ABSTRACT
The thermal efficiency of most commercially used engine ranges from 38% to 42%, as nearly 58% to 62 % of energy is lost in the form of waste heat. Nearly 30% is retained in exhaust gas and the remaining is removed in cooling water/air, in order to save energy the hot parts are insulated thermally. This will lead to reduction in heat transfer through the engine, involving an increased efficiency. Change in combustion process due to insulation also affects emissions. Higher gas temperature should reduce the concentration of incomplete combustion products at the expense of an increase in nitrogen oxides (NOx). However a decrease in carbon monoxide (CO) unburned hydrocarbons (HC) is observed. Also the highest temperature of any point on piston should not exceed 66% of the melting point temperature of the alloy. This limiting temperature of the piston alloy can be increased by using TBC. Ceramics have higher thermal durability than metals, therefore it is usually not necessary to cool them as fast as metals.[6]
Thermal Barrier Coatings (TBC) provides the potential for higher thermal efficiencies of the engine, improved combustion and reduced emissions. In addition ceramics show better wear characteristics than conventional materials. A lot of experimental study has to be done to utilize these ceramic prosperities to improve thermal efficiency by reducing heat loss, and to improve mechanical efficiency by eliminating cooling system.[5]