Talk:Fuel cell/Archive 2

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Carnot efficiency

What do you mean with Fuel cells are electrochemical devices, so they are not constrained by the maximum thermal (Carnot) efficiency? I thougth that second thermal law and Carnot's theorem should always stands. AnyFile 21:09, 30 Jan 2005 (UTC)

I agree that this is a somewhat confusing statement. Fuel cells, like any other device, have a maximum theoretic efficiency equal to delta-G divided by delta-H (almost 90% for hydrogen; over 98% if the lower heating value, LHV, is used instead of delta-H). However, fuel cells do not require high temperatures or pressures to reach high efficiency. The term Carnot efficiency normally applies to the efficiency at which the temperature difference between two heat reservoirs can be converted into work. Starting from a fuel is not the same thing, although it is possible to compute the maximum temperature of combustion, in which case the Carnot efficiency is equal to delta-G divided by delta-H. I guess what people mean when they say that an engine is limited by the Carnot efficiency is that the maximum temperature is limited (due to material constraints.) PeR 07:31, 4 Feb 2005 (UTC)
I would disagree about your definition of efficiency; it should rather be "energy extracted as work" divided by the Delta-G. This because there is no way to get the Delta-H anyway, and it makes sense to define the maximum theoretical efficiency as 100%.
It does make sense to define the maximum theoretical efficiency as 100%, but unfortunately that is not the definition that people use. (Hence the need to compare with the Carnot efficiency rather than then number 100%.) --PeR
Delta-G=Delta-H - T x Delta-S, or dG=dH-TdS. dH is fixed for a scenario, while dG depends on your reaction temperatures, so while dH is the same at room temperature, 1000°C or 2000°C, dG isn't. To complicate things more, Carnot-efficiency is a function of temperature too. Also, for water, for the reacton 2H2+O2-->2H2O, 3 molecules generate 2, the entropy change dS is negative, so dG=dH-TdS gets less negative(less spontaneous), to the point that about 2500°C dG is 0, the free energy of the reaction is 0, no energy is extractable. See the reverse process, high temperature electrolysis. So Carnot requires high temperatures for high efficiency, but dG for hydrogen/water requires low temperatures for high Delta-G. The lower the temperature you react hydrogen, the more energy is freely available from it, i.e. the more negative the Delta-G change.
Carnot efficiency only relates to thermal engines, and it limits the maxium efficiency extractable, based on the temperatures you use in a thermal engine. As PeR noted, all the available energy could be extractable through cyclic thermal ways (assuming you get the same energy per mole at high temperatures too, which is not true) if you had no limit on your upper use temperature. The formula for Carnot efficiency is eff=1-T1/T2, T2 being the upper use temperature, temperatures in Kelvins. So if you had a heat engine operating on "heat falling between thermal heights" of 10,000°C and 0°C, you could extract 1-273.15K/(10000+273.15K)=1-.0266=.9734, or 97% of the energy, only 3% would be handed over as waste to your cold temperature reservoir at 0°C, at your low height. However, using a 100°C high temperature instead of 10,000°C, gives you only an efficiency of 1-273.15K/373.15K=1-.7320=.2680, or only 27% maxiumum theoretical limit, 73% wasted on heating the cold temperature reservoir (you'd essentially be heating the outside atmosphere, ocean, world, giving your energy away to non-useful purposes.) There is simply no way to have a cyclic thermal engine, one that recovers to inital state without the purging some heat out to the universe during the recovery process. Think of one if you can, then you can beat the Carnot limit that's pretty much a law set in stone for now. You can get 100% thermal to mechanical energy conversion efficiency easily, by going just one way in an engine, if you had engines that just go one way but the very need to complete a cycle makes you waste some energy, ruining your 100% numbers. So, for instance, if you have a gram of fuel to burn, and a cyclic thermal engine to extract the energy from it, and have the option, of say, to heat 1 ton of water by 1°C, or heat 1 gram drop of water to 1,000,000C, then run a Stirling engine with your 1°C and 0°C, or 1,000,000°C and 0°C reservoirs to extract the work, you should opt for the heating 1 gram water to 1,000,000°C, because that gives you a 99.97% theoretical maxium efficiency of converting heat energy to mechanical energy, that wastes only 0.03% heating the outside world, instead of the 1-273.15/274.15K=0.36% maxium efficient 1°C to 0°C thermal engine, that has to use 99.6% of the provided energy to heat the outside world during its recovery process in its cycle. However, finding a heat engine that won't evaporate at 