Tuesday, 24 April 2012

The grand gas experiment...

So we have funding (yay)! Now for something far more trivial. This one concerns the grand stove experiment (which wasn’t really that grand). The whole thing is rather flawed and incomplete as an experiment and the data collection was shoddy (I am a bad scientist), but otherwise confirms a couple of things and gives us something to think about gear-wise.

                Firstly, the heat of combustion of butane and propane, if the units are converted to Kcal/g (which is much more convenient for our purposes) is about the same- 12Kcal/g. As such if a perfectly efficient system is used, it should take around 6.7g of gas to bring room temperature water to a boil (from 20˚C to 100˚C). Now keeping this in mind, the experiment:
                Four stoves, the Hi-Gear Blaze (50g), Primus Gravity (269g), Primus ETALite (242g) and an Old Primus (398g) of mine were tested with a half full cylinder of butane (75%/propane 25%- thus only butane left). The test was the amount of time- and gas- needed to boil a litre of water under room temperature and pressure. The old primus was tested with a normal stainless steel pot (1.5L) and a 1.2L titanium heat exchanger pot (see- an unfair comparison already as the dimensions aren’t the same). Now the results: The old primus took 5min and 14g (~50% efficiency) with the normal pot and 3.45min and 10g (~67% efficiency) with the heat exchanger. The Gravity took 4.50min and 10.5g (~64%) with the heat exchanger. The ETAlite took 5 minutes and 9.5g (~71%) with the heat exchanger and the Blaze took 4.30min and 10g with the heat exchanger, although the pot did not sit well at all. In any case, this basically means that with a heat exchanger roughly 30% less fuel and took 25% less time. My tentative conclusion for this shoddy experiment is that it may be worth investing in heat exchanger pots (of a diameter that will fit on your stove) or using using Jetboils (which are theoretically even more efficient with smaller quantities of water). If we use only jetboils/heat exchanger pots, we can take 30% less gas (1.8kg in real terms) and not have to wait for quite so long for tea after/before a long route. All this taken into consideration, it should still be theoretically possible to save another 3g of gas per litre of water boiled, possibly by boiling smaller quantities of water at a time. When it comes to picking a stove, If I was thinking of a rational compromise on weight (Oldy>Gravity>ETA>Blaze), efficiency (all about the same) and power (Oldy>Blaze>Gravity>ETA) I’d go with the Blaze. Sadly I’m rather attached to the old primus, so we’ll see.

The other thing we tried was squeezing all of Vlad’s personal Kit, plus half of a team rack, plus the 4 Man Base camp tent (7kg) into his 50L rucksack and 30L daysack (this assumes that I, or someone else, take the light tent the rope and the other half of the rack). Apparently it is. The weight was 22kg. So it’s nice to know that our gear list gives a similar weight on paper (between 18-25kg) and on actual scales. That gives 14kg of luggage allowance (9kg for most of the rest of everyone) for unaccounted “stuff”, a fairly safe margin of error I think.

-Alek out

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