An all-ceramic swirl chamber has been developed. All inner walls of the chamber fire made of a high-strength, sintered silicon nitride and are heat-insulated from the cylinder head with air gaps. This new construction has held thermal stress at permissible level and has assured satisfactory durability. Ignition quality was improved and particulate emission was reduced by raising combustion gas temperature. This combustion improvement, combined with optimized EGR control and injection timing. control, could make the light-duty diesel vehicle meet the 1987 U.S. diesel particulate regulation without sacrificing other engine performance characteristics.