other cars. But the most interesting one for me, is that if you switch the car off with the wipers going, the body control module will wait until the end of the cycle before cutting the power, so the wipers never get stuck halfway up the windscreen.
See the video.
Other things are the fact that it’s a 20 year old car and it has automatic headlights. If I had the more posh version (which I used to have until it got written off), it even used the auto headlight sensor to adjust the fan speed of the climate control. You also get speed dependent volume (which is adjustable), and you also get speed dependent windscreen wipers.
If you have a wagon, when reversing with the wipers on, the rear wiper will wipe continuously. On the higher trim models, different keys had different driver settings, so I could give someone another key, and they can set the car up however they like, and it’ll remember the profile for that driver.
These cars are full of nice little touches that only geeks like I would notice and appreciate.
P.S. here’s some more random LPG facts:
For some reason you can’t start a dual fuel car on LPG, at least not cold. What happens is that the car starts on petrol, and then automatically switches over to LPG straight away.
My car has two ECMs. One is the normal engine/gearbox ECM, but the LPG system also has its own computer, which has tentacles into the factory computer. When the engine starts and is running on LPG, the LPG computer takes over the factory one. One of the things the LPG computer does, is kill the fuel injectors. This actually sets a trouble code in the main computer for an injector voltage monitor fault, basically the computer is complaining that it’s not seeing any voltage at the fuel injectors. This is normal. Thankfully this code does not generate a CEL. It also clears itself as soon as you switch back to petrol.
You can switch between LPG and petrol on the fly, as long as you have some throttle input or some load on the engine. Switching fuels while stationary may cause a stall, because there is a short period of time where the engine is getting no fuel or gas.
When you run out of LPG, the engine doesn’t die, it just sort of… stops accelerating. Like you’ll give it throttle input but it won’t respond, the rpm will just sort of hang. At this point, you’ll switch back to petrol.
As to why LPG was ever a thing in Australia: well, we don’t drill much of our own oil. We’re very reliant on imports, which is actually a pretty decent national security risk. We don’t have more than three days of emergency fuel supply should Australia get cut off from the rest of the world for some reason. The US, I believe, has two weeks emergency supply.
But we don’t make a lot of fuel here. What we do make shitloads of, however, is coal. Apparently LPG is a byproduct of coal production, so LPG is actually something we make here. Its pricing is not at the whim of the global oil market. It’s more stable. Same deal with ethanol. We produce lots of ethanol here, and some servos stock E85, which is basically racing fuel these days. Some Commodores even ran it factory as a flex fuel setup.
Apart from the whole fuel vs food debate, ethanol is nice because it dilutes our reliance on foreign oil, same as LPG, and that can only be a good thing.
But yeah. There’s your lesson on alternative fuels.
