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I'm working on solid propellant based microthrusters and I am using NCNG as the solid propellant. I want to know the reaction taking place and the mass fraction of the products obtained on combustion of NCNG propellant.

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Nitrocellulose is complex stuff. It is generally considered to be the fully nitrated version of cellulose, in which every available alcohol functional group is converted to a nitrate:

$$\ce{[C6H10O5]n +3HNO3 -> (C6H7O2(ONO2)3]n +3H2O}$$

In principal it probably contains some small amount of partially and/or non-nitrated units.

If we consider nitrocellulose to be fully nitrated, then the combustion reaction is:

$$\ce{ 2C6H7N3O11 + 9/2O2 -> 12CO2 + 3N2 + 7H2O}$$

For nitroglycerin $(\ce{C3H5N3O9})$:

$$\ce{2C3H5N3O9 -> 6CO2 + 3N2 + 5H2O + 1/2O2}$$

It will depend on the ratio of nitrocellulose to nitroglycerin what the overall $\ce{CO2}: \ce{N2}:\ce{H2O}$ mole ratio is. I'll leave you to figure out the mass ratios using the molecular masses of the products.

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Energetic materials can emit a significant fraction of their carbon as CO. Take advantage of excess local oxygen with more fuel, or push to CO2 with more oxidizer. The lower the average molecular weight of the exhaust, the higher the Isp, all other things being equal. US hydrogen/LOX engines run heavy on hydrogen.

re Cordite and Ballistite, grain size, and internal channel geometry if any.

The Mechanism of the Burning of Double-Base Propellants
DOI: 10.1021/j150480a015
http://www.google.com/patents/US4072546
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA425264

Solid Propellant Chemistry, Combustion, and Motor Interior Ballistics, Volume 185. Vigor Yang, Thomas B. Brill, Wu-Zhen Ren, Paul Zarchanm, 2000,. p. 288 ff.

Double-base propellants (DB) give minimal smoke with medium-high performance, Isp ~ 235 s. Adding aluminum gives Isp ~ 250 s with visible smoke. DB have 50-60% nitrocellulose and 30-40% nitroglycerin content. High nitroglycerin for extrusion and casting, low for pressing. DBs are boosted by adding dispersed micronized ammonium perchlorate. Both nitrocellulose and nitroglycerin decompose to afford nitric acid. This must be neutralized during long term storage, certainly if perchlorate is in there. Beware of detonation under pressure, hence phlegmatizing agents.

double-base propellant energetics

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