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