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Multi-Fuel Generator Run-Time
#1
(my generator is already set up for gasoline or propane)

As we have seen recently, an extended power failure (more than 1 week) is very possible (Hurricane Sandy). I have about 1 week worth of gasoline stored (40 gallons). I would like to add another week worth of propane to the stash. How much propane do I need to equal the gasoline that I already have stored - this is the main question that I need to answer.

I have consulted the Google, but all I seem to find is pros/cons of using one fuel over the other, and "how to convert" questions. Nothing about fuel usage.

With that said, my question to you folks is:

Generator run-time is typically given as
- X gallons (gasoline) at Y load provides Z hours of run-time

How does the above translate into propane run-time?

That is to say - X unit (weight or gallons) of propane at Y load provides Z run-time.

Some formula would be great. Plug in these gasoline numbers, solve for X, where X = propane used to equate power provided by gasoline. I don't care what unit of measure X is in. Converting units of measure is not a big deal.


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"We must all hang together, or assuredly we shall all hang separately."
- Benjamin Franklin
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Proud to be a member of pa2a.org since Oct 2012.
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#2
I think gasoline has about 115,000 btu per gallon, and propane is about 90,000 btu per gallon.
So i'm thinking about 25% more propane to equal the same run time as gas.Shrug

Note: I'm not an engineer or a chemist. Hell, I've never even stayed at a Holiday Inn Express.Big Grin
60-15, proud to be a member of pa2a.org since Oct 2012.
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#3
I meant to do this test with my generator when I converted it to Tri-Fuel. I'll have to do that and give you some answers.
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#4
streaker69;39528 Wrote:I meant to do this test with my generator when I converted it to Tri-Fuel. I'll have to do that and give you some answers.

Don't forget to convert between gallons and pounds to measure propane.
gascolator, proud to be a member of pa2a.org since Nov 2012.
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#5
gascolator;39535 Wrote:Don't forget to convert between gallons and pounds to measure propane.

Why are propane containers referred to in pounds, but when I get the bill from the gas company I'm billed in gallons?
60-15, proud to be a member of pa2a.org since Oct 2012.
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#6
60-15;39555 Wrote:
gascolator;39535 Wrote:Don't forget to convert between gallons and pounds to measure propane.

Why are propane containers referred to in pounds, but when I get the bill from the gas company I'm billed in gallons?

Because the easiest way to measure how much propane you just bought is to put the tank on a scale. In this day of cylinder exchange, many people have never seen the refilling process. I'm fortunate in that I have a local guy that sells propane at rock-bottom prices as long as he's just refilling your tank. He also only sells you as much as he pumps, so you can "top up" the tanks before a big barbecue without wasting what's still in the tank.
gascolator, proud to be a member of pa2a.org since Nov 2012.
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#7
Assuming that the btu/hr burn rate is consistent no matter what fuel is used, it looks like I need about one 40 pound propane can to equal one 5 gallon gas can.


Here is the math that supports the above statement:
- gasoline / propane (btu per lb) = 115k/90k = 1.278
- gasoline = 6.25 lb/gal
- 6.25 * 1.278 = 7.99 lbs of propane

Call it 8 lbs of propane = 1 gallon of gasoline (in btu per lb).
.
"We must all hang together, or assuredly we shall all hang separately."
- Benjamin Franklin
-------------------------------------------------
Proud to be a member of pa2a.org since Oct 2012.
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#8
Those calculations of course assume a perfectly running engine. YMMV <-- Finally got to use it where it makes sense. Smile
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