Thermojet: An Old Idea Can Define a Novel Family of Jets

This paper investigates the ancient idea of augmenting the thrust produced by a rotating fan by producing a thermal gradient by heating the outflow. Some of the pioneers of aeronautics have originally conceived this idea: the indirect jet (Bleriot Coanda Monoplane, 1910) and the “thermojet” (Caproni-Ciampini CC2, 1942). They were abandoned because of the better performances by traditional jets such as the ones developed in Germany and USA during 2nd World War. Antony Colozza (NASA), one of the modern fathers of high altitude airships, has recently proposed it again to be used on fuel cells powered airplanes and airships. Most fuel cells have a large thermal dispersion at high temperature (about 40%), but it could be possible to use it for heating the propulsive stream of high-speed air produced into ducted fan propulsive units. The actual state of the research is only introductory and aims to verify the feasibility of this energy recovery, which could in future enhance the energy efficiency of electrical airplanes powered by ducted fan units especially for high altitude operations. The preliminary research activities presented are conducted assuming a reduced scale system in order to have the possibility of future costless experimental activity for validation. The CFD evaluations have been performed by two different codes: the well tested Ansys Fluent and a lightweight academic code EasyCFD.