After I posted that, I realized that cyanogen would probably not be a good rocket fuel despite its extremely high flame temperature in oxygen. It contains no hydrogen. HCN would probably be better, and it's probably safer than hydrazine...
HCN would be better in terms of molecular weight, but temperature is just as big a factor. Exhaust gas velocity is proportional to (T/M)
1/2 so the higher the temperature and the lower the molecular mass, the better the propellant. Of course specific heat ratio is also a big factor.
I determine the best mixture ratio by experimentation, but a good starting place is to include enough oxygen to oxidize the carbon to CO and the hydrogen to H
2O. For cyanogen and HCN that's,
C
2N
2 + O
2 --> 2 CO + N
22 HCN + 1.5 O
2 --> 2 CO + H
2O + N
2That's an average molecular weight of 28 for cyanogen and 25.5 for HCN. Neither is great but HCN is better.