Effect of ethene (C₂H₄) on the plasma DeNO _x process from diesel engine exhaust

Effect of ethene on the DeNO_x conversion process in a simulated diesel engine operating conditions was investigated experimentally and theoretically. With the addition of even a small amount of ethene the NO to NO₂ conversion enhances greatly. The energy required to convert one NO molecule is 27 eV with 250 ppm ethene added, while 137 eV without ethene at 473 K. The effect of energy density, temperature, and the initial concentrations of ethene and oxygen are also discussed and the results show that the increase of the mentioned parameters lead to the promotion of NO oxidation. A kinetic model used in this study shows good agreement with the experimental result. Byproducts like formaldehyde (CH₂O) and methyl nitrite (CH ₃ONO) predicted by model calculation are broken up into CO and H ₂O eventually when high energy is delivered to the gas mixture. Sensitivity analysis shows that the main reactions of NO oxidation when ethene is added are: HO₂+NO→NO₂+OH, RO₂+NO→ NO₂+RO, where R is a hydrocarbon radical. Also the direct oxidizing reaction of NO with O cannot be neglected.