portion 28 that slopes downward as well as a wall portion 30 vertical wall portion 30 is just one example alternatively the wall portion may angle backwards toward injector 12 or angle away from injector 12 also shown in fig4 is a piston crown for an intake piston 34 piston crowns 22 and 34 are opposed pistons and are shown in their closest position during reciprocation within the cylinder wall cylinder wall not shown in fig4 the piston top of intake piston 36 is substantially a concave sphere of the same diameter as the sphere of surface 18 so that the gap between the two is nearly constant between raised surface 18 and piston top 36 in fig5 an isometric view of an intake piston crown 44 is shown piston top 46 has channels 42 to accommodate the fuel jets from two diametrically opposed fuel injectors injectors not shown to obtain access to the combustion chamber without hitting the piston top in fig6 an exhaust piston crown 50 is shown which accommodates fuel sprays from two injectors 52 tips of the injectors are arranged on a dashed diametral line 53 across piston crown 50 piston crown has a raised portion 54 and recessed portion 56 raised portions 54 have protuberances 58.