Analytical modeling was coupled with experimental results to evaluate heat Bow around the combustion chamber of an un-cooled diesel. Good agreement was obtained between the model and experiment. Both experimental and analytic results showed that total heat rejection was roughly proportional to fueling rate, and that during the intake and compression strokes the uncooled engine transferred significantly more heat to the air charge than did the equivalent water-cooled engine, resulting in poor volumetric efficiency.The model indicated that the greatest fraction of heat rejection occurred through the piston, and that spatial temperature variations in the air-gap-insulated metallic firedeck were much greater than the corresponding variations over the air-gap-insulated metallic piston crown. The low-heat-rejection diesel engine has been investigated because of its potential for improved fuel economy and reduced vehicle mass. Development of the LHR engine requires addressing the complex structural and lubrication problems arising from severe thermal loading.