We sometimes go to higher altitudes and have issues with butane fueled devices like some stove lighters.

Recently we were high and there were a lot of gnats and so we tried to use a Thermacell we had along.

It was extremely hard to light. We had a new one that lit right off, but after it ran a little while it became as hard to start as the used one. The altitude where you'll start seeing the Stoichiometric fuel air ratio getting out of balance is about 4000 feet.

Since I like to think outside the box and first understand and secondly modify things, it became a challenge to understand the Thermacell mechanism and get them to work.

The back is held on by 6 small screws and is easily removed. I took all the guts out [needlessly as it turns out] and cut open the plastic enclosure that houses the combustion chamber.

Learned a lot tho.  



Ultimately, the inside of the metal rectangular combustion chamber revealed a small brass cylinder ~.200" in dia, with what looks like a platinum catalytic screen/disk on the end. I drilled a small hole into the brass cylinder thinking that would allow more air to mix with the fuel, but partly reassembling the unit and trying to light it, it didn't help.

I might mention, the Thermacell is a beautifully engineered device that makes me wonder how many iterations were required to reach the final design.

Seeing that drilling the brass cylinder was a mistake I closed the tiny hole with a bit of solder with a Weller station set to 850F.

There is a hi temp sillycone tube that connects the brass cylinder with the white plastic gas valve. When I put it back together the first time I mistook where the tubing slipped over the white plastic gas valve. Taking the white valve apart, I saw that where I thought the gas came from, it didn't. There is a tiny, polished metal domelike 'insert' in the plastic, that under magnification, revealed a tiny hole for the butane to jet thru. I mean tiny, far smaller than a pin POINT.

The piece of plastic filter material under it on the pressure side gave it away.  



Then it became clear, the butane jetted thru the orifice and into a part of the white valve asm, a small moulded tube with an opening for mixing air, that the other end connected to the sillycone tubing and then to the brass 'burner'.

Like a tiny gas furnace burner.

What I did then was to take a new X-actor knife blade and carefully enlarg the plastic opening about 1 mm, being careful not to leave any shavings inside and to minimize any roughness that would disturb the aerodynamics of the butane jet and air mixture.


Now the burner 'lit' with a snap or two of the piezo-electic ignitor.

Watching the flame, such as it is, there is a space about 1 mm between the catalytic screen [on the end of the brass cylinder] and the blue glow disk.

When you look into the inspection opening of a burning Thermacell, you'll see a red hot line. Turns out that is the ignition wire that in located on the outside and in front of the blue flame 'disk'.


If you do this mod, you do so at your own risk because obviously, the Thermacell wasn't designed for higher altitudes and this mod voids any warranty and likely removes liability if it blows up in your hand or sets your pants on fire.  

Mod'ing it makes no dif to me though....  


Preparing the device for mod'ing requires removing the 6 back screws, the black plastic on-off lever, and the obvious spring, so as to gain access to the mixture opening --by raising the metal valve lever.

The whole mod can be done in about 4 minutes after you are familiar with the design. I don't even remove the gas cylinder.  

Now the units start with a click or two -or three. Same as a gas engine, you can 'flood' the fuel-air chamber somehow, and you may need to wait 15 seconds with the fuel off, for things to normalize before restriking again.

Hope this is useful to somebuddy.