Half a croissant, on a plate, with a sign in front of it saying '50c'
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Iron powered engine

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I was watching the truly excellent Periodic Table of Videos and thinking about the oxidation of iron, and iron as fuel. This is not that different than the thermite engine, but is more practical and safer. Thermite is dangerous (although one could make the case that gasoline is even more dangerous!) but iron less so. I am not confident plain iron will burn in air - the frustrating trick with steel wool and O2 gets the iron hot but I am not sure the lump will burn up once hot. But as seen on the internet, iron will burn briskly in pure oxygen or even explosively in LOX.

Could a hopper of pulverized iron, perhaps initially heated via induction, burn in unenriched air? And by burn I mean like a nice, orderly charcoal fire, not some furious flame frenzy.

I envision this hopper of iron bits as the fuel chamber, much like the fuel chamber of the old Stanley Steamers grandpa used to talk about. A blower fan provides lots of air and with it O2, and the iron starts to burn and emit heat. Once it does you can turn off the battery and the induction, and once you have steam you can set off in search of more scrap iron, recharging your battery on the way.

Here at BUNGCO we were a little skeptical that a strong breeze would be enough - and plus as we ramped it up it started kicking the iron bits all over and then out the vent holes. You can't have a strong breeze in one end and not out the other, but when it is carrying glowing bits of iron oxide some people start to fuss, especially when his fancy motorcycle is in the way.

We rigged up an oxygen concentrator borrowed from an emphysematous friend to provide more O2 with less gusty N2. Of course this taxed the battery even more but once the steam started chugging along all was forgiven.

bungston, Apr 18 2015

Steam car http://en.wikipedia.org/wiki/Steam_car
[bungston, Apr 18 2015]

Thermite engine Thermite_20powered_20steam_20car
Good old iron seems more friendly and predictable than that johnny-come-lately, aluminum. [bungston, Apr 18 2015]

Burning iron for kids http://topscience.o.../FreeDownload11.pdf
These folks also knew about the combustion properties of steel wool. They are linked because of their practice of conducting experiments naked except for safety goggles. New to me but possibly familiar to others around here. [bungston, Apr 19 2015]

Engineuity’s wire+O2 hydrogen+steam generator http://wayback.arch...2520&CategoryID=354
[CraigD, Apr 20 2015]


       Might use magnetic fields to suspend the particles and to ignite it ?
FlyingToaster, Apr 18 2015

       Feeding iron powder into an air jet and then into a combustion chamber might work. But the fuel is going to have to be stored either under dry nitrogen, or as a slurry in oil, otherwise it will oxidise and "clump" into large particles.   

       The energy density of the fuel will be low, and the whole system is going to have to run at a fearsome temperature. The fact that the primary combustion product is a non-volatile solid is an additional challenge.
8th of 7, Apr 19 2015

       //Could a hopper of pulverized iron, perhaps initially heated via induction, burn in unenriched air?   

       I think a counter-example is given with grinding. Plenty of white hot sparks, which extinguish before full oxidation. What is interesting is that the alloys seem to burn first: the carbon causes the spark to frizzle (good word, that); the Manganese causes spears, and so on, as they burn off.   

       As an aside: Liquid steel does oxidise, but not explosively. Most of the time, there will be a covering of slag/scum. However if the covering is actively removed, by bubbling Argon gas, you can see the liquid steel directly (around 1650C). What is strange is that it is so hot, I could swear that it is past white colour, and appears to have no colour at all in certain patches.
Ling, Apr 19 2015

       /Liquid steel does oxidise, but not explosively/   

       I wondered about that,given that air or oxygen is bubbled thru iron in the making of steel. I wonder if that has to do with surface area - a dense fluid will not have that much of the volume in contact with the oxygen at any one time.   

       /run at a fearsome temperature/ - This is the part I wanted to sidestep. If steel wool burns in oxygen and not in ambient air, there must be some middle ground where combustion is sustained but at a moderate pace.   

       /grinding/ what is grinding? Like with a grindstone?   

       /energy density low/ OK I am going to try and see about that. I am sure there are bakers for whom solving that would be trivial but I am not one.
bungston, Apr 19 2015

       //This is the part I wanted to sidestep. //   

       ... thus neglecting the fact that the Carnot efficiency is directly proportional to the change in temperature of the working fluid.
8th of 7, Apr 19 2015

       //If steel wool burns in oxygen and not in ambient air//   

       Typical steel wool will burn in air, but only if there's a forced draft. Sufficiently fine steel wool will burn in still air. A fine iron powder would burn just... fine.
MaxwellBuchanan, Apr 19 2015

       /Carnot efficiency/ is this proportionality true when there is a phase change?   

       I found loads of different carbons but I have come up empty for figures showing energy density of metals to be oxidized.
bungston, Apr 19 2015

       // I wondered about that,given that air or oxygen is bubbled thru iron in the making of steel   

       Ah, but the Carbon oxidises first....then the alloys. Pretty much last to oxidise is Iron. Bessemer, or his underling, was a brave man.
Ling, Apr 19 2015

       Ling, if you were to let the Bessemer process go would the iron all rust eventually too? Or is it somehow too hot to oxidize?
bungston, Apr 19 2015

       There are some better choices of metal for schemes like this, such as aluminum or magnesium, and it’s not necessary to have a flame, only the reactive metal and oxygen.   

       Something much like this was briefly baked in an aggressively businessly manner in 2005 by the small innovation company Engineuity R&D Ltd (see link). They (chiefly its lead inventor, Ammon Yogev) claimed a good working prototype of a hydrogen + steam generator fueled by spools of thin aluminum or magnesium wire in a cassette that could easily be recycled back into clean wire, then retracted all mention of the idea almost more quickly than archive.org could snapshot its webpage.
CraigD, Apr 20 2015

       bungston, yes the iron would oxidise. I must admit, we never oxidised a whole heat (batch), but some operators at the steel plant had a bloody good go at it...
Ling, Apr 20 2015


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