Abstract: A metal of which the body of a piston is formed contains iron as its main component, and the configuration of a silicon nitride member, the high-temperature strength of the silicon nitride material that composes the silicon nitride member, the melting point of the iron-containing metallic material and the inserting conditions satisfy the following formulae (1) and (2) or formulae (3) and (4):k.sub.1 .multidot..DELTA.T.multidot.(1/R.sub.1 -1/R.sub.2)+k.sub.2 .multidot.l.sup.2 .multidot..DELTA.T<0.5 .sigma..sub.c ( 1)T.sub.c =T.sub.m -0.413.multidot.l.multidot..DELTA.T (2)k.sub.1 .multidot.T.sub.m .multidot.(1/R.sub.1 -1/R.sub.2)+k.sub.2 .multidot.l.sup.2 .multidot.T.sub.m <0.5.sigma..sub.c ( 3)T.sub.c =T.sub.m -0.413.multidot.l.multidot.T.sub.m ( 4)The joint between the silicon nitride member and the metallic material need not be subjected to machining. Therefore, the manufacturing process is simple and the cost is low.

Abstract: The disclosure relates to a novel arrangement of a combustion chamber for diesel engines, which is defined by an inner wall including a fuel-impinging area formed of a metallic material, and a remaining area which at least partly is formed of a ceramic material or a like heat-resisting material. The arrangement serves to achieve an effective exhaust gas clarification, including the minimization of NOx emission, and to realize increased power output and reduced fuel consumption of the engine.

Abstract: A direct injection-type diesel engine includes a piston head formed with a novel piston combustion chamber, with an inner wall surface composed essentially of ceramic material having a low thermal conductivity. The combustion chamber has a reduced opening diameter to enhance a squish air flow out of the clearance space between the piston and the cylinder head, and allows significant reduction of smoke, unburnt hydrocarbon and particulates in the exhaust gas, as well as minimization of thermal loss of the engine.