The auxiliary piston may function as a compression and ignition means by moving rapidly toward its top dead center position only when {HEAD ~ the working piston} is close to {TAIL ~ its top dead center position} 
is close to
The auxiliary piston may function as a compression and ignition means by moving rapidly toward its top dead center position only when { HEAD ~ the working piston } is close to { TAIL ~ its top dead center position }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL