According to one embodiment of the invention, {HEAD ~ the pockets} are defined by {TAIL ~ upstanding walls} in the movable element adjacent the surface exposed to gases of combustion 
According to one embodiment of the invention , { HEAD ~ the pockets } are defined by { TAIL ~ upstanding walls } in the movable element adjacent the surface exposed to gases of combustion
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH