Expansion deflection nozzle
The expansion-deflection nozzle is a rocket nozzle which achieves altitude compensation through interaction of the exhaust gas with the atmosphere, much like the plug and aerospike nozzles. == Description == It appears much like a standard bell nozzle, but at the throat is a 'centrebody' or 'pintle' which deflects the flow toward the walls.
Source: Wikipedia — Expansion deflection nozzle (CC BY-SA 4.0)