A stove with a top and side fuel ports

This stove with top and side fuel ports, can resolve the charcoal choking problem that I encountered while testing the similar Miniature Dome Stove that only has a side fuel port.

Fortuitously, swapping from the side to the top fuel port can make the stove very much hotter (100-150C) for warming winter trekkers bodies while the excess charcoal is burnt off.

It may sound complex, but it as simple as swapping between the two ports and blanking off the unused one. Also, when dinner cooking is not required, it can still provide snow melting and abundant boiling water for hot drinks in this ‘top fuel port mode’ while optimizing performance for warming alpine bodies.

The stove modification maintains all the ‘lazy’ convenience of the cooking mode (side fuel port) with long fuel sticks used for fuel as describe for the Miniature Dome Stove.

The hybrid modification does not prevent the charcoal choking problem that eventually will be encountered in the side feeding mode. However importantly, it does provide a seamless, simple, safe and ‘mess-free’ way of clearing the charcoal choking when it happens. “Just enjoy the turbocharged heat while the charcoal clears.”

Lastly, the hybrid modification, for tent stove use, makes the stove have full functionality with regard to its second and third uses as an alcohol stove and as a powerful blower stove for outside cooking.

Introduction

While writing my post on the Miniature Dome Stove, I hinted at the possibility of an improvement to a stove that I foolishly called my ultimate backpacking wood stove. In the back of my mind I held the image of the superheated glowing fire dome of my Pudding Bowl Stove. The Stella performance depended on that pesky, but magical inverted J-burner that unfortunately can reverse burn and disrupted the stovetop’s ideal area for cooking.

I know that good cooking is very important, but that extra glowing heat was just too good to let go of for the sake of making the cooktop clear for cooking.

“At the time, I did think: What if I had a top and a side fuel port? But then I thought it would be too complex. However, the ‘bower bird’ in me did hang on to the ideas and also the prototype fire bowl that could make this experiment easy to do.”

Charcoal choking

Most of my tent stoves with inverted J-burners suffered from a problem of charcoal build-up (I call it ‘charcoal choking’) that eventually restricted the stoves performance if not cleared in some way. In inverted J-burners, this charcoal choking often props up incoming fuel sticks and deprives the stove of ‘new’ wood to make wood gas that drives the flame and the flue pipe draft. This, in turn, encourages or caused the inverted J-burner to reverse burn the incoming fuel sticks. Clearing this charcoal is not exactly easy in the confines of a small tent!

The recurring deficiencies of charcoal choking and reverse burning stimulated me to develop my Miniature Dome Stove.

By simply not having an inverted burner, it eliminated the possibility of reverse burning. With great optimism, my initial test, that I have already reported, did not reveal a charcoal choking problem. However, my extended testing over many hours has revealed this as a problem with the Miniature Dome Stove.

“Most users will wish to run the stove for several hours when winter camping when the shadows fall so early and the cold nights are so long.”

In the horizontal stick burner, the choking slowly blocked the exit path for the flames and combustion gases.

The stove is conveniently fuelled with long sticks through the fuel port on the side of the fire dome. In the process of feeding the sticks in, there is, a somewhat unavoidable, tendency to push the residual charcoal chunks across the diameter of the fire dome to the terminal end of the flame guide. The gap between the end of the flame guide and the wall of the fire dome is an already constricted part of the stove exhaust labyrinth.

This means that there is a growing obstruction of the only pathway for the flame and exhaust gas to pass through. However, while not causing reverse burning it does cause the heating performance of the stove to slowly diminish.

The charcoal that is accumulated by this process does not burn away readily, as it does in the Pudding Bowl Stove. This is because the abundant wood gas from the long fuel sticks has used up most of the oxygen in the incoming air stream before the charcoal can have an opportunity to be burnt. Also, near the choke point, the gas/flame is ‘smoothed out’ and flowing along the ceiling of the fire dome. This means that there is minimal turbulence to mix any remaining oxygen to speed the combustion of the charcoal. “It just forms a ‘gently glowing and growing ‘whale hump’ of charcoal in the wrong place.”

Clearing the pathway with a tiny long-handled titanium wire ‘rake’ is possible but it is not a simple or a satisfactory solution to the problem.

Back to the Pudding Bowl Stove

While evolving the Miniature Dome Stove, I made tests with simple downdraft stoves (Coffee Tin & Pudding Bowl stoves) where the fuel sticks and air were essentially entering the Fire Dome through a top fuel port in the stove’s ‘would-be cooktop’.

