TNO GAS GENERATORS: INITIAL DESIGN AND ANALYSIS OF A SOLID STATE FUEL STORAGE SYSTEM FOR HYDROGEN POWERED SCRAMJETS

Hydrogen has long been an attractive fuel for scramjets because of its fast chemical kinetics, but its low volumetric energy density is a major drawback. As an alternative for high-pressure gaseous hydrogen storage the current study examines solid state hydrogen storage using the TNO gas generator. The hydrogen carrier in this gas generator is ammonia borane (AB) (NH<sub>3</sub>BH<sub>3</sub>), which releases gaseous hydrogen upon ignition. The study consists of two parts: the reference vehicle X-43A is first used as a case study to assess the viability of using gas generators for the fuel supply system of a scramjet. A comparison with liquid hydrogen storage is also made. It is found that gas generators allow 9.1% more hydrogen to be carried than for gaseous storage, albeit at a small mass penalty. In the second part the decomposition behavior of AB is studied up to 1450 degrees Celsius (1723 Kelvin), in order to optimize the gas generator design. The decomposition characterization is performed using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), mass-spectrometry (MS), and Fourier-transform infrared spectrometry (FTIR). Both pure NH<sub>3</sub>BH<sub>3</sub> and a mixture of NH<sub>3</sub>BH<sub>3</sub>and NH<sub>4</sub>Cl are examined. A significant amount of hydrogen is found to be released in the form of borazine. The results of this study can be used to iterate on the proposed conceptual design and improve the performance of the fuel supply system.