Hello dear friends!
Rocket use the fuel to cool the engine walls, where polymer deposits would be deadly. This precludes unsaturated fuels up to now. Though, cooling the engine with oxygen would enable alkenes and alkynes
, and for instance plain ethylene is very
efficient. This significant change looks easier than the existing oxygen-rich staged combustion and turbine.
William P. Dailey reported in 1992 a promising synthesis for spirohexenewww.dtic.mil/dtic/tr/fulltext/u2/a248465.pdf
just 1s short of cubane's performance, so I checked his cyclopropenes and similar alkenes.
Would you know data about the oxygen-free detonation risk of alkynes?
Sensitivity to shocks, detonators, heat... I foundwww.dtic.mil/dtic/tr/fulltext/u2/028238.pdf
but the result pages 28 and 75 are classified since 1953. Butyne is known to detonate, bigger compounds are unclear to me.
In the appended list, the safe and affordable "kerosene" RG-1 is the performance reference. Methane engines are being developped currently. Spiropentane (and cyclopropane) are alternatives to methane, and cubane the fantasy of rocket designers.
The Isp is 99% of what Propep computes at optimum mass ratio. The gain in seconds versus RG-1 is divided by G. Flammability is "bad" up to C9
. Heat sensitivity indicates the °C where 10g decompose from 1000 moles in 300s; for ethylene it's at too easy 0.13bar.Tetravinylmethane and divinylcyclobutane
don't justify to cool a rocket engine with oxygen, but they outperform cyclooctatetraene for ramjets. Tetravinylmethane is less flammable, and divinylcyclobutane is the dimer of butadiene over a catalyst.-Ladderdiene is storable and efficient
. To produce it, just try to make cyclobutadiene, and you get the dimer - looks scalable to 100t.https://en.wikipedia.org/wiki/Ladderane#Dimerization_of_cyclobutadiene
Seems interesting for Ramjets too.  or -Ladderdiene would be less flammable.Cyclobutene
looks simple to produce, but less so than ethylene
which is the prime incentive for oxygen-cooled engines.https://de.wikipedia.org/wiki/Cyclobuten
(or French or Spanish)
Dailey gives synthesis paths to dimethylcyclopropene
(rather trimethyl, and with a hydrazine, yuk) and to spirohexene
(looks sounder and scalable if recycling the byproducts). To evaluate Hf=+333kJ/mol for liquid spirohexene, I observe that spiropentane has 34kJ more strain energy than two cyclopropanes, add arbitrarily half that at spirohexene, and neglect any spiro-ene interaction. My estimate gives a bigger performance advantage than Dailey's to spirohexene over dimethylpropene; spirohexene is also easier to produce and less volatile.
The saturated but fragile bicyclobutane
fits in the list as I wouldn't cool an engine with it.
And because Dailey achieved cyclopropenes in spirohexene in dispirodecadiene, I imagine to adapt his synthesis to dispirooctadiene
. The start is simpler (heat propadiene over glass beads), the result would outperform cubane. Full debromination would afford dispirooctane or "soctane", a rocket fuel in the +5s range. One alternative debromination therehttp://pubs.acs.org/doi/abs/10.1021/acscatal.6b01914
it's a question of reactant cost and ease of recycling.
Dailey told that spiropentene is "unstable" and spiropentadiene "very unstable" (on a chemist's scale) while the fuels above are at least unknown.
Marc Schaefer, aka Enthalpy