Experimental Downwards Blast Furnace. (Making a reverse-flow flue fire) 

Cheap infrared thermometers typically don't go very hot, not anything near a glow you can see. Also, most glass is infrared opaque, so it wouldn't work through the glass.

Until I found this channel, I'd never realised I needed a plasma cutter and a MIG welder.

Your little channel seems to be attracting "the right crowd"

This comment is here to boost your standing in the youtube algorithm

What you made is basically whats called gasification stove. You don't want the fuel to burn directly, but instead become so hot it gasifies, then lead the gas downwards and mix it with air to have it ignite. Try to add less air to the fuel, but add a second air inlet below the fuel where you force air in with a blower

Be careful, Tim! Wear some protective gear. We need you safe and sound for these amazing experiments. :)

You are a good chunk of the way to building a wood gassifier!

Hi Tim, The glass did not break due to the heat but rather the cooling from the refueling! The coker glass is high temp. but nothing like we use on our gas fires and solid fuel stoves. Try a small stove glass as they are cheap on line from ceramic glass specialists. Very interesting though!

it kind of resembles rocket mass heater. or a rocket stove. sort of.. great content!

You need to look into “ rocket stoves” its basically what your making. Great vids, love the railroad.

Brilliant Tim! Love the experiments.. .as a gas engineer all the condensing appliances of today are downward facing burners with premixed gas and air..and combined with three sets of tubular water heat exchangers it extracts as much of the heat from the flue gases leaving as you know condensate waste .hope.that helps.cheers Andy

If I remember correctly, longer funnels result in stronger draft through the firebox. You may als want to consider having sideways inlets to the fire area so that no matter how much fuel you pour in on top, the air can still continue to flow through the fuel at all heights. This could be achieved by having the pipes or the grate in an L shape.

That was cool! Pleased you (apparently) were not hurt when the glass went bye bye. ☮

I almost jumped out of the chair when the glass exploded 🤣

Agree with one of the other posters.... You are only one step away from a rocket stove. As I understand it, rocket stoves get their efficiency by running the combustion zone at really high temps. Taking the heat from the exhaust gases. By having your water pipes in the grate, you are cooling the combustion zone and losing that efficiency? My own workshop heater is now a rocket stove, and mighty impressed I am. Far more fuel efficient than my earlier pot bellied stove (19kg gas bottle built).

Excellent work I love your ‘out of the box’ thinking.

An S-bend furnace! Brilliant. :)

"rocket mass heaters" or "rocket stoves" use these upside-down fires with tall chimneys, the heat in the flue gases in the chimney draws the fresh air into the fire and so needs no artificial airflow.

what a science project

this look like a variant of 'rocket stofe' - suggest you look it up - it has been optimized for airflow, fuel feed. nicely done vid!

you are always fun to watch. creative and frugal.

At least you a prepared to give things a try bro, nice one. All the best

Several years ago rocket stoves, were the rage several guys experimented with down draft stoves they also played with secondary air injection

Interesting experiment! It kind of looks like a rocket stove or a Franklin’s Pennsylvanian fireplace. On a larger scale model you will probably need some way to access underneath the fire to clean the ash out. A longer chimney might work too.

Rocket stove and wrap copper piping around the outside of the old oil barrel, and capture the chimney heat in a lovely seat/bench

*@Way Out West - Workshop Stuff* You might probably want to build in some kind of "bypass pipe" for the air, because when you add enough fuel, it starts blocking the airflow and could maybe choke the fire, but if a small part of the air can bypass the fuel, then it can keep the fire burning, you might also get a "secondary burn" out of the fuel-gasses, in case the gas/air mixture becomes optimal again & the temperature is high enough. 3:46 I guess you could drill a few small holes in the area between the pipes & tip of the arrow in this clip, that would work as a bypass, maybe a small hole also just straight under the chimney, for a second burn (needs more experimenting). But be careful, each hole also lowers the amount of "suction" that the chimney can provide, so it's a balance there, you probably need a much longer chimney too.

