Conclusions Of Translucence Study

1. Translucence was found to have a significant detrimental effect on the heat barrier effectiveness under realistic diesel engine conditions. It allows the radiation heat flux to pass through the ceramic and be directly deposited on the substrate. This increases the convective heat transfer and thus the total heat flux, which can increase by 50% and more over the opaque case.

2. The effects of translucence depend strongly on the material absorption and scattering coefficients. Significant effects begin to be felt for absorption coefficients smaller than 10,000 m"-*-, and scattering coefficients smaller than 20,000 m"l. Above these values the ceramic is almost opaque from the point of view of the total heat flux. The above values are well within the range of expected properties of engineering ceramics.

3. Significant translucence effects were found to occur within the range of radiative properties considered possible for engineering ceramics. This means that translucence is an effect that cannot be ignored in consideration of ceramic materials especially for ceramics that have very low conductivity. Thus, the radiative properties of proposed ceramic materials should be among the properties that are measured and reported.

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