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Since there is a trade-off relationship between NOx and particulates in exhaust gas emitted from a diesel engine, simultaneous reduction of the amounts of NOx and particulates in a combustion chamber is difficult. However, the amount of particulates produced in the combustion process could be reduced in a state of almost complete combustion, and the amount of NOx produced during the combustion process could be reduced by the use of a catalyst and reducing agent in the exhaust process. It has been demonstrated that the use of ethanol as a reducing agent on a silver-base catalyst in the presence of oxygen is an effective means for reducing NOx, although the mechanism of the reduction has not been elucidated. Therefore, in the present study, an NOx-reduction apparatus was conducted, and model experiments on NOx reduction were carried out in an atmosphere simulating exhaust gas emitted from a diesel engine and at the same catalyst temperature as that in a combustion chamber.

This study attempted to measure the concentration of NOx in a small gas sample, with a chromatograph equipped with a flame ionization detector (FID), by reacting NOx as an organic gas with alcohol and converting it into esters of nitrous acid having organic carbon atoms. It was found that since the FID is highly sensitive to hydrocarbons the measurements were difficult with high concentrations of hydrocarbon components with low boiling points at the elution position of the esters of nitrous acid. To resolve this a gas chromatograph equipped with an electron capture detector (ECD), which is selectively sensitive to esters of nitrous acid and not sensitive to hydrocarbon components with low boiling points was used.