--- In biofuel@yahoogroups.com, MH <[EMAIL PROTECTED]> wrote: > > murdoch wrote: > > Very handy list, thanks. > > Your welcome. > > > At a glance, I'd like to find out the numbers for H2, and as to the > > fuel cells, the important number is the one for the fuel, not the > > cell, in my view.... though it is useful to know the weight of the > > "engine" or other energy conversion device, particularly for certain > > applications. For example, a car engine carries not only its own > > weight and all attendant machinery, but the weight of its fuel and all > > attendant machinery, over the lifetime of the vehicle. This has a > > significant effect on the lifetime energy-usage of the device (car). > > If more is learned about fuel cell energy density to mass-or-volume > please share with us and the use of links is helpful. As for H2 > my interest is usually peaked when Robert Luis Rabello writes.
The oxidation of hydrogen produces more energy per molecular weight than any other non-nuclear reaction. If we're discussing automotive applications then we're probably talking about PEM (polymer electorlyte membrane) fuel cells. The energy density is a function of operating voltage which impacts efficiency. Fuel cell operating efficiency is derived from polarization curves relating operating voltage to output current. A good example of one is on p. 6 of the attached link. http://electrochem.cwru.edu/NSF/presentations/NSF- Barbir_Diagnostics.pdf So you can have high energy density and low efficiency because you're operating at a lower cell voltage but higher current density. Also complicating the matter is what reactants are used. Pure hydrogen and oxygen improve operating efficiency over mixed gases such as reformed hydrocarbons and air - for a given operating voltage you'll have higher current density. Because of the trade-off between efficiency and energy density the fuel cell energy density is up to the designer and system constraints. Some automotive targets I've seen are ~1 kW / kg but I don't know if that's been achieved. People have considered supplying hydrogen following a distributed generation model, creating it on-site at fueling stations by partially oxidizing hydrocarbons and then storing as compressed gas or cryogenically. It has potential but then you're still basing your energy production on fossil fuels. Maybe one day we'll have hydrogen home brewers producing fuel by solar powered electolysis ;) =Gordon > > The remainder of your commentary would be interesting hearing > further views comparing electric and Internal Combustion Engines (ICE) > to energy density storage device, of electrics and liquid fuel, replacement > and its impact to engineering, monetary and environmental effects, etc. > Such as hybrid vehicles improved efficiencies using a combination > of liquid fuel ICE an electric control comparisons to electric and > more traditional vehicles of today. > > > I prefer the way your lists are done (energy per unit mass) to the > > other simplified direction (energy per unit volume at some sort of > > generally defined conditions for temperature pressure, etc.) in part > > because it's more scientific (both energy and mass are objectively > > precisely defined without much fanfare.... especially if we do not > > confuse mass with weight), but I do think that studying both is > > important for full perspective. > > Additional information is welcomed and further conversions of > energy density to volume such as the methanol link below which > includes gasoline, diesel and others is welcomed. > > > For example, #2 Diesel is generally more energy dense than gasoline > > per unit volume, although it is apparently (from the list you give) > > slightly less energy dense per unit mass. And though Natural Gas is > > apparently very energy dense per unit mass, I doubt that per unit > > volume it has nearly the density of some of these other fuels, unless > > it is compressed to a very strong extent, or liquified (similar > > comments probably go for Hythane and Hydrogen). > > > > Aside from H2, I'd like to see numbers for DME, Vegetable Oil, > > Hythane. > > > > MM > > The list archives has touched upon this one time or another IIRC. > > > > > murdoch wrote: > > > > Both Methanol and Ethanol are somewhere around 70 or 80% energy > > > > density of gasoline. Close enough, I think. Battery electric fuel is > > > > not as energy dense as any of these liquid fuel, though I haven't > > > > checked figures. > > > > > > Pasted below are some comparisons of energy density to mass > > > in MegaJoules per kilogram (MJ/kg) for various forms and > > > storage devices. Additional information is welcomed. > > > > > > Table 2. A Comparison of Different Fuel > > > Lower Heat Values (LHV) for > > > Burning Different Sources of Energy > > > http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/cl3019 > > > 53.18 MJ/kg Natural Gas > > > 46.37 MJ/kg Propane > > > 43.80 MJ/kg Gasoline > > > 42.80 MJ/kg Diesel (#2) > > > 37.80 MJ/kg Biodiesel > > > 37.00 MJ/kg Fuel Oil (#1) > > > 26.70 MJ/kg Ethanol > > > 24.00 MJ/kg Coal > > > 20.93 MJ/kg Coal (Sub-bituminous) > > > 20.90 MJ/kg Methanol http://web.archive.org/web/20020713201640/http://www.geog.umd.edu/home page/courses/jboberg/units.htm > > > 19.97 MJ/kg Flax Straw (dry) > > > 19.80 MJ/kg Wood Pellets > > > 17.86 MJ/kg Wheat Straw (dry) > > > 17.50 MJ/kg *Corn Stover (dry) > > > 16.20 MJ/kg *Shelled corn (15 percent moisture) > > > 15.43 MJ/kg Flax straw (20 percent moisture) > > > 15.00 MJ/kg Wood (15 percent moisture) > > > 13.74 MJ/kg Wheat straw (20 percent moisture) > > > > > > BATTERIES > > > 0.396 - 0.576 MJ/kg Lithium-Ion > > > 0.216 - 0.432 MJ/kg Nickel-Metal-Hydride > > > 0.162 - 0.288 MJ/kg Nickel-Cadmium > > > 0.108 - 0.180 MJ/kg Lead-Acid > > > http://www.batteryuniversity.com/partone-3.htm > > > > > > ALTERNATIVE BATTERIES > > > 0.0108 - 0.108 MJ/kg Ultracapacitors > > > 0.0207 MJ/kg Compressed air tanks > > > 1.39 MJ/kg Superflywheel - Buckytubes give 10x this amount! > > > 1.97 MJ/kg Fuel cells > > > 304K pg 14 of 29 PDF http://www.inf.ethz.ch/vs/events/dag2002/program/lectures/starner_2.pd f ------------------------ Yahoo! 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