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