Feasibility study and preliminary design of a Ram-Pulsejet for hypersonic passenger Air Transport

In hypersonic aircrafts, the necessity of operating at speed lower than Mach 1.0 obliged the designers to use the complicate propulsion plant of the mixed compression turbojet. Fast commercial passenger transportation will probably shorten the flight time by a factor 5, from the actual 6 hours to 1 hours for the London-NYC flight route. Therefore, the engine will work for a shorter time. The subsonic part of the flight is very limited. For this reason, a possible solution can be to substitute the turbojet with a pulsejet in the ramjet duct. Valveless pulsejets are extremely, simple, reliable, lightweight, fully throttable jet engines. The main limitations of the pulsejet are very low efficiency, relatively low "thrust density" and noise. Noise is naturally reduced as the main working frequency passes from the 150Hz of small pulsejet to the 40Hz of larger ones. Efficiency can be increased inserting the pulsejet in a ramjet-duct. This solution increases the pressure at the pulsejet intake and efficiently recovers heat from the pulsejet walls. Finally, it is possible to decelerate the jet with an ejector exhaust thrust augmenter. The feasibility of this concept is investigated in this paper. For this purpose, it was imagined to develop a transport aircraft with the aerodynamic of the Valkyrie and the new propulsion system. A cruise speed of MACH 3.5@25,000m was simulated with CFD. In this cruise condition the pulsejet works as a combustion stabilizer for the ramjet. Also, the take-off condition was simulated. At take off the thrust is obtained only by the pulsejet