A propulsion assembly having a propulsion system including an exhaust nozzle fastened to the nozzle wall on the outside thereof so as to define between them a chamber, and a heat exchanger system ensuring an exchange of heat energy between the hot combustion gases circulating in the exhaust nozzle and the colder fuel circulating in the supply pipe at least in part by thermal radiation through the nozzle wall. The heat exchanger system has a pipe portion arranged in the chamber and the exchange of heat energy takes place at this pipe portion. With such an arrangement, the heat energy of the combustion gases is transferred to the fuel for better combustion.