Isochoric combustion

In an isochoric combustion it is also assumed that the combustion occurs without any loss of heat to the surroundings (adiabatic) but at a constant volume (isochoric) and the combustion products are found in chemical equilibrium (e.g. gun propellants). 

For isochoric combustion processes, the following parameters (amongst others) can be calculated ... 

In order to elucidate the different properties of single, double and triple base gun propellants and to compare these values with the ones obtained for a new high-nitrogen propellant (e.g. NILE, see above), we calculated the relevant combustion parameters using the EXPL05 code under the assumption of isochoric combustion. The results are summarized in Table 4.15. 

Inspection of the experimental results guides the modeling of the state inside the bubble. We consider several steps, see Fig.3 From Pq to pg the compression is adiabatic, then follows an isochoric combustion leading to the state Pg, Tg. On the new adiabate 3, a further compression to the maximum pressure Pg Snay take place and, finally/ the products will be expanded to p. Since at r the gas temperature will still be high, there is little condensation up to this point, especially due to the buffering effect of the inert gas component. The process will be finished by a slow isobaric cooling and condensation to the end point In this first approach, effects like radiation, heat conduction, and compressibility are neglected. 

Isochoric Flame Temp, K,T Force,ft-lbs/lb,xlCT F v Unoxidized Carbon,% Combustibles,%... 

The decomposition reactions of both detonation and powder combustion are assumed to be isochoric, i.e., the volume is considered to be constant, as above for the explosion of industrial explosives. 

In closed vessels (fully confined), the eventual peak pressure obtained depends primarily on the energetics of the mixtures. The burning rate controls to some extent the amount of heat (hence the pressure loss) during the combustion process itself and this will result in a lower value for the final peak overpressure. The peak overpressure for confined explosions corresponds closely to the theoretical constant volume or isochoric explosion pressure for the particular mixture, which can be calculated readily from equilibrium thermodynamics when losses are ignored. The estimation of the rate of overpressure rise, however, is much more difficult since it depends on the mass burning rate or flame speed. 

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