Experimental Investigation of Low Cost, Low Thermal Conductivity Thermal Barrier Coating on HCCI Combustion, Efficiency, and Emissions 2020-01-1140
In-cylinder surface temperature is of heightened importance for Homogeneous Charge Compression Ignition (HCCI) combustion, as the combustion mechanism is thermo-kinetically driven. Thermal Barrier Coatings (TBCs) selectively manipulate the in-cylinder surface temperature, providing an avenue for improving thermal and combustion efficiency. This thermal phenomenon sidesteps charge preheating during gas exchange, while a surface temperature swing during combustion/expansion reduces heat transfer losses, leading to more complete combustion and reduced emissions. The magnitude and profile of the dynamic surface temperature swing was found to be affected by the material properties and TBC thickness. This study is the continuation of the author’s work to systematically engineer coatings that are best suited for HCCI. A parametric study was used to assess the impacts of various TBC material properties (density, specific heat, thermal conductivity) on the temperature swing effect. Previous work investigated the effect of reducing TBC density via increased porosity, however fuel entrapment and durability concerns found this route initially unattractive for robust TBC performance. Shifting focus to the remaining material properties, this study experimentally investigates the impact of lower thermal conductivity TBCs on HCCI performance, efficiency, and emissions. A Novel TBC formulation was developed, leveraging a class of materials that, to the author’s best knowledge, have not been used as a thermal barrier coating previously.
Engine experiments with a dense, natively low thermal conductivity coating applied to the piston indicated advancement in the start of combustion location, with reduced combustion duration. Heat transfer measurements indicate a net reduction in heat flux over the entire cycle, the reduced heat transfer losses manifest in higher thermal efficiency, (5-6% relative improvement). The results of the novel TBC are compared to that of other TBCs with higher thermal conductivities, and the trends are discussed.
Sean Moser, Ryan O'Donnell, Mark Hoffman, Eric Jordan, Tom Powell, Zoran Filipi