The Right CATALYTIC Fuel – DME
Several people have asked us at CNW why we chose DME to be the fuel of choice. In fact, this was not done without literally a year or more of analysis, and tremendous effort to make other fuels work too.
We have devised methods, (even working on patents for some of them) to use more common fuels. But the results have shown us that there is such a huge advantage to DME that the use of any other fuel is going to be considerably more expensive, and is definitely more complicated and inevitably more prone to problems.
A bit of chemistry is necessary to explain the reasons, but probably not beyond the grasp of someone reading this. Basically, to have a reaction where something successfully burns, you need three components: fuel, heat, and O2. Fuel is supplied in the canister, heat is supplied by the ignition and then the heat released by the reaction. Oxygen is usually supplied by the environment. An open flame like a candle is a good example of this. Studying what happens in a candle burning is beginning chemistry. Air is made up of lots of gases, but the one we are interested in is Oxygen. The percentage of oxygen in the open air is approximately 21%. But at altitude, while the percentage doesn’t change, the amount of O2 decreases significantly. About 2/3 of the amount of O2 that is available at sea level is available at 10,000 feet.
Different fuels require different amounts of O2 to burn. For example, of the potential fuels that could be supplied in a canister:
- Propane requires 25/1 air to fuel ratio for complete combustion.
- Isobutane requires 32.5/1
- DME requires 15/1
Stoves don’t work as well at altitude, as it is considerably harder to find enough O2 to make them burn efficiently. But “flame combustion” stoves don’t burn that efficiently in the first place. There have been considerable discussion and testing of stoves in the last 10 years concerning their inability to burn fuel completely, without producing unacceptable amounts of CO, and unburned fuel.
Tests done by Roger Caffins, published in BackPacking Light, showed that the average backpacking stove produced about 250 ppm of pollutants in combustion. It was suggested that this was potentially harmful, to the user, especially if in an enclosed area. It is true, that a few of the stoves tested much better than that, but none were better than 20 ppm. AND, significantly, the most popular stoves tested, were actually worse.
Our own testing found much worse results too for the two most popular stoves. 3000 ppm, and 1100. These tests were done at sea level. IF the tests were done at altitude, the results would be much worse still.
The reason that Roger’s test results were different from ours is explained by Roger that his method was difficult to repeat, in that it involved a closed box. IF he had just tested the flames or exhaust his results would have been the same as ours. Our testing is definitely more sensitive and exact. Roger cited many authorities that agreed that this level of pollution was certainly alarming, and quite possibly dangerous. IF he had cited our figures, then assuredly those authorities would have agreed that the gasses were dangerous.
CNW does not consider these rates to be acceptable. Coolfire® technology is NOT open-flame burning. It is our aim to burn fuel cleanly and completely. Both for health reasons and because complete burning is obviously more efficient.
All open flame devices use a Venturi in the nozzle to supply the majority of the air to the combustion. There is a wide degree of quality of the orifices used, and most are significantly lower than a 20 to 1 ratio, (20 parts air to one part fuel) While theoretically possible to make an orifice that might be 30/1, no such orifices are used.
So, ALL devices that use isobutane as a fuel, cannot burn completely with the air supplied by the Venturi alone. Much of the air must be from air surrounding the flame, which means it cannot be as clean or efficient.
For Propane, it is better, but as anyone knows that has used such a device, pots still invariably have a coating of soot on the bottom of the pots, a good indicator of incomplete burning. Additionally, propane is rarely used for portable devices as the pressure requires a stronger walled cartridge.
For Natural gas, it would be quite good. No additional air would be needed. However, Natural gas can’t be used in a canister as the pressure required is immense, at the walls of the canister would be VERY thick.
DME, it turns out, is a great candidate, as it does not require additional O2 outside what is easily produced by a Venturi and requires wall thicknesses equal to that of IsoButane.
Coolfire® technology is NOT open flame technology. There IS NO flame. The combustion process is totally internal and in an enclosed catalytic process. NO outside air is available other than what is supplied by our Venturi. If we use isobutane as a fuel with our technology, without an additional pump of air, then we produce some pollutants also. Not as much as open flame devices, but still unacceptable to us. Consistent long term testing of Coolfire® technology has shown that our devices burn extremely efficiently and that the amount of unburned fuel and CO is astoundingly low. We actually can’t give a precise measurement as yet, because it is so low. Our apparatus only gives is accurate to .5 PPM. In our tests, the readings are consistently 0 PPM. That COULD mean as high as .49 PPM. (as it rounds off.)
NOTHING else using a fuel can come with 2 orders of magnitude. (100 TIMES worse). DME has been a common propellant used for over 70 years. It is listed as NON-Carcinogenic, unlike isobutane, or propane. The amount of heat per gram of fuel is equal to that of isobutane also, but DME also is much better at altitudes and in the cold.
Thus DME is the fuel that is indisputably best for catalytic devices.