F2008-06-099
Combined Diesel Aftertreatment System for NOX and PM Reduction in an MD Diesel Engine
More stringent diesel emissions regulations are scheduled to be effective in the very near future. For the sake of reducing NOx and PM emissions simultaneously, it is important to utilize exhaust gas aftertreatment system effectively. In this study, the urea SCR system with DOC combined with catalyzed DPF system were introduced in an LD diesel engine. A 4.0 liter turbocharged diesel engine with intercooler was used in this study. In the upstream of the SCR catalyst, a DOC for the generation of NO2 from NO was installed. In the downstream of the SCR catalyst, a DOC was equipped in case of NH3 slipping. The test fuel used was low sulfur diesel fuel. The effect of urea injection control on NOx reduction efficiency was evaluated under each exhaust gas temperature and space velocity. The conversion rates of NOx emissions were low at low load conditions. The decomposition and hydrolysis of urea to NH3 were enhanced by the installation of mixer and diffusion plate. Under the conditions of low exhaust gas temperature, it was found that increasing the amount of NH3 adsorption contributed to improve NOx reduction performance. However, the maximum amount of NH3 adsorption reduced with increasing exhaust gas temperature. In a transient operation, the adsorbed NH3 was desorbed and slipped with increasing the engine load. Therefore, logic to control NH3 adsorption amount was developed in this study. By adopting the NH3 adsorption control in transient operations, NOx emissions were significantly reduced in the SCR system without NH3 slip. On the other hand, the SCR catalyst reduced SOF in PM. However, it can not reduce dry soot in PM. Therefore, the catalyzed DPF was combined with the urea SCR system. NOx and PM reduction performance of the urea SCR system coupled with catalyzed DPF was strongly improved over JE05 transient mode in Japan.
Poster presentation: Future powertrain solutions