F2008-12-303
Impedance Materials for Low-Heat-Rejection Diesel
A theoretical study of a new class of impedance materials based on transparent, semitransparent and opaque heat-insulating materials for combustion chamber (CC) elements of low-heat-rejection diesel is discussed. Suggested impedance materials as known model semitransparent heat-insulating coatings (SHIC) promote low heat losses of a diesel engine due to heat-regenerating effect for a cyclic heat transfer in the internal CC walls during “hot” (combustion) and “cold” (admission, compression and exhaust) phases. The effect is transformation of absorbed (in subsurface semitransparent coating volume) radiant component to conductive flux, which is directed back into CC during the “cold” phase. The modeling is carry out for non steady conditions. The radiant and temperature fields of thin and thick layers materials are investigated. Thin coatings up to 1 mm represent model opaque or semitransparent porous ceramic coatings at operating conditions of real high-speed diesel engines CC. Thick layers of materials are analogues of model hypothetical quasi adiabatic CC with the wall thickness to 3 сm executed completely from ceramics. Physical parameters simulation of the impedance material consisting of two-layer transparent and semitransparent coatings with different optical and thermal physical property is considered. One of the layers of this material bordering on CC wall is made from semitransparent scattering and absorbing porous ceramics for near IR of the heated soot particles radiation. Another (bordering on CC volume) is made from optically homogeneous substance with extremely high transparence coefficient for the same wavelength range. Besides this layer shows high value emissivity in the middle and (or) long IR - ranges. Boundary conditions for heat-regenerating effect are analyzed under a cyclic heat transfer for optimum parities optical and thermal physical parameters of two-layer material. Distinctive feature of a suggested two-layer coating is local scattering and absorption on its set depth (in semitransparent layer) as stage of radiant energy accumulation. The following stage (heat-regenerating effect) is simulated by a certain thermal diffusivity coefficients of these two layers for acting of impedance coating. It has been theoretically evaluated that two-layer impedance materials (for low-heat-rejection diesel CC) based on combine transparent and semitransparent heat-insulating coatings can provide the essential decrease in temperature and its gradient on the internal surface CС during the ”hot” phase in comparison traditional opaque single-layered heat-insulating coating. Thus impedance materials application allows to control by diesel heat losses improving the efficiency of engine. This new class of impedance materials can be presented as the independent device of transformation of radiant energy for the various purposes and problems in a science and the engineering.
Poster presentation: Simulation and testing