Kinetic study of methanol and ethanol oxidation in presence of NOx

Alcohols are an important category of bio-fuels. The use of oxygenated fuel additives provide more oxygen in the combustion chamber and has a great potential to reduce emissions. The present work is the extension of our previous work which was presented in SMARTCATs 3 rd General meeting at Prague 2017 aiming to develop an oxidation model for a wide range of fuels while controlling NOx formation and NOx-fuel interaction. In literature, there are wide range of experimental data available at various conditions for pure methanol and ethanol. However, there is limited experimental data available for methanol and ethanol oxidation in presence of NOx for kinetic studies. Alzueta et al. [1] studied the methanol oxidation in presence of NO in a flow reactor. They made a conclusion that only at very lean conditions the presence of NO is responsible for the sensitized oxidation of methanol and appreciable decrease in NO concentration was observed in their study which results into the formation of NO2. Dayma et al. [2] studied methanol oxidation in presence of NO in jet stirred reactor (JSR) and concluded that the presence of NO promotes the oxidation of fuel. Moréac et al. [3] performed experimental work on methanol oxidation in JSR in presence of NO also reached a similar conclusion. In our present study we find that this promoting effect of NO on methanol oxidation can be explained by the reaction sequence converting less reactive HO2 to higher reactive OH. A simplified reaction scheme for NO doped methanol oxidation in JSR can be presented as follows: NO is converted to NO2 via reaction NO+HO2⇋NO2+OH and NO2 is converted to HONO via reactions HNO+NO2⇋HONO+NO, CH2OH+NO2⇋CH2O+HONO, HCO+NO2⇋HONO +CO, CH3OH+NO2⇋HONO+CH2OH, CH3O+NO2⇋HONO+CH2O, and CH2O+NO2⇋ HONO+HCO. The formed HONO is now decomposed to form NO and OH via reaction NO+OH(+M)⇋HONO(+M) recycling back NO. Another reaction that is important in interconversion between NO and NO2 is NO2+H⇋NO+OH. Ethanol oxidation in presence of NO in a flow reactor at atmospheric pressure and temperature range of 700-1500 K was studied by Alzueta et al. [4]. The noticeable NO consumption was seen at very lean (ϕ = 0.03) condition. The highest consumption of NO is observed at around 875 K (see [4]). The reactions involved in NO consumption and formation in this case are similar to those observed for methanol oxidation in JSR. NO reacts with HO2 to form NO2 and OH. Further NO2 reacts with CH2O, CH3O and HNO to from HONO and HCO, CH2O and NO respectively. HONO is now thermally decomposed to form NO and OH via reaction NO+OH(+M) ⇋HONO(+M) which recycles backs NO.