Density of propylene when used as rocket fuel, and advantages (if any) over RP-1?

Question

Recently Vector space from USA has said that propylene is a better choice of fuel than RP-1. See Ars Technica's After a decade of testing, propylene rocket fuel may be ready for prime time

Why is propylene a better fuel than RP-1? At what density is it used for that purpose?

edit: while some level of comparison can be found in answer(s) to Vector-R's LP-1 and -2 engines use liquid propylene as fuel with LOX, advantages and distinctions from kerosene?, I'd like to know more details on how the two fuels compare quantitatively.

I tried to check the density of propylene on internet but it is less dense than RP-1 then how does it provide more performance, and roughly how large is this difference in performance?

If you checked the density of propylene, you should have noted that at normal pressure and temperature, propylene is a gas and RP-1 is a liquid. To use propylene as rocket fuel it should be liquified just as other cryogenic fuels. So youd compare the density of liquid propylene to liquid RP-1. — Uwe, Sep 28 '18 at 10:53
@Uwe yes, but density of liquid RP-1 is greater than liquid propylene — user167195, Sep 28 '18 at 10:59
Relevant patent: ProPoly50 (Mix of 50% propane / 50% propylene). The double bond has a high energy density and subcooled propylene has a decent density of 754 kg/m^3 according to NIST. It is compatible with liquid oxygen (both liquid at the same temperatue) allowing for lightweight common bulkhead tanks. ProPoly50 further reduces the melting point making it even compatible with subcooled lox without compromising the improved Isp. Downside: Propylene results in higher chamber temperatures. — Christoph, Sep 28 '18 at 11:55
Side note: NASA contracted the inventor of ProPoly in July 2017 to build a ProPoly50 engine (electric fed lower stage/pressure fed upper stage) for a small satellite launcher. Seems that propylene is at least interesting. See here. — Christoph, Sep 28 '18 at 12:18
Possible duplicate of Vector-R's LP-1 and -2 engines use liquid propylene as fuel with LOX, advantages and distinctions from kerosene? — Christoph, Sep 28 '18 at 12:21
@uhoh yes ikr. Its a crucial part. But how can we know that? — user167195, Sep 28 '18 at 13:07
@user167195 I've edited your question to make clearer that this is not a duplicate as well as to add a link that helps support your "Vector has said..." — uhoh, Sep 28 '18 at 14:15
I've added the quantitative information from my answer here to my answer on the other question, which I feel makes this Q a closable dupe. — Russell Borogove, Sep 30 '18 at 22:11

score 2 · Answer 1 · answered Sep 30 '18 at 22:05

2

Density is one of two important figures of merit for first-stage rocket fuels; the other is mass-specific impulse, the product of force and time that is yielded from a given mass of fuel.

Specific impulse varies with engine design and other factors, but all other things being equal, propylene's specific impulse is about 2% higher than that of RP-1. When both fuels are cooled until they reach a viscosity of 3.3 cP (which is the point at which Falcon 9 FT keeps its RP-1), RP-1 is only 3% denser, according to a chart originally posted on nasaspaceflight.com (the chilled propylene/RP-1 callouts are mine.)

Because the tanks themselves are extremely thin and lightweight, the mass penalty incurred by needing a 3% larger tank for propylene is less significant than the specific impulse advantage gained.

answered Sep 30 '18 at 22:05

Russell Borogove

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Nice answer. Maybe you could add in the rocket equation and show how 2% more impulse results in around 6% less lift-off weight for a typical launch to low earth orbit (I think of a delta-V of 10 km/s). I can provide performance data from cpropep like in this answer later today if anyone requests it. This would show e.g. the high chamber temperature compared to the alkanes. Propylene is quite known for its polymere so I could imagine that this might be an issue with cooling the chamber. Anyone got information on that? – Christoph Oct 01 '18 at 07:24
@Christoph if RB is too busy, then in a few days you could consider adding an answer of your own as well. – uhoh Oct 02 '18 at 09:05

Density of propylene when used as rocket fuel, and advantages (if any) over RP-1?

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