The figure on the right is a cross-sectional diagram of the Pro-type.
From now on, each part will be referred to by the name shown in the figure to the right.
Itemize the combustion process





From the above, there are two main points of production


It is the Top and Partitions that transmit the heat of the flame.
When aligning the Top and Bottom, the Top should be inward and the Bottom should be outward for better heat conduction.
It is difficult to decide on the size of the opening above the top. If you make it small, it will be difficult to ignite at first, but if you make it big, the area to be seared by the flame will be small and the heat conduction will be disadvantageous. It is also more interesting to make the flame rising from this opening as small as possible to make the erupting flame from the Outlet Hole more noticeable. Also, the flame in the center of the chamber has less oxygen supply, so combustion (heat) efficiency will be poor. The only way to determine the size of the flame is to try to find out by trial and error

The pressure chamber must be perfectly sealed between the top and the partition, as well as between the top and the bottom, as well as between the top and the bottom of the partition, even if the partition is made of a rectangular aluminum cylinder.


Alcohol is explosive. Vaporized methanol and air mixtures explode over a wide range of vapour densities of 7 to 36%

Even glass alcohol lamps, which have a much smaller risk because it is difficult for fire to get inside, are not to be used with small amounts of fuel and are banned for use in elementary school science experiments. This was in response to an incident in which an object with a crack or defect in the top of a glass container was used to explode.
Two things to consider are that fire can enter through the smallest of gaps and that the density of alcohol vapour in the vessel can be contained within a wide range of explosions

If you know the nature of methanol, you might think that you can't use such a dangerous thing just by looking at the structure of an alcohol stove.
Open Chamber is not a problem. It's not sealed, so if it were to explode, there would only be a light popping sound.
The problem is in the Pressure Chamber, which is likely to be in the vapor density range to explode as a result of the alcohol injection and if fire enters through the outlet hole, it will explode. The ignition point is in the upper part of the Open Chamber, away from the outlet hole, but that does not mean that fire will not enter the chamber

In the event of an explosion, the small diameter of the outlet hole will not provide an escape route and will push the alcohol in the pressure chamber down and push the alcohol in the open chamber out of the upper opening through the slit at the bottom. This will spread the alcohol around the stove. Moreover, you can't see the flame of the alcohol burning in the light.


So how do we deal with it?

For one thing, don't use these risky alcohol stoves and use a much safer butane fueled cooker

Alternatively, you can use the known methods of wrapping carbon felt around the partition or filling the pressure chamber with a moderate amount of carbon felt. This will keep the vapor density of the pressurized chamber high and prevent fire from entering the outelet hole after alcohol injection.

This does not interfere with the jetting from the outlet hole. Carbon felt can be substituted with a fine steel scrubber



Also, the combustion of alcohol fuels produces formaldehyde (a toxic substance), so make sure to ventilate the room when testing indoors



Most beverage cans are made of aluminum and some are steel

According to a little research, the aluminum cans are made of 3000 series or 5000 series aluminum alloy with a synthetic resin coating on the inside to prevent corrosion. It can be used for fruit juice and beer. However, since the synthetic resin coating is lost on the machined part, I am a little concerned about whether it can withstand alcohol fuel.

Comparing the pull-top and screw-cap beverage cans, the latter is harder and has a relatively thicker overall wall thickness. The latter is harder and has a relatively thicker overall wall thickness to withstand the stress of turning the screw cap. The type of alloy may also be different

Speaking of hard, it is steel, but it is more likely to corrode than aluminum. It is more resistant to heat and less likely to be deformed than aluminum, but it's a material you don't want to use very often. It may be good if it is a usable part without much processing.

