SYNOPSISAn experimental, uncooled, single cylinder DI Diesel engine with ceramic coated cylinder head and valves, a heat insulated steel topped piston and a short, partially stabilized zirconia cylinder liner in the area above the piston rings provided 4 to 7% improvement in fuel consumption at operating conditions typical of the EPA CVS driving cycle for light duty vehicles relative to the baseline water-cooled engine. An engine simulation model was used to explain the measured improvements in fuel consumption. Generally, the uncooled engine provided reductions in HC, NOx and particulate emissions. The trend of lower HC and NOx emissions was explained by the reduction in the amount of premixed combustion resulting from the shortened ignition delay period. The trend of lower particulate emissions was explained by an increase in the diffusion combustion rate. Reduced rates of pressure rise for the uncooled engine were projected to result in lower noise levels.