Method for diagnosing SCR catalyst and feed gas quality in a diesel after-treatment system

摘要

An exhaust diagnostic system. The system includes a diesel engine having an exhaust system with a diesel particulate filter (DPF), a diesel oxidation catalyst (DOC), a selective catalytic reduction (SCR) catalyst, a first NOx sensor located upstream of the SCR catalyst and a second NOx sensor located downstream of the SCR catalyst. In addition, an engine control unit (ECU) is in electronic communication with the first NOx sensor and the second NOx sensor. An SCR coordinator can be included and be configured to execute a non-intrusive SCR deNOx efficiency test, an intrusive SCR/DOC deNOx efficiency test and an intrusive DOC non-methane hydrocarbon (NMHC) conversion efficiency test on the exhaust system. As a result of the conversion efficiency tests, a distinction can be made as to whether the SCR catalyst or DOC is failing.

主权项

1. An exhaust diagnostic system for a diesel engine, said system comprising:
a diesel engine having an exhaust system with a DPF, DOC and SCR catalyst, said diesel engine operable to supply exhaust gas to flow through said exhaust system; a first NOx sensor located upstream of said SCR and a second NOx sensor located downstream of said SCR catalyst; a malfunction indicator light (MIL) system; an ECU in electronic communication with said first NOx sensor, said second NOx sensor and the MIL system; said ECU configured to execute a non-intrusive SCR deNOx efficiency test on said exhaust system, said ECU also configured to execute an intrusive SCR/DOC deNOx efficiency test when said non-intrusive SCR deNOx efficiency is below a first predetermined threshold after a DPF regeneration event and an intrusive DOC NMHC conversion efficiency test when said intrusive SCR/DOC deNOx efficiency is below a second predetermined threshold on said exhaust system after said DPF regeneration event; said ECU further configured to determine that said SCR is degrading when said intrusive DOC NMHC conversion efficiency test determines said DOC efficiency is not below a third predetermined threshold and to determine that said DOC is degrading when said intrusive DOC NMHC conversion efficiency test determines said DOC efficiency is below said third predetermined threshold and to signal the MIL system that the SCR is failing when the DOC NMHC conversion efficiency is below the third predetermined threshold and to signal the MIL system that the DOC is failing when the DOC NMHC conversion efficiency is not below the third predetermined threshold.