1,000,000 °C is very hard. Practical temperatures in internal combustion engines are near 300-1200*C, and you can calculate how efficiently an internal combustion engine car can work, usually well below 40%, and over 60% of energy is vented through the exhaust pipe, heating the world. An analog scenario would be lifting a ton of water by 2 mm, or 1 gram to 2 km heights, and then letting each fall down, pulling a pulley, but unlike in this case, in thermal engines you have a minimum height you can drop to, say 1 mm, and then you have to let the water freely drop from there, on its own, without doing useful work, otherwise it will never flow out of your engine. So it's like 1 ton of water falling 1 mm doing useful work, then another millimeter without doing useful work, vs. a 1 gram drop of water falling 1 km doing useful work, then another millimeter as waste, before it gets lifted again. This "minimum required waste height" in cyclic thermal engines is fixed by the cold reservoir operating temperature, and if you had a cold reservoir with a 0K temperature, that unattainable absolute 0, then eff = 1-Tcold/Thot = 1-0/T2 = 1-0= 1 = 100%, you'd have your thermal engines operating with 100% efficiency. However, in the world we live in, the practical cold temperature reservoir is near 0-30°C=273.15-300.15K, and not absolute 0, however in outer space things are different, though the extreme vacuum there is very insulating and doesn't make a good heat transfer medium (so most thermal energy is exchanged through black body radiation, instead of thermal conduction.)
Therefore on this planet, in the practical world we live in, you should always avoid resorting to thermal ways of energy conversion, if you can. For instance, mechanical to electrical or electrical to mechanical energy conversion efficiency in electric generators, alternators is routinely above 95% at room temperature conditions, at very practical conditions. Imagine you had a weight tied to a pulley, and while this weight drops, you had the option for the pulley shaft to either directly drive the rotor of an alternator to harness the energy, or, to rub against something, to heat it via friction, then use the heat generated as the hot temperature reservoir for your thermal engine. Then, if you're smart, you will opt for directly driving the alternator, and you will avoid the thermal/friction way, unless you have a tiny bit of material that you can rub to 1,000,000°C via friction, in which case you'd be okay, only wasting 0.03% in your thermal engine, theoretically speaking. In practice, most likely you'd only be able to rub it to, say, a maximum of 100C, even wasting some energy on air/bearing friction. Dynamos and alternators are incredibly efficient devices at sucking mechanical energy into electrical one, provided they have strong magnets and huge amounts of thick low resistance copper, or better, superconductors, and relatively little is wasted in the bearing and air friction, or copper electrical resistance heating.
Fuel cells are devices intended to directly convert chemical stored energy to electricity, instead the conventional ways, going through thermal means, through free combustion in air to obtain high temperatures then harnessing the heat via a cyclic thermal engine. Converting any form of energy into thermal storage at temperatures well below 1,000,000C means it will be only 35% efficiently convertable into other forms of energy, such as mechanical energy through a carnot/stirling engine, or electrical energy, through direct heat-to-electric devices called Peltier elements. Mechanical/electrical forms of energy are up to 97% efficiently convertable into other each other (mechanical bearing friction and copper resistance losses being the culprit for losses), or into chemical energy, inside a battery, which, in the case of lead acid, is 90% recoverable into mechanical/electrical.
Note that you can always convert everything 100% efficiently into heat, because everything heats its external universe as a wasting mechanism, whether it's bearing friction, copper resistance, battery operation, they all heat up as a wasting mechanism, and you just add your 97% efficiency to that 3% waste heat and always get at least 100%. At least, because, in fact, even more than 100% heating efficiency is possible, from other forms of energy, by running a Carnot engine exactly backwards, in which case you "steal" warmth from your cold reservoir, as in heat pumps, the cold reservoir being at some higher temperature than absolute 0 K. So for electric heating, instead of a resistor heating element, that only gives 100% heating, you're better off running a heat-theft-device-heat pump, that gives you even more heat, it steals some heat from the outside cold weather. The lower the heat-to-mechanical efficiency of a carnot engine is, the higher its mechanical-to-heat efficiency, which is its mathematical inverse, heat-pump-effcy=1/carnot-effcy. So heat pumps