Played a lot with my new Ti-Tri on my patio (warm, no wind) with an MSR 0.85 liter Ti pot and got the following approximate formulas:
(ml alcohol to get rolling boil) = 6 * (number of cups of water) + 2
(burn time in mins) = 0.5 * (ml of alcohol)
(time to boil in mins) = 3 * (number of cups of water) + 1
I've posted these before.
But now I made a simmer ring and measured simmer times.
The simmer ring is nothing more than a one inch strip cut out of a soda can, slit so it fits over the stove. It can cover all the air intake holes, or one hole can be left open. The left shows one on the stove, to the right is another ring partially coiled up. The ring weighs 1 gram.
If you add the ring after boiling the simmer times are:
(simmer time in mins after boiling) = 1.5 * (remaining alcohol in ml)
Thus with 20 ml and two cups of water it will use about 14 ml to boil, then have (20-14) * 1.5 = 9 mins simmer time.
If you put the simmer ring on immediately after lighting the stove it simmers quite a bit longer:
(simmer time in mins, no boiling) = 2.5 * (alcohol in ml)
I guess this is because the stove is relatively cool if you put the simmer ring on right after lighting, so it burns more slowly.
I also tried covering the top of the stove with foil with a hole cut in the center. Without a simmer ring, but with a 1/2 inch hole the stove ran too hot for simmering. With a 3/8 inch hole the stove ran erratically until it blew itself out.
I may try a combination of simmer ring and foil cover, but since it works fine (at least on my patio) with just the simmer ring, I may not. I also need to see how well the simmer ring performs in wind and cold.