Russell P. Durrett

Analysis of the effects of wall temperature swing on reciprocating internal combustion engine processes

A thermal wall temperature swing model was built to capture the transient effects of various material properties and coating layers on the intra-cycle wall temperature of an internal combustion engine. This model was used with a thermodynamic engine simulation to predict and analyze the effects of different types of in-cylinder insulation on engine performance. Coatings that allow the surface temperature to swing in response to the gas’ cyclical heat flux enable approximately 1/3 of the energy that was prevented from leaving the gas during expansion to be recovered while improving volumetric efficiency. Reductions in compression work due to better volumetric efficiency and less heat transfer from the walls to the gas accounted for half of the improvements, while additional work extraction during combustion and expansion accounted for the other half. As load increases, the temperature swing and benefits derived from it also increase. NSFC improvements of 0.5% to 1% were seen with a highly swinging coating in the throttled regime for a realistic engine geometry and coating area, up to 2.5% at high loads.

Assessing the capability of conventional in-cylinder insulation materials in achieving temperature swing engine performance benefits:

Materials that enable wall temperature swing to follow the gas temperature throughout a reciprocating internal combustion engine cycle promise the greatest benefits from in-cylinder insulation without detriments to volumetric efficiency or fuel autoignition behavior. An anisotropic barium–neodymium–titanate insulation was selected as a promising off-the-shelf material to begin investigating temperature swing characteristics while maintaining adequate strength and adherence to the aluminum components it was applied to. Experimental analysis showed that permeable porosity within the barium–neodymium–titanate coating resulted in increased heat losses despite thermal insulation, fuel absorption losses, and a reduction in compression ratio. Additionally, the thickest coating suffered severe degradation throughout testing. Any potential benefits of temperature swing insulation were dominated by these losses, emphasizing the need to maintain a sealed coating surface.