Experimental ceramic stick burner

Experimental ceramic stick burner

A report on an experimental micro ceramic stick burner made as an inverted J-burners. It is made from largely clay free loam soil and sodium silicate. It is configured for; natural or forced draft operation. It also was designed with an optional fussed quartz charcoal-burner glass that could make and transmit incandescent light. The burner design also allowed the glass to be removed and be substituted with a charcoal grate or a blanking plate over the grate. The post describes and compares the performance of the burner with the above options deployed.

Introduction

There are multiple posts on my ultralight stoves that have inverted J-burners that can burn a tiny amount of damp bush sticks to provide cooking and warmth in a tent. I essentially use stainless steel and titanium for their construction small bento box stove and large oval stove. Weighing between 500-1,000g, they can give off a delightful amount of radiant heat for the people in a small tent.

 

I have used DIY refractory coatings to protect these stoves from the ravages of the high-temperature combustion that is involved, particularly the charcoal burning phase which can exceed 1,000C.

Two stage combustion. The inverted J-burners normally combusts only on the bottom tips of the loaded reserve of fuel sticks. The sticks move downwards as their tips are, dried, roasted and pyrolyzed to make wood gas and flames in the first phase of combustion.

In the second combustion phase, the resulting charcoal tips break off and form a glowing bed of charcoal. This confined two-phase combustion process makes these little stoves very hot, efficient and clean (smoke-free).

Ideally, only a tiny portion of the fuel is being burnt to completion at any time. However, it does mean that air must flow down the hot burner/fuel tube before it can go up the flue pipe.

Conventional stove. By contrast in a conventional wood stove, the draft path is always horizontal or upwards, a fire can run down to a bed of coals and the flue draft should naturally continue. Fresh wood can just be added at any time (anyhow) and the fire will probably smoke for a while until it ignites into flames once more. At no stage will the natural draft stall.

Draft failure with an inverted J-burner. Continued draft in an inverted stove burner is not so easily assured. If the stove becomes choked with charcoal which stops the entry of ‘new wood’ into the pyrolytic burn zone then the following sequence of events will occur. The flame will be absent, the major draft up the flue pipe will stop and the small residual draft will instead go back up through the fuel sticks (and possibly burn them in the wrong place. “I call this reverse burning and it is not good”.

Consequently, the balance between the combustion of wood and charcoal requires a particular understanding and management of the multiple air ports for successful inverted burner operation.

Strong heat feedback into fuel sticks. When camping out in the snow and cold wet weather, my stoves must run on damp and even frozen sticks. Consequently, my inverted J-burners are designed to burn damp or frozen wood by providing for strong heat feedback into the incoming fuel sticks. This dries and ‘toasts’ the sticks in preparation for pyrolysis. This heat feedback is provided by the close proximity of the sticks to the radiant heat of a glowing charcoal bed (~1000C) and also the conducted heat being transferred up to the fuel sticks by the heated metallic fuel stick tube.

A tricky heat feedback balance. Because of the strong heat feedback into the sticks, there is a risk that if a too bigger proportion of the loaded fuel sticks are dry or rotten they may cause preignition in the fuel tube and cause reverse burning.

Charcoal combustion. The heat from the charcoal is localised and intense (~1000+ C). Its combustion makes no new gas to carry the heat way. Instead, the heat is largely on the charcoal and cannot move away as a flame does to sustain burner draft. “Additionally, the charcoal must await the arrival of oxygen for its combustion, because it can not go forth to find oxygen.” 

Wood gas combustion. The pyrolyzed gas from the wood in contrasts increases the molecules of gas and expands and moves away. As long as there is gas, oxygen and a suitable source of ignition, there will be a hot tongue of flame and gas that moves away from the pyrolyzing wood. “It can go forth to find oxygen to complete its combustion and transport its heat to distant places.”

Doubling of gas molecules in wood combustion. The number of gas molecules doubles during the complete combustion of wood gas and thereby sustains the gas flow to drive the burner draft.

The draft is improved by extra steam from the water in the damp fuel and the heat expansion of all the gases, including the ~78% nitrogen in the air. All this adds to flue pipe draft, providing the flue temperatures are kept high enough to prevent condensation.

No pyrolysis, no draft. All this means that, when pyrolysis stops, the heat from the charcoal cannot move to the flue pipe to maintain draft. Instead, with an inverted J- burner, it radiates heat into the fuel sticks above, heats the gas in the fuel/burner tube and will start reverse smoking and eventually reverse burning. This will burn up through the fuel/burner tube unless stopped by a sealed cap on top of the fuel tube (or other action). An undesirable fire will work its way back up the fuel tube through the waiting fuel sticks.

