The Application Of SCR System For A Heavy Duty Diesel Engine

The No.3 era emission standards for motor vehicles will be carried into execution in China, and the No.4 era emission standards have been planed to be put into practice in Beijing ahead of schedule in 2008.It is generally assumed that the No.4 era emission standards will be no longer feasible by primary measures but will require additional exhaust after-treatment techniques. Among exhaust after-treatment techniques for diesel engines, the selective catalytic reduction is presently considered as the most promising way to diminish NO_x originating from heavy duty vehicles.The application of the SCR System on a heavy duty diesel engine usually adopts the following route: Optimizing the engine to obtain low fuel consumption and low particulate emission, and at the same time, allow NO_x emission to increase. Then the SCR System can decrease the NO_x originating from the engine by the means of injecting aqueous urea into the exhaust pipe. The engine equipped with the SCR System will serve inspiring fuel economy and excellent emission performance.The article investigated the SCR System introduced from Germany basically. The contents include SCR elements functions, the appropriate pressure for compressed air, the felicitous on-off frequency of the dosing valve, the lowest temperature suits aqueous urea to inject and the relation between aqueous urea flow and pulse. The sensitivity of the SCR catalyst to the sulfur in fuel determines the applicability of the SCR System in China, so the SCR catalyst reliability test was conducted on a certain heavy duty engine after the grip of the system performance. The conclusion was induced that the catalyst activation is stable when the aqueous urea injects over a temperature of 280℃ and that the catalyst activation gets some attenuation after suffering a period of running with a injection temperature about 200℃. At the last the SCR System was demonstrated according to GB17691-2005 requirements for diesel engine and exhaust after-treatment systems. Three pertinent European Stationary Cycle tests find out the reduction of NO_x and HC emissions is apparent with the SCR System, but the particulate (PM) emission originating from the...