What a very interesting and ingenious idea! If I were to scale this up and add water tubes in where the grate is, I would ensure that your pipes are all slanted up at one end, somewhat like you have the grate now. That way, you can inject water at the lower end, and steam will collect at the higher end. I'd also pipe the collected steam up into the exhaust flue for further heating. (maybe collect it in a small tank within the flue?) Then the wet steam can be further heated. Lastly, if you have trouble drawing a fire at first, I might consider using a steam blower. This would take some of the steam produced and blast it up the chimney, drawing the fire. At least that's what they do on steam locomotives when they need some "helping along" to get the fire going. Just some ideas of mine. I'm excited to see where this goes!

Pretty nice design, little more work and I think you will have something useful for your needs.

We just love you Tim and what you do your a genius at everything you do we love it when you can hear the donkeys we just love Irish Donkeys.You help us to unwind after a stressful day.Wishing you all the best.

I had a bio mass boiler business. I installed 'Vigas' wood burning boilers. They are what's known as inverse combustion technology where the flame is at the bottom of the chamber. The oxygen feed is controlled buy a fan and a gate valve. The valve opening is with a servo and the combustion is monitored by a lambda sensor in the flue. The gate valve is weighted and in the event of a power failure will automatically close.. The flame reaches temperatures around 2000⁰c. The hot gases run up the back of the stove past a matrix of pipes exchanging heat to the water system. Heated water is held in an accumulator tank, typically 2000 litres minimum. Heating of the tank is achieved with a smart valve and pump ( laddomat 21)... The system is highly efficient and almost carbon neutral. Obviously this summary is just the basics... Feel free to message me back for more advice and information...

One thing to consider would be that the ash is being pushed into the chimney, instead of falling out of the way, and if not cleaned out over a longer burn, would eventually plug the works up.

Roll the sheet steel round formers to make the flue more serpentine, thus removing a significant amount of drag from the airflow (bulge out the bottom of the LH flue wall & put a similar radius on the bottom of the RH flue wall).

another handy advantage of this is it must be a dream to scrape out the ash from a second door on the side of the chimney

Look up rocket stoves. One way to help it to start would be to have a damper in the stove between the chimney and combustion chamber that you close off when it gets going nice and good. Also to have an ash cleanout on the chimney side. The reason why the glass shattered is that it was heated in one spot instead of evenly.

A very similar design to the Trianco gravity feed coal boilers of the 70s and 80s except the fan blew air direct into the fire not through the fuel load. The fuel was loaded into a hopper with a sealed lid and as it burnt the fuel level went down by gravity, Cheers

That reminds me of the open fire we had when I was a young one I think it was a baxi it had a back boiler and you could close the front part of the chimney off and draw all up the back. The Ash pans was below the fire.

What a pretty demonstration piece! Very surprised the glass didn't crack earlier. I don't know if the grate holding your fuel will last longer because the air is pretty devoid of o2 by the time it gets there, or if it will erode more quickly because of the higher heat. Either way, in that design I think it makes sense to have the grate be a loose piece that's a bit oversized so it wedges into the bottom right corner and leans against the left wall. Easy maintenence that way, and easy removal for emptying ash if you don't want to put in a door for that.

Interesting! This all looks very rocket stovey. At least some of the door glass in woodstoves is actually some kind of weird transparent ceramic. It’s designed to withstand the fire up against it. Maybe you can find a piece of that even if just for the section directly against the flames. Also, modern Wood stoves have cleaned their exhaust by incorporating recirculating channels for the combustion gases. Maybe that sort of design could play some rolling all this. Also tacking an extra length of chimney to the top may create enough draw that you don’t need to augment. That’s how the rocket stoves do it.

I've been thinking about buying one of these "twinfire" ovens. The "Nemo" type looks cool.

You should make something like that to make a steam locomotive for your railway? I would love to see that

It is helpful for stoves with long and windy flues to start a smaller fire near the chimney first to get the draft going. In your case, that could be in the back of the ash pan.

Maybe once you scale up you’ll get a stack effect and good draft. I’m interested in a similar idea, manipulating airflow for a fast and efficient pyrolysis of damp Sitka forestry residues to make biochar during harvesting

eBay sells inexpensive thermometers that read up to 1800°C. I bought one for about AU$45 a few years ago and it has never missed a beat.

