Improvement of HC-SCR Performance by Fuel Reforming Using a Low Temperature Oxidation

A fuel reforming technology using a low temperature oxidation was developed to improve a NOx reduction performance of HC-SCR (Hydrocarbons Selective Catalytic Reduction) system, which does not require urea. The low-temperature oxidization of a diesel fuel in gas phase produces NOx reduction agents with high NOx reduction ability such as aldehydes and ketones. A pre-evaporation-premixing-type reformer was adopted in order to generate a uniform temperature field and a uniform fuel/air premixed gas, and to promote the low temperature oxidation efficiently. As a fundamental study, elementary reaction analysis for n-hexadecane/air premixtures was carried out to investigate the suitable reformer temperature and fuel/air equivalence ratio for generation of oxygenated hydrocarbons. It was found that the reforming efficiency was highest at the reforming temperature around 623 to 673K, and aldehydes and ketones were produced. It was inferred that the NOx reduction performance by the reformed fuel was higher than diesel fuel itself. The FTIR measurements of reformed-fuel-vapor composition and the experiments of NOx reduction in the catalyst temperature range of 473 K to 773 K were performed for n-hexadecane and diesel fuel using the developed reformer. A Ag/Al2O3 catalyst was used as the NOx reduction catalyst. As a result of composition analysis, it was confirmed that low-temperature oxidization of hydrocarbons occurred in the reformer as estimated by the elementary reaction analysis. The NOx reduction efficiency by reformed diesel fuel vapor was up to about 90%. Improvements of the efficiency of diesel fuel reforming and the NOx reduction performance in wide range of the catalyst temperature are challenges.