Thermodynamic assessment of a nitro-organic plasma with an experimental design method

The modelling of the plasma ignition of gun propellants requires the thermodynamic properties of a plasma generated by a CHON organic compound. The electrothermal launcher produces pressures up to some hundreds of megapascals and temperatures up to some tens of thousands Kelvin. We have developed a code, ALJAN-EP, to calculate the thermodynamical equilibrium for a CHON plasma by extension of the conventional method of minimisation of the enthalpy. We have presented results of calculation of the enthalpy and the isobaric thermal capacity for a nitrocellulose up to 500 MPa and 50000 K. Furthermore, we have used ALJAN-EP to determine polynomial expressions for a model of the second order in pressure and in temperature by experimental design. These expressions allow thermodynamic state functions and the composition of the gaseous phase to be calculated quickly and accurately. We present results obtained for nitrocellulose in a small temperature and pressure range from 100 to 500 MPa and 5000 to 10000 K. These results show that to cover a wider area, considering reactions in gaseous phase, it is necessary to consider a mosaic of adjacent elementary areas in parameter space or a more complex expression.