I should also add that the reverse burning phenomenon can be stopped altogether by removing the hot long fuel tube and dropping in a few chips of wood onto the charcoal bed. This immediately initiates pyrolysis and establishes a tongue of flame and restores the flue pipe draft. Being able to re-establish flue draft after a ‘stall’ in this way indicates that my theory of the cause of reverse burning is probably correct. However, removing multiple long burning sticks is not a very practical manoeuvre in a tiny tent.

Longer fuel/burner tube- bigger reverse burn problem. As a lazy stove innovator I was always tempted to make the fuel tube very long. This means that the fuel sticks can also be very long and lazy. However, the longer the fuel tube means that it competes more with the real flue pipe to be the draft path. Also, once reverse burning is established there is a lot more burning fuel to be removed and managed to resolve the problem.

The good and the bad news of forced draft blowers

To prevent or correct the reverse burning situation described above I have successfully used a USB fire blower with a refractory restrictor nozzle placed into the primary air port of my tent stoves. This means that the blower can be used to rapidly burn the charcoal and prevent charcoal choking and force heat and extra hot expanded gases from the extra air (essentially air is 21% O2 and 78% N2) into the flue pipe to maintain the stove draft. Alternatively, it can be used continuously, at an appropriately restricted flow rate, to prevent charcoal build up.

The good news. In either case, the addition of the blower ‘turbocharges’ the stove and increases its heating power.

Imagine a little pile of charcoal that is slowly building up below the fuel sticks. The charcoal is just passively waiting for some air  (~21% oxygen) to come along to infiltrate its ash covered carbon surface to form carbon monoxide which gently drifts up to find more oxygen to complete its combustion into carbon dioxide. The charcoal is just steadily building up until the charred ends of the wood sticks are sitting on the pile of charcoal and are left out of reach of the air supply and the tongue of flame is extinguished and the flue draft fails. 

Then imagine the same situation with a small and persistent jet of high-speed air blasting into the same pile of charcoal. The ash is blown away. The whole charcoal pile glows incandescently brightly and is ripped apart in a frenzy that eventually sends the smaller particles flying off like shooting stars.

“The two situations are such a contrast and it is a joy to be able to see it in clear view for the first time through the fused quartz charcoal-burner glass. See the video below.”

Merging of two paths. This is the fulfilment of a prophecy that was made some years ago. An un-named person suggested that someday they could envisage my two separate investigative paths of natural draft tent stoves and outdoor cooking blower stoves merging together. 

The bad news. I find that all breakthroughs come with new problems or challenges. The forced air injection makes the charcoal extremely hot (1000+C). 

Such temperatures will be destructive to any metal stove part, particularly when in an oxygen-rich atmosphere. This happens even when the surfaces are coated with a DIY refractory coating. The temperature is so high that after about 8h of use there are signs of slow devitrification of the inside of the fused quartz burner glass.

“The above mentioned clear view is gone, but the light still comes through the glass. I am not surprised or particularly disappointed. I imagine that after it has had many hours of use it will look like the diffuser glass that they have on many gas lanterns. When I am no longer entertained by the sight of the dance of vigorous charcoal destruction, a diffused light source may be welcome.”

The Experimental ceramic burner concept    

Please note: This is not intended to be a practical burner, rather it is a versatile experimental platform that enables me to test my theories and hunches about inverted stick combustion. It was also the first serious device made from posthole soil and sodium silicate refractory mix. It demonstrated its survival while containing fierce forced air charcoal combustion.

“Consequently, even if it did not work as a burner it was a great success because; it survived its birth in white-hot coals, cost almost nothing and is so hard that it requires a tungsten carbide masonry bit to slowly drill a hole in it!”

Putting the soil refractory mix to use. I have tinkered with refractories for some years now, and have dreamed of making high-temperature burners with them so that they (and I) could just laugh at the super temperatures that exceed my humble measurement range. In addition, refractories should provide low thermal conductivity properties that could limit unwanted heat transfers such as that in my metal fuel stick tube. 

