Workshop Methods for Troubleshooting the Performance of the After-treatment system

Sammanfattning: New legislations are constantly arising in Europe that puts stringent restrictions on the emissions coming from heavy-duty vehicles. The latest one is the Euro VI that has tough limits on both nitrogen oxides (NOx) and particulate matter (PM). To be able to cope with these tough limits, many developers of heavy-duty trucks have chosen to mount an after-treatment system after the engine containing several different catalysts. The emissions are monitored by an On-Board Diagnosis (OBD) system during operation, and if the emissions are too high a Malfunction Indicator (MI) lamp is lit and the truck needs to be serviced in a workshop. In the workshop the fault is investigated, which could be caused by several things, one of which may be a performance loss of one of the catalysts.This master thesis investigates different methods for testing the performance of two of these catalysts. The catalysts that were investigated was the Diesel Oxidation Catalyst (DOC) that oxidizes hydrocarbons (HC), carbon monoxide (CO) and nitrogen monoxide (NO), and Selective Catalytic Reduction (SCR) that uses ammonia for the reduction of nitrogen oxides (NOx). A comprehensive literature study was made to get an insight in how the current system works and to be able to develop concepts for future workshop methods. From the literature study, three concepts were developed for each catalyst. These concepts were tested out on Scania’s 13 litre 6-cylinder Euro VI engine with Scania’s Euro VI after-treatment system. The concepts are mainly consisting of three measuring principles that investigates the changes in temperature, NOx-conversion and ammonia storage. The tests resulted in that one concept per catalyst could be used to isolate and measure the performance. The performance of the DOC could be measured with the increase of temperature due to the exothermal reaction when HC is injected into the catalyst, called Measurement of HC-slip. To be able to measure the performance of the SCR, the changes in the maximum ammonia storage that the catalyst could achieve during an ammonia sweep was used, called Measurement of ammonia storage.