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