Nozzleless rocket motor

It should be noted that the gas flow process in the port is not isentropic because mass and heat addihons occur in the port. This implies that there is stagnation pressure loss and so the specific impulse is reduced for nozzleless rockets. When a convergent nozzle is attached to the rear end of port, the static pressure at the port exit, Pj, continues to decrease to the atmospheric pressure and the specific impulse of the nozzleless rocket motor is increased. The expansion process in a divergent nozzle is an isentropic process, as described in Section 1.2. 

Liou, T.M., Lien, W.Y., 1995. Numericd simulations of injection-driven flows in a two-dimensional nozzleless solid-rocket motor. J. Propul. Power 11, 600-606. 

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