Thread: Photovoltaic combustion cars?

It's known that hydrogen burns in ultraviolet
range of spectrum.If I no make mistake the
more energetic photons we have the greater
efficiency photocells could have.And also it's
easier to make photocells which are designed
for some narrow range of spectrum.
What prevents to create and use highly efficient ultraviolet photocells which work from
burning hydrogen or gasoline?Maybe it's cheaper than fuel cells?And what about gasoline,in what range of spectrum will it burn?There's plenty of hydrogen atoms.

You could possibly use it as well as a fuel cell.

Most of the energy, though, is turned to infrared rather than ultraviolet/visible light.

Most of the energy, though, is turned to infrared rather than ultraviolet/visible light.

Do you mean burning of hydrogen or gasoline?As I know hydrogen burns with invisible ultraviolet flame.Or you mean that
photocells are so non-efficient that they
waste much of energy as heat?
How do you think efficient could be photovoltaic system for a car?I think if we will
create a good thermal isolation,maybe even vacuum isolation,so energy from combustion
will not be able to escape otherwise as radiation,and will make few layers photocells,
efficiency could be closer to 100%.

I suppose most of the combustion energy from burning hydrogen is not instantly emitted from the flame (as UV or any other radiation) but remains in the hot water vapour. Photovoltaic cells would not be able to use that, and so this solution would be very inefficient, dissipating lots of energy as unused heat.

It would make much more sense to use the hydrogen in an ordinary internal-combustion engine (such as contemporary pertol or Diesel engines). Fuel cells are another option (I am not sure which is better).

Just my gut feelings - I have not studied the maths or physics behind any of this.

I can work it out for you;











So yes, if the energy is released in a single photon it would be very near ultraviolet radiation, you are correct. However, electrons will more often de-excite in steps, rather than in one go, releasing a number of lower-frequency photons (not ultraviolet). This is why we see the following in the combustion of hydrogen;




In addition, the efficiency of even the most modern photovoltaic cells is around 33%, compared to around 50% in a hydrogen fuel cell. So while using a photovoltaic cell may technically be possible, it makes more sense to use a fuel cell.

Hope this helps.

In addition, the efficiency of even the most modern photovoltaic cells is around 33%

In conventional solar cells there is number
on looses which could be avoided in combustion camera.For example light reflection.If some photon will be reflected in
camera it will just get in other photocell (on other side).

I will look into it, but I think it's 33% of energy absorbed is converted to useful energy.

I do maintain that this could be used in conjunction with a fuel cell, though.

I do maintain that this could be used in conjunction with a fuel cell, though.

Do you know why fuel cells have such low power density?Is there some hope to increase it?There exist entire bunch of technologies which convert heat directly to electrics:

1)Thermoelectrics
2)Pyroelectrics
3)Thermovoltaics
4)Infrared antennas
5)Fuel cells

It's strange that non of them works better than
internal combustion.And especially great problem is power density.

Originally Posted by Stanley514

I do maintain that this could be used in conjunction with a fuel cell, though.

Do you know why fuel cells have such low power density?Is there some hope to increase it?

Yes; put the fuel through the cell at a greater rate. Or find better catalysts for ionising the hydrogen. As the price of petrol increases, I'm confident more money will go into fuel cell research, and any problems will be solved.

That's an interesting picture. Hydrogen flames do emit IR as well as UV, due to the main product of combustion being water vapor. However, IR and UV are not visible to the human eye so what are we seeing? Usually a yellow flame is associated with burning hydrocarbons. Is it in fact the burning of the rubber balloon that the hydrogen was contained in, or is it perhaps not a true-color photo? I'm just curious because I've seen many hydrogen flames, and I've seen hydrogen filled ballons exploding but I've never seen a yellow flame. The Hindenburg disaster exhibited a yellow flame and this was attributed to burning of the aluminum paint on the cover, and/or burning diesel fuel.

(I was curious enough to google up the source of the photo, which is here
http://uw.physics.wisc.edu/~wonders/DemoH.html and was a bit shocked to find this statement on a university physics page:

Helium is a special gas called a Nobel Gas

The word is noble not Nobel.)

The colour of the flame depends very much on the availability of oxygen. In a balloon, oxygen is only present in tiny amounts to the hydrogen in the middle. The hydrogen around the outside probably burns with an invisible flame.

I think the IR in combustion comes from the new bonds formed moving/bending/stretching to de-excite.

Another point; the calculation I did before was slightly wrong; I should have used the bond enthalpy for the O-H bond rather than the enthalpy of combustion. Luckily, the two are very similar values.

I did try to find a spectrum of the photons released by burning hydrogen, but could not find one on google.

Hydrogen has a very wide flammability range with oxygen and I don't believe it ever burns yellow.

I remain skeptical that the color was due to the hydrogen, and not some other combustible material. However I'm more than willing to be proven wrong.

Interesting words and pictures here:

http://books.google.com/books?id=Hju...um=7#PPA165,M1

I suppose most of the combustion energy from burning hydrogen is not instantly emitted from the flame (as UV or any other radiation) but remains in the hot water vapour. Photovoltaic cells would not be able to use that, and so this solution would be very inefficient, dissipating lots of energy as unused heat.

A burning hydrogen flame, for instance, radiates strongly in the 185 to 260 nanometer range and only very weakly in the IR region, while a coal fire emits very weakly in the UV band yet very strongly at IR wavelengths;
http://en.wikipedia.org/wiki/Ultraviolet

So maybe it's just question of technique to
get UV light from burning hydrogen and use it
in highly efficient UV cells?
And also I thought that in specially designed
combustion camera all radiation not absorbed
by photocell could be reflected back to heat source.

Yes; put the fuel through the cell at a greater rate.

What is main limitation of fuel flow in fuel cell?
Is it mostly chemical, like speed of catalysis or
rather mechanical problems?
I thought that catalysis should happen in milliseconds.

Originally Posted by Stanley514

Yes; put the fuel through the cell at a greater rate.

What is main limitation of fuel flow in fuel cell?
Is it mostly chemical, like speed of catalysis or
rather mechanical problems?
I thought that catalysis should happen in milliseconds.

The think the limit is how fast you need to go; I suspect they are built more for economy than for speed. It may be technically possible to get more power out of a fuel cell, but there is no need to do so in a car.

I suspect they are built more for economy than for speed

But catalysis all the same always happens with
the same speed.How could they slow it down
and thus increase fuel economy?
In general fuel cells seems to me less fortunate then their metal-air siblings.
The latest don't need any catalyst or bulky
membranes.It could be good to see the same
improvement in fuel cells which work on hydrocarbons.

You also may take in account this:
http://www.triplepundit.com/pages/nanoantennas-so.php

I also interested to know how could we
insulate combustion camera so energy would
be able to escape only as radiation?
Is usual glass OK for this purpose?
Is it prosorous for IR?