High Temperature Wear Coatings for Improving High Output Military Diesel Engine Performance and Durability

Future military combat engines require high power density, low heat rejection designs like the Achates Opposed-Piston Diesel. This design places higher tribological performance requirements on the piston/ring/bore. Various coatings have been tried on piston skirts but durability of the cylinder kit remains a challenge due to heat, high side loads, bore distortions from ports, and marginal lubrication of the piston skirt and rings. Additive/Abradable Powder Coatings (AAPC’s) are thick, self-fitting, self-polishing, lubricant retaining coatings that lap in to find and preserve the ideal functional geometry of pistons through a “Stribeck-Fitting” process. Better fitting pistons reduce peak contact stresses by distributing the loads evenly. AAPC’s are tolerant of bore distortions and contaminating particles like sand. Lower Integrated Piston Wall Clearance (IPWC) reduces rock and secondary motions to diminish wear modes and improve oil control by the rings. The textured coatings burnish to a polished plateau structure with pockets for oil to promote hydrodynamic lubrication even with marginal supply. This work seeks to document friction, wear, and load bearing capabilities of AAPC’s and benchmark competitive technologies. It also aims to extend the thermal range and load bearing capability of commercially available AAPC’s, with the goal of surviving tribo-conditions of future combat engines.