Thermal mode optimization of combustion chamber walls for power-plants using semitransparent porous ceramics

Abstract

The paper examines control and management by thermal mode of the internal surface of heat-insulated combustion chamber walls for green & ecient diesel and gas turbine engines due to the application of opaque or semitransparent thermal barrier materials (coatings). The authors' model is devoted to combined radiant heat transfer both inside the heat-insulated combustion chamber and its ceramics walls, which could be scattering and absorbing for penetrating radiant component in the subsurface volume of optically heterogeneous porous material. The influence of thermal conduction, scattering (absorption) and external convective effects on the increase of the internal overheating zone in subsurface layers is simulated under intensive radiation. The unique set of optical, thermal-physical and mechanical properties of structural ceramics, depending on their porosity, were first proposed. The radiation fields of the absorbed energy in the near IR region and the corresponding temperature distributions in the modeled opaque and semitransparent ceramics walls were calculated under a stationary radiant-convective heat load during the active combustion phase at time intervals 0.01... 0.1 s (diesel engines) and 10...100 s (turbine ones). In order to control the emission of nitrogen oxides, the authors propose a generation model of NOx, its growth or reduction caused by the management of radiant overheating inside semitransparent heat-insulation in which surface temperature is due to volumetric radiant absorption. It is shown that for semitransparent materials (coatings), the optimal thermal mode is determined first of all by thermal radiant characteristics in near IR at heating small times and it begins to correct at long ones due to the effect of thermal conductivity. This process may be modeled and regulated by the selected microstructural porosity of ceramic heat insulation.