Combustion Characteristics of Silicon Carbide Porous Ceramics Based on Hexahedral Cell Structure

To solve the problems that the porosity is difficult to accurately control and the pore structure uniformity is insufficient in the traditional process of replicating polyurethane foam with ceramic slurry, a biclinic body design method based on regular hexahedron cell structure was introduced to prepare porous ceramic parts for high-performance porous media burner. The influence of parameters (i.e., cell edge length, pore rib diameter and array layer number) on the strength and combustion characteristics of porous ceramic materials was investigated.

The model was firstly designed by a software named ANSYS Spaceclaim modeling, and then the samples were prepared by 3D printing. The compressive strength of porous ceramic structures was tested by a model TSE104B universal material testing machine at a loading rate of 0.5 mm/min. A circular loading plate with a diameter of 100 mm was used to apply pressure to the samples, and the maximum compressive strength σ_s of each sample was calculated by recording the failure load. Combustion performance testing was conducted in a porous media combustion platform, and the composition and temperature of the flue gas were monitored by a model testo 350 flue gas analyzer. The temperature changes were recorded by an infrared thermal imager.

The stress distribution and internal combustion mechanism of the porous ceramic under uniaxial compression were analyzed by numerical simulation methods. Among them, ANSYS Static Structural module was used for stress distribution analysis, and ANSYS Fluent module was used for finite element analysis of the flow field of porous media, thus evaluating the effect of porosity on gas disturbance, heat transfer behavior, fluid pressure drop, and heat exchange efficiency.

In a high porosity range (i.e., ε≥90%), extending the residence time of premixed gas and enhancing turbulence effects can effectively promote gas mixing and combustion, thereby improving the overall combustion performance. Moderately reducing porosity (i.e., from 93% to 86%) improves the compressive strength of the material (approximately 100%) although this leads to a decrease in the maximum surface temperature (about 18.4 ℃) and an increase in CO emissions (about 8.75 mg/m³). This indicates that a moderate reduction in porosity sacrifices combustion efficiency at a high porosity can enhance the strength. In contrast, the structure in a low porosity range (ε<90%) restricts the free flow of gas flow, resulting in uneven velocity distribution and reduced turbulence, hindering effective gas mixing and combustion, thereby reducing combustion efficiency. This indicates that it is difficult to simultaneously improve combustion efficiency and strength at a low porosity. It is thus possible to balance combustion efficiency and strength via finely adjusting the porosity in the high porosity range (i.e., ε≥90%), achieving a synergistic effect.

The strength of SiC porous ceramic structures could be effectively improved via reducing the cell edge length a, increasing the number of layers n, and pore reinforcement diameter d. The pore reinforcement diameter d had a more significant impact on the strength of SiC porous ceramic structures. There was a certain enhancement effect on the maximum surface temperature of SiC porous ceramic structure via increasing a and decreasing n and d. At a high porosity, a and n had a more significant impact on the maximum surface temperature of SiC porous ceramic structure. At a low porosity, d had a more significant impact on CO emissions from SiC porous ceramic structures.