work best when heating a room from 0°C to 1°C, being 1/(1-273.15/274.15)=1/.0036=27000% efficient, but they are less efficient at heating from -30°C to +30°C, 1/(1-243.15/300.15)=1/.018=500%. There isn't too much market for heating something by 1 degree or half a degree, and heat pumps are expensive to build compared to simple heating resistor elements, but still, a number above of 500% effiency is not too shabby. Unfortunately, electricity needed to run a heat pump is generated via a forward Carnot process, so the backwards way in theory only gets you back to the original available energy, "undoing" the waste at the power plant with your heat-stealing heat-pump. But this was not even considering delivery losses through the long-long copper or aluminum cable from the power plant, so you're back to square one, because it's more efficient to deliver the natural gas to you through a fat hollow pipe, than electricity through a heavy, solid conductor, so if heat is what you want, then use the fuel directly, instead of converting it to electricity in a power plant. But in fact, if you ran an efficient ideal carnot engine between 0°C and 1000°C in your home, then used its mechanical output to drive another, "less efficient" carnot engine operating between only 0°C and 30°C "thermal heights" in reverse mode, as a heat pump, the net effect of an efficient carnot engine driving an "inefficient" carnot engine in reverse mode is heat stolen, higher than 100% efficiency. However most practical engines are not ideal, the carnot engine numbers of 40% maximum efficiency being theoretical, and practical engines are much less efficient, say 25-30%, plus there is a huge capital cost and maintenance nightmare associated with this scheme, but it works, with natural gas delivered to your home, instead of burning it, use a dual-carnot engine setup that steals heat as a net effect from the cold weather outside. Still, a power plant can usually operate at much higher temperatures because of scale and size, thus thermal insulation, than a tiny device you need at home, plus maintenance costs of one big device are less than a million tiny generators, so the economies of scale dictate having power plants in general, at least for electricity. There are other reasons too, such as safety, especially if we start heavily relying on nuclear fuels, you wouldn't want everyone to run a nuclear based home generator, such as submarines do, with customers purchasing fuel rods in a lead case from a store, that's free-market with-zero-big-gov't-interference gone-wrong, you'd rather have it done in a government controlled/licensed, secured large-scale facility, and only deliver safer forms of energy, whether it's hard-to-store electricity, or easier to store liquid ammonia, magnesium or aluminium rods, green-house neutral hydrocarbons such as biomass+hydrogen converted to methane or liquid butane, or even ethanol/methanol, or hey, even that hard to tame/store hydrogen, in a fictional hydrogen economy. Ammonia you could even use as a fertilizer, and ethanol, if 100% pure, you could dilute 50% to brandy. :) Imagine an ethanol economy with everyone with an alcohol pipe in their home, they can use like tap water to cook, heat, clean, disinfect, drink, refill the car etc. :)I don't even want to think of what all wrong you can do with supercool liquid hydrogen. Magnesium rods are relatively safe, easy to handle - car wheels and engine blocks even made from it, but if powdered/grinded, the dust can catch on a very severe fire, even releasing blinding UV radiation while burning, but magnesium is easier to make or react than aluminum is.)
Returning back to the point of trying to avoid heat as an intermediate energy storage medium, of course if heat is what you want, the thermal intermediate is fine, such as for solar heaters, but to get electricity or mechanical motion from sunlight, you either need a super high temperature stirling engine solar concentrator to get reasonable Carnot efficiency numbers, or avoid thermal means by using direct photovoltaic light-to-electric conversion. Currently all nuclear, coal and natural gas electric power plants use conventional thermal engines and they cannot break the Carnot efficiency barrier, meaning they heat the outside world 65%, and only deliver 35% of the available energy to you. Fuel cells on the other hand directly harness the chemical energy to electricity, they directly harness "dropping through chemical heights" without "dropping through thermal heights", (through chemical potential energy gradients instead of thermal potential energy gradients), but because fuel cells are not 100% efficient, they still release some of the energy as waste heat, that you can still use in your thermal engine, so they give a 30-50% electric + 35% thermal means of harnessing the energy, instead of just 35% thermal means, wasting only 15% to heat the outside world, instead of 65%. Sillybilly 17:35, 11 December 2005 (UTC)


