A Study on NO Reduction Caused by Thermal Cracking Hydrocarbons during Rich Diesel Combustion

This study tries to investigate the reduction of nitric oxide by thermally cracked hydrocarbons under rich condition during diesel combustion. Experiments using flow reactor system, which follows the chemical process of fuel at high temperature and atmospheric pressure, show that thermal cracking of fuel starts at about 1000K, and lower hydrocarbons mainly composed of C_2H_4 and CH_4 are formed. NO can be reduced when fuel is thermally cracked and oxidized. A larger amount of NO is reduced when thermal cracking hydrocarbons are increased in quantity under rich and high temperature condition. Among decomposed hydrocarbons, C_2H_4 is easily decomposed and affects deNO mechanism. Chemical kinetic calculation using CHEMKIN III reveals the mechanism. NO is reduced through the reaction of HCCO or CH_2 with NO. In these reaction paths, C_2H_2 is an essential species. The computation also shows that this deNO mechanism can be actualized in the practical diesel combustion.