A Study on the Thermal Cracking of Ethanol for Regenerative Cooling of Scramjet Engines

Abstract

In this study, the thermal cracking reaction of ethanol for the regenerative cooling of scramjet engines was comprehensively investigated. Based on a thorough survey of the existing research on scramjet engines and thermal cracking as a regenerative cooling technique for those engines, the thermal cracking of ethanol was selected as a theme worthy of scientific interested, for which further research was still necessary. An existing setup was improved in order to conduct flow-type experiments of the thermal cracking of ethanol, and suitable analysis methods were selected in order to identify and quantify the reaction products. In parallel, a simple simulation model based on the Cantera python package and the chemical kinetic mechanism developed by Mittal et al. [16] was developed for the thermal cracking of ethanol. The experiments were conducted for six different target conditions, at temperatures of 400, 450 and 500 ℃ and pressures of 5 and 7 MPaG, while the target mass flow rate remained unchanged, at 20 g/min. The experimental results showed that hydrogen was the most abundant gas product, while carbon monoxide, methane, ethylene and ethane completed the gas mixture. They also indicated that the mass fraction of unreacted ethanol decreases both with temperature and pressure, and that the liquid products of the reaction are water and acetaldehyde. Finally, the experimental results showed good agreement with previous research on the thermal cracking of ethanol. The numerical results, on the other hand, indicated a strong dependence of all product selectivities on reaction temperature, while only some were significantly affected by pressure (hydrogen, ethylene, ethane). In addition, the numerical results showed that the heat absorbed by the reaction is dependent on both temperature and pressure, with a maximum value of 500 kJ/kg at a temperature and pressure of 1050 K and 5 MPaG. Further, these results demonstrated that the real gas version of the model did not show any significant improvement with respect to the ideal gas one. Lastly, the numerical results exhibited a trend similar to the experimental measurements, but the model could not be properly validated due to a mismatch in reference temperatures between experiments and model.