The present invention is directed to repair compositions for thermal barrier coatings and methods of use thereof. The repair compositions include a ceramic composition, a colloidal solution, an aqueous binder, an aqueous dispersant, and an aqueous ammonia solution. The ceramic composition includes a first population of yttria-stabilized zirconia particles having a mean diameter from about 250 nm to about 1000 nm, a second population of yttria-stabilized zirconia particles having a mean diameter from about 2 m to about 10 m, and a third population of yttria-stabilized zirconia particles having a mean diameter from about 20 m to about 250 m. One method includes depositing the repair layer onto the damaged region, the repair layer including the repair composition, and heat treating the repair layer.

In a spark ignition engine, a thermal insulation thin layer is formed over a wall surface, facing an inside of a combustion chamber, of a base material forming the combustion chamber, and for a thermal conductivity [W/(m.Math.K)], a thermal diffusivity [mm.sup.2/s], and a thickness L [m] of the thermal insulation thin layer, L16.7 and L207.4().sup.0.5 are satisfied. With such a configuration, a heat loss Q_total escaping from gas in a cylinder to the wall of the combustion chamber over all strokes can be reduced, and the thermal efficiency can be improved without inducing degradation of knocking due to an increase in an amount of heating Q_intake of the gas in the cylinder during an intake stroke.