These were extremely simple stoves. They were inspired by the primitive but effective ski chalet stove of my youth. My experiments showed that miniature versions of these stoves burned exceptionally well and the fire dome surface reached ~450C. This is 100-150C hotter than the Miniature Dome Stoves typical peak temperature. “The nature of the combustion meant that they did not accumulate charcoal.”

To lighten up, here is an ode to the Hybrid Miniature Dome Stove creator:

He scratched his grey wily head, trying to decide,
A hole for good cooking, when made in the side?
Or on top with more heat, for the charcoal to beat?
Ahhh, he'd ave both, one on top, plus one on the side!

My speculations about combustion differences with top and side fuel ports

I think that the higher temperatures in the Pudding Bowl Stove (top port) were achieved because both the wood and the charcoal were being totally burnt in complete balance within the fire dome. This is caused by the downdraft air entry that:

• Restrict wood pyrolysis to a narrow band on the fuel sticks (Or it pulls the smoke and flame away from the sticks and past the glowing charcoal).
• Spares more oxygen for charcoal combustion by having a lower rate of wood gas production.
• Creates more turbulence to make the combustion hotter and be completed largely in the fire dome.
• The turbulence also distributes the heat more uniformly to the fire dome including its walls.

I also noticed that with a Miniature Dome Stove with a side stove pipe elbow (as shown below) the temperature was much higher than at the same pipe connection point on the Pudding Bowl Stove. This indicates to me that the poorer gas/oxygen mixing in the Miniature Dome Stove leaves more combustion to be completed in the stove pipe.

To me, this strongly indicates the this inverted J-burner configuration should make it a much more effective body heater for winter campers by spreading heat to the walls of the fire dome.

Such a burner would be great in a hybrid tent heating stove with a side fuel port optimized for cooking and a top fuel port for body heating. The top fuel port could be used when the stove is not needed for bulk cooking.

Cooktop obstruction by a top fuel port

The obstruction of the cooktop surface for cooking in large dinner pots by the flue pipe and fuel ports was both the inspiration and major limitation of such designs. “It probably distracted me, at the time, from seeing the real potential value of the top fuel port stove design.”

Consequently, without enough thought, I rapidly, moved on to Miniature Dome Stove development to find a way of clearing the entire stovetop for convenient cooking and having lazy fuel preparation.

Design in haste and discover the truth slowly?

Downdraft burners rule! I slowly discovered that charcoal choking eventually occurs in my ‘ultimate’ Miniature Dome Stove (with side fuel port) after burning multiple hours.

Now, in retrospect, the addition of a simple and very hot downdraft fuel port could be a delightfully easy way to prevent or clear up an unwanted charcoal accumulation. It could be incorporated into any stove design.

Even better, I later discovered that a large cooking pot could be used with a tiny stove with both the stove pipe and fuel port simply located on the top of the stove. This was achieved by adding a ‘V-wire’ bracket to support the pot overhang (As in the photo below). “The cooking or snow melting is not fast, but it is perfectly adequate when confined to a winter tent when nights are so long.”

A comparison of the above photo with the photo of the stove with top and side fuel ports (below) reveals the relative simplicity of the KISS tent stove with only a tope fuel port.

Many other little embellishments such as ultralight stove leg mounts for mounting the stove up above deep snow are considered in the KISS tent stove post. It is yet another ultimate, or should I be cautious and say, ‘penultimate’ Keep It Simple Stupid tent stove design.

The simple stove still can have a side fuel port that is mainly for using the same stove fire dome as an outside cooking blower stove. However, the port can be used in tent stove mode to feed in otherwise useless chunks of fuel sticks. “Not essential, but a nice feature on a long cold night.”

Conclusion about top and side fuel ports

The KISS stove may have ended the short reign of the stove with top and side fuel ports, but it owes so much to the lessons learnt from the experiments with that complex stove and many of its best features live on even if used in uninteded ways.

The use of a top feeding port provides the best heat for comfort. It prevents charcoal choking and reverse burning and provides adequate cooking and snow melting.

The continued use of a side dual side fuel port also lives-on in a similar but large base camp tent stove that is made from a cooking oil drum. It incineration power has caused me to extend its capabilities and I crudely call it the Alpine TurdBuster tent stove. “Heat your body, cook your dinner while environmentally burning your alpine turds.”

Here is a little Instagram video of a little dome stove in top feeding mode.

Tim