I use three cans, two 350ml cans and one 250ml can, you can do just two 350ml cans.
In the left image, the Top is already cut out of one 350ml can and finished. A moderate opening is made in the center and a few to a dozen small holes are drilled in the shoulder area. Drill a dozen or so holes at a height of about 10mm below the shoulder opening and cut underneath to form a strip of paper

The 250ml aluminum cans are used for partitions, which can be made from the leftover parts of the other cans, in which case you can make the whole thing in two cans.
There is a slight band around the mouth of the 250ml aluminum can, and this diameter fits into the groove of the Top (and Bottom), so I cut it out here to adhere to the Top. Cut out the required length + 1mm and make a dozen holes at 2mm from the bottom. Then I cut a dozen holes in the bottom of the slit. A dozen holes will be slit.
Bottom is only cut out

The print was removed from the adhesive surface and the parts that are expected to conduct heat. As a result, only the printing on the bottom part is kept

Also, a good amount of fine steel scrubbers. Strong heat-resistant adhesive is a must, and Autoweld is recommended



First of all, I glued the Top and the Partitions together. Use plenty of glue to prevent any gaps between the Top and the Partition.

Once it's fully seated, pack a steel scrubber

Insert the Top with the Bottom facing outward to complete the process

Apply a thin layer of glue to the bottom of the shoulder except for the top strip and fit it in.

In this process, the Top and Bottom are pushed in at the same stride all the way around to ensure that the angle between the Top and Bottom is not blurred. Otherwise, the bonding surface of the Top will be distorted internally



It was the most orthodox build, and it was also able to control the flames from the center.
Is that a passing score? I thought,
Compared to the one I made in the next chapter, I found out that the combustion (heat) efficiency is really low

To make 500 ml of espresso in a percolator-type device consumes about 30 ml of alcohol fuel and takes about 17 minutes
--Those depend on the water temperature and environmental temperature

For the things in the next chapter as a comparison, I will describe the results first
I was able to make 500ml of espresso three times with the same 30ml of alcohol fuel under the same conditions, including room temperature. The time required is a little longer, about 19 minutes per batch, but it is not a big difference.

The big difference was in fuel consumption

The thermal efficiency is poor due to the lack of oxygen supply to the flame in the center, and if the flame erupts through the outlet hole, it would be more efficient to cover the opening of the open chamber

The series of tests were conducted on a cool autumn night, and time is reduced when done in the daytime or other warm weather conditions. Perhaps even lower fuel consumption

Using up fuel is not suitable for actual use. You will want something with a lid that can store fuel. I don't want to store alcohol for a long period of time, and it's enough to avoid wasting fuel even during the camping period.
It works the same way as the prototype, but with an outlet hole in the partition and a lid on top of the partition to seal it off



You need two cans. A can with a stroked shoulder screw lid and a standard 350ml can. The diameter of these two cans are equal and the bottom part of the can is almost the same.
Get the Top and Partition from the can with the lid at the center of the right image, and the Bottom from the other can on either side. In addition, prepare wire and steel scrubber of about 1mm diameter

Partition is the most time-consuming part.
Drill a few outlet holes upward in the top of the most narrow groove under the screw. Glue a ring made of wire to the top of the outlet hole. This ring catches the Top and glues it together to ensure a good seal and a high level of accuracy.

The bottom part of the partition is made by cutting a dozen holes along a certain height, and then bent inward to make the opening fit into the groove of the Bottom. It is ideal if the folded strip fits closely to the slope of the bottom.
The Top has a hole in the center where the mouthpiece passes through and stops with a ring, and the bottom is shaped like the prototype Top.

Bottom is just cut out like the prototype

The lid will need to be trimmed down a bit. It can only be sealed by pressing the mouthpiece against the plastic gasket, so the lid should not interfere with the Top to close it off

The outer screw part of the bottle opening is shaved off the coating. This coating melts in the heat and cracks and floats away in small pieces, which is a detriment to tightening the cap. Scrape off the coating, either after completion or after use, so that the cap can rotate smoothly



Glue the partitions to the Top. Use plenty of heat resistant glue to ensure a good seal. After it is fixed, seal it perfectly by applying glue from the back side through a narrow gap between the ring and the Top

Pack a steel scrubber in between

Push the Bottom in and complete it. The gist is the same as it was done on the prototype



Add alcohol, close the lid, and shake it upside down to make sure no fuel leaks

A homogeneous, nicely shaped flame rises up. The height of the flame is about 7 to 10 cm. When surrounded by a trivet and when the environmental temperature rises, the flame can grow to about 15cm

It was possible to make 500ml of espresso in a percolator-type device three times with about 30ml of alcohol fuel, each time taking about 19 minutes
--Those depend on the water temperature and environmental temperature

