Propane Vehicles

[Thehardway]

It's from experience here in NZ, it's Natural Gas, that sucks. It was used in the past, but an engine running on it looses too much power. LPG (a propane / butane mix) is still used, and works well, with little power loss, good economy and arguably better engine life. It's generally only used in fleet vehicles that are doing high mileage, where you get a sensible payback.

Safety? There is an extra regular safety inspection for gas powered vehicles. But in terms of accidents, they don't seem to be involved in any more incidents than petrol. When you think about it, carry a big can of petrol around in your car isn't 100% safe either....

This is just observations from a place where the fuels HAVE been tried on a fairly large scale.

Ian

I think the experience here is the US is exactly opposite.  I have driven a lot of LPG converted forklifts and they are gutless.  When on gasoline they work just fine.  All those who have CNG converted US vehicles seem to be very pleased and see no appreciable loss in power and much cleaner oil and extended engine life. 

I have heard that US diesel fuel for automobiles is much lower in quality than that used in europe, australia, and africa and gasoline here is better than in those countries. Don't know much about NZ.  I suspect volume of use and competition for better product is the determining factor for quality.

Not saying you are wrong Ianab, I believe you are correct in your country, I just don't know how well it applies here in the US and suspect quality of fuel source is the culprit.

[John Mc]

I think the experience here is the US is exactly opposite.  I have driven a lot of LPG converted forklifts and they are gutless.  When on gasoline they work just fine.  All those who have CNG converted US vehicles seem to be very pleased and see no appreciable loss in power and much cleaner oil and extended engine life. 
...

Not saying you are wrong Ianab, I believe you are correct in your country, I just don't know how well it applies here in the US and suspect quality of fuel source is the culprit.

I might suspect the quality of the propane conversion, or the fork truck itself for that poor performance.  We had a fleet of propane forklifts at the wire plant where I used to work in Ohio. When it came time to replace them, we leased a bunch of brand new 6000 and 8000# rated trucks.  The 8000# trucks were complete dogs.  The 6000# models were great - started easy, ran smooth, good power. The difference was so noticeable, that all of our 8000# trucks were WELL under the allowed hours of run time on the lease. All of the 6000# were way over.

They were all from the same manufacturer... closer examination revealed that the engines were from different suppliers (the good-running 6000# fork trucks were Mitsubishi engines, if I recall. I can't remember the other engine.)

[Randy88]

Not saying it explains it all, but most dual fueled engine are designed for one or the other fuel and set to burn both.   I'm also told there is a difference in timing of the engine for one or the other, not sure which now is which, and also the compression is usually slightly higher for lp gas engine, due to the lower btu content on those, the same reason why a gasoline pickup converted over to run on lp won't get quite the same performance and fuel economy as one designed for lp gas.    Those conversion done also start harder in the winter verses one designed for lp gas specifically, or at least that is the explanation I was given in the past when I asked.

With the newer engines, the timing can be computer advanced where as years ago, that wasn't as easily done and things only advanced slightly.   

I've also been told lp gas engines ran a slightly hotter spark plug in them too, verses gasoline engines, or at least that's what I remembered from decades ago, we had a lp gas tractor and an identical gasoline tractor, the plugs, and timing were different, along with if I recall the compression and also the valve adjustment was also different if I recall, but I could be wrong, that's been over 30 years ago now and my memory isn't what it used to be.   

Just something to toss into the discussion, not sure it matters much if any.   

[John Mc]

I know when I converted an old generator to from gas to run on either propane or gasoline, the conversion kit came with a recommendation to re-gap the spark plug for better performance on propane. (I'm not sure, but I think I recall that they wanted a larger gap for propane?) That might jibe with what Randy is remembering about hotter spark plugs for LP engines?

[Ianab]

Not saying you are wrong Ianab, I believe you are correct in your country, I just don't know how well it applies here in the US and suspect quality of fuel source is the culprit.

You are probably correct about the fuel. LPG is a blend of Propane and Butane. If the % of the mix changes then so does it's power output. Likely you have a different mix? This changes the air / gas ratio, power output, and optimal engine tuning. Where LPG is commonly used as motor fuel they try and keep the mix pretty standard, then the engines can be tuned to run on it properly. If the mix varies, the fuel air mix is likely to be "out" most of the time. Running a heater or furnace, it doesn't really matter what the blend is, it just burns slightly hotter or cooler, but you stIll stay warm.

Also because the octane rating is higher it will work better with higher compression engines and slightly advanced timing. Different from the standard petrol setting anyway.

Both CNG and LPG should burn pretty clean as they are relatively pure and mixed as gasses, so get more complete combustion. So clean oil and good engine life for both.

But it was the lower power and shorter range of CNG that killed it off here. CNG tanks have to be heavier to take the pressure, and don't hold as many pounds of fuel (gas vs a liquid). CNG is also a mixed gas, methane and ethane, so again the % in the mix can vary and change things.

Ian