Re:SpaceX test flight of Starship SN-5 [video]
by credit_guy on Thursday August 06, 2020 @09:47AM
(#24070807)
Sorry, I skipped some steps in my calculation.
The chemical reaction is indeed CH4 + 2 O2 -> CO2 + 2 H2O. So, for each 16 grams of CH4 you get 64 grams of O2, that's a stoichiometric mass ratio of 1:4.
The fuel ratio for the Raptor engine is 22:78, according to Elon Musk's tweet. So, for each 100 g of propellant mixture you get 19.5 g of CH4 to burn using 78 g of O2 and you are left with 2.5 g unburned CH4.
I simply neglected the H2O resultant from the reaction because, while H2O is a very potent greenhouse gas, it has a fast cycle in nature (rain, etc). Also, I have no idea how to account for it as a greenhouse gas.
Re:SpaceX test flight of Starship SN-5 [video]
by bryanlarsen on Thursday August 06, 2020 @03:54PM
(#24074782)
From what I've heard there is a significant fraction of carbon monoxide in the exhaust, so there will be a lot less CH4 in the exhaust than you have calculated. CO is only a weak greenhouse gas.
Re:SpaceX test flight of Starship SN-5 [video]
by credit_guy on Thursday August 06, 2020 @04:46PM
(#24075296)
That is very interesting. Do you happen to have a link? I'm not doubting you, I think you are right, but a link that goes into this type of detail would be a very interesting one to read.
Re:SpaceX test flight of Starship SN-5 [video]
by bryanlarsen on Thursday August 06, 2020 @05:07PM
(#24075467)
I probably heard that here: https://everydayastronaut.com/rocket-pollution/
Otherwise it would have been in a comment on an Eric Berger Ars Technica article.
> that results in CO2 and CH4
The chemical reaction of O2 + CH4 -> CO2 + CH4 does not compute.
More likely is the reaction 2 O2 + CH4 -> CO2 + 2 H2O.
So no methane emissions, that's the actual fuel. Only CO2 (and water) emissions.