"And I thought you'd be interested to see it too, aren't you? A little bit interested?" Always Tim! Keep up the good work. For down the road with a more advanced model, you can preheat the incoming air with the flue gases and heat the water even more efficiently.

I build a model of a steam locomotive out of cardboard. You can build one out of metal, with two small wheels at the front and two big driving wheels at the back, don't forget the outside cylinders for driving the wheels.

I'm loving these experimentation videos, very fun to watch!

I was thinking of building something similar. My initial plan is to just use a computer fan to pull the air from beneath the fire. Naturally, the fan will have to be some distance away to allow the exhaust to cool off before it reaches the fan. When the fan expires, I will use something else, depending on what caused the fan to fail. If temperature doesn't do it in, I'm guessing the soot will.

Interesting subject! There are two things that most are interested in: Efficiency & Heat output. Wood stoves have thermal efficiencies with dry wood of circa 80%, this is measured as (heat out)/(energy in fuel). These efficiencies are achieved by extracting as much energy as possible from the exhaust gas, using what for wood burners is called secondary burn and this is currently done either with a catalytic convertor or by igniting the combustible gases in the smoke just below the heat exchanger so that one has flames over the wood and secondary flames at the top of the fire. Gains can also be achieved by using stone rather than cast iron or steel for the construction. The second factor is heat output which is related to the rate of burn which is related to the amount of oxygen available for combustion. A wood fire supplied with forced air will burn far hotter and use more fuel than one with out. This has been used for centuries by blacksmiths with forges, originally blown by bellows to increase the heat output and in this way Smiths can raise the temperature of wrought iron or steel to welding temperatures with coal, charcoal or dry wood fuel etc. Welding temperatures are just below the point where the steel/iron begins to burn. For such applications one can't have any steel or iron around the piece being worked as otherwise it would burn and so the Smiths use the fuel as the insulator that is relatively clean in an insulator which need not be clean and is in the most primitive applications is made by digging a pit in the soil. This is still current practice for many Indian Smiths and they create some extraordinary quality work. I personally can see no advantage to having the downward flame and the big disadvantage of all the ash above that is a thermal insulator that would reduce the heat to any boiler pipes. You will also have to be careful to avoid so enriching the fire that the heat becomes enough to ignite the steel boiler pipes even if you can control the buckling. In my humble opinion an above flame heat exchanger would suit your application better, but no doubt you want to have experimental fun with your idea and it is entertaining to watch so perhaps another efficiency of getting more eyeballs is worth your trouble. For the glass door, you probably would avoid cracking if you put the glass in its own door surrounded by length of insulation as in the original oven so that no steel can press on it expand and break it. `There are also thermocouples in ovens that you could remove and use for temperature measurements although an infra-red thermometer would be easier. I am not sure whether the glass doors on cookers will transmit infra -red, and for wood burners there is a big surface are in the glass door, but there is a huge difference in the heat one feels with the door open, so likely these glasses also attenuate infra-red. I once built an infra system with a plastic window and I was surprised to find that the optically transparent plastic was infra-red opaque. Good luck!

You are well on your way to making your own steam engine!!

If you're generating steam with your final product you'll definitely want to put a blower at the base of the exhaust flue to pull the air through, like on a steam engine.

That looks like some of the gasification plants I’ve seen for running internal combustion engines on wood. You might want to look into this technology.

When you go to a larger scale, it would be a good idea to shake the grates/pipes the fire is sitting on to clear the ashes. A removable ash pan would make cleaning a lot easier too.

Yup, you need to keep a window in the full scale version, too. Many great video opportunities (better images, practical uses such as when to reload fuel, etc). There are certainly fire proof glass lessons to be learned (use a fiberglass tape to add padding / insulation between steel & glass, and others). Mostly, and perhaps most importantly, we will get to see better video images if you keep a window in the final version.

From my reading on steam locomotives: Many schemes were tried but it's amazing how little experimentation was done first. Mostly they tried what "sounded" like it would work and that's what they built. If you'll recall, this ended up with a lot of small pipes connected to the firebox running through the core of the boiler portion. It wasn't until nearly the end of the steam era that someone finally figured out that what really made a lot of very hot "dry" steam was the length of the firebox that actually touched the boiler. The longer the firebox, the better the amount and quality of the steam produced.

