High-pressure ethanol oxidation and its interaction with NO

Ethanol has become a promising biofuel, widely used as a renewable fuel and gasoline additive. Describing the oxidation kinetics of ethanol with high accuracy is required for the development of future efficient combustion devices with lower pollutant emissions. The oxidation process of ethanol, from reducing to oxidizing conditions, and its pressure dependence (20, 40 and 60 bar) has been analyzed in the 500–1100 K temperature range, in a tubular flow reactor under well controlled conditions. The effect of the presence of NO has been also investigated. The experimental results have been interpreted in terms of a detailed chemical kinetic mechanism with the GADM mechanism (Glarborg P, Alzueta MU, Dam-Johansen K and Miller JA, 1998) as a base mechanism but updated, validated, extended by our research group with reactions added from the ethanol oxidation mechanism of Alzueta and Hernández (Alzueta MU and Hernández JM, 2002), and revised according to the present high-pressure conditions and the presence of NO. The final mechanism is able to reproduce the experimental trends observed on the reactants consumption and main products formation during the ethanol oxidation under the conditions studied in this work. The results show that the oxygen availability in the reactant mixture has an almost imperceptible effect on the temperature for the onset of ethanol consumption at a constant pressure, but this consumption is faster for the highest value of air excess ratio (λ) analyzed. Moreover, as the pressure becomes higher, the oxidation of ethanol starts at lower temperatures. The presence of NO promotes ethanol oxidation, due to the increased relevance of the interactions of CH₃ radicals and NO₂ (from the conversion of NO to NO₂ at high pressures and in presence of O₂) and the increased concentration of OH radicals from the interaction of NO₂ and water.