Micro oil heater for a small tent

The testing of a natural draft 134g DIY micro oil heater for a small winter backpacking tent. The heater can cleanly burn waste sump oil at a rate as little as120g/hour. It also burns, vegetable oil, tea candle wax, milk bottle plastic, wood chips and gum nuts etc. This prototype heater must be batch-fed to provide tent heating for about one hour per batch. Nevertheless, with the addition of a suitable drip oil feeder, it could possibly become an ‘all-night-tent-heater’ which is the Holy Grail of winter hot tenting.

Introduction and background to my waste oil heater

Compact diesel heaters have fascinated me for years. They can efficiently and cleanly produce wonderful amounts of warm air from a tiny quantity of diesel fuel and they occupy the volume of about three house bricks. They also require a DC power supply to run.

Many years ago, I encountered a diesel heater that effectively heated a 30-person drying room in a remote alpine chalet where we stay each year for a week or backcountry skiing. They are compact, complex and efficient devices. However, they can’t easily be repaired as evidenced by the accumulation of ‘dead’ heaters in the drying room over the years. For the ski week just passed, we had no effective drying room heater despite our best efforts to repair the unit by an electronically savvy person.

While such heaters would never be suitable for winter backpacking and skiing camping, they did inspire me to think of other ways of using energy-dense liquid fuels for tent heating. It would also be so nice if the device was so simple that it would need no power to run, could be fixed with a pocket knife and even better could use cruddy and free waste cooking oil or sump oil for fuel.

For years I have made very efficient tiny tent stoves that burn fallen sticks for fuel using a downdraft gasifier. I also use a little oil to supplement the wood stick fuel and to give wet and frozen wood a ‘kick start’ under trying alpine camping conditions. “A tiny trace of my olive oil (from my cooking kit) can provide oil gas for instant and powerful heating that is so welcome when retreating to the tent after a day of skiing.”

I adapted the above tiny tent stoves to essentially become an oil-fired wood-burning tent stove. In these stoves, the wood sticks became smothered with oil and acted like giant candle wicks. This stand-alone oil-burning was difficult to manage and it invariably was very inefficient and left dirty soot that would be a pain in the butt for backpacking equipment.”

On the other hand, I had brief moments of success with simple natural draft oil burners that would burn savagely bright (much like a scary kitchen oil fire) for only about 20 seconds before they turned into a black smoke generator. “The earliest of these burners was formed with a macro ceramic wick in a sardine tin of oil with a 40mm diameter*1850mm long roll up stove pipe that was very carefully placed closely over the oil surface. “The brief roaring sound and bright hot flame were tantalizing, but consistent clean combustion was elusive.”

Part 1 of this micro oil heater post is a description of my serendipitous prototype development. Additional post parts will be added as my testing of possible improvements progresses. Part 2 will be about heater optimization and drip-feeding of fuel. Part 3 will consider the addition of heat robber to provide a cooking surface for traditional backpacking cooking pots. Other, improvements and embellishments such as tent lighting from fire, heat reflectors and mounting of the heater/stove on deep snow will be explored.

Part 1. A micro oil burner based on an oil smudge pot- From flashes of success to a persistent hot, clean burn

About smudge pot oil burners

Smudge pots date back to the 1900’s when they were used to protect crops from frost damage. They are still made today as Demon Heaters as outdoor (or ventilated workshop) heaters. So I thought; “How difficult could it be to make a miniature version of one of these burners?” Well, I got my answer pretty quickly by making one from a tiny Cavendish & Harvey fruit drop tin to which I fitted a slotted burner tube/chimney device. It did look much better than my sardine tin burner, and once started, it could run on any oil, paraffin, fat, wax or similar hydrocarbon fuels. My micro smudge pot did burn brightly for brief brilliant moments. Whilst providing a more tantalising glimpse of success than the sardine tin, it had multiple defects that were difficult for me to understand at the time:

• A flame that could escape from its crucial role in the oil pot and up into the stove pipe,
• Micro explosions in the stove pipe that eventually would cause flame-outs and
• Generation of thick dark sooty smoke that was very difficult to reignite and made everything filthy.

As with my numerous stove/burner failures, I put the burner up on a shelf between the exposed log beams in my bathroom. I thought that with my daily bathing, I could see this failure and hopefully subliminally work out how to make it work to its full potential.

Then many months later, I was looking at a video of the bombed-out base of soldiers (terrorists) who had invaded Ukraine and lost their lives doing their ‘special operations duty’. In amongst the bombed-out wreckage in the dugout, I could see two primitive oil heaters (probably hand-crafted from stolen war booty).

Unlike the terrorists, these rugged stoves had survived the bomb blast (presumably no tungsten balls to make extra vent holes). They gave me a clue about what I was doing wrong with the operation of my carefully designed smudge pot. “In short, I was not getting the appropriately lean mix of oil gas and air for efficient and hot smoke-free combustion.”

Understanding how my micro oil heater can burn cleanly

The micro oil heater oil bowl. This makes a good starting point as it was this component of the smudge pot that I least understood and this was standing in the way of my achievement of stable, hot, efficient and clean combustion. Having very hot liquid fuel within the smudge pot is key to getting hot fuel vapour to sustain good combustion. Consequently, I inserted a slightly smaller (squat) dog food can into the fruit drop tin and packed the space between the two cans with layers of aluminium foil to act as a reflective insulator to keep more heat inside.

Copper heat sink. In my micro oil heater design, I placed several strands of heavy copper wire that extended well into the burner tube (shown above). The wires have bent ‘feet’ at their bottoms and these fan out where they are immersed in the fuel oil. The wire gathers heat from the flame in the burner tube and conducts it down into the oil to speed its evaporation.

The slotted burner tube/heat exchanger. I made this ~300mm tall tube out of 0.1mm thick hard stainless steel alloy foil. The burner tube is formed with a taper, as can be seen in popular smudge pot designs such as Daemon Heater. I don’t yet know why or if the taper is essential. In my case, I made the bottom diameters ~30mm which fits into the lid of the tiny oil pot. At the top, it is ~50mm diameter where it can be easily fitted onto a ~50mm diameter backpacking roll up stove pipe.

The numerous slit were easily cut into the stove pipe with the tip of a craft knife. Then to increase the area of each opening, the lower side of each slot was deformed inwards to form ‘cheese-grater-teeth’. These were made to discourage gas escape and encourage air entry, possibly aided by the venturi effect. “Regardless of the theory, the slots seem to function as intended.