Most definitely a boiler system for baseboard heating with auto feed either corn or coal or pellets with an ash discharge .

amazing experiment Tim! That was so interesting :D

Tim I have to watch this video again

Really interesting, thanks for sharing with us. Can't wait to see the bigger version!

Looks like the higher in the box you put the fire the more heat you will be able to extract with pipes below, also a slower variable air flow would help to regulate the fire.

This is like a wood gasifying boiler, the literal translation of the german "Holzvergaserkessel". I'd recommend going to the german wikipedia article of the "Holzvergaserkessel" and look at the graphic at the top. Sadly, the english version of the wikipedia article is a jetstream furnace, which is similar but not the same.

100% of all modern woodburners/house-waterheaters here in Sweden are downdraft/blueflame, like BAXI, NIBE etc etc. Typical efficiency 90-95%. The only reasonable way to burn wood/coal with efficiency. Most of them are suction stoves, and have a secondary air inlet to completely burn all the gasses. A long "pipe" in the prime air inlet are not needed. A hole with a regulator in the inlet hatch is ok, or if you want to take the non heated air from outside,, even better as long as you can regulate the flow. Its important to insulate the chimney above the roof, or where it may get chilled, so you dont loose draft, cause you dont want to run the suction fan all the time to save power. The suctionfan are allmost always a simple Diameter 150-200mm centrifugal fan made of steel,, typical 0,25kW. Warmest regards from a -25C Sweden. ❤️❤️

Some (or most?) extra efficient condensation boilers fire downwards like yours. More to save space than anything else I presume. A boiler smaller than your model can heat a big house in a pinch. When I saw mine I was amazed, it's the size of a shoebox. (and it's the bigger they make). They extract so much heat from the combustible that the exhaust is so cold that it can not hold the water from the combustion anymore and condenses. Basically, they use a water pre-heater in exhaust, and a heater in the heart of the fire. As it is a "closed" circuit, the domestic hot water uses a "water-water" heat exchanger, also really small.

What a brilliant idea 💡 I was just working out a sawdust/woodchip/pellet burner for hot air or hot water. Maybe I will do some experiments with you idea. There are some good benefits. I hope will do and show some more experiments with this.

You make it so interesting well done

Consider stainless hard brake line for your tubes. One thing to consider is that in a traditional steam boiler the fire is completely under water which provides some protection for over heating. When it stops being submerged the typical failure is either a melted crown sheet or a flash boil as water is added, both will kill the operator.

boiler, firebox hmmhm... this sounds interesting!

Very cool! Just remember to build some sort of ash shaker to clean out the bottom of the pit!

Burning downwards also has the added benefit of burning the VOC's that escape in the smoke. It is more efficient and creates less green house gas. When you burn up from the bottom, the flames heat the fuel above it, driving the VOC's off with the smoke. Burning top down (or in this case bottom up because it is upside down) the VOC's pass through the flames and get combusted.

Pre heat your water pipe Going downward in the cheminée , going to the highest heat point.then out through the brick wall to a radiator systems

Good experiment, well done.

Yikes, hope you were well clear when the glass failed! I suppose glass from a solid fuel stove would have a higher tolerance.

Rocket stove. Good step forward. I'm starting fire with wood from top in a normal fireplace since few years already. All of the Woodgas is burned and there is almost no smoke at all. I hope that the idea will spread widely, so that the air will be cleaner. Check out the topic of rocket stove.

A Japanese "Raku" pottery kiln has a similar "fire-path" that is mostly horizontal, wending its way backwards and forwards across all the pots being fired, then eventually up a tall chimney. It's not quite "upside down" like yours, but just goes to show that *"a fire will do what it's told to do"* in the interests of efficiency! 😳

This is fascinating.

id suggest thermocouple probes, Cheap and damn accurate. Maybe try building it out of pipe. Sure you wouldn't be able to see the inside but an easy way to scale up on the cheap. Maybe even steel barrels, or a combo of both. Try a tapered flu, might help along with air flow in a up-scaled version. Would be interesting to see in a small scale. Another issue is ash. Some type of ash removal system might be beneficial. Just thoughts.