For Anyfile: the reason the Carnot limit does not apply in fuel cells is that the energy conversion does not pass through heat: the Carnot limit is normally understood (at least in the terminology I learnt at my university) as the limit of heat cycles, and the fuel cell is not one. Of course, the second principle stands.
For AnyFile: I've corrected the article text to read: Fuel cells are electrochemical devices, so they are not constrained by the maximum Carnot cycle efficiency as combustion engines are. This sentence could be worded much better, but atleast it isn't misleading now. Faraz Syed 06:44, 19 October 2005 (UTC)

Rerversible fuel cell - only a configuration

By definition a fuel cell can be operated in reverse. Reversible fuel cells should not be considered a separate type of fuel cell. I realize that the page for reversible fuel cells states:

"So while the reversibility is applicable in principle to any fuel cell device, a practical device may not be built with this intent. Hence the distinction between reversible fuel cells, and generic fuel cells."

However, this does not mean it is a different type of fuel cell. Operating a fuel cell in reverse is simply a matter of configuration/capability and has nothing to do with "types" of fuel cells, which should only distinguish between cells which utilize different fuels and/or different half-cell reactions.

My suggestion is that the page simply state:

All types of fuel cells can also be operated in reverse. However, most fuel cells are constructed for the purpose of generating electricity only and therefore may require alterations before a reversible process can be run. For more information, please see Reversible Fuel Cell.

Faraz Syed 02:04, 30 August 2005 (UTC)

Removal of external links

As per Wikipedia:External links, I've removed a large number of links. If there are any that really scream to be replaced, here's a good place to talk about it.
brenneman(t)(c) 06:55, 26 September 2005 (UTC)

Thanks for doing that. This article has attracted an unusual amount of linkspam. -Willmcw 22:36, 26 September 2005 (UTC)
The list was building up again and I reduced the number of links. Only the best sites for the article should be kept. I say "the best for the article", because a site can be good, but not be useful for the purposes of an encyclopedia article. For example, a site with fuel cell components for sale, and no significant content about how fuel cells work and such, would not be helpful for most readers. Rather than removing the links immediately, it might be best to do it periodically, so that there is not a fight about the addition and removal of every link. Also, editors might be less likely to take the removal of a link they added personally. However, if an editor adds the same link to many web pages or if the site is a linkfarm, immediate removal might be better. -- Kjkolb 05:03, 21 April 2006 (UTC)

Research Development Links

Added a section for links on research development for fuel cells, as I think this is really needed, especially since fuel cells are still under researched and being continually developed.

The link I have placed is a huge break though in hydrogen fuel cells, allowing for cars to store hydrogen (for use in a fuel cell) without a potentially dangerous compressed hydrogen tank. So that is why I thought it would be important to add in.

If anyone has any other links for future or previous dates which reveal a breakthrough in research development into fuel cells, then please add them.

  • What's preferable is if the information is summarised and added into the article. And please do sign you name with these, ~~~~, please.
    brenneman(t)(c) 09:10, 4 October 2005 (UTC)
  • The information will be severly disadvantaged if it is 'summarised'... perhaps a link and a summary?
Please understand that the purpose of this project is to amass information, so links to outside sources do us little good. Breakthroughs are important, but as an encyclopedia we're more interested in technologies that have already been proven one way or another. We can be the last to report an innovation. -Willmcw 16:37, 4 October 2005 (UTC)

Low Efficiency

"Fuel cells running on compressed hydrogen may have a power plant to wheel efficiency as low as 22%"

What is the purpose of stressing how low an efficiency a fuel cell may have? Aren't we more concerned with the current and theoretical maximum efficiencies of fuel cells? Anyone can make an engine with 1% efficiency, or lower.

The total efficiency (from coal or methane to hydrogen to fuel cell to vehicle motion) is important and should be included, but the theoretical maximum efficiency and the current efficiencies should also be given without taking that into account. It would be odd for an article on internal combustion engines to give only the efficiency after the energy used for oil exploration, drilling, transporting, refining and distribution are taken into account, and not give the efficiency you get just gassing up the car and driving. The efficiency given for a combined heat and power fuel cell is also incredibly low. -- Kjkolb 12:23, 2 January 2006 (UTC)

Types of Fuel Cells

A number of experts in fuel cells, including Karl Kordesch, have noted that the main advantages and disadvantages of a fuel cell stem from its electrolyte, and that this is why fuel cells are classified by their electrolyte. It seems that the Wikipedia article underemphasizes the importance of the electrolyte by placing the "Types of Fuel Cells" section at the bottom, and not providing any discussion or comparison at all of the various types.

