Effect of products of low temperature oxidation reaction on NOx reduction in HC-SCR system

Fuel reforming technology using a low temperature oxidation reaction was applied to improvement of NOx reduction efficiency of hydrocarbons selective catalytic reduction (HC-SCR) system, which does not require urea. The low temperature oxidation reaction of hydrocarbons produces oxygenated hydrocarbons which has high NOx reduction ability such as aldehydes. A pre-evaporation and premixing-type fuel reformer was developed in order to generate uniform fuel/air premixed gas. To prevent from hot-flame ignition, the reaction chamber of the fuel reformer has a high surface/volume ratio and the wall temperature of the reaction chamber was controlled. As a fundamental study, NOx reduction experiments and elementary reaction calculation were carried out to investigate the suitable fuel reformer temperature and reforming equivalence ratio for the promotion of NOx reduction on the surface of the catalyst. It was found that the reforming fuel gas has a higher NOx reduction efficiency than the fuel vapor in the catalyst temperature range from 473 to 773 K. The NOx reduction efficiency was highest at the reforming temperature of 673 K. The NOx reduction efficiency at the catalyst temperature of 723 K increases with the increase in the reforming equivalence ratio. It was suggested that alcohols predominantly affect NOx reduction reaction at low catalyst temperatures, and aldehydes at high catalyst temperatures.