That's how it seems to work for three seasons, but the middle of winter may be tough

The series of tests were conducted on a cool autumn night, and time is reduced when done in the daytime or other warm weather conditions. Perhaps even lower fuel consumption

It would be ideal to have something that can be used in 4 seasons without being dependent on the environment, but that may not be possible, so I tried to make something that can be used in winter as well



In addition to the same structure as in the previous chapter, I crawled a wire in the hope of transferring the heat of the flame to the alcohol fuel. The only difference is the Partitions in the left image, but everything else is exactly the same

The wire is wrapped around the inside of the mouthpiece where the flame rises so that it doesn't interfere with the lid, and the wire is passed through the pressure chamber to the bottom. The heat is transferred by the steel scrubber and the alcohol fuel at the bottom.

Close the holes where the wire was threaded

The wire is copper wire, which is a good conductor of heat



Exactly the same way as the ones in the previous chapter

To summarize in bullet points,



I failed to push in the Bottom. Because I pushed it in a little slanting way, the Top was deformed and the hole on the strip protruded, and the Bottom was torn open.
I replaced the bottom part of the stove, but it can be taken off easily. Even after its completion, the bottom body part of the stove is still thin and the sides of the stove are not strong enough, and it may be torn by something trivial, so you should be careful not to damage it.
Maybe we should make a heat-resistant cover to protect the sides and keep them warm



Add alcohol, close the lid, and make sure it doesn't leak when shaken upside down

The height of the flame is about 10-15 cm. It seems to have an effect. As it warms up? The flames will be stronger and will be about 20cm high. The trivet also need to be raised a bit

It is impossible to make 500ml of espresso in a percolator-type device with about 30ml of alcohol fuel three times, twice and a half, and each time it takes about 15 minutes
--Those depend on the water temperature and environmental temperature

Compared to the last thing, fuel economy is a little worse and heat is up.
However, there is no big difference in the record itself. However, considering the fact that the cold weather was more severe than in the previous test, it might have been a pretty good result.

Considering the drop in water temperature, it is only natural that the journey would take longer and require more fuel

We'll have to wait for the mid-winter test to see how long it will last.

I made it with the idea that the firepower might increase if the mouth is wide-mouth. The wider the opening, the less oxygen will be supplied in relation to the amount of alcohol burned, so efficiency may not be so good.
Steel cans are tough to work with, but apart from that, they are surprisingly easy to make




You will need three cans: one steel can with a 170ml lid and two standard 350ml cans.
The steel cans are used for Partition. This can is slightly thicker than the grooves on the bottom of the can, which is the same as the 250ml can I used for Chapter 1 Prototype, and the bottom of the can is made to fit the same way. I don't want to cut off the printings because I'm afraid of corrosion of steel. You need to remove the surface to glue the top and the screw part.

The reason I'm cutting off the screw part on the outside of the drinking port is because if the print melts and cracks in the heat, it will make the lid less tight, but it might be fine after it's finished or used.
Drill several outlet holes upward in the top of the most enclosed groove below the screw site

Cut the opening of the Top so as to remove all the curved surface. In other words, cut at the very edge of the bend. This is easy if you have a nibbling cutter.
This opening is slightly wider than the most raised area under the screw section of the partition, and can be filled with glue to glue the Top and the partition together. The top and the partition can be glued together by filling it with adhesive.
Cut out the Partition at the required length + 1mm, make a dozen holes at 2mm from the bottom, and cut underneath it to make a strip of paper. And I cut a hole in the bottom of it. I used the same method as the lower part of the prototype.


When joining the Top and the Partition, the sealing must be perfect, and the leveling accuracy of the joint must be precise. In addition, since this is a part that is subject to stress when the lid is opened and closed, adhesive strength is also required.