An evening photo of the red hot burner tube (several photos down) possibly reveals a little more about the gas flows in this tricky device. The photo shows dull or ‘less hot’ patches immediately above most of the air slots. I think this is because the inflowing air is initially cooling the flame and the adjacent metal surface.

Stove pipe. When the top of the burner tube is connected to 1800 mmm long backpacking roll up stove pipe it creates a strong draft to drive the oil heater and safely discharges the combustion gases above the tent canopy. With such a stove pipe connected, there will be considerably more draft and vacuum inside the heater than would be the case without the pipe. I think this is why this oil heater requires a tiny primary air port and is so sensitive to small changes in the port aperture.

Oil burner start-up and oil vapourisation. The oil in the heater does not burn in the liquid phase but it must first be vaporised at very high temperatures to support the required clean and hot combustion. Radiant heat from the smudge pot flame eventually heats the fuel oil in the bowl of the smudge pot. At start-up, a primer wick can help accelerate this vapourisation by causing a tiny amount of oil to be exposed to much of the radiant heat.

Similarly, a bulky ball of paper can also act as a large oil wick to rapidly get the burner hot enough to start the natural feedback of heat to sustain the oil vaporization temperature. With caution, a suitable liquid accelerant with a low vapourisation temperature can make the start-up very quick and quite exciting. “There,…..I have avoided criticism from the no-that-is-not-safe zealots.”

During the oil burner start-up, there is usually a pathetic starting flame that sooner or later will become an uncontrolled big flame that can race up the stove pipe. This can result in a small explosion that can put the damn thing out.

Consequently, keeping the flame the right size and in the right part/s of the burner is a fine balancing act. I found this critical balance could be achieved by quickly sliding a flat steel shutter across the 30mm diameter smudge pot primary air port opening. The full-size port is still available for adding large items such as paper balls, solid fuels and various accelerants when required. A largely open port is also essential for a critical short period while cold-starting the burner. Please see Addendum 1 for a start-up method that uses DIY backpacking fire starter strips. These are made from wax-soaked egg cartons (waxie fire starters) that can quickly start strong oil combustion.

The primary air port aperture acts as the fuel vapour throttle. Previously, I had thought of the primary air port as a source of combustion air to prevent excessive smoke (as for my tiny downdraft wood stoves). Hence, I made the hole big (30mm diameter). However, this port sets off a series of interrelated undesirable reactions when it is left too big.

Too much fuel vapour can be drawn up into the burn tube. At the same time, the reduced vacuum within the burn tube causes less air to be drawn in through the multiple small slits where most of the combustion should happen.

Additionally, there is an excessive inrush of air into the oil bowl. It cools and slows the vapourisation of the oil in the oil pot. I think this series of reactions accounts for the pulsing of the burner flame and the little periodic ejections of smoke puffs that come from every available hole in the heater. “This behaviour can be seen as the prelude to failure. Equally, it can be taken as a timely warning to restrict the primary airflow to avert the impending failure.”

[Add a link to the evening video of the slow burner pulsation and the warning smoke puffs. Include the sequence of the burner pulsing being rapidly restored to its gentle rapid pulsation roar by rapid throttle adjustment. ]

Consequently, I now think of this aperture as the stove’s throttle. Its main purpose is to ‘sweep-in’ a suitably restricted supply of oil vapour from the oil pot to support a lean and clean hot flame in the burner tube. At the same time, the airflow must be strong enough to sustain the pathetic little pilot flame that must be in the oil pot.

Now for the good news. An appropriate constriction of the large port with sliding steel plate can set very favourable combustion conditions by:

• Reducing the rate of fuel vapour delivery,
• Maintaining high vaporization temperatures and combustion conditions within the oil pot,
• Maintaining a high system vacuum to pull more air in through the burner slits where it is most needed and
• Allowing a suitable range of throttle settings for a wide variety of fuels to burn at high or low rates.

Suitably constricted primary air flow and heater pulsing. The above air restriction can eliminate the most obvious slow flame pulsation, smoke puffing and chimney explosions. However, the fast and gentle pulsing roar of the heater is a constant indication to me that rapid flame pulsing is still an integral part of the heater’s wonderfully steady performance as is demonstrated in this little video. “I came to a similar conclusion about the magical self-regulating mechanisms that are at play in my downdraft stick burning stoves that have an identical gentle roar while pyrolysing wood smoke and burning it. Even commercial pressurised liquid fuel stoves and lamps exhibit similar pulsation”

Also, if the heater is cranked up too high (too much primary airflow, it will be provoked to give occasional micro-smoke-puffs. I think this is similar to an old motor car carburettor trick. “If you have ever had a car that is old enough to have a manual choke and a carburettor, you may have cleared carburettor blockages by pulling the choke out with the motor spinning at high revs. We called it the carby-pull- through and it often cleared minor blockages and made some nasty popping sounds.”

The strong pulsing and smoke puffing should be a timely reminder that the fuel mix is too rich and the fuel mix needs to be cranked back a little. Conversely, if the heater’s pulsation becomes quieter it will probably be warning me to attend to topping up the fuel pot.

Slow addition of extra fuel. I also observed that the addition of fuel needs to be done gradually to prevent excessive cooling of the oil reserve and the subsequent reduction of oil vapourisation. Adding a little cold oil to plenty of hot oil is a good strategy. This also indicates that a drip feed (as discussed later) will have advantages in this regard.

With the above air restrictions, most of the combustion will take place in the slotted section of the burner tube where it is most needed. The slotted surface will become red hot and provide effective direct radiant heating for the camper’s bodies.

To a lesser extent, the air in the tent will be heated by convection heating from the heater and the stove pipe. In a frozen alpine world inside a single-skin tent, the air heating will be welcome. This higher temperature, however modest, will set good conditions for keeping the tent dry and free of condensation, particularly if it is made of a suitably permeable fabric such as unproofed polyester umbrella fabric.

Restricted and variable air entry into the micro burner oil bowl. The 30mm diameter port in the lid of the oil bowl is large for multiple reasons: Adding paper balls during start-up, High air input during start-up and shut down. It also allows easy inspection of fuel levels, topping up and the addition of a variety of solid fuels.

After the start-up, the open area of the primary air port area must be rapidly reduced to:

• Optimise the fuel vapour/air mix,
• Prevent smoky combustion,
• Maintain the required flame in both the oil pot and the slotted burner tube,
• Prevent explosive flame-outs and
• Provide adjustments to the primary air flow rate according to the heat requirements and various fuel types.

