Experimental and Computational Studies of Combustion and Instantaneous Heat Transfer in a Ceramic Diesel Engine

Simescu, S. Experimental and Computational Studies of Combustion and Instantaneous Heat Transfer in a Ceramic Diesel Engine. University of Wisconsin-Madison, 1997.

This dissertation is an experimental and computational study of the effects of high surface temperatures on instantaneous heat transfer and combustion.

An Isuzu monolithic ceramic diesel engine was used for the experiments. Head surface temperatures up to 560$\sp\circ$C and equivalence ratios up to 0.73 were obtained without exceeding peak pressure limits by using a combination of homogeneous charge compression ignition and diesel combustion. Heat transfer data were obtained from measured instantaneous temperatures on the engine head. Platinum film resistance temperature detectors were developed for the specific geometry, ceramic material and temperature range of this engine. Heat release was obtained using measured cylinder pressure data. A correction algorithm was developed using experimental and theoretical methods to remove pressure oscillations induced by the recessed position of the pressure transducer. The heat release showed no deterioration in combustion characteristics although small changes in end-of-combustion could not be determined from heat release data.

Time-averaged surface temperatures and temperature swings showed a linear dependence on the fueling rate. Peak and time-averaged positive heat flux increased with fueling rate and showed no unusual effects at high wall temperatures. The heat flux time-averaged over the cycle started to level off with fueling rate due to increased heat flux to the intake air. For similar combustion events, increased surface temperatures had no adverse effects on the local instantaneous heat flux. However, the injection characteristics deteriorated at higher temperatures and limited the ability to obtain steady-state running for higher equivalence ratios.

The effects of surface temperature on intake flow and combustion were investigated computationally in a hypothetical Caterpillar ceramic engine, using the computational fluid dynamics code KIVA. Elevated wall temperatures showed little effect on large scale and turbulent energy levels before the start of injection. Diesel combustion and fuel-air mixing appeared to be dominated by the fuel spray. With increased boost pressures and non-deteriorated injection, combustion did not deteriorate, with no indication of lack of mixing. Combustion duration and soot emissions decreased, but peak cylinder pressure and NO$\sb{\rm x}$ emissions increased.