Discussion: “Heat Transfer With Insulated Combustion Chamber Walls and Its Influence on the Performance of Diesel Engines” (Woschni, G., and Spindler, W., 1988, ASME J. Eng. Gas Turbines Power, 110, pp. 482–488)

Abstract

increase in bsfc -% engine speed [rpml The turbocompounded engine with insulated pistons would eliminate this gain in consumption, which means that the compounded engine with insulated pistons is inferior to the turbocharged engine with bare aluminum pistons over the whole engine map, as can be seen from Fig. 15. ConclusionFurther experiments confirmed the fact presented in [1] that insulation of the combustion chamber yields savings in fuel consumption only at low load, if ever. The reason is that only for relatively low surface temperatures of the combustion chamber walls do the heat losses through the combustion chamber walls decrease according to the decreasing temperature difference between gas and surface. With higher surface temperatures the heat transfer coefficient rises rapidly, so the positive effect of the decreasing temperature difference is overcompensated. The possible gain in fuel consumption at part load in any case is paid for dearly with a significant fuel consumption increase at full load. This holds true for the naturally aspirated engine as well as for the turbocharged engine without and with an additional power turbine.