The effects of NO 2 on catalytic oxidation of unburned species from a methanol fueled spark ignition engine

Abstract

Catalytic oxidation processes of unburned species in methanol combustion products are examined with emphasis on the role of NO 2 . Two kinds of experiments were carried out. One was on the catalytic oxidation of the exhaust gases from a methanol fueled spark ignition engine, and the other on prepared gases which simulated the engine exhaust gases. Exhaust gases of air-fuel equivalence ratio ranging from 0.8 to 1.5 were investigated. In the catalyst bed, unburned methanol, formaldehyde, NO and NO 2 concentrations were determined at gas temperatures ranging from 400 to 540 K. Experimental results were expressed by two parameters, methanol oxidation ratio and NO 2 reduction ratio. As soon as the exhaust gas entered the catalyst bed, methanol was oxidized and its concentration decreased. At the same time, NO 2 decreased, while NO increased. The methanol oxidation ratio had a maximum value at an equivalence ratio of about 1.2 and was related to the NO 2 emission characteristics. The conversion of NO 2 to NO was improved by the presence of methanol and the oxidation of methanol was promoted by NO 2 , within the experimental range. In comparison with ethanol combustion products, the effect of NO 2 in catalytic oxidation was greater for methanol combustion products because of the higher NO 2 concentration in the methanol combustion products.