Anyone have success using metals inside their rocket stoves?

To me real rocket is insulated to reach proper temperature and combustion.

OK Gentlemen......

I took some time and went back and read what your true definition of a Rocket Stove was. If it absolutely HAS to have a firebrick riser, or a non metal riser, then I guess I have built a really good pellet stove that makes a rocket noise and burns wood pellets very efficiently.  My initial prototype lasted 3 years of heavy duty use. When I did my autopsy, yes the metal riser had compromised and I will admit I made the same mistake with my Mark 2 out of ignorance. That does not mean I will not continue to it to keep my house warm by using the Mark 2. I am certain that burns clean and hot.  But what I will do is, when I build my next one with a refractory riser I will repost it as a true Rocket Stove. I can survive knowing that my design cannot be a "definition grade" rocket stove and I will enjoy heating my entire home for less than a the cost of a fast food chain "Americano" coffee.  Thank you for the dialog.

Peter,

Lately, for prototyping, i use superwool 607 grabbed on eBay. And metal outside of the superwool.  Just to hold it.

I know how to weld,  and my first rockets were metal too.

But i ended melting  a gas bottle, up to the point it sagged under it's own weight and turning 6mm thick tube, into puff pastry.

Then switched to chamotte flue elements. They can last  three years if supported.

Then to the 5 minute riser described above.

I have never delved into 3 inchers. But from people who've built some. They're underpowered.

I have a 9 incher batch with a broken riser, and 4 ton mass. And when you have heard such a thing go at full tilt, in the midst of the winter, with minus twenty celcius outside.  I  think you start to understand what real rockets are.

Satamax Antone wrote:
Lately, for prototyping, i use superwool 607 grabbed on eBay. And metal outside of the superwool.  Just to hold it.

Have you tried this ceramic board super wool too?: Ebay superwool board link

Perhaps if it's more rigid you can minimise the amount of metal?

Henry Jabel wrote:

Satamax Antone wrote:
Lately, for prototyping, i use superwool 607 grabbed on eBay. And metal outside of the superwool.  Just to hold it.

Have you tried this ceramic board super wool too?: Ebay superwool board link

Perhaps if it's more rigid you can minimise the amount of metal?

I haven't , but i think Peter did at some point.

Satamax Antone wrote:To me real rocket is insulated to reach proper temperature and combustion.

OK, what is proper temperature? Where in the core is it measured?

What is proper combustion? Must this measured by a Testo?  So if someone's rocket has not been Testo Tested is not a Rocket?

As I understand it, the correct temperature for complete combustion is ABOVE that which steel can survive intact.  

Therefore permies.com currently does not recognise a stove to be a rocket if the core is made of un-insulated metal such as steel.  

And unless anyone can show that their metal cored stove really does reach that temperature, we will not accept that it is a rocket.

Therefore, I suggest that any reference to an untested metal stove NOT be called a rocket in this forum.

Bruce Woodford wrote:

Satamax Antone wrote:To me real rocket is insulated to reach proper temperature and combustion.

OK, what is proper temperature? Where in the core is it measured?

What is proper combustion? Must this measured by a Testo?  So if someone's rocket has not been Testo Tested is not a Rocket?

Bruce, you start to do my head in, always searching for confrontation.

I would say proper temperature is above 800/900 celcius, in at least the burn tunnel and 2/3rd of the heat riser. And this has to be for the whole column of gases, even the boundary layer tiutching the burn tunnel and heat riser walls.

This. In turn would allow for full combustion of creosote and dioxyns.  Up to 1200c° is nice i would say. Above is hard to reach.

Yes i'm aware that this is in nox territory.

Not actually found the references I want (yet) but I did find these 2 pages:

melting points of metals.  Steel actually isn't "molten" at the temperatures you want to achieve, but it might well be hot enough that it's no longer structurally sound,  because steel doesn't change from solid to liquid like ice changes to water - it becomes progressively softer and more malleable until it reaches a point where it flows and could be considered "molten".  Steel will and can also oxidize, if there's any surplus oxygen around.  For example, an Oxy-acetylene torch cuts steel by using a narrow jet of oxygen applied to oxidize bright red hot steel.  However, in a stove, you'r fairly unlikely to have much surplus oxygen.

