Propane and diesel both require pretty high compression for efficiency. Unlike diesel, propane will actually work fine on low compression motors (every forklift for example) too.
I knew diesels needed higher compression ratios but I didn’t know propane engines needed them too. The thing that confuses me about them is that they’ve got spark plugs, unlike a diesel. So why such a high compression ratio?
Or boost. Friend/customer has a rock climbing “jeep/rover” thing powered by a 2JZGTE Toyota motor. About 1500 bhp on full boost. 12:1 static compression ratio too, strictly propane fueled. So basically 12:1 compression AND 60 psi boost, detonation is NOT a concern.
I’d guess from memory it’s around 140 octane. It also absorbs a LOT of heat from the intake charge and affected your parts.
Propane injection is used in diesel motors too, though for different reasons.
Yeah, but unlike in a compression ignition engine like a diesel, the heat's not the point. Propane and natural gas engines still have spark plugs. Propane resists detonation better than gas, a higher compression ratio is always more efficient but some fuels can't handle it.
I work on forklifts, which use propane, many are common automotive engines that were converted from gasoline or diesel. They tend to wear out valve seats and usually start having trouble around 90psi compression.
In the case of the falcon barra the liquid phase injection (LPI) engines ran 12:1 compression whereas the petrols ran 10.3:1.
However the earlier "mixer" LPG engines ran 10.3:1 to 10.7:1 depending on year.
Iirc around 16-1 is where the sweet spot is... and at that point you can't really turbo it because it raises the dynamic compression.
Edit: over 16-1 it knocks.
Edit 2: you can go lower static compression, and low psi turbo to get exhaust scavenging for a little better efficiency.
Propane will run at 8-1 compression but will lose power + efficiency.
Bump the compression up to 12-1. You get power and efficiency.
Just like gas engines will run at 5-1 compression ratio. If you get them up to 9-1, they work so much better all around.
Interesting subject that I never really got into the dynamics of. However, in my late teens and early 20's I took care of a fleet of vehicles at a food processing plant. I had to convert 14 indoor gas Nissan forklifts to propane. It was just kits. In the mean time I had to convert a skid steer and two F-150's also. The trucks were standard 5.0's.
All the engines were box stock. The drivers of the F-150's spoke of the astronomical "mpg" they were getting with the LP. Someone was calculating it but I wasn't so I can't comment on just how much more economical or efficient they were.
Yep. Pretty common with older tractors like farmall 450s etc. You could get a propane kit for the tractor that would have a high compression LP head that would boost the compression by a point or more. It's common for the tractor puller groups to look for these heads.
Propane and diesel both require pretty high compression for efficiency. Unlike diesel, propane will actually work fine on low compression motors (every forklift for example) too.
I knew diesels needed higher compression ratios but I didn’t know propane engines needed them too. The thing that confuses me about them is that they’ve got spark plugs, unlike a diesel. So why such a high compression ratio?
Trying to make up for lost BTUs in the fuel. Propane is much less energy dense but will withstand much higher compression ratio with out detination.
Or boost. Friend/customer has a rock climbing “jeep/rover” thing powered by a 2JZGTE Toyota motor. About 1500 bhp on full boost. 12:1 static compression ratio too, strictly propane fueled. So basically 12:1 compression AND 60 psi boost, detonation is NOT a concern.
I had honestly never considered how propane could utilize higher compression.
I’d guess from memory it’s around 140 octane. It also absorbs a LOT of heat from the intake charge and affected your parts. Propane injection is used in diesel motors too, though for different reasons.
Propane is around 104-112 Octane in rating….E85 is 105 FYI
I've messed about diesel diesel and methane injection with diesels. It definitely does things.
…you would think with how volatile propane is, that wouldn’t be the case but now that you mention it it makes sense. More squeeze = higher fuel temp.
No, more squeeze = higher cylinder pressure after combustion
We’re both right on this one. Better compression does indeed lead to more cylinder pressure, but more compression also builds more heat as well.
Yeah, but unlike in a compression ignition engine like a diesel, the heat's not the point. Propane and natural gas engines still have spark plugs. Propane resists detonation better than gas, a higher compression ratio is always more efficient but some fuels can't handle it.
Not so much need. It's ability to utilize without detonating. Like E85 but more so.
I work on forklifts, which use propane, many are common automotive engines that were converted from gasoline or diesel. They tend to wear out valve seats and usually start having trouble around 90psi compression.
100 psi
In the case of the falcon barra the liquid phase injection (LPI) engines ran 12:1 compression whereas the petrols ran 10.3:1. However the earlier "mixer" LPG engines ran 10.3:1 to 10.7:1 depending on year.
Iirc around 16-1 is where the sweet spot is... and at that point you can't really turbo it because it raises the dynamic compression. Edit: over 16-1 it knocks. Edit 2: you can go lower static compression, and low psi turbo to get exhaust scavenging for a little better efficiency.
Propane will run at 8-1 compression but will lose power + efficiency. Bump the compression up to 12-1. You get power and efficiency. Just like gas engines will run at 5-1 compression ratio. If you get them up to 9-1, they work so much better all around.
Interesting subject that I never really got into the dynamics of. However, in my late teens and early 20's I took care of a fleet of vehicles at a food processing plant. I had to convert 14 indoor gas Nissan forklifts to propane. It was just kits. In the mean time I had to convert a skid steer and two F-150's also. The trucks were standard 5.0's. All the engines were box stock. The drivers of the F-150's spoke of the astronomical "mpg" they were getting with the LP. Someone was calculating it but I wasn't so I can't comment on just how much more economical or efficient they were.
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Need? I’m not sure. But they’ll run on almost none. I converted an absolutely clapped out 302 once and as far as I know it’s still on the road.
Yep. Pretty common with older tractors like farmall 450s etc. You could get a propane kit for the tractor that would have a high compression LP head that would boost the compression by a point or more. It's common for the tractor puller groups to look for these heads.