Overview of thermal barrier coatings in diesel engines

An understanding of delamination mechanisms in thermal barrier coatings (TBCs) has been developed for diesel engine applications through rig tests, structural analysis modeling, nondestructive evaluation, and engine evaluation of various TBCs. This knowledge has resulted in improved TBCs that survive se-vere cyclic fatigue tests in high-output diesel engines. Although much conflicting literature now exists regarding the impact of TBCs on engine performance and fuel consumption, changes in fuel consumption appear to be less than a few percent and can be nega-tive for state-of-the-art diesel engines. The ability of the TBC to improve fuel economy depends on a num-ber of factors, including the fuel injection system, combustion chamber design, and initial engine fuel economy. Limited investigations on state-of-the-art diesel engines have indicated that surface- connected porosity and coating surface roughness may influence engine fuel economy. Current research efforts on TBCs are primarily directed at reduction of in-cylinder heat rejection, ther-mal fatigue protection of underlying metal surfaces, and possible reduction of diesel engine emissions. Significant efforts are still required to improve the plasma spray processing capability and the economics for complex-geometry diesel engine components.