The core of this paper is reduction of exhaust emission and increase of diesel efficiency due to application of microstructure ceramic semitransparent heat-insulating coatings (SHIC). The authors conducted experimental study of thermal state of internal-combustion engine piston head with a heat-insulating layer formed by plasma coating method. The paper presents physical and mathematical simulation of improved optical (transmittance, reflectance, absorption, scattering) and thermo radiative (emittance) characteristics determining optimal temperature profiles inside SHIC. The paper considers the effect of subsurface volumetric heating up and analyzes temperature maximum position inside subsurface of this coating. Decrease of SHIC surface temperature of the coated piston in comparison with temperature of traditional opaque heat-insulating coatings causes NOx emission reduction. Experimental test of heat-insulated piston in comparison with unprotected one confirmed improvement of power characteristics and burning capacity by 5 10% for typical high speed diesel tractor engine.