Heat Transfer Suppression Effect by an Air Layer on the Wall of a Combustion Vessel

As a means to improve engine thermal efficiency, a technique has been proposed in which stratified EGR gas along the cylinder wall reduces cooling losses from the combustion gas to the wall surface. Using a MEMS heat flux sensor for engine wall surfaces, the heat transfer suppression effect of an air layer formed near the wall was experimentally investigated under laminar combustion of premixed gas. The air layer was formed by a short-duration injection from a flat nozzle. Experiments were conducted under conditions where the premixed gas was stationary and continuously mixed by a fan, and it was shown that a heat transfer suppression effect of 60–70% could be achieved depending on the conditions.