a filter pack disposed in {HEAD ~ the combustion chamber} along an inner diameter of {TAIL ~ the outer wall} 
a filter pack disposed in { HEAD ~ the combustion chamber } along an inner diameter of { TAIL ~ the outer wall }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL