Ethanol oxidation with high water content: A reactive molecular dynamics simulation study

MY Feng and XZ Jiang and WL Zeng and KH Luo and P Hellier, FUEL, 235, 515-521 (2019).

DOI: 10.1016/j.fuel.2018.08.040

Ethanol is a potential alternative to conventional fossil fuels. However, the required dewatering process to produce anhydrous ethanol is extremely energy-intensive and expensive. A promising solution is the direct use of hydrous ethanol for combustion applications, which can dramatically reduce the production cost. Many researchers have undertaken experiments demonstrating the feasibility and advantages of burning hydrous ethanol solely as a fuel. In this study, molecular dynamics (MD) simulation with the reactive force field (ReaxFF) is employed to investigate the fundamental reaction mechanisms of hydrous ethanol oxidation in comparison with the ethanol oxidation under fuel- air condition in order to understand the effects of water addition on ethanol oxidation. The results show that the reaction rate of ethanol oxidation is faster in water than in nitrogen environment and the presence of water advances the ionisation process and accelerates the radical production rate thereby enhancing the oxidation reaction. Additionally, it is suggested that the water content plays a vital role in reactions at low temperatures but that effect can be ignored at high temperatures. The detailed reaction pathways and time evolution of relevant key species indicate that H2O promotes many reactions involving OH generation and these OH radicals also facilitate its reactions with C-1 & C-2 intermediates as well as the dehydrogenation of C-1 & C-2 intermediates. Similarly, CO production is reduced in hydrous ethanol oxidation as a result of CO reaction with OH converting the CO to CO2 ultimately. Therefore, it is the addition of water that promotes the OH production due to the chemical effect of H2O leading to the enhancement of ethanol oxidation and reduction of CO production. In summary, this research provides the scientific base for the direct use of hydrous ethanol as a fuel for combustion systems with a low cost.

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