The Study Of Strategy For A SCR System To Reduce NO_X Emission From A Heavy Duty Diesel Engine

The after-treatment technologies are the major measures to meet the emerging stringent emission legislation limits. Inducing all the Routes studied by diesel engine manufactures to deal with Euro IV and Euro V treaties two kinds are concluded, which one is reduce NO_X emission with selective catalytic reduction (SCR) technologe on the basis of combustion optimization to reduce PM and the other debase NO_X emission with exhaust gas recycle (EGR) and PM with PDF.By the analysis of the principle and the ultilization of SCR, the author draws a conclusion that the SCR System is very the proper choice taking into account Chinese reality. So a set of SCR devices are fited on a YC6L350-40 HD diesel engine and investigated, including the base performance of the SCR System, the study of reducer control strategy, the investigation of the SCR System, the applicability evalutation of the SCR System for running with high sulphur content fuel on the engine and the analyse of issues with the system. As a result the first Euro IV HD diesel engine is produced by China.At the very start the action mechanism of the metal oxid catalyst with redox and the reaction mechanism of NH₃-SCR are introduced detailedly, and then the dosing unit performance is calibrated, and the on-off frequency of the dosing valve is investigated also. The control strategy of reducer is studied combining with raw NO_X emission map, exhaust gas pressure map, catalyst reduction map and NO_X conversion map obtained through engine test and theory analysis, and then the strategy is amended according to exhaust temperature and urea solution temperature, at the same time the thought about the modification due to the effect of the ammonia storage capbility of the catalyst is induced. The SCR System is demonstrated according to GB17691-2005 requirements for diesel engine and exhaust after-treatment systems through ESC tests and ETC tests at the Chinese Automobile Test Center and the conclusion is drawed that the HD engine equipped with the SCR System even in the case of running Euro III standard diesel meets the NO. IV era emission standards.In order to investigate the applicability for the SCR System to work as city bus after-treatment device, fifteen modes most located in low speed and portial load are induced as 1000 hour cycle modes with nearly 2000 ppm sulphur content fuel. The conclusion is drawed that on the condition of high sulfur content the catalyst activity keeps steaty with reducer lowest delivery temperature of 230℃and some attenuation with 200℃. In the end, the project and troublesome concerning "Adblue" station constructure is discussed referring to oversea correlative experience.The author's production possesses important reference value for Euro IV HD diesel engine development. The reasonable technology route for the NO. IV era emission control is explored according to the situation of our country. The production takes on rich utility value and has far-reaching society meaning for China to low engine baleful emission and to decrease environment pollution.