SPPS Development of an Ultrahigh Performance Piston Coating and Why It and Similar Coatings are not Likely to Work

Reducing the heat loss from combustion in internal combustion engines has the potential to improve fuel efficiency. It is recognized that to achieve this it is necessary that the coatings reduce heat transfer upon ignition but cool rapidly to avoid pumping work penalties during intake and compression. This can be accomplished by “swing coatings” with low thermal conductivity and low thermal inertia. The key property is thermal effusivity. A new coating was developed from a ceramic, bismuth doped lanthanum zirconate known to have a thermal conductivity less than 1 W/mK and a density of 6 g/CC. Lacking any commercial powder for this material it was first demonstrated using solution precursor thermal spray. A thermal spray powder was then made commercially to aid in coating complex Ford EcoBoost pistons. Extensive testing of multiple versions of this coating showed efficiency improvements at low loads and RPM and penalties at higher loads and RPM consistent with the theory of convective Vive suggesting that such coatings are not likely to work except when low temperature combustion is dominant.