My recent success with mixing dense and cheap refractories with low water content gave me the incentive to try to make a novel experimental ceramic stick burner that would easily cope with 1000+C. “Also it would cost nothing but time if it did not work”

Desired performance features of the experimental ceramic stick burner

I aimed for the burner to have the following features:

1. Be immune to high temperatures that are associated with forced air charcoal burning and can withstand repeated heating and cooling cycles 
2. Have insulating properties to keep combustion temperatures as high as possible to make the combustion complete and less sensitive to thermal shock and occasional ‘flame-outs’ as experience in my ultralight stoves (that have near-zero thermal mass).
3. Reflect heat of combustion so well that it can burn a single long stick
4. Have a low thermal coefficient of expansion and be compatible with connection to a fused quartz charcoal-burner glass
5. Be a good prototype device where easy modification is possible
6. Have an option of a very long fuel stick feed tube that can provide for multiple hours of burning (self-feeding)
7. Have minimal smoke released when refuelling 
8. Control the combustion heat flows so that; the burn or pyrolysis zone does not progress upwards into the reserve of fuel sticks
9. Control of the combustion so that; it can successfully burn any sticks, regardless of moisture content
10. Separate the pyrolysis combustion zone from the pure charcoal burning zone
11. Allow the fitting of a fused quartz charcoal burner
12. Provide sloping support for the bottom of the intact fuel sticks that minimises their contact with the charcoal-burner. At the same time, it was to provide a bending force that would break off the weakened pure charcoal from the ends of the fuel stick and allow them to slide down to the charcoal-burner
13. Charcoal burning to be fast enough for it to stay in balance with the pyrolysis so that the burner will not choke up with charcoal and stall the pyrolysis
14. Have the capacity for forced air injection to increase the power of the burner without destroying the burner.
15. Trap wood ash in a place where it does not hinder combustion
16. Provide a visible indicator of good charcoal combustion which is key to the good operation of the burner.
17. Given that I wished to separate the charcoal burning it would be delightful if it also could be a steady source of cheery bright incandescent light for the user at night time and be so hot as to prevent carbon deposits on the glass that would obscure the light emission as in my previous stoves with burner glasses.  

The experimental ceramic stick burner build

I will start with the mold that the burner was made around because it reveals more of the inner details than any other photo does. The inner mold is made of rolled thick paper or thin cardboard and PVA glue and joining fillets are laminated strips of newspaper. After glueing the paper was coated in olive oil to provide waterproofing during molding. The mould outer is a chipboard box that is screwed together and lined with thick silage plastic sheeting that was smeared with olive oil. The larger outer chipboard panels were split into two parts so that they could be added progressively as the mold cavity was progressively filled and compacted from the bottom up.

The photo below shows the molded refractory burner body assembled with ancillary fittings that were attached with various DIY refractories.

A glimmer of success

The next photo is of the prototype micro ceramic stick burner at night time. The fire blower is; blasting the charcoal bed away, turbocharging the fuel stick pyrolysis and producing a large tongue of flame in the internal burner zone

The flue gas was clear, indicating that the combustion was clean and complete.

When I quickly lifted off the flue pipe the flame was reaching about three-quarters of the way up the burner body in the exhaust channel. The burner made a gentle chuffing sound that seemed to be coming from the pulsing of the pyrolysis flame and being transmitting through the secondary air port.

This little video may better describe the combustion.

Evaluation of experimental ceramic stick burner  

Overall I was delighted with the performance of this experimental ceramic stick burner. It was a little trickier to get started when compared with similar burners made with fine sheet metal. The thick ceramic needed a little more heat input to get started. However, once heated it became a much more stable burner, presumably because of its much greater heat reserve.

The highlight for me was the success of the separated charcoal burner in the fused quartz tube and the incandescent light that it produces without the glass being obscured by carbon deposits.

With only about 8 h of burn time, it is to soon to assess the long term stability of the burner body, but I think it will be indestructible, even if it needs a few cracks filled.

Checking off the performance list

I have made a quick evaluation of performance characteristics of the experimental ceramic stick burner according to the above long list of desired features (in the same numbered order and most get a tick).

