View Full Version : Super Cat Alcohol Stove Modification

Odd Man Out
11-26-2010, 22:08
A few weeks ago I posted the results of my first attempts at making alcohol stoves (Penney Stoves). I got a lot of helpful comments, including the suggestion to work on Super Cat stoves as they are among the easiest, most reliable, and hence most popular stoves. However, I was not too happy with my first attempts at at a super cat. I made one with two rows of 10 and 15 holes using the template from the Zen Backpacking Stoves web page (http://zenstoves.net/Templates.htm)

What I didn't like was the high heat output and limited fuel capacity (I like to simmer stews in addition to boil water). The wide flame also overheated the handle on my 6" diameter pot. I also didn't like the narrow base (I have been know to tip over my oatmeal off of my Mini Bull BIOS). It was suggested I make a Simmer Cat from the great web page by Jim Wood (http://jwbasecamp.com/Articles/SuperCat/) which has one row of 15 holes.

This Simmer Cat cooks slower, has a higher fuel capacity and narrower flame pattern, but it is still tippy. I noticed that the flame pattern of the Simmer Cat was initially very small but grew to be much larger toward the end. I know that on many side burning stoves, pot of cold water on top acts as a heat sink, slowing fuel vaporization. I also noticed that when the stove first primed, if I lifted the pot just above the stove, I got a flame pattern similar to the end of the test.

So my idea was to make a pot stand that it would hold the pot just above the Simmer Cat. This should allow the stove to function at maximum output right from the start and at the same time give me the extra pot stability I wanted.

So I did three tests: Simmer Cat with pot stand, Simmer Cat w/o pot stand, and Super Cat w/o pot stand. All tests were done with 15 mL of ethanol and 4 cups of room temperature water in my 1.3 L non-stick REI Aluminum pot. I set the stove and stand on a thin sheet of Styrofoam covered with Al foil (to insulate from the cold counter top). I set the stove on a soup can lid (for priming, although I didn't prime in these tests). The soup can also lifted the Simmer Cat high enough so the top was about 2 mm from the bottom of the pot when resting on the pot stand. The pot stand was a ring of 1/2" square hardware cloth (12.5 inches or 25 squares perimeter and 1.5" or 3 squares high). I lit the stove and started the timer. I lowered the pot over the stove every 10 seconds until the stove was primed. The Super Cat primed in 20 seconds and the Simmer Cats primed in 30 seconds. I measured the temperature (in deg C) every 20 seconds starting at 1 minute until the flame went out. The results are plotted here. Tests were done in my basement with no wind screen.

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs975.snc4/76887_10150348194220595_811535594_16098150_8019320 _n.jpg

Temperature increase is quite linear, so the stove power is the slope of the regression line (deg C per min). However for the Simmer Cat (no stand), the flame was noticeably larger after about 6 minutes, so I calculated a different slope for the last 2 minutes of that test. The calculated stove power is as follows:

Simmer Cat with Stand: 9.2
Simmer Cat w/o Stand (start): 5.4
Simmer Cat w/o Stand (end): 7.4
Super Cat w/o Stand: 10.5

You can see from the graph that stove power is inversely proportional to burn time (stoves that burned hotter, burned out sooner, as expected). You can also use the data to measure efficiency (total heat delivered to heat water per amount of fuel burned). Since all tests used the same volume of fuel and water, the final temperature is a measure of stove efficiency. You can see from the graph that the least powerful stove is also the most efficient. I also am not surprised at this result, as with most energy transduction devices, there is usually a trade-off between power and efficiency.

Conclusions: I much like using my Simmer Cat with the pot stand. It give the stability this klutz needs and it make the Simmer Cat function almost like a Super Cat, but with a larger fuel capacity, if I want it. Plus I have the option of using the Simmer Cat without the pot stand if I want to have a long slower heat.

11-27-2010, 09:27
You've been very scientific with your test. Congratulations on that.

Can you be more specific regarding the height of the stand and/or the width of the space. The term "just above" is rather open to interpretation.

1/4 inch 1/2 inch???

Thanks for all the work

11-27-2010, 14:58
You're a stovie now

there is no turning back

Odd Man Out
11-27-2010, 15:20
You've been very scientific with your test. Congratulations on that.

Can you be more specific regarding the height of the stand and/or the width of the space. The term "just above" is rather open to interpretation.

1/4 inch 1/2 inch???

Thanks for all the work

Thanks Grinder. Can you guess I am a scientist in my day job?

Here are a couple of photos. The first is a close-up before lighting. You can see the foil covered Styrofoam insulating base, the soup lid priming cup, stove, pot stand and pot. The pot stand is 1/2 inch hardware cloth wire mesh (25 squares perimeter and 3 square high). I measure the gap between the top of the stove and the bottom of the pot to be about 3 mm.

The second picture is the stove in action. I notice no noticeable change in flame pattern from the instant the stove is primed until a few seconds before it burns out. I also see no flames coming out of the gap between the pot and stove top. I did a test with a larger load of fuel today (1.0 oz = 29.6 mL of ethanol) and 4 cups of water at 20.6 deg C. It burned for over 8 minutes and got to 91.8 deg C. Temperature increase was very linear over the whole time at 9.2 deg C per minute (same as with the 15 mL fuel test). I need about 1 more minute (3.7 mL) of fuel to boil 4 cups of water. The stove has a capacity of at least 60 mL so in theory it should be capable of 16 minute burns.

http://sphotos.ak.fbcdn.net/hphotos-ak-ash2/hs495.ash2/76884_10150348717790595_811535594_16106527_110461_ n.jpg

http://sphotos.ak.fbcdn.net/hphotos-ak-snc4/hs975.snc4/76884_10150348717795595_811535594_16106528_4780135 _n.jpg

11-27-2010, 16:49
A couple of years ago I spent some time making stoves.
Several where along that idea . Some had an extra "collar" added others a built in pot stand.
Here are some shots :