Cylinder head, exhaust and inlet valves of the diesel engine used in the tests were coated with MgO–ZrO2, which is a ceramic material, to a thickness of 0.35 mm over a 0.15 mm thickness of NiCrAl bond coat, by the plasma spray method. The piston surface was coated with 0.35 mm of ZrO2 over a 0.15 mm layer of NiCrAl bond coated by the plasma spray method.