[AR] hydrocarbons (was Re: SSTO)
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Wed, 14 Feb 2018 20:35:14 -0500 (EST)
On Wed, 14 Feb 2018, Keith Henson wrote:
Is anyone aware of a careful comparison of LH2 vs. Propane fueled SSTO?
I suppose REL could burn propane up to where they go pure rocket.
Given how much heavier the propane would be, I don't know if the trade
would work or not.
I suspect it wouldn't, but for a different reason: Skylon's airbreathing
fuel also has to be a very good coolant, since it's ultimately soaking up
the heat that the incoming air deposits in the heat exchanger. LH2 is an
outstandingly good coolant (one of the attractions of triprop concepts),
and even so the Hotol/Skylon engines in airbreathing mode end up using
rather more fuel for cooling than for combustion, so I'd conjecture that
propane wouldn't be adequate. Making it a triprop engine -- using LH2 for
cooling and propane only for combustion -- is unappealing because then
you've got a whole extra fuel system that replaces only a modest fraction
of the LH2 flow.
Henry
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