Which is cheaper to run LPG or Diesel car

The only Skodas I'm familiar with are '70 carburetted slugs. :-)

That's surprising. It's certainly not a difficult thing...

That's disappointing.

We get some pretty crap stuff like that here, too.

No, I'm saying that if you are going to compare fuel systems, you should compare similar technologies. The fact that a technology is available for petrol but not for LPG _yet_ means that the LPG equipment currently commercially available is not really comparable to the petrol injection systems currently available. In spite of this, a simple mixer system _can_ equal a petrol injection system, indicating that an improvement in LPG technology would make the LPG

It is to me. :-)

Almost all of the conversion work that I've done has been carby V8s that are converted to straight LPG. Compression ratio increases, manifold changes, etc. are par for the course.

A simple conversion to me is where you remove the entire petrol system and install a nice simple LPG system.

Indeed, I probably went a little far for someone who is trying to work out whether converting a boring little petrol engine to LPG will result in better running costs than a similarly boring little diesel. :-p

Only if the engine is designed to not be compatible with LPG.

Most engine types are fine with LPG, but some are not.

"Cooling" has nothing to do with it.

LPG does not wash oil off the bores like petrol does (particularly during cold starts), has less damaging by-products in the blow-by and hence cleaner engine oil, etc.. As such, an engine that is compatible with LPG can achieve life expectancies of 5 to 7 times that of the same engine on petrol, even in dual-fuel systems. A straight LPG engine can achieve better still.

The main issue with highly tuned petrol engines such as the Honda items mentioned above is consistency of mixture. They are building engines that _require_ mixture control far better than a simple LPG mixer can achieve. Build a reliable liquid-phase injection system and it should work better than petrol ever could in the same engine.

You following me around again? :-p

Misinformation or technical incompetence.

Mind you, you could argue that the correct mixture does keep the combustion at the "right" temperature, while a transient lean mixture allows it to be too hot...

Nope. Even trying hard to make it sound like "cooling", I can't.

I'd have to guess that whoever made the claim simply knew that there was a problem with running LPG in the engines without having any real idea why.

nah . I've been here for ages...

bit of both..

but the same thing would be said about lean petrol..

lpg runs fine in all the motors I have used it in . 7 so far..

clueless :_) ( they were indeed ) experience tells me a well tuned lpg engine runs every bit as well as conventional petrol and considerably cleaner and with a similar output with little work .

Yeah, okay. It's a fairly multi-national group in spite of being in the uk. heirarchy...

Well, I'm in the real world, even if it isn't the UK. :-)

Given that fuel is cheaper here than there, that strikes me as a ludicrous situation! With your fuel prices, I'd expect the manufacturers to be falling over themselves to market dedicated LPG models.

Our LPG is getting additional tax phased in over a few years starting in 2008 IIRC. :-( Still cheaper than petrol but getting closer. :-(

On or around 1 Mar 2005 03:30:18 GMT, athol enlightened us thusly:

depends on the engine. tuning parts for big V8s are readily available, such as HC pistons, say. probably not so easy for an average eurobox. and, indeed, modern euroboxes have quite high compression engines anyway.

but in any case, you're probably talking engine out and considerable work on it, which will add a lot of labour compared to fitting a kit, and increase the cost accordingly. Labour rates for that sort of work in the UK are fairly high if you want someone that knows their job, and I doubt it'd be worth it in most people's eyes, especially given that you lose the ability to run on petrol in an emergency, and the gas supply position, while still improving, is not such that I'd want to rely on it without arranging to have at least 300 mile tank range; which in itself is not too easy. The petrol tanks on modern cars are mostly silly shapes, and thereby larger by a good bit than the sort of gas tank you can get on it.

On or around 1 Mar 2005 03:38:12 GMT, athol enlightened us thusly:

a good closed loop system ought to work - after all, that's what the petrol system is anyway.

I have heard about Honda's problems, and Ford had problems with early Zetec(?) engines. This also seemed to be because they were using marginal materials.

But LPG is not generally damaging to engines. In fact quite the opposite.

I could tell you about a '60s one I owned once as a teenager. The handbook (a literal translation) said that to start the car you had to turn the key until you felt it snap. That was only the start of the problems.

Skoda now are (apparently) an entirely different proposition.

Possibly not, but if you are not undertaking the work yourself it may be unreasonably expensive. I doubt many converters would undertake it; I doubt many owners would want to pay for it.

The internal combustion engine is pretty crap in the first place (a paltry 25% or so efficiency is considered good), but usually a properly done conversion is OK.

But we *have* to compare dissimilar technologies - they are all we have. To do otherwise misses the whole point of the original question. But I look forward to a time when liquid phase LPG injection is readily available.

Well that is good news, but I have to say that you are the only person I have heard it from. Unless you redesign an engine around LPG (which is not the point at issue here), you have to make compromises when converting. This usually means a little more consumption and a little less power.

But I agree that the potential of LPG is there.

Hmmm, marginal materials is not somethign Honda have been noted for, quite the opposite. Just check out the manufacturing technique for the new Diesel.

Yes that seems to be the general advertising I see from the LPG suppliers, but not from the car manufacturers.

I understand that LPG is a cleaner fuel, that much is not rocket science.

No manufacturer is going to advertise something it doesn't supply.

Or advertise the bad points.

That's pretty much the accepted norm for dual fuel.

Some years ago, a company called Parnell something were playing with liquid injection. They modified petrol injectors to avoid getting vapour behind the pintle and ran them in an essentially unmodified engine. Apparently they got to something like 3 times the petrol horsepower from a BMW 6-cyl, got worried about the bottom end and deliberately detuned the fuel system.

Using the latent heat of vapourisation to cool the intake air meant that the density was much higher - much like supercharging but with no mechanical pumping and the extra heat that goes along with that.

Unfortunately, the modified injectors had a life expectancy of about 30,000km. :-(

On or around 2 Mar 2005 04:28:43 GMT, athol enlightened us thusly:

I reckon I could live with that, if I could get that much power out of it...

I had thought about trying to run a K-jet (continuous injection) system on liquid LPG. The fuel pump pressure on the k-jet is already about 5.5bar or something.

Unlike the fuel pump pressure on my disco, buggrit, which is zero 'cos the pump ain't running.

Luvly an' all. Combine that with a CR more in keeping with the octane rating of LPG and you should get a dramatic improvement in efficiency, too. Smaller engines, more power, less pollutants, less consumption.

They tend to freeze up, too, apparently. And I believe there are other problems to be solved with metering and delivery.

Having said that, the Channel 4 website briefly refers to Tickford's conversions for Ford, and says they are liquid phase. They may be talking crap, though - I can't find any other reference to it, and they talk crap elsewhere on the site.

I was reading the abstract of a research document somewhere on the web a while ago. It seemed to imply that liquid phase LPG injection showed marked improvements in mixture formation and flame propagation only if the inlet valve was open at the moment of injection. If the valve is closed it was worse, which suggests that a CI system like K-Jet probably wouldn't be suitable.