Help with a little detail (Thermodynamics)

  • Thread starter timman_24
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  • #1
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I am working on a physics project that has to do with running a gasoline engine on an aqueous fuel mixture. I need some help on one part of my energy balance. The cylinder wall is hot in a running engine, I need to know how much of that heat energy (in kJ)is transfered to the liquid inside of the cylinder by conduction and radiation. I know I would need how long the liquid is exposed, but I don't know if there is an equation to just plug and chug.

Does anyone have an idea?

Thanks
 

Answers and Replies

  • #2
turin
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Are you sure you want there to be liquid in the cylinders while the engine is running!?

I don't know of an equation for you. I imagine that the radiation part can be:

ΔErad = σT4integral{dt A(t)η(t)}

where σ is the Stefan-Boltzman constant (I think that's what it's called), T is the temperature (I'm assuming that the temperature doesn't change significantly over the process), A(t) is the area of the inside of the cylinder wall exposed to the fuel mixture (which can be calculated if you know what the piston position is as a function of time), and η(t) is the emissivity at the fuel mixture-cylinder wall boundary (which I don't know much about).

Then, you might want to use:

H = - k gradT

where H is the heat energy current density in the fuel mixture and k is the thermal conductivity of the fuel mixture. I imagine that this should give the conduction through a quasi-static fluid element. I have no idea bout convection.
 
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  • #3
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Are you sure you want there to be liquid in the cylinders while the engine is running!?
Well it would seem that would not work very well, but the patent that I am researching says the water turns to a vapor once it hits the cylinder. The vapor then get exposed to a large electric shock and dissociates into hydrogen and oxygen which burns. I thought it was bogus from the start and the more I research it the more my first assumption seems true.

Any info on the convection?
 
  • #4
turin
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Originally posted by timman_24
... the water turns to a vapor once it hits the cylinder.
This doesn't sound far-fetched to me. I'm pretty sure it would evaporate during the intake stroke if the valve was closed early enough (due to the lowering of the pressure by the expansion of the cavity).




Originally posted by timman_24
The vapor then get exposed to a large electric shock and dissociates into hydrogen and oxygen which burns.
This part smells pretty bogus to me. The electric dissociation of the water molecules will require some amount of energy. The combustion of these elements back into water will not return more energy than this amount. What is the proposed storage of this energy? A battery? Maybe it's solar? Furthermore, I'm pretty sure that the elements would want to immediately spontaneously recombine (or at least well before the completion of the compression stroke), so it doesn't sound like a very controlled process (and would probably cause a lot of knocking and such). There are a lot of details missing, though, so who knows?




Originally posted by timman_24
Any info on the convection?
No.
 
  • #5
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The water is also exposed to a hydrogen producing catalyst, such as nickle and platinum. This would aid in the dissociation of the water. I agree it does sound bogus, but from my research the city of reno used the process in a few of their city buses with great results.
 
  • #6
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Can anyone give me more information on the n(T) part of the equation that turin suggested. I have all my information except this part.

Thanks
 

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