1. The burner body appears to be completely immune to high temperatures that are associated with forced air charcoal burning and (to date) can withstand repeated heating and cooling cycles 
2. It has insulating properties that keep combustion temperatures high and makes the combustion complete and less sensitive to thermal shock and occasional ‘flame-outs’ as experience in my ultralight stoves (that have near-zero thermal mass).
3. It did not reflect the heat of combustion so well that it could burn a single long stick. However, it could happily burn one big stick if it was split in two.
4. The thermal coefficient of expansion of the ceramic is low and is compatible with the connection of the fused quartz charcoal-burner tube.
5. The experimental ceramic stick burner body was easy to modify by drilling, grinding and filling & bonding with sodium silicate.
6. The burner operated without fault with the fuel tube topped with a cover/extension that was made from a soft drink can. This allowed the loading of the tube with sticks up to 350 mm long. (A longer fuel tube is yet to be tested, but the maintenance of low tube temperatures and absence of reverse burning bodes well for it working with large fuel stick loads.)  
7. There was minimal smoke released when the fuel stick cover was lifted for refuelling. 
8. So far, the combustion heat flows are such that; the burn or pyrolysis zone stays stable and does not progress upwards to cause ‘reverse burning’ of the fuel sticks and the fuel stick tube has not got hot.
9. So far I have not tested if it can successfully burn dry sticks without causing ‘reverse burning’. High moisture sticks burn well.
10. The burner has effectively separated the pyrolysis burn zone from the pure charcoal burn zone, but some small sticks fell through. This was not a problem, but the design could benefit from a better separation.  Nevertheless, the two-compartment burn chambers worked well together. The rapid charcoal combustion provides concentrated intense heat for the pyrolysis of the lower tips of the fuel sticks. At the same time, the charcoal provides only minimal heat to the upper reaches of the fuel sticks and thereby discourages ‘reverse burning’. Additionally, the separation of the chambers and the rapid destruction of the charcoal means that charcoal stalling of the wood feed process is eliminated. A self-regulating mechanism is apparent; if there is a lot of charcoal in the glass then its rate of decomposition is greatly increased. Conversely, if there is only a small amount of charcoal in the glass it burns slower and the forced air flow is used to burn the ends of the sticks more rapidly and make more charcoal.  
11. The ceramic burner body made for easy fitting of the fused quartz charcoal-burner glass. The dried (but not cured or fired) molding could be easily drilled, ground, filed, filled and added to with various sodium silicate refractories that I have listed.
12. The sloping floor of the burn chamber confluence provided support for the bottom of the intact fuel sticks. At the same time, it provided the desired bending force that would break off the weakened pure charcoal from the ends of the fuel sticks and then allowed them to automatically slide or tumble down into to the charcoal-burner for their rapid and ultimate destruction.
13. The forced air in the charcoal-burner caused the charcoal to burn so rapidly that the burner did not choke up with charcoal and stall the pyrolysis.
14. The forced air injection greatly increased the power of the whole burner. It also appeared to contribute to the prevention of reverse burning. 
15. The ash trap worked better than expected and collected a significant amount of ash (est. ~7g over 3 h). It is probable that this ash would have collected down in the charcoal-burner glass if it was not caught in the trap. Despite this, there was a considerable amount of ash collected in the charcoal-burner glass and I need to work on an ash removal device that will work with minimal disruption the burner function. Lastly, unlike any of my previous burners, this turbocharged burner spits out many tiny sparks that can be seen at night time. I am sure that this is because this prototype burner does not have a useful heat exchanger for the flue pipe to terminate in and do some useful heating, cooking, smoking, BBQing or refractory drying or curing etc. When such a burner is put to practical use, the sparks and ash will die in the heat exchanger (as with my other stoves). This will require a suitable ash removal port.
16. The charcoal-burner glass provided a visible indicator of good charcoal combustion which is key to the good operation of the burner. The ‘chuff chuff’ sound from the secondary air port was another indicator of continued good burner performance.
17. The addition of the charcoal-burner glass has resulted in the stove producing a delightful cheery bright incandescent light for the user at night time. It gets so hot that it prevents the formation of carbon deposits on the glass and is a wonderful improvement on my previous burners. Unfortunately, the temperature and oxygen levels caused clouding of the fused quartz glass. 

Further experiments with the ceramic stick burner

1. Experimental ceramic stick burner with a vented charcoal grate without blower or charcoal burner glass

I wished to find out if the success of the experimental ceramic stick burner was dependant on the blower so I removed the charcoal-burner glass. I put a substitute stainless steel cylinder in place of the glass and fitted a refractory grate to the top and welded an end cap with a blower connection on the bottom.

The burner worked unexpectedly well without the glass and blower. The burner power was, as expected, less than with the blower. However, it worked well and also had fewer sparks shooting out of the flue pipe.

The video below, of the burn, is more informative.

video of burner without a blower

2. Experimental ceramic stick burner with burner glass and charcoal grate blanked off

Given that the burner performed quite well without the blower I just had to try the burner with no glass, no blower and no primary air port, just the single sloping port that is formed in the ceramic burner body.

