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Benzene hybrid?

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Benzene hybrid?

Unread postAuthor: saefroch » Wed Jun 01, 2011 5:04 pm

GasEQ says a 5X benzene hybrid will produce max chamber pressure about 897psi, whereas a propane 5X hybrid will only produce about 553psi. Unfortunately this is about the limit from the vapor pressure of benzene, but the pressure difference is so great, has anyone considered trying this?

-Chamber fueling suggested
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Unread postAuthor: DYI » Wed Jun 01, 2011 7:09 pm

Why go to all that trouble for 900psi when one can use a higher mix with propylene or similar gaseous hydrocarbons? A much more sensible modification is to use helium as a buffer gas, which considerably boosts the achievable pressure (based on a fixed starting pressure and fuel quantity) for any fuel, and vastly improves the sound speed in the propellant gases. Also, benzene is rather toxic, and not quite so easy to purchase as propane or propylene.
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Unread postAuthor: saefroch » Wed Jun 01, 2011 7:26 pm

Well I guess that idea was simply a random ejaculatory product of cramming for a chemistry final... Back to serious work :roll:
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Unread postAuthor: SpudBlaster15 » Thu Jun 02, 2011 3:37 pm

Where did you get those numbers from?

Under adiabatic conditions, GasEQ gives constant volume values of 47.9atm (~704PSI) for 5X benzene/air, and 47.4atm (~696PSI) for 5X propane/air. They're essentially identical in terms of combustion pressure.

If you want to see a real performance benefit, try nitromethane. Its high partial pressure in the mixture and low room temperature vapour pressure make it unsuitable for high mixes, but you'll get almost 200PSI out of each atmosphere of nitromethane/air.

Hydrocarbons are typically going to give you 130-140PSI per atmosphere, and it doesn't vary much across the board.
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Unread postAuthor: saefroch » Thu Jun 02, 2011 5:20 pm

I used the detonation option... does that give much higher pressure values?
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Unread postAuthor: jimmy101 » Thu Jun 02, 2011 6:31 pm

DYI wrote:Also, benzene is rather toxic, ...

Not really. It is carcinogenic with chronic exposure. For acute toxicity you would either have to repeatedly spill large quantities on yourself, swallow a fair amount (several cc's) or be exposed to high (>0.5% v/v or so) vapor levels for a while.

If you need to work with benzene for extended periods the usually solution is to use toluene instead of benzene. Toluene has the same basic chemical properties but is much less toxic.
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Unread postAuthor: SpudBlaster15 » Thu Jun 02, 2011 8:58 pm

saefroch wrote:I used the detonation option... does that give much higher pressure values?


In general, yes. The Chapman-Jouguet model is not accurate for deflagrations. The option you want to use is 'Adiabatic temperature and composition at constant volume'.
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