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AuthorTopic: Spontaneous ignition discovery  (Read 859 times)

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Offline blobrana

Spontaneous ignition discovery
« on: April 20, 2005, 07:37:43 PM »
In a paper scheduled to appear in the May 18 2005 print issue of the American Chemical Society's Energy & Fuels, professor Zhiyu Hu will propose a highly efficient method to convert chemicals into thermal energy, and to achieve spontaneous ignition and sustained combustion at room temperature.

The "nano-catalytic reaction" uses nothing but nanometre-sized particles of platinum stuck to fibres of glass wool in a small jar with methanol and air – with no source of external ignition.
This appears to be the same technique used by natural organisms such as microbes, plants and animals to obtain energy from oxidation of the same organic chemicals at [ their ] body temperatures. Biological reactions also use metals as part of their enzyme catalysts.
"Since the caveman days, we have burned things to utilize their energy, and the high temperatures and the entire process have created a lot of problems that we're then forced to deal with." - Zhiyu Hu, a physicist in the Life Sciences Division of the Department of Energy's ORNL.

This will have deep implications for the energy crisis: By using this phenomenon, we will have the ability to create much higher efficiency and less environment damaging engines, due to the lower combustion temperatures. Even an advanced fuel cell is only about 50% efficient, and it must be operated at high temperatures, which of course requires more costly components.

"What we have is the possibility of retrieving energy at a lower temperature with greater efficiency and lower environmental effects."

The method outlined in the paper "Nano-catalytic spontaneous ignition and self-supporting room-temperature combustion," co-written by ORNL's Vassil Boiadjiev and Thomas Thundat, was discovered unintentionally while conducting another experiment with platinum particles, methanol and cotton swabs. Zhiyu noticed the mixture spontaneously  produced smoke.
"This wasn't research that was funded, so I worked evenings and weekends to try to understand why and how this happened".
Various experiments replicating the discovery under different conditions produced reactions that reached temperatures greater than 600 degrees Celsius, and `low` temperatures of just a few tenths of a degree above room temperature, dependant on the varying amount of fuel-air mixture, and by changing the particle size or the particle's morphology, or shape.

Offline Cymric

Re: Spontaneous ignition discovery
« Reply #1 on: April 20, 2005, 10:18:25 PM »
The research is interesting, if nothing particularly new save for the morphology of the catalyst (quite a few metal hydrides combusts spontaneously at room temperature, and so does white phosphorus), but there are some remarks in that story which have me raising my eyebrows over their validity.

For one thing, the remark that the discovered reaction will have profound implications on the energy crisis is, how to put this nicely, bogus. Carnot's Law tells us the maximum thermodynamic efficiency of a combustion cycle is equal to 1 - T_l / T_h, where T_l is the lowest temperature in the system (often the coolant), and T_h the highest. In other words, you want high combustion temperatures, as the efficiency goes up! Or in yet other words, combustion at slightly elevated temperatures is a waste of precious energy. Of course, high temperatures put a strain on the materials used to contain such conditions, but that has nothing to do with efficiency.

Second, fuel cells have much higher efficiencies than claimed by these researchers. The trick is that you can extract energy not only from the reaction in the fuel cell, but also from the hot gasses these things invariably produce. Carnot's Law only applies to the last part; chemical energy converted directly into electrical energy (which pretty much amounts to the same thing, really, but okay) are not restricted since they lack the steps involving heat. Commercial efficiencies for large SOFCs are expected to reach 70% or thereabouts. Of course, the fuel cell itself accounts for about 55% (bringing it in line with what is claimed) and any improvement in the cell will immediately increase the total efficiency. But these are hardly state-of-the-art designs, and if the total is already 70%, it sounds a whole lot less spectacular, doesn't it?

Also cause for some raised eyebrows: some of the reactions themselves produced heat sufficient enough to heat the samples to well over 600 degrees C. I'll eat my shoe if those reactions are not what people want: they indicate a high reaction rate, and thus, in a fuel cell, a large current. People are all for large currents because of P = V * I.

Finally, the research doesn't say a single thing about the physical stability of the catalyst (is it subject to Ostwald ripening, for example, as this would seriously diminish the total reactive surface and render it useless) or the chemical stability (can it tolerate low concentrations of CO or sulphur). People have produced beautiful materials for use in fuel cells, but I can virtually guarantee you that if they are not sulphur-tolerant, they are of little commercial use.

The research is a beautiful illustration of serendipity, but I fear the researchers succumbed to the disease of too much publicity :-). They'll return to Earth sooner or later.
Some people say that cats are sneaky, evil and cruel. True, and they have many other fine qualities as well.
 

Offline blobrana

Re: Spontaneous ignition discovery
« Reply #2 on: April 20, 2005, 11:47:36 PM »
Hum,
Well its early days yet and I assume that there is a great deal more research to be done.
But then again, as you say,
perhaps it’s bogus, but the principle of lower temperature and better efficiency doesn’t violate the Second Law of Thermodynamics. So i  think the nano-catalytic reactions  that can propel a cheetah along at 60mph using `low` temperature reactions is what he’s trying to achieve…

Offline Cymric

Re: Spontaneous ignition discovery
« Reply #3 on: April 20, 2005, 11:59:56 PM »
Well, lower temperature and better efficiency does violate the 2LoT if it involves conversion of chemical energy into heat first. Our cells do not, they follow the 'fuel cell'  approach, hence the theoretical efficiency of about 42% for the Krebs (a.k.a. citric acid) cycle. That cycle oxidises carbohydrates, but it does not convert them completely into heat---otherwise the efficiency would be approximately 11%, given a core temperature of 310 K.

And perhaps the authors know perfectly well what they are trying to achieve, but that the translation of what they wrote down is just exceedingly bad. Either way, it is cause for some head scratching, although---and I agree with you there---that it is beautiful research and that a lot still needs to be done before practical applications are viable.
Some people say that cats are sneaky, evil and cruel. True, and they have many other fine qualities as well.