The other interesting page (to me at least) is about combustion of wood.  It's actually, I think, referring to it from the point of view of building fires and safety, but combustion is combustion after all and burning wood is more complex than I at least imagined it to be:
burning wood

I'd imagine the hardest bit of the wood to burn is the carbon.  Completely unburnt carbon will show as soot or "tar" (carbon made sticky with other stuff) in the flue; partially oxidized carbon will show as a high percentage of Carbon Monoxide (CO) in the flues gas.  Thus I contend that you can measure how good your combustion is by measuring the CO in the flue gas.  I know this is done to tune oil and gas boilers - they put a CO probe in the flue and adjust the burner to minimise the CO.  The same is done for car exhausts, in addition to, these days, measuring unburnt hydrocarbons (HCs).  I've never tried that on a stove of any kind, mind you.

Satamax,
Please understand, I am not seeking confrontation, just information so we can accurately address facts and come to proper conclusions.

So you say a real rocket will develop flame path temps of 800-900C or 1472-1652 F   (this is well above 900F or so where steel starts to glow red and will very quickly oxidize and spall.)

Now while my air-cooled core does not glow red, the flame path within it far exceeds 900F!   I have melted aluminum  (temps above 1220 F) 2 feet up in my heat riser in about 30 seconds from lighting the fire!  Do you not think that by the time the system really gets heated up that that temp range just might go up another 200 -400 degrees F???   I know it does but I don't have equipment to measure it.  I have been doing this for two complete heating seasons now and starting the third with this same core.

So I have conclusively proven that the flame path temps far exceed the actual temps of an air-cooled core and that my air-cooled steel cored rocket actually does develop temps well within your range of a real rocket. Thanks for your help to verify this!

Bruce Woodford wrote:
So you say a real rocket will develop flame path temps of 800-900C or 1472-1652 F   (this is well above 900F or so where steel starts to glow red and will very quickly oxidize and spall.)

Now while my air-cooled core does not glow red, the flame path within it far exceeds 900F!   I have melted aluminum  (temps above 1220 F) 2 feet up in my heat riser in about 30 seconds from lighting the fire!  Do you not think that by the time the system really gets heated up that that temp range just might go up another 200 -400 degrees F???  

Melting aluminium at 1220F is nowhere near the temperature max said was required, it's only around 660C.

Unless you have real proof that your stove is burning at rocket temperatures, you need to stop trying to claim that it's a rocket.  

I'll be removing any posts that make such claims very shortly.

Bruce Woodford wrote:Satamax,
Please understand, I am not seeking confrontation, just information so we can accurately address facts and come to proper conclusions.

So you say a real rocket will develop flame path temps of 800-900C or 1472-1652 F   (this is well above 900F or so where steel starts to glow red and will very quickly oxidize and spall.)

Max also said that the (minimum) temperature of 800-900 °C has to be through the whole of the gas column including the layer touching the walls.  You can't pick just the bits you want from the information...

Austin Shackles wrote:Not actually found the references I want (yet) but I did find these 2 pages:

melting points of metals.  Steel actually isn't "molten" at the temperatures you want to achieve, but it might well be hot enough that it's no longer structurally sound,  because steel doesn't change from solid to liquid like ice changes to water - it becomes progressively softer and more malleable until it reaches a point where it flows and could be considered "molten".  Steel will and can also oxidize, if there's any surplus oxygen around.  For example, an Oxy-acetylene torch cuts steel by using a narrow jet of oxygen applied to oxidize bright red hot steel.  However, in a stove, you'r fairly unlikely to have much surplus oxygen.

Austin, actually, the rocket suffers from an excess of oxygen.  That's why these spall so badly.

You have heat creep starting between 400C° to 650C°, depending on the steel.

There is also "carbon starvation"  where the combination of steel and excess oxygen rob the carbon of the layer exposed to the fire, basically burning it. This is one of the mechanism of spalling.

