Experimental Study of Low Thermal Inertia Thermal Barrier Coating in a Spark Ignited Multicylinder Production Engine

Thermal barrier coatings (TBCs) have long been studied as a potential pathway to achieve higher thermal efficiency in spark ignition engines. Researchers have studied coatings with different thicknesses and thermophysical properties to counteract the volumetric efficiency penalty associated with TBCs in spark ignition. To achieve an efficiency benefit with minimal charge heating during the intake stroke, low thermal inertia coatings characterized by their larger temperature swings are required. To study the impact of low thermal inertia coatings in spark ignition, coatings were applied to the cylinder head, piston crown, intake and exhaust valve faces, and intake and exhaust valve backsides. Tier III EEE E10 certification gasoline was used to keep the experiments relevant to the present on-road vehicles. This study is aimed at analyzing durability of the coatings as well as efficiency and emissions improvements. Thus, a 100-hr. durability test was conducted to assess the durability of the coatings. Pseudo-cold start testing was also compared between the coatings and metal baseline to investigate any benefits pertaining to emissions reduction during cold starts. These experimental results show that low thermal inertia coatings can be developed for spark ignition engines that survive a 100-hr. durability test, though there is no significant change in steady state engine performance with the application of these coatings. However, there was a substantial reduction in particulate matter and unburned hydrocarbon emissions during pseudo-cold start testing.