{HEAD ~ An ion current detector} detects {TAIL ~ an ion current} in at least one of the engine cylinders 
detects
{ HEAD ~ An ion current detector } detects { TAIL ~ an ion current } in at least one of the engine cylinders
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH