Is LPG OK for 1UZ?

[cribbj]

Hi Franz, and welcome!

By way of introduction, (and this is taken from the overleaf of his book) Franz has over 38 years experience in the automobile service industry and more than 18 years with Alternative Fuel vehicles. He is also a current and past ASE certificate holder as a Master Automobile Technician, Master HD Truck Technician, Advanced Drivability, and Alternative Fuels, a member of the Society of Automotive Engineers, and possesses other licenses and certifications referencing alternative fuels and automotive service.

He is the author of one book "Diagnostic Guide to Alternative Fuels" and (I think) is currently working on another?​

Franz, we look forward to your contributions. As you've probably already seen, Lextreme is a forum for hotrodding the Toyota & Lexus UZ engine family, and lately, alternative fuels have been an active topic. Our Australian membership, as well as several in Holland and the UK are already running LPG or CNG in their vehicles, so this is old stuff for them, but it's new and interesting for many here.

 

[Cobber]

Franz,
Welcome also to the forum.

I would like to point out the that gas engines for power generation and automotive engines converted to run on gas are two very different animals. Many power generation applications are indeed lean burn engines and of considerable size. 2 and 4 stroke.

Gas engines depending on their design will require a specific ash content in the oil (generally called low, medium & high .5 - 1%) for valve and seat protection. Anyone who plays with gas engines and looks down the plug hole with a boreoscope as I do will know that the first and most important thing to look at is the exhaust valve and seat.

The oil in gas engines is designed to be somewhat sacrificial and is designed to be burnt and leave an ash on the valve and valve seats for protection.

Automotive engines the additives in the fuel (petrol) will burn and leave an ash for valve and seat protection. Here in Australia many cars when converted to LPG also have an upper cylinder lubricator fitted to add a small amount of "special" oil to the intake that burns off and leaves the required ash.
The main reason for this is the valve stem seals on an automotive petrol engine don't allow enough oil leakage to the cylinder.

Yes valve and valve seat design have improved in recent years but not to the extent where no ash protection is needed.

Of course one of the best was lead but that's long gone for automotive use.

As mentioned before we have many taxies here running around with standard engines with very high miles on the clock that have run on LPG their entire lives to no ill effect.

In my view a gas engine oil is the key to valve and seat life when running LPG in a petrol engine.

I do think that LPG is a great fuel and here in Western Australia and there is a $3,000 government grant available for private vehicle conversion. $2,000 federal and $1,000 state.

 

[cribbj]

Andy, good points about the oil. Waukesha used to recommend a medium ash oil for their natural gas engines, and they didn't suffer as many valve recession problems as we did at Cat, and we specified low ash for ours. I understand Cat's head design was improved in the late 90's, but apparently valve recession is still a problem.

 

[striker]

hmmm again something new to me.

should a good idea to keep the valves and seats in shape, but we're not allowed to do that I just found out. the only fuel-additive legal in holland is the lead substitute for very old cars, and still you need that mentioned on your cars registration paper (year of manufacture)

so helas no go here. but still on the renault it was 1 rebuild per 180.000 km and 200K was what renault thought to be the age of car at which serious work was needed anyway so that's not much off,
the Honda however is still going very nice with 220.000 on the clock. (a friends accord has done 270.000 now on the stock head.)

thing is we don't use LPG for power anywhere, it's just that petrol is so expensive we more or less must run on LPG.
1 liter of petrol @ 1.43euro($1.92) per liter VS 0.47euro($0.63) per liter of LPG + LPG is very inviromently friendly compared to petrol so a considerable road Tax bonus is also aplied every month.

as always it's a money kind of thing, and when you do enough millage the head rebuild once every 2 years doesn't matter that much.

grtz Thomas

 

[cribbj]

Thomas, sorry for confusion - it's not a fuel additive we're on about, it's the type of lubricating oil in the crankcase.

It can be difficult to find this information in "normal" specifications for passenger car oil, but it can be found out on the web if you're diligent enough.

I think using medium ash oil in an LPG fueled engine would be a winning combination and would help or minimise the valve recession.

 

[Lextreme II]

This is very interesting topic since the gas price is sky rocketing around the world. Understanding LPG and how we can prepare our engine for it would be just awesome. There many benefits and few draw back with LPG. In the US, LPG is a foreign vocabulary. As this thread develop, we are learning alot more about it.

 

[striker]

Ah that's it, thought it was a bit confusing...

I'll try and look that up in holland, never heard of it btw.

grtz Thomas

(indeed david learning more by the second here)

 

[Franz]

By and itself, octane is not an indication of power, but increased octane will allow an engine with higher compression (either static or artificial) to operate more efficiently. Propane has 104 octane compared with premium quality gasoline/petrol of 93 to 95.

A fuel with higher octane has a longer burn duration and is harder to ignite. A longer burn duration can lead to exhaust valve damage simply because the combustion process is still taking place when the exhaust valve opens, effectively torching the valve.

Ignition timing enhancements can help contain the combustion during normal processes by initiating the combustion sequence earlier (we cannot control when the combustion ends, only when it begins).

Rough rules: Engines with high compression (starting around 9.5:1) need less ignition timing advance both initial and total. These engines are also very critically dependant upon closer air-fuel ratios than low compression engines.

Engines with low compression ratios need more timing advance and are more tolerant of air to fuel ratio variations.

Lastly, there is no one-size-fits-all timing recommendation, it takes time to properly set up an engine on a rolling road dynamometer, while measuring exhaust out temps, AF ratios, detonation, and rear wheel power.

It is a careful balancing act where any single event can have a cascading effect on other events.

Franz