Development of a Novel Numerical Methodology for the Assessment of Insulating Coating Performance in Internal Combustion Engines

In recent years, the automotive industry has been increasingly committed to developing new solutions for better and more efficient engines. One of them is the use of new insulating materials (thermal conductivity < 0.4 W/m-K, heat capacitance < 500 kJ/m3-K) to coat the engine combustion chamber walls, as well as the exhaust manifold. The main idea when coating the combustion chamber with these materials is to obtain a reduction of the temperature difference (thermal swing) between gas and walls during the engine cycle and minimize heat losses. Experimental measurements of the possible performance improvements are very difficult to obtain, mainly because the techniques available to measure wall temperature are limited. Therefore, simulations are typically used to investigate insulated combustion chambers. Nevertheless, the new generation of insulating coatings is posing challenges to numerical modelling, as layer thickness is very small (~100 μm). Indeed, a detailed modelling would require additional cells refinement for the coating layer and therefore significant increase in computational effort and simulation time. In this regard, a novel strategy to model thin coating layers in the combustion chamber walls is presented in this paper. The approach consists in the definition of a thicker equivalent coating material that reproduces the thermal behavior of the real thin coating. The calculations are performed using a commercial 3D-CFD software for a Diesel engine considering two configurations: conventional metallic piston and coated piston top. Finally, the results are compared to assess the impact of the new generation of insulating coatings on engine performance.