Initially, the cover plate with two 3mm diameter holes in it (shown below) was my breakthrough that could make sump oil burn very well.

When using sump oil as the micro oil heater fuel, the two holes provide a steady maintenance burn, and the combustion could be increased a little by slipping the cover backwards to provide a bigger airflow. “See the smiley face of red-hot success in the photo below.”

The evening photo below best shows the potential heating power of the micro oil heater. You can imagine what a joy it would be to have this heat source in the middle of a small winter backpacking tent.

Later I found that for other fuel types, I required either a greater or lesser airflow to provide the desired burn rate and clean combustion. Consequently, I made an elongated cover plate with two holes at one end and none at the other. This meant that for the most volatile fuel (tea candle wax), the air inflow could be restricted to just the leakage of air under the plate. Importantly, this simple plate can be adjusted quickly to manage the combustion conditions for all fuels including sump oil, canola oil, tea candle wax, milk bottle plastic and wood.

Burn time and fuel consumption. The burn time from a fuel load depends on the throttle setting. When run at a gentle low power, the usage of sump oil was about 120g/hour and I have not yet determined what it is at the highest setting. Nevertheless, an hour of winter tent warmth from 120g of waste oil sounds like a good deal to me, especially if the burden of carrying the fuel can be shared by 2-3 tent occupants. “For remote ski-accessed base camps, a stash of bulk sump oil could be delivered by vehicle during summer.”

Discussion

Possible oil drip feeding for extended burn times. While testing the micro heater over extended periods, it occurred to me that the oil fuel could be drip-fed from a bulk fuel bottle. The drip rate could be regulated by suspending the fuel bottle at an appropriate height on the tent pole. This could lead to long burn times without the need for manual filling.

It would also address the previously mentioned problem of chilling a small oil pot when adding a large amount of cool oil. Drip feeding may also make the start-up even quicker and help to regulate the burn rate in concert with the throttle.

Keeping the micro oil heater clean for backpacking. Sump oil is a messy fuel at the best of times. Even clean vegetable oil or wax will get messy during combustion in the oil pot. Not surprisingly, my early failed micro smudge pot tests left ghastly oil remnants in the oil pot. These remnants would not be welcome in anyone’s backpack and cleaning with a cloth or paper was unpleasant.

Consequently, I was delighted to see that eventually, the throttle control could make the fuel burn out to completion with suitable adjustments toward the finish of the last batch load of fuel. This applied to all fuels that I tested. A light, fine and greyish ash was all that remained after hours of burning.

A robust multi-fuel micro oil heater. It is nice to be able to run a heater on a wide range of fuels, particularly if they are low-quality free waste products. Many liquid pressure stoves purport to be multi-fueled. However, in my experience, they quickly clog up with heavy fuels that are not of the highest standard. “They even clog up with the best light fuels that money can buy.”

Consequently, I was delighted to see that my improved micro oil heater could run on various heavy oils such as used cruddy unfiltered sump oil and claggy polymerised old canola oil. The stove also ran happily on tea candle wax, even on milk bottle plastic (HDPE plastic) and on wood chips etc.

All these fuels required individual throttle settings and start-up routines, but all could produce abundant clean heat without visible smoke when the throttle was adjusted appropriately. The heater could also burn well on a mixture of fuels.

The wax burned clean with no visible throttle opening and I presume leakage of air under the throttle plate was enough to sustain the fuel vaporization. In contrast, the plastic fuel could burn cleanly even when the throttle was wide open. This feature was fortunate as the feeding in of the plastic as long cut strips took a considerable time with a wide throttle setting.

The temperature profile of the heater. When the burner throttle is appropriately set, the combustion in the oil pot is quite gentle and the pot with surrounding insulation does not get particularly hot. The majority of the vapour combustion occurs just as the vapour passes the slots in the burner tube.

In this zone, the air jets that are sucked in from each slot vigorously mix in with the hot oil vapour. Firstly, this action creates turbulence that speeds the combustion. Secondarily, the turbulence also disrupts the, otherwise, laminar flow within the tube. This all means that most of the heat of combustion is created in a narrow band and is transferred quickly to the thin stainless steel foil, making it an excellent high-efficiency heat radiator.

Oil heater burn tube temperature profile. The burn tube reaches very high temperatures that are difficult to measure and describe. My best estimates come from the comparison of the colour of the burner tube (shown in the evening photo above) and a temperature/colour chart (shown below). At the highest power output, I estimate that about 70% of the burner tube runs at temperatures between 500C (dull red) to 1,000C (lemon-yellow).

Table from Quora

Burner pulsation, chuffing and popping. The third effect of the inrush of air, through the burner slits, is to momentarily cool the flame, and cause a slight reduction of the gas volume and a corresponding increase in the system vacuum. The lower vacuum causes a richer fuel mix that is followed by a stronger momentary burn and a higher temperature.

The rapid cycling between these two conditions gives rise to the chuffing sound and the rapid pulsation of the burner flame. I think that a satisfactorily large oil pot volume (or rather the available gas head space above the oil) cushions these pulsations so that the gas and flames do not permanently escape from the system (popping) and are sucked back in. Such pulsation can be seen and heard in this video.

Residual heating. As the hot gases pass up through to the stove pipe, laminar flow is established once more (crappy conditions for heat exchange) and there is only gentle heat exchange to the pipe. Depending upon the throttle setting the 100C point on the pipe is typically 800 to 1500mm up from the burner tube and this can still provide useful tent heating. Some of the heat could also be used for cooking. Beyond these heights, the surface temperature lapses considerably. At an 1800mm height, the temperature will be below 100C* and very compatible with a DIY silicone rubber tent stove jack that can withstand 300C.

Note*: The stove pipe surface temperature that is well below 100C belies the temperature of the much hotter core of gas that passes up the centre of the stove pipe at the tent exit point. This high internal temperature is essential to maintain the burner draft and prevent the condensation of water/tar within the pipe.

Radiant heat distribution. I was delighted with the heat distribution from the micro oil heater. It provides intense radiant heat with a 360-degree distribution around the tent right where it will be most appreciated by seated campers. Later, a reflector will be tested to see if it can provide a more focused heat distribution when required. Higher up the 100C section can be used for drying clothes and keeping the tent dry and a little warmer.

