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Old 23-01-2014, 22:37   #31
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Re: Is a Propane Generator Feasible?

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Originally Posted by pbiJim View Post
Unfortunately, I find conflicting numbers from this source - http://www.afdc.energy.gov/fuels/fue...ison_chart.pdf. The chart on page 1 seems to claim that a gallon of propane has 73% of the energy of a gallon of gas, as compared to the 80% figure that you stated.

Either somebody has done some bad math, or else basic data sets exist that contain conflicting data. Perhaps different grades of gasoline &/or propane were used in different studies? I'd kind of like to figure out where the discrepancy originates.

Could you possibly list your basic data source?

Thanks,
Jim
Actually its not bad math, btu's per gallon of propane, gas and diesel are not fixed constants, but vary based on well source, refinery and exact blending of the fuel. Gasoline varies based on summer or winter blend and amount of ethanol in it.


I used Gasoline gallon equivalent - Wikipedia, the free encyclopedia for the gasoline btu content.

Having designed a ton of propane systems including large 1.5 to 2 MkW gensets I'm very familiar with propane heat content.

Here's one distributors information: Geeking Out Over Propane | AmeriGas Propane Blog

which covers properties of propane quite nicely.

Oh, I noted that the wiki data pulled the propane btu value from the afdc.energy.gov source. via footnote 6. I've never seen a propane heat value that low. Which is why I like to confirm, when possible with actual available fuel data. No I don't trust the government either.... Which is where the amerigas website comes in handy.

I should note that many plumbing and Ashrae data book's also list propane at about 91,500 btu's. I personally believe that 84,000 ish listed for propane in the afdc site is in error. However most of the various gasoline btu's contents actually looks pretty nominal.

So the exact efficiency will vary based on what fuel is used, and what part of the country its distributed to or blended for.


As they say, your mileage may vary. :-)
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Old 23-01-2014, 22:44   #32
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Re: Is a Propane Generator Feasible?

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This brings up a pet peeve of mine. Those new "spill-proof" gas can nozzles that are being forced upon the public in the US these days, do not work well at all. In addition to having very slow flow rates, I find that they tend to cause more spillage than they prevent. I've gone so far as to machine down custom fittings so that I can get better performance from my gas cans. I now get flow rates of about 12 seconds per gallon without spilling a drop.
You can thank our friends at the CARB, in California for giving the country such a well thought out design for a fuel container. I have been modifying every one of the bloody things. Yes they do seem to spill more too. Totally agree that its an abomination designed by committee.
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Old 23-01-2014, 23:02   #33
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Re: Is a Propane Generator Feasible?

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Thanks Happy.

That site gives lots of data. I guess I'm looking for more
subjective responses.

There's a 1350w generator on Ebay for $304US. Would it
stand up to the marine environment? Anybody use one?
I didn't find the exact one you were looking at, but unless the generator is rated super quiet it usually means it's somewhere around 90 dB of sound.

I think you'd be better off with the Yamaha conversion. The Yamaha is around 60 dB.
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Old 24-01-2014, 00:14   #34
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Re: Is a Propane Generator Feasible?

I warned you not to question sailorchic about engineering

Greg
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Old 24-01-2014, 03:09   #35
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Re: Is a Propane Generator Feasible?

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Lancerbye:

That's true, just like any generator on board.
I don't think all generators produce the same risk of explosive vapors in the bilge. Diesel generators produce practically no such risk. Gasoline-powered generators would probably be less dangerous, it seems to me, than propane, inside the boat, as the gasoline is not under pressure. But I wouldn't, personally, want any kind of either gasoline or propane engine inside my boat, and I wouldn't mind losing the propane stove, either, actually. Propane is really very dangerous inside a boat.

But as others have said, as long as you keep the gas and the generator outside of your hull volume, you will be fine. Lots of people use portable generators on their swim platforms or on deck; it works fine.
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Old 24-01-2014, 06:55   #36
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Re: Is a Propane Generator Feasible?

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Having designed a ton of propane systems including large 1.5 to 2 MkW gensets I'm very familiar with propane heat content.
Do you happen to know if the BTU content of propane varies depending if it is grade 5, 10 or I?
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Old 24-01-2014, 06:58   #37
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Re: Is a Propane Generator Feasible?

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You can thank our friends at the CARB, in California for giving the country such a well thought out design for a fuel container. I have been modifying every one of the bloody things. Yes they do seem to spill more too. Totally agree that its an abomination designed by committee.
It is my firm opinion that the world would be a better place if we had more engineers/craftsmen/artists/poets/farmers/chefs & fewer politicians/lawyers.

What does your modification look like?
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Old 24-01-2014, 06:59   #38
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Re: Is a Propane Generator Feasible?

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I warned you not to question sailorchic about engineering

Greg
Why warn me against it? Her response was wonderful.
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Old 24-01-2014, 07:04   #39
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Re: Is a Propane Generator Feasible?

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Here's one distributors information: Geeking Out Over Propane | AmeriGas Propane Blog

which covers properties of propane quite nicely.
Thank you for that excellent resource.

