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-   -   How does propane burn hotter with fewer BTU than gas? (https://ecomodder.com/forum/showthread.php/how-does-propane-burn-hotter-fewer-btu-than-21756.html)

itsnotme1988 05-04-2012 12:49 AM

How does propane burn hotter with fewer BTU than gas?
 
Had this conversation with my brother today and everything I have found shows I was wrong and propane has a higher flame temperature than gasoline. Came up because he was talking about sweepers in the warehouse where he works ran much hotter than if they were gas powered. How is this possible? From what I have found 1 gallon of gasoline has 125000BTU and 1 gallon of propane has 91700BTU.

Stan 05-04-2012 01:00 AM

Maybe it's because fuel in an ICE is metered by weight, not volume. Propane has about 22,000 btu/lb, whereas gasoline has about 17,5000 btu/lb. Or maybe it's because gasoline engines chill the incoming air charge through evaporative cooling, while propane is already vaporized before being mixed with the air.

skyking 05-04-2012 01:10 AM

as stated above, use weight instead of volume. The most convenient method for me is Gallon Gas Equivalent (GGE)
Gasoline gallon equivalent - Wikipedia, the free encyclopedia

Look how diesel shows up there, far above any other common fuel. It does indeed contribute to approximately 10% of the economy difference between a petrol and a diesel engine. The rest is due to the better efficiency of the diesel cycle.

big shafe 05-04-2012 10:08 AM

A bit technical, but the diesel cycle isn't more efficient than the otto cycle. Diesel engines are more efficient because of increased compression ratio's.

mechman600 05-04-2012 10:43 AM

Quote:

Originally Posted by big shafe (Post 305092)
A bit technical, but the diesel cycle isn't more efficient than the otto cycle. Diesel engines are more efficient because of increased compression ratio's.

+ less pumping losses because of no throttle plate
+ more energy content in fuel

big shafe 05-04-2012 10:50 AM

Compression ratio is the dominant factor for thermal efficiency, but those factors help.

Stan 05-04-2012 10:54 AM

There is a better explanation of diesel versus gasoline engines here.

Phantom 05-04-2012 01:49 PM

I think most of the reason is the air fuel ratio gasoline is 14.7lbs of air to 1lb of gas and propane is 15.67 to 1 so propane is burning one more pound of air.


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