Abstract
For an airbreathing vehicle, the generated heat fluxes increase with the flight velocity. Above Mach 6, the heat fluxes to be evacuated are so high that a cooling system adapted to hypersonic speed becomes indispensable. The idea is to use a hydrocarbonated liquid fuel, called “endothermic fuel.” The heat is absorbed by fuel circulation behind a double wall, where the fuel undergoes thermal or catalytic cracking (endothermic reactions). In the cooling system, the fuel is under high pressure and temperature, corresponding to supercritical conditions. Thermal and catalytic cracking of hydrocarbons under these conditions are mainly unknown. To catalyze the hydrocarbon cracking reactions, two zeolites, the zeolites Y and ZSM-5, are selected. This article presents the results of a parametric study of the thermal and catalytic cracking reactions of a model fuel (n-dodecane) under supercritical conditions. The tests are carried out in a stirred batch reactor heated up to 425 °C and under pressure up to 150 bar. After cooling down, the cracking products are characterized by several analytical techniques in order to determine the influence of the operating conditions on the cracking reaction mechanisms. The efficiency of catalytic cracking with the zeolites Y and ZSM-5 are compared with the thermal one. With the increase of temperature, a logical raise of the parent hydrocarbon conversion and the number of products are observed. The product distributions are significantly different between the thermal and catalytic cracking. This is explained by the cracking mechanisms (free radical and carbocations) and the supercritical conditions.
Published Version
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