Optimally, the residual engine or exhaust heat, or {HEAD ~ heat} from {TAIL ~ the catalyst}, may be used 
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Optimally , the residual engine or exhaust heat , or { HEAD ~ heat } from { TAIL ~ the catalyst } , may be used
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH