Principles of the Nozzleless Rocket Motor

A nozzle used for a rocket is composed of a convergent section and a divergent section. The connected part of these two nozzle sections is the minimum cross-sectional area termed the throat The convergent part is used to increase the flow velocity from subsonic to sonic velocity by reducing the pressure and temperature along the flow direction. The flow velocity reaches the sonic level at the throat and continues to increase to supersonic levels in the divergent part. Both the pressure and temperature of the combustion gas flow decrease along the flow direction. This nozzle flow occurs as an isentropic process. 

The combustion gas of an internal burning of a propellant flows along the port of the propellant If the nozzle attached to a rocket motor is removed, the pressure in the port becomes equal to atmospheric pressure and no sonic velocity is attained at the rear-end of the port. Then, no thrust is generated by the combustion of the propellant However, if the mass burning rate of the propellant is high enough to choke the flow at the rear-end of the port, the pressure in the port is increased and the flow reaches sonic velocity. The increased pressure in the port is converted into thrust. The thrust F is represented by 

An adaptation of Eq. (14.38) for a nozzleless rocket indicates that the port area increases as the burning surface of the propellant regresses, decreases and Aj increases, and so the choked condition is varied. Thus, the thrust generated by the nozzleless rocket is determined by the relationship of the mass generation rate in the port and the mass discharge rate at the rear-end of the port.I - l 

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