To do this test, I simply put a blanking disk on top of the grate fitting as used in the previous experiment. This modification closes off the entry of any air below the charcoal and elevates the charcoal bed so that it is supporting the bottoms of the fuel sticks and may induce the old problem of ‘reverse burning’.

” I can just imagine some reader thinking that this sounds like ‘Back to The Future’. Yes, these modifications made the burner configuration very similar to my original tent stove design. However, would it behave the same way or would it avoid the ‘charcoal stall’ and ‘reverse burn’ or would it work at all?”

The answer to these questions is simply; NO, YES, YES and YES. The little video tells how well it worked as it put on quite a show.

video of the burner with the primary air blanked off

The burner burnt damp sticks impressively well and the burn was very stable. When provoked with a trace of more volatile hydrocarbon fuel, the flame pulsing was so vigorous that popped out periodically from the air port. This probably was because there was only one air port in this configuration.

There was no evidence of charcoal choking or reverse burning, although I did notice that the fuel stick tube was warmer (uncomfortable skin contact temperature) than the previous two burner configurations (slightly warm). The higher fuel/fuel tube temperature meant that considerable drying of the damp fuel sticks was happening and water condensate could be heard as exploding steam within the burner.

However, the tube temperature was much less than that of my all-metal tent stoves of a similar configuration (skin burning temperature).

I consider the fuel tube is hotter because it is once again close to the radiant heat from the charcoal bed, but it does not get as hot as in the all-metal stoves because of the low conductivity of the ceramic burner material where it connects to the fuel tube

The absence of charcoal choking and reverse burning is probably because in this configuration the only remaining air port on the ceramic burner is the downward sloping one. It goes directly into the raised charcoal bed as the fuel stick tube is covered (sealed off) with a drink can and the primary air zone is blanked off. I think this means that the available oxygen is used preferentially by the charcoal combustion and keeps the build-up of charcoal to a minimum while depriving the upper reaches of the fuel stick of oxygen to allow reverse burning.

“The way the air is attacking the charcoal is very evident in the above video.”

It also could be possible that the blast of hot air from the secondary air port (the only one) acts like an ‘air curtain’ to prevent the fire from spreading up into the fuel sticks

There was no problem with ash build up in the burn zone. “There was no room for it and it was simply blasted away.”

The ash did collect in the ash trap. It was the first time it filled almost to the top after some hours of running! There also seemed to be fewer sparks coming out through the flue pipe. It could mean that most of the ash is collecting in the trap (“As dreamed of in the original design”). Consequently, an ash dump hatch would be a good feature to have in a functional stove of this design.

This blanked off burner configuration resulted in the highest temperature of the metal fuel tube, in this series of experiment. It was at a temperature that was right on the cusp of an uncomfortable to touch with my hand. However, the temperature was much lower than in my all-metal stoves and probably as a consequence this there was no problem with the reverse burning that I had hoped that the experimental burner design might address.

Reflections

During my morning walk, I contemplated the roaring success of my little experimental ceramic stick burner in all its configurations. I slowly realised that this success should be put into proper context.

My experimental ceramic stick burner is not a stove! “It is just a burner that could be used as part of a stove”. A such, the heat produced by the combustion of the sticks is largely not harvested or converted to useful heat by a heat exchanger for warmth, cooking, drying, baking, meat smoking etc.

This means that, unlike my previous stoves (all metal inverted burners), the heat is largely used to perpetuate exuberant combustion conditions. Consequently, I expect more modest combustion (still useful but a quieter growl and fewer flying sparks) when such a burner is integrated into a functional stove that diverts most of the heat energy to a useful purpose.

It will also mean that the pulsating tongue of flame may no longer issue forth from the air port as shown in the video above. The entertainment value of this will only be a small loss! I will attempt to add a heat exchanger to put the theory to the test.

Note: I have subsequently posted on Micro tent stove design for strong radiant heat and robust draft and also on my Miniature Dome Stove design that is my ultimate design that gets this balance right.

3. Experimental ceramic stick burner with burner glass and charcoal grate blanked off and burning only dry fuel sticks to provoke ‘reverse burning’.

Given that all the above experimental burner configurations performed quite well without evidence of ‘reverse burning’ I thought it was time to test the above configuration when fueled with only dry fuel sticks.

The fuel tube was too hot to touch in the lower reaches, but there was no ‘reverse burning’.

