Plug nozzle

Plug nozzle

The plug nozzle is a type of rocket engine nozzle that, unlike traditional designs, maintains its efficiency at a wide range of altitudes. It is a member of the class of altitude compensating nozzles, but unlike the aerospike, the plug design is considerably more "traditional". Confusingly, a common form of the aerospike design using a truncated spike looks much like a bottle plug, and are also referred to as "plug nozzles" in some references.


The plug nozzle looks from the outside like a normal engine bell, as used on most rocket engines. Inside, however, there is a "plug" (referred to as the "centerbody") that can seal off the exit from the combustion chamber above it. It is similar in form to a sink turned upside down, with the exhaust from the combustion chamber coming out the drain, past the plug (stopper), and into the bell (bowl).

The key to the plug system is to use a bell designed for high altitude use. In a normal nozzle this would result in the ambient air pressure forcing the exhaust in from the walls of the bell, leading to a loss of thrust. However in this situation the plug is "closed" by moving it closer to the combustion chamber outlet, and the exhaust is forced out from the plug to the sides of the bell.

Two similar designs, the reverse-flow and horizontal-flow, squeeze the flow between two complete bells which are moved in relation to each other. The existence of three such designs, along with the similar aerospike, has led to all such designs becoming known as radial out-flow nozzles, or in NASA parlance, expansion-deflection nozzle. [ Nozzle Design] , Pratt & Whitney Rocketdyne]


Further reading

* [ Aerospike Engine] , Jeff Scott, Fall 1999. This paper gives an extensive review of the various altitude compensating nozzle designs.

ee also

*bell nozzle
*aerospike engine
*expanding nozzle

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