Sustained combustion limits of a central dump solid fuel ramjet combustor at high altitude operational conditions

Solid Fuel Ramjet (SFRJ) technology is a very attractive propulsion option to extend the range of gun launched projectiles mainly due to the combination of high specific impulse inherent to airbreathing propulsion and mechanical properties of the solid fuel capable of withstanding the very high launch loads in the gun. In 2004, the Netherlands Organization for Applied Scientific Research (TNO) performed the world’s first successful demonstration of a 35 mm spin-stabilized air defence projectile capable of maintaining its initial flight velocity at 1400 m/s. After the first demonstration, TNO continued the research on SFRJ and currently is working on the integration of this technology into a precision guided large calibre extended range application, which requires long duration functioning of the propulsion system at high altitude operational conditions. Since these operational conditions of the SFRJ combustor vary largely during the flight profile, it is important to know the limits of sustained combustion, the so called flame-holding limits, which dictate the operational limits of this combustor type. Although general research on this subject has been done in the past, specific research into the flame-holding limits at the operational conditions of gun launched large calibre extended range applications is lacking. A flame-holding model previously developed by the Delft University of Technology (DUT) and TNO has been reviewed, modified and applied to predict the flame-holding limits of a gun hardened ‘high performance’ Hydroxy-Terminated PolyButadiene (HTPB) fueled SFRJ combustor at high altitude operational conditions. Subsequently, dedicated SFRJ experiments using the TNO SFRJ direct-connect test set-up have been performed to validate the predicted flame-holding limits. Comparison of model and experimental results shows that the flame-holding model allows for accurate prediction of the sustained combustion limit at the operational conditions currently investigated. Because of the large similarity in size and operational conditions, the knowledge generated is also relevant for integration of the SFRJ technology in tactical missiles. © 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.