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| Re: [GMCnet] yamaha inverter generator: how to run inside? [message #113181] |
Wed, 26 January 2011 13:07  |
mlincoln
Messages: 107
Registered: August 2006
Location: Salt Lake City
Karma:
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Lunch break time….
There was a question of oxygen starvation raised. As a pulmonary physician, I couldn't let that go without trying to figure out if it was likely to be true or not.
1. Combustion calculation:
1. Gasoline is a mixture of hydrocarbons, nominally about C8 H18 (isooctane), specific gravity 114.23 gm/mole
2. Stoichiometric complete combustion of hydrocarbons:
CxHy + (x + y/4)O2 --> xCO2 + (y/2)H2O
4. Substituting into the equation: C8H18 +(8 + 4.5) O2 à8CO2 +9H2O
5. Thus every molecule of isooctane completely combusted will yield 8 CO2 and 9 water molecules and consume 12.5 oxygen molecules
2. Determine how much isooctane is in a gallon of gas
1. Isooctane specific gravity 688 kg/m^3 liquid state
2. 1 m^3 = 1,000 liters = 264.172 gallons, so one gallon contains 2.60 kg of isooctane
3. 2,600 gms of gasoline / 114.23 gm/mole = 22.76 moles of isooctane.
3. Determine the waste products resulting from burning a gallon of gas completely (assuming no CO, NO2, etc here…complete combustion into water and CO2) All this goes out the exhaust pipe (Shan hopes!)
1. 22.76 moles burned x 9 = 204.84 moles water produced …at 18 gms/mole that’s 18 * 204.84 = 3684.12 grams of water (almost a gallon)
2. 22.76 moles burned x 8 = 182.08 moles of CO2 produced…at 44.01 gm/mole that’s 8013.34 grams of CO2 produced. CO2 weighs (at standard temp and pressure dry) 1.977 gm/liter, so that’s ca. 4000 liters of CO2 produced (Global warming!)
4. Determine the oxygen consumed from burning a gallon of gas completely
1. 22.76 moles burned x 12.5 moles oxygen consumed/mole of gas burned = 284.5 moles of oxygen consumed.
2. With oxygen at 16 gm/mole, that’s 4552 gms of oxygen consumed when a gallon of gas is burned. Oxygen’s density (100% oxygen) is 1.429 gm/liter at zero centigrade (ok, you’re living in a cold coach). In room atmosphere at sea level, with 21% oxygen, that’s ca. 0.30 gms oxygen/liter of room air.
3. If 4552 grams of oxygen are consumed, ca, 4552 / 0.30 = 15,173 liters of room atmosphere are going to be pumped through the engine. That’s ca. 536 cubic feet of atmosphere. If the coach is 7.5 x 6 x 26 feet inside, the total volume of the coach is ca. 1200 cubic feet.
Conclusion: A catalytic heater (which exhausts inside) doesn’t create a negative pressure in the coach by dint of producing 8 CO2 and 9 H2O molecules that take the place of every 12.5 molecules of oxygen consumed. I'd say that a catalytic heater can surely deplete oxygen concentrations if you burn enough fuel. If you could really use up 536 cubic feet of atmosphere by running through a gallon of gas (or equivalent molar weight of propane), using a catalytic heater, that'd be serious, and not just from oxygen starvation but from CO2 acidosis. I suggest that nobody run a catalytic heater without several windows open! On the other hand, an internal combustion engine is a volume air pump and it exhausts all the air it takes in. It thus creates a negative pressure that will be supplied by leaks inward to the coach from the surrounding air. So I don’t think Shan’s arrangement would necessarily cause oxygen starvation because as 21% oxygen room air is consumed and pumped out more 21% oxygen atmosphere will leak into the coach. I think one can practically guarantee that a 35 year old coach _won't_ develop a subatmospheric pressure, even with the windows closed: a multitude of small leaks will suffice to let in all the air pumped out :-).
HOWEVER, I still have a dire concern that Shan will kill himself, German engineering genes and all, from incompletely exhausted carbon monoxide. Shan, think of how your obit might look: do you really want even a small chance of that? Then there'd be the humiliating post-mortem endowment, in your name, to the local firefighters. For the next 50 years they'll to go to the elementary and high schools to warn kids about the dangers of carbon monoxide poisoning, all in your name (imagine a flower-wreathed picture on an easel in the gymnasium, standing to the firefighter's podium, and the bored kids texting each other about what a turkey you must have been to have engendered a perpetually endowed safety assembly in your name). I know that such an ignoble end would be too embarrassing for me by far.
Run the generator outside!
Now it is time to return to work!
Mike Lincoln
On Jan 26, 2011, at 12:59 PM, Shan Rose wrote:
>
>
> My Onan runs like a top, the reason for the smaller gen is 4 fold, one is the fact that it uses about .1 gal an hour at 1/4 load the onan with almost no load burns about .4 gallons an hour. Second is noise, unless running the roof AC, water heater, or some other electrical appliance which demands heavy current, the onan is overkill. Third is portability, I can take the smaller gen with me anywhere without having to drive the coach there. 4th is to reduce wear and tear on the onan, since mantainance costs are significantly more ofor the onan (last oil change for the onan was about $40, compared to just $6 for the yahmaha) the onan is a great genset, once I worked out the bugs, mine has provided me with several hundred hours or reliable service, and by splitting the load with another APU I can make the onan last even longer before a major overhaul will be required, so now I will only need onan under severe usage conditions and not just to nuke something or watch a little TV whe
> n im in my rig...
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