The rapid depletion of fossil fuels, their ever increasing prices and the harmful effects of their emissions (greenhouse gases) on the environment have necessitated the search for an alternative fuel which is renewable and has comparatively less percentage of emissions .Such properties can be obtained by using biodiesel instead of pure diesel. Increasing the performance and reducing the emissions of the diesel engines using biodiesel could be achieved by coating the piston head with ZrO2 & CeO2. These materials have low thermal conductivity and hence can create a thermal barrier. The coating could be done by plasma spray method. Corn oil methyl esters (COME), produced by transesterification process with 75% diesel with 25% corn methyl esters blend (B25) was used as fuel in a Direct Injection Kirloskar, Vertical, 4 Stroke, Single acting, and diesel engine. The performance and emission characteristics at various loads of the engine run at a constant speed of 1500 rpm were studied in both the coated and uncoated engines. The results obtained were compared with those of pure diesel.