Instead of using an equilibrium reaction like 3H2 + N2 2 NH3 to heat a boiler maybe there are fast reacting chemicals you could feed to the intake of what would otherwise be an internal combustion engine.
Eliminate the large heat transfer surface areas of vapor power cycles.
Bret Cahill
Like, um, gasoline and air?
Don Kansas City
Gasoline! Do you have any idea how flammable that stuff is? How will you transport it? How will you store it?
Gasoline is waaay to dangerous for use in internal combustion engines. ;-)
Good Luck, Paul D Oosterhout (from SAIC)
The kinematics would be different, not the reversibility.
Bret Cahill
Hollywood likes to have a lot of exploding cars but in real life I've only seen many accidents that resulted in burning cars in one place: SE Texas.
My only theories on the issue all hinged on the proximity of the petro chemical industry. They had gotten into such a habit of sabatoging refineries for "upsets" they even did it to the fuel lines on their own motor vehicles.
Bret Cahill
You'll often hear about a chemical plant generating electricity from burning, say, sulphur to heat a boiler as well as to make the product, H2SO4.
They often also expand a product gas through a turbine to recoup some of the power used to compress it in the first place, but I haven't heard too much about "internal" chemical reaction engines.
Bret Cahill
Just what do you think combustion *is* exactly?
Don Kansas City
With gasoline it's an irreversible reaction.
What's fast, highly exothermic, reversible, nontoxic and the products and reactants liquify at 200 psi, 150 F?
Bret Cahill
No, it isn't. You can generate hydrocarbons using steam and CO2 as feedstock.
If it's fast and highly exothermic, then the reverse reaction will require enourmous energy input. That's just energy balance at work.
Tom.
Remember the universal statement of thermodynamics: deltaG = deltaH - TdeltaS. If you're going to make a highly exothermic reaction reversible, the reverse reaction had better have a huge positive entropy, and you need to run the reaction at very high temperatures, in order to get a deltaG anywhere near a practical definition of reversibility (as close to 0 as possible). In practical terms, this means the reverse reaction needs to involved lots of fragmentation--a very few molecules of condensed material being converted to a very large number of molecules of gas. Take the polymerization of ethylene for example (it's one reaction that I know the thermodynamics of well). It's very modestly exothermic (ca. 25 kcal/mol), and the depolymerization meets the criterion I described above. However, it takes very high temperatures to depolymerize PE. Fundamentally, since you're expecting an exothermic forward reaction, you're going to have to be making some very strong bonds. Reversing the formation of those bonds is kinetically also going to require either extremely high temperatures or a very reactive catalyst--and you better hope that something else in the molecule doesn't decide to react before those very strong bonds.
Eric Lucas
I guess you're trying to cause a reaction without need for ignition?
Furfuryl alcohol will react hypergolically with a nitric acid oxidizer. It's made by reducing furfural (from distilling corn cobs, sawdust, etc.) I think they used to use it in rockets. Have fun.
Don Kansas City
Well H2 +1/2O2 = H2O leaps to mind. But the temp need to thermally split H2O is well above solar thermal. And transport of H2 gas in pipelines is not really feasible.
Ghostwriter
So we are stuck with PV, and closed "air" and vapor cycle engines, nuke as well as solar?
That's IT? That's ALL we have for sustainable power?
With all this talk about getting off of fossil fuels there seems to be very little discussion about engines that run on any chemicals other than fossil fuels.
There are lots of H2 pipelines in SE Texas.
Bret Cahill
No, it is not....We have stirling cylce engines, AMTEC devices, Thermionic diodes, betavoltaics, thermoelectrics
You can run a stirling from solar, The betavoltaics run from energy released in natural decay of radioisotopes, thermionic diodes and thermoelectrics are direct energy conversion devices, while AMTEC convert heat to electricity through phase change of metal salts....
So for these you just need heat, whether it be from the sun with solar concentrators, direct combustion of a fuel (wood, kerosene, gas, oil, whale blubber, your ex wifes menopausal heat flashes....even biodiesel) combustion due to catalytic reaction (external combustion engines)....
then there are other "fuels" like boron..
That's a subset of "air" engines, regardless of if they run on He or H2.
We're looking for 100 quadrillion BTUs/year.
Bret Cahill
Stirlings are heat engines, the "air" or "He" is a working fluid so it is not consumed and only changes phase...the heat source can be concentrated solar.....or you get your heat by direct burning of fuel by ignition or catalyst combustion....
I like the amtecs because they are reasonably efficient when compared to internal combustion engines, and much more efficient than thermoelectrics....and about twice as efficient as PV.
Not sure what you 100 quadrillion BTUs/year for, but none of these will likely be cost effective or even available in the numbers that you would require....there is also direct solar, and solar concentrators which might suit your needs at much less cost.....
You could also use hydrogen peroxide through a catalyst to produce steam to drive a turbine.....
All of these alternative energy schemes fail to address the energy density required - a typical car has an engine that can deliver roughly
100kW at the wheels, and it can do that for maybe 6 hours at highway speeds on a tank of petrol.Now refill the "tank" with any other current or planned energy source ? Suggestions please.
Steve
600 driveshaft kWh? That would be a 58-gallon gasoline tank, so not a typical car, maybe a motorhome.
--- G. R. L. Cowan, former hydrogen fan Boron: internal combustion with nuclear cachet:
Assuming it requires no boiler, THAT'S a start.
Now we need a COMPLETE list of exothermic reactions where
Bret Cahill
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