A pathetic higher air temperature in a frozen winter may not sound like a great comfort improvement. However, it can drive water vapour out through a permeable tent fabric such as cotton, canvas or unsealed polyester. This prevents the formation of condensation as water or ice inside the tent. This drying process is described in my post: DIY Breathing Polyester Tent.

Stronger heat feedback to the oil and wick. The copper wire heat exchanger worked well enough. One time I forgot to place it in position after starting the heater. So, I dropped the exchanger into place down the stove pipe while standing on a ladder. I could see that the heater burn was more settled when it was in place.

A thicker exchanger made from a strip of copper foil might improve the preheating of the fuel oil reserve. Such a thick heat exchanger may provide more effective heat feedback if it is wrapped around the burner wick thus providing intimate contact between the copper and the oil that is just about to be vapourised and then burnt.

More or bigger burner slits? I must have made a reasonable guess about the number of air slits (16* 8-10mm wide) to put in the burner tube. If the tube had more slits or larger ones, maybe it would make good combustion easier to achieve with less sensitivity to the throttle setting.

On the other hand, it would reduce the vacuum in the burner and this may reduce the turbulence that mixes the air into the burning oil vapour within the burner. It may allow more smoke leakage (puffing) outwards through the vents. Also, as with my similar downdraft stick-burning tent stoves, excessive air in the combustion mix leads to lower stove temperatures. So too many slits may easily spoil the heater’s performance.

The cooking potential of the micro oil heater. While my heater design did not include a cooking surface, it could be used to toast food. Also if a suitable container of water was nestled onto the hot burner tube it may provide snow melting and boiling water for small creature comforts. A stove pipe heat robber will later be tested as a cooking platform.

If the heat robber should fail to work well, there would be another simple cooking option. A stick-burning tent stove could be used for cooking. Then when the cooking is finished the oil heater could be quickly sat on the cooled stick stove and the stove pipe from the stick burner could be connected to the oil heater.

Conclusion

From my initial micro smudge pot failure, I am pleased that I have been able to convert it, at last, to make a red-hot micro oil heater. Without electrical input, it is capable of producing stable, smoke-free and intense radiant heat in a winter backpacking tent. “So simple and unlike other complex oil heaters, it can be serviced by a halfwit with a pocket knife”.

The limited testing demonstrates that with a simple air throttle control, various crude liquid and solid fuels can burn cleanly and efficiently. Above all else I learned a lot more about the effective combustion of these wonderful energy-dense waste fuels. If you are still interested, and not nodding off, please read on to the addendums for Part 1, Part 2 Optimisation and Improvements and Part 3 A Heat Robber For Cooking as they become available.

Addendum 1. A better oil heater starter

After some more testing of the start-up of the oil heater, I have found that strips of wax-soaked egg cartons make an excellent accelerant to start the oil heater. One or two strips can provide the necessary energy to kick-start the oil combustion to the stage that it is hot enough to sustain the oil pyrolysis. Unlike other liquid accelerants, these waxies are innocuous, safe, light, compact, leakproof waterproof and very backpack friendly while being an indispensable part of my winter camping kit.

The generous wax flame can be pulled down onto the oil by the developing stove draft. Here is a little video of the oil heater start-up with waxies. Two-ply tissues can be used for the same purpose. However, I have found that they leave ash behind when the oil eventually runs out. This ash may fly out through the stove pipe, as glowing embers, during the combustion of the last traces of very hot oil. This may be another good reason to use the waxies.

Addendum 2. Improved air control plate

I have used various flat metal plates, usually with small hole/s, to provide a calibrated airflow restrictor or throttle for the oil heater. From time to time they all could allow a little too much air in. This was presumably due to air leaking in between the oil pot lid and the cover plate.

A cover plate made from a small rigid but light screw cap lid seems to be able to provide a more consistent seal. With its use, I put an extra 2mm diameter air hole in the oil pot lid and a 2mm hole in the cover plate. This cover plate also has enough weight to keep itself in place when small gas explosions happen in the burner while settling the throttle setting.

Additionally, the off-centre location of the hole in the cover, allows the hole to be blanked off if required for even slower burning. Here is a short video of the oil heater working with the improved throttle plate.

Part 2. Tent oil heater optimization and improvements

(Progress report, not yet complete)

BACKGROUND

The experimental micro oil heater described in Part 1 was designed as a scaled-down version of a smudge pot that normally has a short and open burner tube. Images of such smudge pots or chooafs* usually show flames and smoke coming from the top of the burn tube. The radiated heat combined with these emissions were to provide frost protection for orchards. I am guessing that these days as workshop and patio heaters the flames might just be for show and the black smoke is an unwanted extra.

However, such emissions, large or small would be unacceptable in a small tent. They also indicate an inefficiency in the conversion of fuel to heat. I added a tall roll up stove pipe to my micro smudge pot to safely exhaust the emissions to the outside of the tent canopy. This addition also meant that the burner draft was greatly increased.

Note*: The ‘choofa’ term is an Australian one and is related to the pulsating sound that these heaters make. Such ‘choofing’ or pulsing is also a feature of my oil heater and other of my downdraft stick-burning tent stoves. It is integral to the self-regulation of the burn process. I think of them as cyclic micro explosions of the fuel gas. Managing and optimising this pulsation will be a constant theme in my optimization process. The choofa term was also used to describe a hotplate cooker device, according to my late father who was attached to the US Air Force during WW2. The device ran on drip-fed diesel fuel and water to cook flapjack (pancakes in Australian lingo) as a special treat on Sunday mornings. I can find no references to this US ‘choofa’ on the web, so I would appreciate any help in discovering more about this device.

The success of my prototype oil heater could be explained by a mix of persistence, good judgement and too many years of playing with fire. It came about by greatly restricting the air admission rate into the oil pot to compensate for the increase in the system vacuum induced by the addition of the stove pipe. Here is a little video of the heater being switched between controlled and uncontrolled combustion by the radical adjustment of the throttle plate.

Having a lucky break does not mean that my heater components have been optimised for heating performance, ease of use and other features that may be desirable in a backpacking small winter tent. Part 2 is about the optimisation of the heater design and exploring some possible redundancy and improvements.

OIL POT INSULATION, OIL WICK AND OIL HEAT EXCHANGER

In my original burner concept, the oil pot insulation, oil heat exchanger and oil wick were intended to improve the fuel vapourisation. The medium Cavendish & Harvey oil pot (and subsequently the minimal one) was made with an insulation layer between the inner pot and the outer cover. This was done with the presumption that it would allow the oil in the pot to heat quicker during start-up and get hotter during sustained burning.

