{TAIL ~ A desulphurization event} includes operating one or more emission control devices at an elevated temperature and with a selected air fuel ratio to reduce {HEAD ~ contamination}, such as sulphur and other contaminants 
{ TAIL ~ A desulphurization event } includes operating one or more emission control devices at an elevated temperature and with a selected air fuel ratio to reduce { HEAD ~ contamination } , such as sulphur and other contaminants
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH