High-Output Diesel Engine Heat Transfer

Gingrich, E. M. High-Output Diesel Engine Heat Transfer. University of Wisconsin-Madison, 2020.

High-output diesel engine heat transfer was investigated using a single-cylinder research engine. Engine operating conditions near 30 bar IMEPg and 250 bar in-cylinder pressure were tested. This study had three primary goals. The first was to compare local piston heat transfer, based on fast-response piston surface temperature data, to global engine heat transfer based on thermodynamic data. A wireless telemetry system was used to acquire fast-response piston surface temperature data, from which heat flux was calculated. The local measurements were then spatially averaged to find total heat transfer, which agreedrelatively well with the global measurements.

In the second part of this research, thermal barrier coatings of various thickness and surfaceroughness were applied to the piston crown. Three coated pistons were tested. Coatings withhigher roughness did not show any statistically significant improvement to engine performancewhen compared to the metal baseline piston, and produced higher filter smoke numbers. The lower roughness coated piston showed an increase of gross indicated thermal efficiency of up to 3.5 % (relative) compared to the metal baseline piston for some operating conditions. The increase in efficiency was found to correlate with additional late-cycle apparent heat release rate and a reduction in in-cylinder heat transfer.

In the third part of this research, a new instantaneous spatially averaged heat transfer correlation was developed using the local heat flux data. Previous correlations are based onthe correlation of Nusselt and Reynolds numbers. The new correlation included an additional term, dimensionless chemical energy release rate. The new term was derived from dimensional analysis, which should enable similitude for diesel engines. A new interpretation of the characteristic velocity, as found in the Reynolds number, was developed and included the integrated fuel mass injection rate. The existing and new correlations were calibrated to the experimental data by minimizing the least squares error. On average, the new formulation was found to match the experimental data better than the existing models.