I don’t know if this insulation helps or is needed. “I took this approach based on my success with DIY backpacking alpine candles. They had insulation and copper heat exchangers to make them burn properly under freezing camping conditions.”

I made another oil pot from another Cavendish & Harvey tin without an insulation liner. The testing of this oil heater was done with the inclusion of a ‘beefed-up’ wick/oil heat exchanger on the pretext that it may compensate for the lack of insulation.

The new heat exchanger was a 12mm wide*0.25mm thick copper foil strip that had a carbon felt wick wrapped around it and was held in place with two fine stainless steel ribbons. The wick height was adjusted so that it would be just above the oil level in the ‘filled’ oil pot with a substantial headspace allowance.

I think this wick arrangement may have allowed the small amount of the oil in the wick to heat up quickly and form oil vapour without the bulk of the oil needing to be very hot. This may make the start-up easier and make the burner less sensitive to the cooling effect of adding cold bulk oil.

After further testing and sustained and powerful running of the oil heater, the copper ribbon partially melted in the burner flame (Copper melting point 1,085C). I concluded that the oil pot insulation was unnecessary and that the oil heat exchanger was not viable and probably not necessary.

Next, I tested the same uninsulated medium pot without a heat exchanger or wick. It burnt very well and the combustion was subjectively similar to that with insulation, heat exchanger and wick. Please see below the evening photo of the simplified burner in action.

The burner was possibly a little slower to start, but a range of accelerants to supplement the sump oil can make the process excitingly fast and fun anyway.

Discussion/conclusion- Oil pot insulation, oil wick and oil heat exchanger. Having no internal oil pot insulation caused the exterior of the pot to increase from about 120C up to 200-300 C. I don’t think that the oil pot insulation, wick or heat exchanger were critical to the heater performance and the pot construction is much simpler without them. Additionally, the available oil capacity is much greater for longer burn times between top-ups.

The heat of combustion that is lost from the oil pot with a higher temperature deprives the radiator of some of its heat output. However, I don’t think that this is a significant loss when it is traded off against simplicity.

As a safety consideration, the higher oil pot temperature can set fire or charr (and make smoke) any organic things that touch it. However, safe separation from such materials would be wise regardless of the use of internal insulation.

Under freezing alpine camping conditions, and when the oil pot is close to a snow surface, maybe insulation could be beneficial. If this is so, an external insulation layer made of scrunched aluminium cooking foil (or similar) could easily be used when and if required.

Now all this is possibly getting a bit heavy so let’s have a little ode to design safety:

I expect the unexpected by design,
From just 75 years of time,
Outwards the safety margin I like to push,
Better this than a failure in the bush,
A tinkerers philosophy that is mine. 

Medium oil pot with oil drip feed

I made a drip feeder that had a terminal fitting of a steel brake line (~5.0mm OD*~2.5mm ID). I attached an adjustable stainless steel clip-or toggle to go over the steel pipe that limited its penetration into the pot lid. The steel fitting was inserted into a tight-fitting ‘bugelated’ hole that was formed in the oil pot lid.

The steel tube was connected via some nylon airline to a long soft PVC tube that had a stop valve fitted in it so that the oil flow rate could then be stopped and started. The oil flow rate was adjusted by the use of a simple inline DIY pinch valve in conjunction with the oil tank head height.

This drip feed rig was first used on the medium oil burner shown in the photo below.

This video of the drip-fed heater shows the medium burner running on a drip-fed sump oil fuel supply. As anticipated the adjustment of the drip rate could limit the rate of combustion. However, the oil pot air throttle must also be used to achieve: clean combustion, avoidance of excessive smoke puffing and the desired heat output from the heater radiator. The two burn rate control mechanisms seem to work well together.

Within reasonable limits, I think that there is a natural balance between the fuel drip rate and fuel consumption. If the drip rate is too low for the burn rate, then the burn rate will slowly reduce as the surface area of the oil pool diminishes slowly. Such slowing can be indicated by the gradual quietening sound of the burner.

On the other hand, when the drip rate is too high for the current burn rate, the oil surface area will steadily increase as the evaporative surface increases until the whole surface of the pot is available for oil evaporation and the burner reaches its maximum burn rate as it would have with bach filling.

Even if the above natural balancing magic should fail, drip-feeding equipment can be used as a simple and clean way to periodically add extra oil manually, without disrupting the combustion, by using the stop valve. The sound of the burner will provide the warning sounds when such filling is required. I imagine that the heater may even make warning sounds before the oil pot is overfilled. This would be due to the loss of headspace above the oil. However, I have not put this to the test yet.

I was relieved to find that the steel pipe that delivers the oil inside the oil pot did not get beyond a warm temperature where it joins the plastic air line connector. I could comfortably grip the warm metal with my fingertips.

However, I eventually allowed the oil supply to ‘run dry’ to make less mess when packing up. Without oil flow the metal eventually became hot enough to soften the airline plastic and made the oil seal at the metal/plastic junction unsatisfactory. “There even was oil vapour fuming out of the end of the tube when I removed it.”

I concluded that the flow of oil through the steel tube was enough to keep it from overheating. A non-conductive oil delivery tip, such as glass or a less heat-sensitive connector such as silicone rubber could make the oil drip feeder more robust in the ‘run dry’ situation for an absent-minded operator.

HEATER OIL POT SIZE

Medium oil pot- The benchmark pot. The original heater had an oil pot made from a Cavendish & Harvey fruit drop tin (steel) that was lined with a smaller pet food tin (steel). The void between the tins was packed with scrunched aluminium cooking foil to act as a reflective insulator. As a result, I estimate that the oil pot capacity was reduced from 263cc to`~150cc by the liner.

With this medium oil pot capacity, the burner flame pulsed very quickly est ~200-300 pulses per minute. This rapid pulsing or resonance meant that, with appropriate, but tricky, throttle adjustment, only small smoke puffs exploded from heater holes and they were then sucked back into the burner before they could escape into the tent. Please see this video as an example. “It is best seen in the eyes of the smiley-face but it happens at every little or big hole.”

The oil pot volume may be an important factor that tunes the heater to have a desirable burner resonance that prevents large smoke puffs. “Maybe a musicologist could help me with this”. However, I speculate that a larger oil pot can more effectively buffer the burners’ micro explosions, making them less likely to escape from the air intake zone.

