Abstract: Selective catalytic reduction (SCR) systems are known and are generally included in the exhaust systems of diesel engines in order to treat the exhaust gases of such engines. Such systems typically involve the introduction of a diesel exhaust fluid (DEF) into exhaust gas flowing in an exhaust passage of an engine. DEF dosing systems are limited by the amounts of DEF that can be delivered without deposits forming on surfaces of the aftertreatment system. An impaction device is dosed with DEF at a first rate based on a set of characteristics of the SCR system. A second set of characteristics, such as an available storage capacity for DEF, is determined based on a set of criteria, such as a decomposition rate of DEF. Based on the second set of characteristics, the DEF dosing rate is changed to a second rate. The dosing rate is reverted to the first rate after a second set of criteria, e.g. a lower threshold of available storage for DEF, are fulfilled.

Abstract: Selective catalytic reduction (SCR) systems are known and are generally included in the exhaust systems of diesel engines in order to treat the exhaust gases of such engines. Such systems typically involve the introduction of a diesel exhaust fluid (DEF) into exhaust gas flowing in an exhaust passage of an engine. DEF dosing systems are limited by the amounts of DEF that can be delivered without deposits forming on surfaces of the aftertreatment system. An impaction device is dosed with DEF at a first rate based on a set of characteristics of the SCR system. A second set of characteristics, such as an available storage capacity for DEF, is determined based on a set of criteria, such as a decomposition rate of DEF. Based on the second set of characteristics, the DEF dosing rate is changed to a second rate. The dosing rate is reverted to the first rate after a second set of criteria, e.g. a lower threshold of available storage for DEF, are fulfilled.

Abstract: A selective catalytic reduction (SCR) system for treating exhaust gases in an exhaust passage is provided. The system comprises a first catalyst for converting urea to ammonia, the first catalyst being located in the passage and having an upstream face and a downstream face. The upstream face is at a right angle to an axial flow path (A) through the passage. The system further comprises a second catalyst for converting NOx to nitrogen gas and water in the presence of ammonia, with the second catalyst being located in the passage downstream of the first catalyst. A diesel exhaust fluid dosing unit is located upstream of the first catalyst. The dosing unit comprises a nozzle arranged so as to inject DEF directly onto the upstream face of the first catalyst.