Allen Lumley at some point showed an article about this.  Can't seem to find it.

There is also this.


https://en.wikipedia.org/wiki/Hydrogen_damage

https://www.corrosionclinic.com/types_of_corrosion/high-temperature%20hydrogen%20attack_decarburization.htm

Austin Shackles, you wrote,
Max also said that the (minimum) temperature of 800-900 °C has to be through the whole of the gas column including the layer touching the walls.  You can't pick just the bits you want from the information...

I'm just curious, how would one measure temps at say three different spots in the flame path....i.e. centre, midway and periphery?  Has anyone here with a rocket actually been able to do this or is this just theorising to maintain the status quo that "a metal cored rocket is NOT A ROCKET"
I'm just curious.

A metal cored rocket, if insulated is a rocket. It won't last long, but it works.

A aircooled metal fumivore is not a rocket. You don't cool rockets. You're looking for more heat to burn the most efficiently as you can.


And measuring "points" can be easily done, in several ways. Therocouple type K on the DMM for example. Or infrared laser thermometer. Careful, metal reflection bugs the temperature reading.

Peter Chauffeur wrote:Hi John.

I recently posted  my prototype Rocket Stove / Mini Thermal Mass Heater on this site. I ran it for 3 Years from fall to spring each year and posted a thread on its autopsy. I used standard thick walled square tube for the burner and 3 inch diameter muffler tube for the riser.  Now 3 years of start and stops every day ( as I shut the pellet stove down each night} is a lot of cycles and the riser did manage to suffer fatigue and I think it was due to bell housing not being able to dissipate the heat quickly enough.  I am currently building a Mark 2 version and I am recycling the burner assembly for two reasons: 1}  The burner assembly works very well and 2} it will be a benchmark for when I actually have a little more time to make a second burn tube with a larger hopper and continue my experimentation with steam injection in the secondary air inlet.  Check out my design, perhaps we can exchange ideas.

Peace Health Happiness
Peter Chauffeur

awesome peter, i was recently talking with another rocket builder and he said his metal has never melted either.  the only time i had metal melt was when i used a thin normal stove pipe for a riser LOL, it melted and disformed but it was only a temporary test riser.  my latest ones have firebricks and cast core, but my metal RMH with internal mass has proper thickness burn chamber 1/4" thick steel and riser is around 3/16" thick steel.  i do recognize metal can melt, if you make a riser out of normal thin stove pipe and insulate it, it likely will melt quickly, but in my experience thick un-insulated metal components work, and burn more efficiently than a regular wood stove.  un-insulated steel rockets might last, i know several people using them, and i have one which i've torture tested for well over 150 hrs.  i can argue both ways, metal will melt if you use a stove pipe and insulate it yes, but also you can achieve a clean efficient burn with thicker materials and avoid meltdowns, use stainless liners and uninsulated risers.  metal has a catalytic effect also when its hot enough.  i'd be willing to look at your design sure.  personally i had to test my metal RMH hybrid (cottage heater) for over 100 hrs before i would consider rating or installing it.  i really lean toward the batch designs now, i like to close the door and walk away more like traditional a wood stove, but i adore the rocket mass concept and efficiency

Metal doesn't melt, metal spalls away.

https://permies.com/t/52544/metal-burn-tunnel-heat-riser

you need to see this, my first rmh hybrid stove.  i did switch to firebircks and cast cores later, (mostly for critics) but my first one is steel with concrete inside, thick burn chamber and riser.  its amazing to watch, super clean burning.  my last builds were masonry type but i've tested my first steel rocket over 150 hrs and it works great.  i put my hand on it and its ice cold!  its truly amazing check it out.  this is a revival episode where i dig it out of the backyard snowbank and fire it up for old times sake.  this is after building the firebrick match box and the cast core, both refractory models, and i find myself returning to the good old faithful original upright massive hybird, which is metal j-tube.  
you need to see this stuff.  this one has been torture tested over 50 episodes and 150 hrs, burns sticks and pellets and bakes pies and pizzas :D
see the revival video here