Minimal oil pot- A roaring smudge pot failure or a new burner. This perversely takes the pot size to the minimum limit. It was possibly inviting failure, but accepting the risk of failure sometimes results in significant learning and gains. “Calling it a pot is even a bit of a stretch”.

I made a minimal pot from welded 0.1mm thick stainless steel foil. “Being so small and light (~23g), it could have been a raging backpacking success or a flaming failure.” It was made with a matching taper to fit tightly onto the bottom of the original tapered burner tube and that tube could be fitted to a standard 50mm backpacking roll up tent stove pipe that could be part of a stick-burning cooking stove/tent heater as well.

Next, I lined the outer pot with the bottom portion of an aluminium Berocca tube. This portion of the tube had a capacity of about 15ml (about 1/10th of the original oil pot). The gap between the inner and outer vessels was wrapped with an insulating DIY foam refractory that was made from aluminium cooking foil DIY sodium silicate. It also had a copper oil heat exchanger ribbon (12mm wide*0.25mm thick) that was larger than the original one made of six copper wires that were ~1.0 mm in diameter.

The heat exchanger was placed inside the oil pot liner and the bent foot of it lay across the bottom of the oil pot while the carbon felt wick lined the oil pot to promote rapid oil evaporation and combustion. The ‘pot’ was made with a slide valve on its wall to tightly regulate the primary airflow or act as the burner throttle.

This minimal oil pot only could hold about 8g of oil, below the air entry slot, and arguably had no headspace when full. Despite these shortcomings, it ‘sort-of’ worked, but the burner flame pulsed on and off causing unacceptably large and frequent smoke puffs that were not sucked back into the burner. Consequently, it would not be welcome in my tent.

[Add a daytime photo or video to show the beauty of the smoke rings that would make a Hobbit very proud.]

I thought that the large wick may be causing the excess puffing by making the burner run too rich. I ran the heater again after removing the carbon-felt wick. It was possibly a little slower to start. However, this did not stop the excessive smoke puffing. Alas, without the protection of the carbon felt wick, the aluminium liner became so hot that the upper portion started to melt* and oxidize. Consequently, I abandoned the addition of the oil dripper, as planned, because of its multiple defects.

Note*: It was interesting to see that the heat that destroyed aluminium appeared not to harm the carbon-felt material. Indeed, when the wick was removed, it had adopted a new curved shape, was clean to the touch and not the least bit crumbly as I may have expected. This also indicated that most of the oil and combustion residues must have burnt off during the last moments of combustion.

I think that the hot carbon-felt acted as an ignition surface to restart the oil gas flame-outs. Maybe the carbon felt was even acting as a clean combustion catalyst? “This is an amazing material for fire tinkerers.”

The minimal burners’ redemption. With a sad heart, I had given up on the minimal oil pot because its’ behaviour was almost as bad as my original smudge pot. I moved on to testing other ‘real’ oil pots. I realised that I did not have a video of the minimal burner failure to share with you in this post. So, somewhat reluctantly, and belatedly, I reassembled the burner with the minimal oil pot.

I included the curved felt oil wick, mainly to protect what remained of the aluminium pot liner from more melting. I left out the heat exchanger ribbon, well…….. because it was buggered as it had already melted when used in another larger oil pot test. Also, by then, I had concluded that such a heat exchanger was not needed. I also added the oil dripper to give it a workout to extend the burn time.

I started the heater and quickly set the slide valve to a half-open (or half-shut) setting. It predictably produced the horrid on-and-off bad behaviour that I had previously observed but it allowed me to film this unacceptable behaviour.

The half-open throttle setting was chosen because my first successful oil burner and others all required small throttle apertures to get a stable, clean combustion and a hot heater radiator. So I mistakenly assumed the same for the minimal burner.

However, when I opened up the slide valve completely, the burner gave a couple of little spluttering smoke puffs of protest and settled down to noisy, savage, stable and hot combustion. The two running states are recorded in this little video.

I was delighted that the minimal burner could stop blowing smoke rings and work so well. However, I did note that the burner tube did not appear as hot over its full length as with the original benchmark (Harvey & Cavendish) heater.

The very hot area had shifted downwards somewhat toward and into the oil pot and connector fitting. This seemed to be at the expense of a lower temperature higher up on the burner tube.

This little video gives a glimpse, beneath the savage hot flame. The sump oil surface can be seen boiling and then burning immediately just inside the fully open throttle port.

I think the ‘lowering of the hot area’ is caused by the extra air that is drawn into the oil pot with the throttle fully opened to sustain a stable flame. This means more oil vapour burns within the pot and just above it and this zone gets very hot. Unfortunately, it means that the many upper air vents on the burner tube will be sucking in cool air that is not contributing to additional combustion, but just wastefully cooling the radiator surface.

I now think that this minimal burner/heater has strayed too far away from the original smudge pot design:

• The primary air entry is horizontal and not down drafting as in the benchmark device.
• The very high-temperature flame dances on the oil surface rather than being a considerable distance up the burner tube as with the other burner designs,
• The minimal oil pot is behaving as part of the high-temperature burner, rather than being a separate and limited source of hot oil vapour.
• The high temperatures that are reached in the ‘oil pot’ are not compatible with the survival of the ‘tin can metal’ that the pot is made of.

However. it is still a very interesting burner and is deserving of further investigation. The original smudge pot design that can simply use a suitable ‘little tin can’ is probably more suited to a DIY backpacking heater.

In my mind, this minimal heater has accidentally morphed into a very small heat cell that can convert oil to heat in a tiny space, albeit a little noisily. Its matchbox size and burning of about 2g of sump oil/min make it an attractive DIY alternative heat source to diesel heaters that can burn ~4g of diesel/min to produce 5 Kw of heating power.”

These diesel heaters were an inspiration for my experimentation with tiny experimental smudge pots as discussed in the introduction to Part 1 of this post. Luckily, my cell does not require pumps, very clean fuel, electrical power or an electronics degree to service it. It could be yet another very small way of providing warmth while winter backpacking camping.

I also think that a minimal burner pot could be made from DIY lightweight insulating ceramic, which is another passion of mine. “can you see another post coming?”

Large oil pot. As part of my exploration of oil pot size, I thought that a larger pot would be more convenient for refuelling, provide longer run times and may better buffer the micro explosions. Consequently, I made a larger oil pot from a steel cookie tin (Connossurs’s Butter Cookies). It had a diameter of 137mm and an internal capacity of ~450cc which was about three times the effective volume of the original medium oil pot with a liner.