4. Experimental ceramic stick burner with burner glass and charcoal grate blanked off and a short 450mm flue pipe

All the above experiments were run with a full length flue pipe ~1.6m long) attached to the burner. Observing what is happening inside a ceramic stick burner is difficult, so in the above reporting, I have provided images of the burn at the secondary air port. While quite exciting to someone like me, it is not the whole picture. Earlier, I attempted to describe the flame that I saw coming out of the burn chamber when I quickly lifted off the flue pipe. This observation is inappropriate for the burner with the flue pipe connected. The removal to observe the flame changes what is being observed. It is a bit like the ‘Heisenberg uncertainty principle’.

A peep inside the experimental stick burner

As a compromise, I made a short (450mm long) flue pipe to drive the stove and also allow simultaneous observation of the burner or after-burner flame. It is still not a good image, but it is a hazardous place to take photos.

I don’t like to finish with a boring photo, so here is another from the same burner configuration, but with a little bit of provocation with some slightly more volatile hydrocarbon fuel.

5. Experimental ceramic stick burner with burner glass and charcoal grate blanked off and a short 450mm flue pipe that is inserted into a coffee-tin heat exchanger

So far for all tests of the experimental ceramic stick burner, I have made no effort to extract useful heat. This means that most of the heat energy from the combustion is used to drive the burning chemistry. This likely accounts for the savage burning shown in the above photos and videos and also the plume of sparks from the flue pipe with some burner configurations.

A more modest burn should happen when much of the heat energy is dissipated as a useful source of heating. The above 450 mm experimental flue pipe functions as a ‘heat riser’ as used in rocket stoves. It should provide a substantial draft to maintain adequate combustion rate in the experimental burner when it is put into a heat exchanger (coffee-tin). The coffee-tin has the original flue pipe connected via an elbow and it should provide an additional draft to drive the combustion.

The burner continued to burn well with a heat exchanger in the exhaust path. I was anticipating that a lot of ash would be trapped in the coffee tin. However, after a lengthy burn, most of the ash was in the ash trap within the ceramic burner and very little was in the can.

I was somewhat disappointed with the heat coming off the top of the can as it took a considerable time to boil a pot of water. I will need to re-run this testing to estimate the temperatures of the various surfaces as my thermometer had a flat battery.

I also noticed that the entry point of the flue pipe was very hot. This means that the heat exchanger is not very effective and did not seem as hot as in my all-metal tent stoves with similar sized burners. “Back to the drawing board or sketch pad.” 

What really surprised me was the high temperature that the outside of the ‘Mother’ cans reached very quickly after the start of the burner. The temperature was well over 100C according to my little ‘spit on the end of my finger test’, where the spit boiled instantly and replied with a ‘zzzst sound’. I can only assume that the temperature inside the riser must have been extremely high.

Nevertheless, the riser should be useful when the burner is used with an effective heat exchanger. The insulator makes the riser much safer for brief accidental contact with my knuckles while adding fuel sticks.

I also think that this type of insulation would be very appropriate for ultralight wood stoves. When they are assembled this way, end to end, there is no reasonable limit to the insulator length and they have considerable radial stability. 

Conclusion

It is early days in the evaluation and evolution of the experimental ceramic stick burner, but my immediate feeling is that it is a bright, growling or purring success that has overcome several of the limitations in my earlier designs.

The burner appears to be able to burn effectively without the USB fire blower connected.

The configurations with a raised charcoal grate or blanking plate seem to be quite powerful and decidedly simpler and still prevents ‘charcoal stall’, ‘reverse burning’ and ‘ash build-up’.

It is my hunch that successful burning with the last two configurations comes from the steep angulation of the air port that is mainly directed downwards toward the charcoal bed.

With the addition of a heat exchanger and the resulting slowing of the speed of the burner gases, the designed ash trap appears to be working as intended. Also, spark emission from the flue pipe has been eliminated.

The remaining challenge will be to find a way of incorporating these design features into a lightweight backpacking tent stove.

Please use the comment section below if you have done something similar, have any questions or need for clearer descriptions or would like to challenge my primitive chemical descriptions of the combustion of wood and charcoal. Alternatively, you may like to use the contact form at the top left of the main menu.

Tim

Related posts:

KISS TENT STOVE- A SIMPLE, LIGHT, EFFICIENT AND POWERFUL BACKPACKING STOVE

Part 1.- DIY ROLL UP STOVE PIPE IMPROVEMENTS

Micro tent stove design for strong radiant heat and robust draft.

Miniature Dome Stove- A three-in-one-stove.