I'd like to add a section either just before or just after the "Science" section that lists the types of fuel cells and their relative strengths and weaknesses, and perhaps some operating characteristics (such as temperature range). This would still leave the separate pages for each type to go in to details regarding how each type of fuel cell works. Any suggestions or comments? -- Thopper 00:30, 8 January 2006 (UTC)

Also, the diagram of the alkaline fuel cell, showing water flowing out with the excess hydrogen flow, is only correct for immobilized electrolyte designs such as those used in the Space Shuttle. Terrestrial AFCs typically have mobile electrolyte, allowing water management to be mediated through the electrolyte itself. I'm not quite sure how to capture this, and certainly haven't the artistic skill to update the diagram. -- Thopper 00:34, 8 January 2006 (UTC)

Hi! I just came to think whether it can be explained: is it possible to carry out virtually any oxidation thermal generation process to a fuel cell process via catalyzation? I mean, in theory it involves exchange of electrons, and essentially represents a reaction whose anergy could be trapped by a wise invented (or accidentally found) catalyst and membrane.

What I wanted to ask may be is this theoretically possible: to generate electricity by mere catalytic oxidation of natural oil or other fuel instead of simply burning it in air stream, to avoid Carnot process? -- mtodorov_69, 16 February 2006


Is it possible to build a nuclear device that will directly transform nuclear bond energy to electricity, without using intermediate thermal stage of energy conversion? Is it possible to covert directly from chemical and nuclear to mechanical, without intermediate thermal or electrical? This could be at least in "See Also", please, this is very intereseting. I hope it's not SF.

"Stranded" diagrams

Coming here to see how a fuel cell works, I eventually spotted the diagrams hiding at the bottom of the article. I understand that not all fuel cells work the same, but one or two of these diagrams, with appropriate explanation, would make the "Science" section a lot more useful to the unknowledgeable reader, if you ask me. - IMSoP 01:05, 28 January 2006 (UTC)

New text for integration

Efficiency of a standalone electrolyzer

As far as low efficiency as a standalone electrolyzer goes, we need to understand a bit about fuel cells. In particular, all fuel cells use a membrane to only allow only ionic species to flow into the reaction zone. That is, the reactants are forced to undergo an ionization process at the surface of the membrane, by either giving off or accepting electrons, before they are granted free passage into the reaction zone. Once ionized, the concentration gradient pulls the ionic species across the membrane, to the reaction zone, where the ionic species are consumed, thus keeping the concentration near 0 on the reaction side, and the gradient across the membrane active. Without the separation membrane the reactants could simply jump and react each other, without giving us the electrical way to tap the energy. With direct reaction we would only get heat, which, according to the principles of the Carnot Cycle, is an even more inefficient way to tap energy - most internal combustion engines are limited to 10-40% efficiency, while fuel cells can beat that easily, providing 40-70%, still falling short of batteries that can return over 65-90% of the available chemical energy as useful work.

The giving off or accepting electrons is the process that harvests the bulk of the available chemical energy. Still, like in any conversion process, not 100% energy becomes available, a lot is wasted. For example, some energy is consumed/wasted because there is electrical resistance by the membrane against the current flow carried by the ions - the ions bounce against the membrane atoms, and generate waste heat in the process, just like electricity passing through an incandescent bulb filament heats it up, consuming energy. The longer the path travelled by the current flow, the more energy is wasted. For this reason a good fuel cell membrane is as thin as possible, and as highly conductive ionically as possible. Also, a good fuel cell has as large a surface area as possible, because a large surface area lowers the overall membrane electrical resistance as well. There is always a balance in how big and thin you can physically stretch a membrane, without risking pinholes or large holes in the membrane, that would completely ruin your cell's efficiency, so the ionic conductivity of the membrane material remains a key player, limited by the available materials science technology at the time.