This large oil burner, without an insulating liner, was fitted with a nifty slide valve on the primary air port. “It did look good, but it did not work as well as a simple throttle plate.” It could burn well but it was less stable than the medium one. It made frequent explosions and smoke-puffs. However, the beautiful smoke rings would not be welcome in my tent.

I did not understand, at this stage, why this large oil pot caused the smoke-puffing issues that were very difficult to ‘tune away’ with the throttle adjustment. There was a massive buffering volume so this would not be the cause. It could be that the elegant slide valve was too leaky so that it let too much air in and periodically ran too rich.

Alternatively, it had a greatly increased surface area for oil evaporation. This may make the available fuel vapour too rich for the throttle adjustment to adjust for a steady burn.

Ring wall thing. To put these theories to the test, I made an oval ring wall device that would have, within it, a significantly smaller surface area than the original Cavendish & Harvey pot liner. The ring was placed below both the air inlet port and the gas exit port. It was designed to isolate ~2/3 of the oil surface area from direct participation in the intense oil heating and the fuel evaporation process that may have caused the excessively rich fuel mix. I ran this modified oil pot with the original oil pot lid.

Well, surprise, surprise…….The oval ‘ring thing’ corrected the problem. Just to make sure that this was real, I removed the ring and ran the heater again and yes the uneven burning, explosions and smoke ring returned. Here is a little video of the comparative burner performance with and without the oil ring thing.

I concluded that the original problem with the large oil pot was that it had an excessively large oil surface area that could supply excessive oil vapour that caused the burner to periodically run too rich. The ring thing appears to be able to suitably restrict the evaporation for much of the oil surface. It still allows the surrounding oil to flow underneath the ring to replenish the oil in the high-temperature zone of the ring. The slide valve made a suitable throttle mechanism, but a flat plate would be simpler and easier to adjust with just one hand.

Could a similar ring make a very large oil pot work smoothly? It would certainly be simpler than drip feeding!

All tin cans are not equal. I noticed very small oil patches on my test bench (flat rock) after some of my tests using the large oil pot. At first, I thought that I had clumsily spilt some oil during refuelling. But now I think that at high temperatures the viscosity of the oil is lowered and there was a very small leak through the bottom rolled seam of the can. I am sure that such leaks can be sealed and even the cooked oil may make a suitable seal in time. However, a can such as the Cavendish & Harvey is a pressed or spun can that has no seams and consequently has no leaks.

Also, I discovered that not all cans that look like the Cavendish & Harvey tin are the real thing when a couple miraculously turned up in my Christmas stocking. Luckily, the look-alikes seem to be quite good (content and the tin) and the lids and pots are interchangeable.

SCUM BUSTING RING-THING

I have observed the formation of scum on the top of the sump oil fuel after a considerable burn duration. Although the scum will eventually burn to ash, it can suppress the normal fuel evaporation and diminish the strength of the combustion, particularly as the fuel level runs low.

Stirring the scum. So far I have found that stirring the scum into the residual oil with a wire poker, via the open throttle hole, can resolve the scum problem. Unfortunately, this causes other problems. This stirring with an open throttle causes a savage increase in the burn rate that can cause undesirable micro explosions and smoke puffs. This little video can better describe the open-throttle chaos. After the savage burn and smoke puffing it takes a delicate manipulation of the throttle plate to reestablish normality. Additionally, a hot oily flaming poker is not good company in a little tent. So steps to avoid this chaos would be very welcome.

One scum-busting option could be to have an in-place wiper device made of bent wire. It could be used to break up the scum without opening the throttle plate. Such a scum-busting wire is shown below, but I never used it as I had a better idea up my sleeve.

“This sounds about as short-sighted as my lovely old car design. It has airbags, central locking, is theft-proof (no one wants it) and a warning sound if the headlights are left on. Why not use the same signal to turn the damn things off automatically, as current cars do?”

Anyway, I put the scum wiper on hold and took another tack, building on the previous success of the ‘ring-thing’ that protected much of the oil surface from involvement with hot vaporisation of the oil. At the same time, it focused the heat within the smaller area within the ring. If this area of heat concentration was taken to the extreme, it might be enough to burn the oil scum so that it would never accumulate. “Little did I know that many other burner improvements would flow from this simple change!”

Using the medium burner (Cavendish & Harvey with no insulated liner), I made a ring-thing that was as small as possible so that it could just bridge between the throttle opening and the exhaust port. The height of the ring was made to reach between the bottom of the oil pot and the inside of the lid. I thought that a tight seal between the ring and the lid was not possible or necessary for the device to act as an effective heat shield. To provide the ring with extra insulation, I coated it with my DIY sodium silicate and baby powder foam refractory. After painting the mix on with a brush and drying, it can be converted into a refractory insulating foam when heated with a propane torch.

This modified oil burner burned delightfully well with an easily controlled burn rate. The use of the ring eliminated the scum problem. I think the smaller inner chamber within the oil pot got much hotter so that the scum did not eventuate or it was destroyed as it formed. The following photo was taken after the combustion of 100g of sump oil over about 70 minutes.

OTHER BENEFITS OF THE SCUM-BUSTING RING-THING

Previously, a somewhat larger ring-thing has prevented a large oil pot from running too rich. If the ring is small enough it can prevent scum formation on sump oil fuel. The inclusion of the ring thing also has other profound and wonderful practical benefits that will make the burner much easier to use and control the heat output.

“Briefly, it has become a sweet burner/heater that is easy to use.” I immediately sensed this tolerance and ease when I first started this modified burner. This little video shows the burner with a scum-busting ring-thing behaving well. This good behaviour, apart from two minor explosions and smoke puffs, was even when the burner was provoked by the action of stirring up residual oil-soaked tissue paper that hitherto would have created explosions, smoke rings, and general chaos that demanded urgent corrective measures. The improvements are:

• The throttle aperture can be more open without stimulating very bad burner behaviour,
• The throttle plate can be opened with only minor and infrequent smoke puffs and explosions,
• Replacement of the throttle plate quickly settles the combustion without fiddling to prevent bad behaviour,
• The outer temperature of the pot is lower,
• The insulating effect of the ring-thing spares more heat for the burner radiator and makes it hotter,
• The insulating effect also creates a less hot zone in which the oil dripper can operate without overheating.
• Lastly, concentrating the combustion in a smaller chamber improves the heat feedback into the oil and enables more stable combustion at low oil consumption rates.