Apply heat-resistant adhesive to the bonding surface of the partition to secure its positioning and secure it temporarily

Once it is completely adhered, apply the heat resistant adhesive through the small gap. It's OK to seal the outlet hole just below. You can drill it again after it has cured. Rather, the heat resistant adhesive is poured into the hole so generously that it does so, to ensure a good seal and strength.
Wipe off any adhesive that is overhanging the bottom of the screw and the Top shoulder. Use anhydrous alcohol to wipe it off completely

The rest is almost the same way as in the previous two chapters

To summarize in bullet points,



Add the alcohol, close the lid, and make sure it doesn't leak when shaken upside down.
It will be taller than the ones in the previous chapter. It is possible to keep it low, but the fuel capacity will be small. If the fire power is strong, then the trivet will need to be taller as well

The height of the flame is around 15cm. The heat of the flame is comparatively greater than that of the smaller diameter ones. As it warms up, the flame reaches a height of about 20cm

500ml of espresso can be made twice with about 30ml of alcohol fuel in a percolator-type device, with each batch taking about 14 minutes
--Those depend on the water temperature and environmental temperature

Fuel efficiency (thermal efficiency) is a little worse than with a small diameter lid, but the heat output is higher.
The time required was close to that of the small diameter heat sink, but considering the fact that it was getting even colder, it was a pretty good result and could be used in the middle of winter. Considering the fact that the water temperature would have been lowered, I think this time is practical.
However, it takes a little longer to warm up, i.e. for the flames to erupt vigorously from the outlet hole, probably because the partition is made of steel.

Maybe this is exactly what we should have with the additional heat transfer wire

I'm going to do exactly the same thing that I did in chapter 3 with the small diameter lidded thing with the heat transfer wire to the wide mouth lidded thing in the previous chapter. I know it works. And if the heat transfer is not good because the partition is steel, we might expect the effect of the heat transfer wire to be relatively large




I just added the heat transfer wires to the Partitions in the previous chapter. Everything else is the same



Exactly the same procedure as the ones in the previous chapter.
It is important to emphasize again that the Top and the Partition should be temporarily fastened to ensure the horizontal accuracy of the Top and the Partition, and plenty of heat-resistant adhesive should be poured through the gaps to ensure sufficient sealing and strength

To summarize in bullet points,



Add alcohol, close the lid, and make sure it doesn't leak when shaken upside down

The height of the flame is about 20-25 cm. It looks like it has a lot of firepower

To make 500ml of espresso in a percolator-type device, it takes a little over 2 times with about 30ml of alcohol fuel and about 9 minutes per serving
--Those depend on the water temperature and environmental temperature

Compared to things without heat transfer lines, the fuel consumption (thermal efficiency) is slightly lower, but the heat content is much higher.
I installed the trivet high, but it wasn't enough and the flames stuck out. If I had set it up a little higher, the time required would have been shorter and the fuel consumption might have been better

This could be done by stewing. However, it is not practical because it needs a lot of alcohol fuel to simmer for a long time. For the percolator, the one with a small diameter lid and an additional heat wire or the one with a wide mouth cover is enough, and this one may be over spec.
The heat and efficiency (fuel consumption) have reached a practical level.

Even if we don't know yet, but even if the firepower is relatively low in the middle of winter, this stove seems to be more than enough to be practical

After ignition, the fire power changes to three levels, with some stopping at two

The first phase is the burning of the alcohol, which naturally vaporizes in the Open Chamber, and the firepower is small. In the second phase, the flame heats up the stove and accelerates the alcohol vaporization, and flames begin to erupt out of the Outlet Hole, resulting in practical firepower. Normally, I think this second phase is the design intent.
The prototype of chapter 1 and 2 and the one with a small diameter lid were a stop on this stage. At least in the cooler autumn weather

The third phase is even more firepower. It changes discrete and becomes stable and equilibrium with one step stronger. The change tends to occur when the stove is surrounded by a trivet and the percolator on top of it becomes hot.
I think there is a threshold as the temperature of the stove itself, and when that temperature is reached, the alcohol vaporization gains a step of momentum. Just like heated water that starts to boil, the momentum of the steam increases. The boiling point of alcohol is 76 degrees Celsius. Maybe that's the threshold?

It's only a hypothesis, but if that's the case, then it means that firepower will change depending on the environmental temperature. That too, as a discrete changeability

Heat transfer from the flame depends on the structure of the stove, but the ambient temperature is influenced by many factors besides climate, such as the location of the stove, the trivet, and the state of the oxygen supply.
Intentionally, there may be things like poor heat-conducting rugs and covers to cool the stove itself and suppress heat radiation, but the biggest influence would be the climate. This can only be tested throughout the year