joseph
Junior Member
Posts: 66
|
Post by joseph on Jan 27, 2014 10:24:24 GMT -8
Let's say you burn the wood, and it produces bright flames that travel into the insulated riser. You can see that the combustion is good.
But then, the flames dies down, and there are hot coals at the bottom, and what is left of the sticks is charred pieces that are still standing but burning slowly.
What is happening? Have all the volatile gasses been driven from the wood, and so the big flames are gone? What is burning now? Different, less volatile gasses?
And is it still working as a rocket, even if the flames are small, and don't reach into insulated riser?
- joe
|
|
|
Post by pinhead on Jan 27, 2014 11:30:20 GMT -8
The "coals" are still pyrolyzing and off-gassing, and the heat from the coals is sufficient enough to burn these gasses. I am of the mind that the coals comprise of mostly carbon, however, and requires high heat to vaporize and burn. Charcoal is a light black residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. It is usually an impure form of carbon as it contains ash.
According to the Testo graphs I've seen on this site, at the coal stage there is a lot of CO being produced (at least in our rocket stoves).
|
|
joseph
Junior Member
Posts: 66
|
Post by joseph on Jan 27, 2014 12:39:28 GMT -8
I am still not understanding something. Initially, the flames are yellow. The coals are red-orange. That implies that the flames are hotter.
However, I see that is an error. Wikipedia says:
"When looking at a flame's temperature there are many factors which can change or apply. An important one is that a flame's color does not necessarily determine a temperature comparison because black-body radiation is not the only thing that produces or determines the color seen; therefore it is only an estimation of temperature."
I have seen small blue flames near the coals. I think they are from the CO. (The ignition temperature of CO is 609 °C or 1,128 °F.)
So can I tell by eye if all the CO is being burnt?
- joe
|
|
|
Post by sparks on Sept 17, 2016 11:53:12 GMT -8
Despite the fact that I am NOT certain this post will actually belong here, I thought I'd give it a go and see what a few of you think, at least that is my theory.
One of the folks in my area (the vet actually) became enthusiastic about the concept of the rocket stove and the multiple purposes that it can perform. He was however asking questions about the fuel. For most of us, the fuel of our rocket stoves has been wood as a rule. I'm sure some folks are working on pellets that are constructed out of just about any biomass available, assuming you can turn it into pellets. (as a matter of fact, I can...)
Given the area where we live, it was his question as to whether or not "stoker coal" would work as a fuel in the rocket stove. I have never tried to burn coal and I have always thought that the requirements for burning coal were different enough as to be incompatible with the rocket stove. However, after thinking about this for a while, there really didn't seem to be any specific caveat to burning coal, particularly a bituminous (soft coal) in the rocket stove, assuming the stove is already burning with a good base of coals at the interface between the magazine and the burn chamber.
There has been research here (IIRC) on the subject of "secondary air" but this is not my interest today. But I do want to know whether or not it would be useful to have if one would try to use a soft coal.
I would appreciate any counsel on this issue of using coal in the rocket stove. Cheers, Trim sends //BT//
|
|
|
Post by satamax on Sept 18, 2016 1:13:00 GMT -8
Tried it. After a certain point, it doesn't work. Too much coal embers, not enough flame to enhance the draft. Same as the coaling stage of wood in a rocket.
|
|
|
Post by Vortex on Sept 18, 2016 1:46:53 GMT -8
|
|
|
Post by tmothy on Oct 19, 2016 23:12:18 GMT -8
Hi Joe, in my experience the charcoal burning phase is very different to wood burning. The wood gas phase has a combustion process that is on the move and results in a tongues of fire as the gas is used up. Also if you consider the chemistry of the fuel components, the hydrocarbons are essentially units of H-C-H which reacts with one molecule of oxygen (O2) to give one molecule each of CO2 and H2O. This results in the production of extra gas in the burning process. In contrast, as you have pointed out, the charcoal burn is on the charcoal surface and is very hot, but it can only make a short tongue of fire in the little blue flames (probably CO) that you observed. Looking at the chemistry if we start with two atoms of carbon and two of molecules of oxygen we can get 2*CO +O2 which will largely covert to 2*CO2. So this charcoal burning unlike, the wood gas, has no more molecules of gas coming out of the reaction than went into it. I think this is what happens at the end of a batch of wood burning in a batch box RMH and some of the charcoal generated CO moves beyond the influence of the hot charcoal surface and it has no more opportunity to be burnt in a persistent flame tongue that is present (in the heat riser) as when the fuel is still making wood gas. The lack of heat transfer to the heat riser, reduce gas flow and turbulence would not help the situation.
In this regard I make an ultralight backpacking tent stove for warmth cooking and snow melting while skiing. At 500 g it is a RMH without mass. It has a small heat exchanger box to act as a radiator and cook top, but it has no heat riser so it depends upon hot gas in the flue pipe to keep the draft going. The stove has a vertical tube feed for the long bush sticks (usually damp or moist) to make a steady column of; a bed of charcoal, charring wood, and drying wood. This works quite well considering how small it is and this because of the continuous feed of sticks down into the stove burner. However, your charcoal issue can be problematic. if the wood sticks are too dry (not often an issue) they can burn too quickly and the charring zone moves too high up the above mentioned column. This produces a lot of heat but in the wrong place and it deprives the flue pipe of heat and the stoves driving force. The stove get locked in this state as gas producing fuel can not get past the charcoal to set things right again. It get worse, because the long fuel tube can become the alternative flue pipe right above this static source of strong heat that is likely to be producing CO. The fuel tube has a cap to stop this. When it come to shut down the stove for the night, the fuel tube can be removed from the burner glass and the opening covered so that the the proper flue pipe is forced to work and there is no second flue pipe to let any CO into the tent. I have also been experimenting with alternative designs that actively attack the charcoal with an extra jet of air. I tried this with a little 5V blower and this worked too well and the stove got just too hot and out of control. The upside of this test was that I found that the small port that I made to fit the fan was just by itself better at attacking and clearing charcoal build up than the original larger port.
I will try to posts a link(when I work out how) to a photo looking down the fuel tube at the burner as it is running out of hydrocarbon and approaching a charcoal only burn. recovery is easy at this stage. Just drop in a few wood splinters and all will be good again.
Tim
|
|
|
Post by tmothy on Oct 19, 2016 23:17:16 GMT -8
|
|
|
Post by tmothy on Oct 19, 2016 23:32:51 GMT -8
Sorry Joe, I will try that link again. 1drv.ms/i/s!AkNtpldPrJ4zg1s3tDkPwVStRn9t
|
|
|
Post by peterberg on Oct 20, 2016 0:32:40 GMT -8
Hi Tim, welcome to the boards. I fixed the link in your second post, in your third post the link is wrong again.
The way to post a link: at the top of the Reply window (NOT the Quick Reply window) there's a row of icons. Click the 9th from the right and there's a pop-up window. First row some random text OR the link, and second row the link. The result is like the one that is in your second post now.
Hope this helps.
edit: Weird... when I copy your link into a new tab in my browser it works. But it won't work when clicked in the forum window, it is redirected to the same forum window in another tab. Sorry, for anyone who like to see the pictures just do it the clumsy way, please.
2nd edit: Fixed it now, "https://" was missing in the link proper. But when that same "https://" is inserted in the text it won't work. Still weird...
|
|
|
Post by tmothy on Oct 20, 2016 1:28:03 GMT -8
Thanks Peter, I still don't see the correct url. I will try again. Tim
|
|
|
Post by tmothy on Oct 20, 2016 1:36:26 GMT -8
Another try. Tim
|
|