The above test ran for 70 minutes while burning 100g of sump oil ( ~1.4g/minute). During that time the throttle was casually adjusted to run at a mixture of high and low controlled burn rates. The run included several provocative wild burns with an open throttle plate to see what happens, as shown in the video where the residual facial tissue was stirred up with a wire poker. Throughout this maiden run, the heater ran smoothly with minimal attention and only a tiny amount of stove pipe smoke was emitted under the worst provocation.

Predicable heating control. Thankfully, the burner now tolerates a much wider range of throttle apertures that produce a range of steady trouble-free combustion rates. These rates are now less influenced by the leakage of air inwards under the throttle plate. This means that it may be possible to use a series of calibrated holes that can be used to set predictable heater output.

Direction of air jets. From my understanding, the air jets must come through holes that direct the air downwards onto the hottest oil surface within the heat concentrator ring. This maximises the destruction of the oil scum and discourages the recruitment of oil vapour from other parts of the oil pot.

I think this simple minimal ring-thing is the most significant improvement that I have made to the original sump oil heater. It should work with all oil pot sizes. Importantly, to enable the high-temperature chamber to be as small as possible, the exhaust port and the throttle hole should be designed to be as close as practically possible to one another. “Does this sound a bit like a burner with a minimal oil pot rising from the ashes?”

DOES CLEAN DIESEL FUEL MAKE SCUM?

It is quite possible that the scum problem was due to the crappy mixture of ill-defined workshop oils, lubricants and miscellaneous water-insoluble liquids that are in my freely-given sump oil. The ring-thing provides a simple way of obliterating the scum before it can cause a problem.

I thought that the use of clean diesel distillate might have been another solution to the scum issue. This strategy was no longer needed to manage scum, but I thought I should follow through with testing this alternative fuel. “After all, who knows what I might find? At about two bucks a litre, one litre of diesel could provide ~8h of gentle heating (est 800g /100g/h). “This sounds like a bargain to me at about $0.25/h to beat back the winter chill while winter camping.”

I used clean diesel fuel (nicked off from my tractor) and started with the medium oil pot without the scum-busting ring and then with the ring in place. “Not much point to looking for scum in a scum-busting configuration!”

The burner was quick to start using only burning wax strips, so that no paper ash would be there. The diesel burned well and predictably it could easily misbehave without the addition of the scum buster ring. However, the explosions were no more violent than those with sump oil. There was no visible scum when the fuel was depleted. I conclude that diesel would be a suitable alternative fuel for the burner and that the scum that previously formed on the sump oil was an attribute of this ill-defined cocktail.

With the scum buster in place, I ran the burner once more on diesel fuel. The burner showed similar improved behaviour as for the sump oil. This fuel made slight stove pipe smoke when provoked by opening the throttle plate, but normal combustion was quickly re-established when the plate was replaced.

THE GOOD OILS AS FUELS FOR OIL HEATERS

Back in the 80’s the Castrol advertisement had the famous gangster lines ….”Oils ain’t oils”.. crudely suggesting that not all oils are equal. This is true for pristine engine oils, from mineral oils to synthetic ones. This inequality also applies to sump oil which is an admixture of all of them and other workshop oil-like fluids that have been thrown in for good measure.

It is hard to find a consistent and definitive reference about the vapourisation* temperature of even these pristine oils. Mineral engine oils can be from 121C to 149C, while synthetic oils can be from 232C up to even 371C. So it is impossible to define such a temperature. Even pristine diesel has a wide range of vaporisation temperatures from 149C to 371C. From practical observations, I sense that diesel fuel is generally more volatile than sump oil and consequently is more willing to burn and requires a narrower throttle aperture to keep the combustion under control without flue pipe smoke.

Regarding the handling of the fuels, the sump oil is almost odourless but is visually messy to handle, but it eventually cleans off the skin and hard surfaces. In contrast the diesel stinks at ambient pressures and temperatures and does not leave a visible mess, but contaminates skin clothing and equipment, leaving a pervasive and lingering reminder, if it is not consumed by incineration.

Note*: Right or wrong, throughout this post, I have used the term ‘vapourisation’ to describe the process of releasing a flammable gas (or particles, smoke etc) from oil. Some authorities say that oils don’t boil, but rather it degrade at high temperatures to form small molecules (that behave like a gas) and become a fuel. Anyway, I will stick with the term ‘vapourise’ to describe, the transformation of oil to fuel, even if it is not strictly correct. This little video shows a ‘boiling’ sump oil surface. It looks like boiling, even if it is only the release of decomposition gases from the parent oil. Additionally, I have a small experimental hole in my original burner lid and normally I block it with an old nail that is ground to form a short round point. When the burner runs at full power with sump oil fuel, with no scum buster or heat concentrator ring, the point of the nail gets coated with oil. I think this is more evidence of some sort of boiling action.

Candle wax. Candle wax or paraffin wax is another exciting fuel that melts at 37C and boils at a surprisingly high 370C. Despite this high vaporisation temperature it is a very frisky fuel and burns very willingly once that high threshold is reached. I love to use it as a starter for camping fuels such as wood and oils. I use it in the form of strips of wax-soaked egg cartons.

They are compact and light, have no significant odour, can’t be spilt or contaminate other backpacking gear and burn even more excitingly if they happen to get wet.

“Just like candles, these fire starters make lots of stinky smoke after the flame is extinguished. So I usually put the smoldering fire starter near the open burner port to playfully dispose of the annoying smoke while it adds to the inferno. Sometimes the oil flame within the burner will ignite the wax smoke and will burn back up along a thin trail of wax smoke, against the flow of incoming air, and re-light the flame on the tip of the smouldering fire starter. It makes a truly persistent flame. Maybe petol is similar and this is why many amateur arsonists experience the karma of burning themselves. “

[Add a video of the of the burning wax smoke trail ]

….That’s as far as I have got…… but there is more flames and explosions to come…..as the snow is calling me…

Part 3. Tent oil heater heat robber for cooking and putting it all together for snow camping

[More to come]

Tim

Other related post for pyromaniacs

Perhaps for those who are a little greener, you prefer to burn little sticks for warmth and cooking? Here is a sample of my many related posts about tiny and efficient stick-burning stoves/heaters for backpacking that may interest you.

A simple tiny tent stove

A large downdraft tent stove

Blower stove gallery index