BTU per pound Propane vs ULSD

[MEXICOWANDERER]

Having a devil of a time with web connection. For friends in the mountains. RV patio heater.

Thank You

My interest is I visit them 🙂

[kellertx5er]

MEXICOWANDERER wrote:
Since LPG has a weight per cubic foot density similar to diesel it would make sense that BTU specs would be the same. However substituting LPG as a motor fuel reveals a drastic sum difference in economy. This is curious.

Water has 20% greater density than diesel, but I have yet to find a way to burn it!

[MrWizard]

i was thinking something similar
engine operation, depends on flame propagation and the pressure created in the combustion chamber, to drive the piston down

[JaxDad]

MEXICOWANDERER wrote:
Since LPG has a weight per cubic foot density similar to diesel it would make sense that BTU specs would be the same. However substituting LPG as a motor fuel reveals a drastic sum difference in economy. This is curious.

Simple science actually, propane makes the same(ish) heat as diesel but it doesn't explode as fast as vapourized diesel, especially under pressure, so it takes a lot more propane to accomplish the same work.

Thus when burning it slowly (compared to an ICE) you get similar heat, because the losses are mostly eliminated.

[MEXICOWANDERER]

Since LPG has a weight per cubic foot density similar to diesel it would make sense that BTU specs would be the same. However substituting LPG as a motor fuel reveals a drastic sum difference in economy. This is curious.

[DrewE]

Since they're both hydrocarbons, I guess it rather makes sense that per pound they have similar energy content.

Per gallon, USLD has about 50% greater energy density (and ordinary mass density).

[MEXICOWANDERER]

I need to do more research 🙂

Kerosun 10,000 BTU heater says one gallon lasts 10-12 hours. A 10,000 BTU LPG heater would therefore last 8 hours or so with a gallon of LPG?

A gallon of ULSD costs $3.90 down here. LPG is about $2.50 gallon but a lot more inconvenient.

Maybe a larger tank? Sure goes not seem to be a lot of difference in energy per gallon or per lb.

[pianotuna]

138370 Btu per gallon for ulsd

about 7 pounds per gallon

so 19767 btu's per pound.

[MrWizard]

One gallon of propane has 91,502 BTUs

1 gallon of propane weighs 4.2 pounds. A "full" 20 lb cylinder should have 4.7 gallons or propane in it.

91502/4.2=21786.19 BTUs per pound