Quote:
Originally Posted by bdub
Awesome info, thanks. How much fuel are you budgeting per day?
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Hey bdub, I just went over my notes/log book from that trip and
the number we used was actually 100ml per person per day, which was the amount that was way too much, especially since we had a group of 5 on that trip. Half that would be plenty for me (50ml per person per day) even leaving a good margin of error, and this is backed up by the number crunching I have done on fuel use today.
Argument 1:
Here’s one way of looking at fuel-stove combo weights, straight from the web.
A 212 gram propane cartridge contains 11 grams of fuel and claims to boil 16 litres of water (4 days worth). The stove weighs about 73 grams. The empty cartridge weighs about 100 grams.
Stove-fuel combo for 4-5 days is about 290 grams. Add another day and you carry another 100 grams of cartridge, which pretty much makes up for the full weight of a Whisperlite (200 grams) and a 375ml fuel bottle (79 grams). At 4-5 days the weight cost of each type of stove is the same.
Argument 2:
Long story short, over a longer trip a white gas stove needs less fuel bottles than iso-propane stoves and their bottles are lighter. This weight savings more than makes up for the extra weight of the white gas stove.
So:
It’s not just about the volume of fuel – the main differences between white gas, isobutene/propane & methanol is the energy density of the fuel, and regular mass-volume (how much mass of the fuel can fit in a specific container).
Propane and white gas have similar energy densities (White Gas is 44.6 MJ/kg, propane is 46.4 MJ/kg) but look at the volume a same mass of fuel would take – A kg of white gas fits in about 1.4 litres of space, a kg of liquid propane fits in about 2 litres of space, so with similar amounts of fuel propane will require larger canisters or a greater number of smaller canisters. It also requires sturdier canisters since it is under pressure.
Here is a scenario:
Assume (for comparisons) that we want to boil 3 litres of water per day. The water is ice cold (zero degrees) and we want to boil it at sea level, so boiling temp is 100 degrees. It takes 4200 joules to raise the temperature of one litre of water one degree Celsius, and 420,000 joules to raise the temperature of one litre of water from 0 to 100 degrees.
We will also assume no heat loss to wind, etc. but will use the net-value of energy in fuels to account for heating the combustion gases & water vapour produced from burning fuels to get as accurate fuel usage as possible.
So, per day we need 1,260,000 joules or 1.26 mega-joules (MJ) of heat.
From there it’s pretty easy to calculate how much of each fuel you require per day, and how many containers you need to carry it. I will let you do that part.
I have included two pictures of the excel sheet I did up. The first is a bare bones example using the above scenario, using 1.26 MJ of heat per day. The second is a more “Realistic Use” scenario, where I double the heat use per day to account for a brew at night, heat loss during transfer, and general entropy.
Conclusion:
You can see on the “Realistic Use” table, that
up to day 4-5 both Propane and White Gas are within 50 grams of each other, but after that White Gas takes off as the clear leader. Notably at day 9-10 and again at 14-15,
a Propane stove with fuel will weigh a full pound more than its White Gas alternative. Adding more people (extra fuel requirements) or more days will increase the lead that White Gas has over Propane.
Also, Methanol Stoves are super light for an overnight or a day trip, but due to its very low energy density (net caloric value) of 19.9MJ/kg Methanol simply can’t keep up. Ethanol is similar at 26.7MJ/kg, which is why it is such a poor fuel for vehicles, and at about half the density of gasoline a tank of ethanol will take you half as far as a tank of gas.
The one thing I did not include is data on heat transfer, which is where the JetBoil might improve things for the Propane stove fans.
Remember, too, that this is just weight considerations, and WEIGHT IS NOT THE MOST IMPORTANT QUALITY.
RELIABILITY MATTERS.
Bringing a heavy stove that is reliable is way better than carrying a broken stove that doesn’t work and is just dead weight.
If anyone wants the excel file to play with send me a pm and an email address I can send it to.
If anyone wants to use this data/ write up in some other format, send me a pm as well.
Cheers,
E. B.
References:
All fuel data is taken from
https://www.engineeringtoolbox.com/f...ues-d_169.html
For Propane I used measurements from MSR IsoPro cartridges, which come in 110 gram, 227 gram and 450 gram bottles, which weigh a total 212g, 377g, & 650g respectively (cartridge plus fuel).
For white gas I used the MSR Whisperlite Fuel Bottles, which come in 375 ml (holds 325ml fuel, weighs 45 grams), 650ml (holds 590ml fuel, weighs 114g) and 975ml (holds 880ml fuel, weighs 158 grams)
For Methanol I take the fuel in an empty soda bottle, or an empty Sriracha bottle with a screw top lid for fine pouring (the best).