One-Dimensional Modelling and Analysis of Thermal Barrier Coatings for Reduction of Cooling Loads in Military Vehicles

There is a general interest in the reduction of cooling loads in military vehicles. To that end thermal barrier coatings (TBCs) are being studied for their potential as insulators, particularly for military engines. The effectiveness of TBCs is largely dependent on their thermal properties, however insulating effects can also be modified by applying different coating thickness. Convection from in-cylinder surfaces can also be affected by manipulation of surface structure. Although most prior studies have examined TBCs as a means of increasing efficiency, military vehicle design is primarily concerned with the reduction of cylinder heat transfer to allow downsizing of cooling systems. A 1-D transient conjugate heat transfer model was developed to provide insight into the effects of different TBC designs and material selection on cooling loads. Results identify low thermal conductivity and low thermal capacitance as key parameters in achieving optimal heat loss reduction. They also indicate a linear relationship between the reduction of cooling load and the thickness of the coating. It was found that heat loss could be further reduced by increasing the exhaust load rather than providing a benefit to thermal efficiency, by employing coatings of thickness exceeding 0.1 mm. This will accomplish the military design goal of reducing cooling load. Additionally it was found that, for sufficiently low k, increasing diffusivity (by decreasing thermal inertia) will decrease cooling load. This means alternatives to zirconia TBCs can achieve similar results despite not having such a low conductivity, provided they have a low enough density and specific heat. Overall however it appears that the best way to reduce cooling load is to minimize the convection coefficient h, which will similarly decrease the overall heat flux during the cycle.