Kinetic interactions of CO, NO_x, and HCI emissions in postcombustion gases

Postflame chemistry is governed largely by moist CO oxidation. During carbon monoxide burnout, trace amounts of many other pollutants formed in and/or surviving through the flame front may be present (e.g., SO_x, NO_x, HCI, and unburned hydrocarbons). The development of accurate chemical models describing these final stages of pollutant destruction requires evaluating the potential kinetic coupling effects that exist among these components. In the present investigation, the coupling between NO and HCI in a moist CO oxidation bath is considered. Experiments are performed in an atmospheric pressure flow reactor by perturbing the CO/H₂O/O₂ reaction system with trace amounts of NO and/or HCI for temperatures between 1000 and 1070 K and both stoichiometric (Φ = 1.0) and fuel-lean (Φ = 0.1) mixtures. The experimental results are compared with predictions from a detailed kinetic model and analyzed by gradient sensitivity and reaction flux analyses. While the addition of the individual perturbing agents show accelerating or inhibiting characteristics depending on the equivalence ratio and temperature, the coupling between NO and HCI generates considerable synergistic inhibition of the CO oxidation rate. Thus, accurate predictions of CO burnout in practical systems, where trace quantities of HCI and NO_x are present, can be achieved only if these kinetic interactions are considered.