556

Figure 16c. Product of soot volume fraction and characteristic depth of the soot layer calculated for the center of the head of a heavy duty diesel engine.

of the parameters. The absorption coefficient was varied from 10 m'^ (approaching fully transparent limit) to 10° m~l (approaching fully opaque limit). The scattering coefficient was varied over the same range of values, and the back-scattering coefficient was varied over the same range of values, and the back-scattering fraction from 0.05 to 0.5. The refractive index of the ceramic was varied from 1.2 to 2.6. Finally, the thickness of the ceramic layer was varied from 1.5 to 5 mm.

A baseline case was set up for this parametric study, and a number of parameters were perturbed around this baseline. The baseline thickness was 2.5 mm (about 0.1"). The absorption coefficient of the ceramic was set at 100 m"!, scattering coefficient of 233 m'l, back-scattering fraction at 0.5, substrate reflectivity at 0.15, and refraction index at 1.6. The thermal properties of the baseline ceramic were conductivity k = 0.80 W/mK and product of density times heat capacity pc = 2.9 J/m3K, i.e., values in the range quoted for plasma-sprayed partially stabilized zirconia.

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