Plasma Sprayed

Figure 7. Redesigned insulated piston top with ceramic coating and a solid ceramic insert
Figure 8. Insulated piston top with extensive coaling crazing

exposed to combustion gases. The coating generally remained intact but crazing is present.

Ceramic Coating Conclusions

Conclusions regarding thermal barrier coatings in the adiabatic diesel engine are:

(1)Insulating the combustion chamber of the uncooled engine reduced heat loss and improved fuel economy.

(2)Ceramic coatings operated successfully for short term experimental tests ranging from 10 hours to over 500 hours; however, long term durability may not be adequate.

(3)Long term durability of the cast iron engine structure operating at the elevated temperature of the uncooled, ceramic coated engine may not be adequate, due to the potential for warpage and phase changes of the cast iron.

(4)The ceramic coated engine is more complex to fabricate than the base line, water-cooled, cast iron engine.

Ceramic Inserts

The engine components evaluated in the ceramic insert concept (Phase II) investigations were fabricated from monolithic partially stabilized zirconia (PSZ). PSZ was selected because of its relatively low thermal conductivity and its reasonably close thermal expansion match to cast iron. The similarity of

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