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<p>Attempts to improve fuel efficiency of internal combustion (IC) engines using thermal insulating coatings have been made for decades. The fundamental concept is to reduce heat loss and convert that heat into useful mechanical work. It is now recognized that for this concept to be effective the coatings must provide an increased wall temperature to limit convective heat transfer, but also cool rapidly to avoid increased pumping work that negates the efficiency advantages. Such coatings are known as swing coatings, characterized by a low thermal effusivity. Bismuth-doped lanthanum molybdate (Bi-LMO) has a very low thermal effusivity and a matching thermal expansion coefficient to aluminum, ideal as a novel thermal barrier coating (TBC) material in spark ignition (SI) IC engines. To apply a Bi-LMO TBC to engine components including the piston crowns, there lacked suitable commercial spray powders, so a solution precursor was developed in the solution precursor plasma spray (SPPS) process for fast composition exploration and concept validation. The SPPS knowledge also led to a custom-made spray powder of Bi-LMO, which was used by the atmospheric plasma spray (APS) for further development of this new thermal barrier coating&#xa0;(TBC). Extensive engine testing showed that the Bi-LMO TBCs improved cold start emissions and the low-load fuel efficiency, but produced a fuel efficiency penalty at high loads, in aggregate negating the coating’s fuel efficiency advantages and likely true for all other similar coatings. These results are consistent with the proposed mechanism of convective vive, in which the air fuel mixtures under a sufficiently high wall temperature could increase the heat transfer coefficient enough to eliminate the reduction of heat loss needed to offset the gain in fuel efficiency.</p>

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A Novel Plasma-Sprayed Thermal Barrier Coating for Internal Combustion Engines and its Fundamental Limits on Performance

  • 期刊论文

  • 发表日期：

    2025年10月6日

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  • Eric H. Jordan,
  • Chen Jiang,
  • Rishi Kumar,
  • John Gandolfo,
  • Brian Gainey,
  • Benjamin J. Lawler

摘要

Attempts to improve fuel efficiency of internal combustion (IC) engines using thermal insulating coatings have been made for decades. The fundamental concept is to reduce heat loss and convert that heat into useful mechanical work. It is now recognized that for this concept to be effective the coatings must provide an increased wall temperature to limit convective heat transfer, but also cool rapidly to avoid increased pumping work that negates the efficiency advantages. Such coatings are known as swing coatings, characterized by a low thermal effusivity. Bismuth-doped lanthanum molybdate (Bi-LMO) has a very low thermal effusivity and a matching thermal expansion coefficient to aluminum, ideal as a novel thermal barrier coating (TBC) material in spark ignition (SI) IC engines. To apply a Bi-LMO TBC to engine components including the piston crowns, there lacked suitable commercial spray powders, so a solution precursor was developed in the solution precursor plasma spray (SPPS) process for fast composition exploration and concept validation. The SPPS knowledge also led to a custom-made spray powder of Bi-LMO, which was used by the atmospheric plasma spray (APS) for further development of this new thermal barrier coating (TBC). Extensive engine testing showed that the Bi-LMO TBCs improved cold start emissions and the low-load fuel efficiency, but produced a fuel efficiency penalty at high loads, in aggregate negating the coating’s fuel efficiency advantages and likely true for all other similar coatings. These results are consistent with the proposed mechanism of convective vive, in which the air fuel mixtures under a sufficiently high wall temperature could increase the heat transfer coefficient enough to eliminate the reduction of heat loss needed to offset the gain in fuel efficiency.