The Influence of Thermal Barrier Coatings on Morphology and Composition of Diesel Particulates

This paper summarizes an investigation of the changes in combustion and particulate emissions caused by thermal barrier coatings placed in the combustion chamber of a diesel engine. The engine was a Yanmar TS 180 single cylinder diesel utility engine with a continuous rating of 15 HP (11.2 kw) @2400 RPM. The test protocol was the International Standards Organization (ISO) 8178 Standard Type-E3 test which simulates a marine diesel engine. Total particular matter emissions were measured by collection on Pallflex, filters via fractional sampling using a Sierra Instruments BG-1 Micro-Dilution Test Stand. The engine was operated with and without the thermal barrier coatings. The coated parts are the piston crown, the cylinder head (fire deck), and the valves. Scanning electron micrography (SEM) provided analysis of particulate size, microscopic structure and elemental composition of the particulate samples. The results show the degree to which thermal barrier coatings on combustion chamber surfaces alter the composition and structure of the diesel particulate matter. In the uncoated engine, particulate morphology changed with engine operating conditions: granular with fine spherules at high speed - high load conditions, and layered and plate-like at low speed - low load. In the coated engine, particulate morphology varied less strongly with engine operating conditions, retaining a more fine and granular appearance. The thermal barrier coatings improve the oxidation of high molecular weight condensable hydrocarbons that make up the soluble organic fraction of the particulate, which reduces the degree to which soot particles agglomerate into large structures.