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Thermal barrier coatings can be used to reduce the heat losses in heavy-duty diesel engines. A relatively new coating method for thermal barrier coatings is suspension plasma-spraying. Single-cylinder engine tests have been run to evaluate how heat losses to piston, cylinder head and exhausts as well as the specific fuel consumption are influenced by coating pistons with two different suspension plasma-sprayed thermal barrier coatings and one atmospheric plasma-sprayed thermal barrier coating, and comparing the results to those from an uncoated steel piston. The two suspension plasma-sprayed thermal barrier coatings showed reduced heat losses through the piston and less heat redirected to the cylinder head compared to conventional atmospheric plasma-sprayed thermal barrier coating, while one suspension plasma-sprayed coating with yttria-stabilized zirconia as top coat material showed increased exhaust temperature. However, the indicated specific fuel consumption was higher for all tested thermal barrier coatings than for an uncoated engine. The best performing thermal barrier coating with respect to indicated specific fuel consumption was a suspension plasma-sprayed coating with gadolinium zirconate as top coat material.

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Internal combustion engines have a key role in the social and economic advancement of modern society but also a significant contribution to greenhouse gas emissions. For these engines, to preserve their role, a higher efficiency, that dramatically reduces the environmental impact, is necessary. To achieve increased engine efficiency, a technical solution is to lower the heat losses in the combustion chamber. Among them, the heat losses to the pistons are the preferential route, due to their extensive impact on fuel consumption. In this paper, porous thermal barrier coatings with large pores were applied to the pistons of diesel engines to improve engine efficiency. Atmospheric Plasma Spray (APS) process and porosity former TBC feedstock were employed to obtain high porosity coatings with large pores. Scanning Electron Microscopy (SEM) was utilized to investigate the microstructure of the coating in coupons and pistons. The optical properties of the coatings were explored with two methods: the spectral normal hemispherical reflectivity at room temperature (SNHRRT) and spectral normal emissivity at high temperature (SNEHT). The coatings’ behavior under thermal cyclic conditions was assessed by Flame Rig Test. Microstructure analysis was also performed before and after the test to identify the failure mechanisms. The engine efficiency was evaluated by measuring the Indicated Specific Fuel Consumption (ISFC) in a single-cylinder engine test. The results showed that porous coating with large pores combined with a higher emissivity can withstand the engine environment well and have the potential to provide enhancements in engine efficiency.