Following is a list of propellant formulations more commonly used by amateurs. By selecting an appropriate link below it is possible to examine specific impulse (Isp) for a range of chamber pressures. Chamber conditions of 250, 500 and 750 psia are examined, rather than usual 1000 psia, as these pressures are more commonly encountered in amateur work.
The Isp data is presented in contour form, with horizontal and vertical axis showing binder and metallic fuel content, the remainder being taken up by oxidizer of choice. Note, that in most instances, the "binder" is a mix of a polymer and a plasticizer.
Each computer model presented here took approximately three hours of solid Pentium (160Mhz) processor time to develop, while running highly optimized code.
Ammonium Perchlorate - Al - HTPB (R45M)/Dioctyl Adipate Plasticizer (2:1 wt)
Ammonium Perchlorate - Mg - HTPB (R45M)/Dioctyl Adipate Plasticizer (2:1 wt)
Ammonium/Potassium Perchlorate (1:1) - Al - HTPB (R45M)/Dioctyl Adipate Plasticizer (2:1 wt)
Ammonium Nitrate - Mg - HTPB (R45M)/Dioctyl Adipate Plasticizer (2:1 wt)
(Performance very similar to CP Technologies propellant)
Potassium Perchlorate(KP) - Mg - HTPB (R45M)/Dioctyl Adipate Plasticizer (2:1 wt)
Oxidixer=N2O, Fuel=Mix of R45M (HPTB) and Mg
Some Interesting Liquid Ideas:
Oxidizer=N20, Fuel=Mix of JP4 and Methanol
Oxidizer=N20, Fuel=Mix of JP4 and Diesel-Gasoline Mixture
These charts are intended to be used during the the initial phases of propellant development. They indicate the optimum mix ratios as well as predicted Isp performance for particular binder/fuel content. This gives the user the ability to examine "what if" scenarios, while eliminating a lot of guesswork.
No fuel additives of any kind were included in these calculations. In majority of the cases, addition of various catalysts will slightly degrade overall Isp performance (but may be necessary nevertheless). Common case would be ZnO (1-3%), a phase stabilizer added by manufacturers of phase stabilized AN, or CuO added as burn rate catalyst to AP fuels. The degradation will vary with the content and quantity of additives but will rarely exceed 3% of overall Isp. Other losses are due to nozzle, chamber heat losses etc. In well-designed, small motors these losses can be estimated at additional 5-10% of Isp.
If you have any ideas regarding propellant mixes, or would like to improve on your own standby, e-mail me, and I might characterize it for you. Remember, the key phrase is sharing, so you must be willing to have it posted here (with due mention). I believe that sharing data is beneficial to all concerned.
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Last update on 7-Sept-96 - Copyright 1996 Chris Krstanovic (WR1F)