DESIGN OF ALTERNATIVE MULTILAYER THICK THERMAL BARRIER COATINGS

Increasing the combustion temperature in diesel engines is an idea which has been pursued for over 20 years. Increased combustion temperature can increase the power and efficiency of the engine, decrease the specific fuel consumption and CO emission rate. Ceramic thermal barrier coatings have been identified as the most promising approach to meeting these objectives. The most commonly used system is Yttria Partially Stabilized Zirconia (Y-PSZ). However, in contrast to the widespread use in aircraft and power generation turbine engines, Y-PSZ TBCs have not met with wide success in diesel engines. To reach the desirable temperature of 850-900 degrees C in the combustion chamber, a coating with a thickness of at least 1mm is required. This introduces different considerations than in the case of turbine blade coatings, which are on the order of 100 mu m thick. The design of a multilayer coating employing relatively low cost materials with complementary thermal properties is described. Numerical models were used to optimize the thickness for the different layers to yield the minimum stress at the operating conditions while achieving the desired temperature gradient.