High pressure ammonia/methanol oxidation up to 100 atm

Abstract

High pressure ammonia/methanol oxidation and NOx formations were investigated using a recently developed supercritical pressure jet-stirred reactor (SP-JSR) at 20 and 100 atm with temperatures between 550 and 950 K and equivalence ratios of 0.138 and 1.15. The experimental results show that NH3 oxidation at high pressure is significantly accelerated by the active OH radicals produced from CH3OH oxidation. Furthermore, the kinetic interactions between NH3 and CH3OH are governed mainly by the reactions CH3OH + NH2 = CH2OH + NH3, CH3OH + NH2 = CH3O + NH3, and CH2O + NH2 = HCO + NH3. A HP-Mech model for high-pressure NH3/CH3OH oxidation was developed in this study. It consists of the most recent NH3 and CH3OH models including some new reactions and updated rate constants from the literature as well as NH3-CH3OH interactions where rate constants of CH3OH + NH2 = CH2OH + NH3, CH3OH + NH2 = CH3O + NH3, NH2 + CH2O = NH3 + HCO, and NH2 + CH2O = NH2CHO + H were theoretically calculated in this study. Our model with these updates improves the prediction for the measured N2O/NOx temperature dependence at 100 atm. In addition, the reaction pathway and sensitivity analysis show that N2O/NOx/HONO interactions with HO2 are very important, especially for a fuel-lean mixture at 100 atm. The HONO mole fraction for the fuel-lean mixture at 100 atm was then measured by off-axis integrated cavity output spectroscopy (ICOS) at wavenumber of 6638.26 cm−1. The experimental data show a significant HONO formation at intermediate temperature that is strongly underpredicted by numerical simulation at 100 atm. Therefore, the HONO related reactions with notable uncertainty at high pressure such as NO + OH (+M) = HONO (+M) and H2NO + NO2 = HONO + HNO need deeper exploration in the future.