Low temperature fuel cells make very expensive electrolyzers, because of the special nature of the membrane surface, which needs a platinum coating. The reason for this platinum catalyst is to provide a low activation energy for the H2 → 2H reaction, the breaking of the hydrogen molecules into atomic species. This reaction is an energy intensive process, but still, like all chemical reactions, in an equilibrium, and any equilibrium can be driven by concentration gradients in either direction. Such catalyst is not necessary for the backwards process, for electrolyzing water, because 2 nascent and reactive hydrogen atoms or oxgyen atoms freely recombine as pairs into a stable, lower energy molecules, which bubble up to the surface. That is, you can effectively electrolyze water with two metal rods, even copper or steel, and produce molecular oxygen and hydrogen gas from the nascent atoms that form at two electrodes, however, you could not use such two-metal rod electrolyzers backwards as a fuel cell, because, even if you bubble hydrogen or oxygen to their surface, they wouldn't be able to generate the needed atomic/ionic species, without either high temperature (600 to 1000 °C), or a low temperature catalytic activity that platinum has. The known catalysts, the metals that are highly active at gaseous molecule splitting at room temperature, are either very expensive precious metals — platinum, palladium — or sophisticated blends of lower cost, but still expensive metals, such as those used in NiMH (nickel-metal-hydride) cells. NiMH batteries blur this boundary between batteries and fuel cells somewhat, at least the hydrogen side of things — the atmospheric oxygen activation may still be an issue - hemoglobin anyone? True, that while almost any metal can be used to electrolyze water, there is the factor of electrode overpotential that limits the efficiency of electrolysis, and these low activation energy catalytic metals make the very best electrodes. Still, there is no need for a membrane for electrolysis, but only for the forward, fuel cell mode of operation. Ideally, the metal side of the membrane would be flooded with the highly conductive water electrolyte for electrolysis, the electrolyte being in direct contact with the metal without a separation membrane, but dry it off and keep the electrolyte on the other, nonplatinated side, during operation as a fuel cell, to force all ions to travel through the membrane.

High temperature fuel cells such as solid oxide membrane (e.g. zirconia) fuel cells have no catalyst-expense limitation, but they are similarly costly because of the very nature of high temperature operation, slow startups (up to 8 hours), bulky size and the need of thermal insulation. High temperature electrolysis is currently an area of active research because it can directly utilise cheap heat energy, partially replacing the expensive electric energy needed to split water. This is based on the thermodynamic entropic drive in the reaction 2H2O → 2H2+O2, 2 moles reacting to for 3 moles of product, therefore increasing entropy, so forward reaction favored at higher temperatures, becoming spontaneous at the impractically high temperature 2500 °C. At temperatures below this point some electricity is required, but the closer the reaction is done to 2500 °C, the less extra 'nudge' needs to be supplied by electric energy. The highest practical temperatures are near 1000 °C, using a solid oxide fuel cell exactly in reverse mode. Even in view of the above cited thermodynamic advantages, this method has its own disadvantages, namely having to separate the reactant steam from the product hydrogen, by energy wasting cooling to liquid water, then having to reheat it back to the reaction temperature to complete the recycling step.

Mostly likely the most efficient large scale industrial water electrolysis method is, as described in the patent literature, via lower temperature steam injected into molten alkali metal hydroxide, near 200–400 °C, this molten electrolyte being hygroscopic enough so that not much steam evaporates with the product gases so no expensive separation step is needed. Molten alkali hydroxides have very high ionic conductivities, allowing very low resistive losses, and extremely high current densities.

nice text, is going to be integrated in Fuel Cell. Mion 10:19, 9 April 2006 (UTC) Coming from Reversible fuel cell Mion 23:19, 10 April 2006 (UTC)

Some images for free...

... here: http://www.anl.gov/Media_Center/Image_Library/engtrans.html about fuel cell.

These images from Argonne's research image library are available for your use with an Argonne acknowledgement.

-- Harp 07:39, 19 April 2006 (UTC)

Use in aircraft

I removed the following from the article:

"Critics of fuel cells have also pointed out that their proposed use in aircraft (in order to cut the use of kerosene, which contributes massively to global carbon emissions) would have little or no impact on mitigation of climate change, since water vapour, itself a greenhouse gas, would be emitted."

First, there needs to be a source for this statement. Second, it is incorrect. Water vapor is a greenhouse gas, but its concentration in the atmosphere is not changed much directly by human activities. Water vapor is important in that increased carbon dioxide levels, causing global warming, may increase evaporation and therefore the level of water vapor in the atmosphere, increasing the greenhouse effect even further. The warmer temperatures may cause more water to be evaporated, which would increase the greenhouse effect further, causing a runaway greenhouse effect. Also, the burning of kerosene produces water vapor and carbon dioxide, instead of just water vapor, so even if water vapor was a problem, at least carbon dioxide would not be released as well (it is released during some types of hydrogen production, however). -- Kjkolb 17:28, 24 April 2006 (UTC)