It reminded me of one very important property of LPG, it's volume varies quite a bit with temperature. That alone could explain a large discrepancy in the two different sources claims to the energy in a gallon of LPG. If ambient conditions in both cases were not at STP at time of testing, then all equality of data is out the window.
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Old 24-01-2014, 07:15   #40
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Re: Is a Propane Generator Feasible?

Back to information that the OP might find useful - I recall seeing a propane powered generator at Home Depot in Coconut Grove the last time that I was down there. I think that it was about 6.5kw. I'll see if I can get some more details the next time I am in that area.

Sorry for the thread drift.
Jim
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Old 24-01-2014, 07:16   #41
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Re: Is a Propane Generator Feasible?

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I've gone so far as to machine down custom fittings so that I can get better performance from my gas cans. I now get flow rates of about 12 seconds per gallon without spilling a drop.
Hmmm, I see a bidness opportunity!

I still have two of the old cans with vents. Makes so much more sense than the crap, "Eco Friendly", cans and spouts.
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Old 24-01-2014, 10:03   #42
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Re: Is a Propane Generator Feasible?

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Do you happen to know if the BTU content of propane varies depending if it is grade 5, 10 or I?
The exact BTU content will vary with propane refined at different sites, even for the same grade. As the composition of the various grades change, IE more propylene in HD10 then HD5, so odds are HD10 will have a lower heat content.

One other tidbit about generators, well internal combustion engines. Gasoline and propane engines run hotter then Diesel and need both a larger radiator/ heat exchanger then Diesel. They also need more cooling air/ ventilation around the engines. This becomes very important in the large 1 to 2 MkW gensets.

Sprint had a 1.2 MkW genset, years back at a POP site, that fried itself after a two hour run, when site power was lost. This happened due to the intake and exhaust louvers to the room housing the generator being way too small. Plus the exhaust through the radiator went into a narrow light well that did not have the cross section to move the amount of air required.

Sprint lost that POP site (where intercontinental fiber meets local fiber/ copper for a bit. It was one of two serving Atlanta. They were not happy campers that day... Bit of an oops on their previous engineers design. The engineers forgot to factor in pressure drop across louvers (which is basic basic engineering 101 and more importantly missed cat's requirement for room ventilation. Plus the light well cross section was tiny. The last probably because somebody though the generator was above ground and did not look at the architectural elevations and cross sections. Like I said... Oops.
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Old 24-01-2014, 10:10   #43
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Re: Is a Propane Generator Feasible?

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Thank you for that excellent resource.

It reminded me of one very important property of LPG, it's volume varies quite a bit with temperature. That alone could explain a large discrepancy in the two different sources claims to the energy in a gallon of LPG. If ambient conditions in both cases were not at STP at time of testing, then all equality of data is out the window.
Very true! Gee it is a very rare day when ambient equals STP. (standard temperature and pressure for the non-engineers.)
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Old 24-01-2014, 13:59   #44
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Re: Is a Propane Generator Feasible?

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One other tidbit about generators, well internal combustion engines. Gasoline and propane engines run hotter then Diesel and need both a larger radiator/ heat exchanger then Diesel. They also need more cooling air/ ventilation around the engines.
This may sound a bit nit-picky, but perhaps you mean to say that at a given HP, gas & LPG motors produce more heat than diesel, rather than saying that gas & LPG run hotter. At least in the case of VW motors, the thermostat for both the TDI & older generation diesels is set to a higher opening temperature (190F) compared to their gas motors. At least in that case, I think that the diesel may be producing less heat, but running at a higher temperature. I do notice that the fuel consumption on the TDI is much higher until it reaches 190. The temperature there seems fairly important.

Thank you for the clarification on the other information regarding LPG grades. You are a genuine wealth of information.
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Old 24-01-2014, 14:31   #45
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Re: Is a Propane Generator Feasible?

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This may sound a bit nit-picky, but perhaps you mean to say that at a given HP, gas & LPG motors produce more heat than diesel, rather than saying that gas & LPG run hotter. At least in the case of VW motors, the thermostat for both the TDI & older generation diesels is set to a higher opening temperature (190F) compared to their gas motors. At least in that case, I think that the diesel may be producing less heat, but running at a higher temperature. I do notice that the fuel consumption on the TDI is much higher until it reaches 190. The temperature there seems fairly important.

Thank you for the clarification on the other information regarding LPG grades. You are a genuine wealth of information.
Hum. While the water jacket operating temperature is the same, the amount of heat rejection required is higher with propane then for diesel. Perhaps at small engine sizes its not so noticeable. But going from a diesel cat genset to a propane cat genset of about 1.2 MkW size, (think it was a V12, but its been a while) the radiator is about 40 percent larger on the propane unit. It was Hugh! When factored with proper ducting and louver size calc's, its a big cost impact. Air flow is lots higher too. Don't have the date in front of me, just noted it years ago, the very few times propane was used, generally by telcom's. Not well know, except by the engine manufacturers and a few crazy engineers.
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