Another fantastic video .thank you

Very interesting! Every time I watch one of your videos I'm impressed about how you think of questions that it would never occur to me to ask.

Thanks for sharing your experiments, TIm. We are all very interested. So cool.

Nice 💡! Air can greatly increase temp even for smelting metals. Perhaps a flat black stainless or cast iron bowl on top of the fire to maximize heat absorbtion thus radiation to the space. Needs a softer airflow to manage heat and allow it to burn longer. Would be a pain to burn through wood so rapidly. Perhaps throttle your air gun. Just a swag. 😎

Great work Tim! When you get your IR thermometer remember that you are only measuring surface temperatures and take into consideration emmissivity as this can skew the numbers a lot.

The cleanest burns are the hottest burns. I like that in this figuration the air is preheated but I would prefer the heat exchange to the water somewhat further where you have only gases no flames. For that I still believe that the exchange should take place in an insulated flue pipe. All the best with your experiments!

Great experiment. I use a wood boiler very similar to this at work to heat water. It's a very fancy German one, but the principle is the same. It draws the fire downwards, and you rake the ash out from the below the grate. it dose have some fan assisted air flow. I will watch with great interest how your home made one goes!

If your intention is simply to heat water then surely steam locomotive boilers have solved that problem by providing exits for the hot firebox gases thru several "chimney" tubes, all being surrounded by a water jacket. Horizontal flames in that case perhaps ... and a tad odd shaped for a living room 🤔 I can attest that a traditional old fashioned metal kettle with hollow pipes inserted thru it boils really very much faster over a gas ring than the original flat bottomed variety. I built one of them over 50 years ago to test the theory and it was a great success for me but not my granny whose kettle it was...proving nothing is new I guess, or that I was daft even then... LOL

I’m no expert but your experiment looks great, almost like a rocket stove..keep it going Tim..

Top down burn is recommended for a lot of wood burning domestic stoves.

There is one major flaw in that design: if all the air needs to go through the glowing charcoal before it reaches the "flame zone", there is no oxygen left for the flames to burn, so the exhaust gas will contain a lot of unburnt flammable gases. It is basically a wood gasifier. To solve that problem, you need to make an adjustable air inlet below the water tubes, or ideally some perforated air tubes between the water tubes. You also need additional water tubes in the exhaust to harvest the heat from the exhaust gases.

Thanks Tim, I learned something as I know that you did too!

I like your concept. What I was thinking is like a Jet Engine, there is a fan at the back that turns a fan on the front to bring in fresh air. What if you had a single shaft from top to bottom that did the same? the hot air rising would spin the fan/shaft, and connect through to the bottom and have a fresh air inlet fan?

Gravity fed charcoal grills work the same way. Charcoal loaded from the top with a stoking fan at the bottom, they can get well over 600 degrees.

That was awesome!

I thought for sure you were going to try to cut the tempered glass. Oh, well, we have to keep in mind that AVE's unspoken rule is valid: in any video where tempered glass is use as part of an experiment, there's a 100% chance of it shattering before the end.

Very interesting experiment. May I suggest adding maybe an insulation or double layers of steel between the file chamber and the incoming air to keep air cold and to add a small taper to the chimney to increase chances of upward smoke draft.

most of the open fires i remember had a back boiler, where the hot gasses pass over a heat exchanger by way of a moveable flap closing a diverting flue (the boiler), before going up the chimney.

A really ingenious idea, I agree, I think if you scale it up it will work much better. In my book on "The Queenie Stove" there's a very interesting version with a side door. I don't know why this idea wasn't kept.

I wonder if a small square metal box grate in the center of the area where you put the fuel could help I think it might add more surface area for air to get to and help it burn hotter faster, while it might mean less room for fuel it could provide heat without needing to use an air blower.

Very interesting Tim, low pressure areas (expansion chambers) at the S bends would really help the flow.

Excellent.

Love this experiment. Maybe consider an air-lock style door for adding the fuel so the system keeps working with the door open?

Fascinating

Fascinating. I've never thought about the limit of heat resistance of my (electric) oven door versus the windows in our airtight woodstove, which gets pretty hot. It's a Jotul (slash through the o), maybe they can tell you.