Bushwalk Australia

Here is another post for fellow MYOG fire lovers or pyromaniacs.




For some time I have used waste oil as a supplement to wood sticks to fire small tent stoves for winter backpacking. Oil is energy-rich and very compact for backpacking. It adds to the vigour of the combustion and extends the ‘burn-time’ for wet and frozen found wood. However, when the combustion was transitioned to oil only, the combustion became disappointingly dirty and inefficient.


As an experiment, I made a miniature smudge pot (134g) that I connected to a roll-up stove pipe. Initially, I had failures, due to my misunderstanding, of the principles of its operation. Now, It burns sump oil cleanly to provide strong infrared heating for a small winter tent. The throttle plate that covers the big hole in the oil pot is critical to setting the correct fuel-air mixture for this clean, hot and efficient combustion.



The heater burns ~140-240g of oil per hour, depending upon the desired heat output. The photo above shows the heater set to run at the low rate while the one below is at the highest rate respectively. The air admission rate delicately controls the burn rate through the adjustable throttle plate.




The burner was primarily designed to burn sump oil. However, it can also cleanly burn tea-candle wax, used vegetable oil, plastic from milk bottles and even wood chips etc. Very different throttle settings are needed to optimise the clean combustion of each fuel type.

I don't have an accurate measure of the temperature, but the top of the burn tube (that is not the hottest part) melted aluminium (MP ~600C) so it provides lovely radiant heat for winter warmth. It is not functional for cooking, but that may come in the next iteration if the clean burning can be maintained.

This little video below probably best describes the heater's performance.



The burner start-up requires a considerable heat input so that the burner can get hot enough to feed back sufficient heat to sustain the oil pyrolysis or vapourisation. Burning trips of wax-soaked egg cartons can provide sufficient heat energy for this start-up as demonstrated in the video below.



For more details, please see https://timtinker.com/micro-oil-heater-for-a-small-tent/

Tim

That's insane that such a small stove can give off that much heat. The flue is out there hot.

Is it safe to keep refuelling?

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crollsurf wrote:That's insane that such a small stove can give off that much heat. The flue is out there hot.

Is it safe to keep refuelling?

Sent from my SM-G998B using Tapatalk

Hi crollsurf, Thanks for your interest, compliment and question. Yes, that red-hot temperature is just so critical to making it a lovely tent radiator. In another post Stove Temperature and Heat Radiation I calculated that changing the surface temperature from 300 to 400 or to 500C the heat emitted goes up by approximately 1.9 and 3.6 respectively according to the Stefan–Boltzmann law. At its best, I think it gets up to at least 600C as it has melted aluminium on the top of the burner tube which is not the hottest part.

The hot refuelling is very safe with oils and waxes as these have a very high flash point for their respective vapours and any flash flame is sucked up into the burner tube. If there is any water in the fuel it can be a bit explosively exciting. With due care, a tiny trace of added water can help accelerate the combustion by creating a steam /oil mist. In my full article, I commented on the need to add fresh fuel slowly so that the vapour production, in the tiny oil pot, is not quenched by the cool oil.

This also leads me to think that a drip feed might be the best for this type of burner so that effortless and long evening burns can be achieved using a bulk oil bottle that is suspended from the tent pole. Another project is underway with a more compact version that incorporates drip feeding, a cooking surface and glass windows for tent lighting. It doesn't hurt to dream! Tim

Awesome. I spent a number of weeks last winter, down in the Snowy Mtns, in a Black Wolf tent that I'd customised to accommodate a Winerall wood stove. Staying warm, cooking, drying out wet ski gear, etc. There was an aesthetic, watching the fire die out, through the glass panel. The heat from the flue. And learning how to keep that glass clear of soot.

And then there are people like you, who just blow my mind. Instead of buying quality firewood, instead of throwing cooking oil away, using it to stay warm in winter!

Maybe not for me, but I love it all the same. It's ingenious.

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Love these posts, please keep posting stuff like this

CasualNerd wrote:Love these posts, please keep posting stuff like this

Thanks CasualNerd. That is good as I love doing stuff like this. Just wait for MK11 oil heater! Tim

HI Tim, very slick.
Do you have any concerns re carbon monoxide production in the confined space of a tent.
cheers
bw

bluewombat wrote:HI Tim, very slick.
Do you have any concerns re carbon monoxide production in the confined space of a tent.
cheers
bw

Hi Bluewambat, Thanks for your question. The short answer is no. The oil's combustion is complete and clean, so it should mainly produce CO2 and water. Most of the burner gas exits up through the stove pipe and outside the tent. Also, the burner and the stove pipe are, for most of the time, at a lower pressure than the air in the tent, so any leakage is inwards. The oil combustion constitutes a cyclic series of micro explosions and the pressure after these explosions can be momentarily positive inside the burner. This can best be seen and heard as little flame 'pops' from under the throttle plate in the 'High power' portion of the video at ~14 seconds. However, if the burner fuel/air mix is made even richer, the system will have slower and larger micro explosions that will 'pop' smoke/flames out through every little hole (I have not yet captured this on video as it is a rare and very transient event). Luckily, these emissions are mainly sucked back into the holes and they certainly warn that the fuel mix should be made leaner. If left too rich, the pulsing will extinguish the combustion with a final flame-out micro explosion that blows out the pilot flame within the oil pot. The stove pipe safely exhausts the smoke after such a flame out or a speedy reignition of the smoke in the oil pot can quickly start the burner again. Lastly, the stove pipes' removal of gas ensures that the tent has a constant inflow of fresh air that will dilute any traces of fugitive emissions from the burner and also anthropomorphic ones. This is much better than burning any fuel stove within a winter tent. I hope this makes sense. Tim

telemarktim wrote:

bluewombat wrote:HI Tim, very slick.
Do you have any concerns re carbon monoxide production in the confined space of a tent.
cheers
bw

...
Lastly, the stove pipes' removal of gas ensures that the tent has a constant inflow of fresh air that will dilute any traces of fugitive emissions from the burner and also anthropomorphic ones.
...

Wowzers that was a comprehensive answer. The bold bit made me laugh. With the effects of my bushwalking diet, I should consider an in-tent heater just for this!

Son of a Beach wrote:

telemarktim wrote:

bluewombat wrote:HI Tim, very slick.
Do you have any concerns re carbon monoxide production in the confined space of a tent.
cheers
bw

...
Lastly, the stove pipes' removal of gas ensures that the tent has a constant inflow of fresh air that will dilute any traces of fugitive emissions from the burner and also anthropomorphic ones.
...

Wowzers that was a comprehensive answer. The bold bit made me laugh. With the effects of my bushwalking diet, I should consider an in-tent heater just for this!

Yes. Bushwalking diets and tents! My tents are light and large, so I usually share the diet and tent with others. Luckily, I set a generous limit of 200 anthropomorphic emissions before penalties apply.