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