Date of Award

2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Lawrence L. Tavlarides

Second Advisor

Radhakrishna Sureshkumar

Third Advisor

Rebecca Bader

Keywords

Clean fuel technology, Diesel fuel surrogates, Supercritical fluids, Thermalphysical properties, Thermal stability

Subject Categories

Biomedical Engineering and Bioengineering

Abstract

The clean diesel combustion technology using supercritical fluids is aimed to both improve fuel economy and reduce harmful emissions. This novel process involves preparation, injection and combustion of supercritical fuel/diluents mixtures. Design and development of this new process require a deep understanding of fuel properties. The current study has attempted to address three fuel property related issues: fuel surrogates, diffusivity and thermal stability.

Fuel surrogates are often used in engine research to mimic real fuel properties. In this work, ten diesel fuel surrogates were investigated, and the ability of these surrogates to predict diesel fuel properties was evaluated. It was found that none of them were able to predict all properties of interest including volatility, critical points, density, viscosity, heat capacity, and thermal conductivity. Different surrogates are suggested for predictions of different properties.

Diffusion coefficients of diesel fuel and surrogate compounds in SCCO2 were determined using the Taylor dispersion method at temperatures and pressures up to 373.15 K and 30 MPa, respectively. Results were correlated by Wilke-Chang, Scheibel, He-Yu, and correlations. It was found that the He-Yu correlation had the best prediction capability, while the correlation gave overall best fit for experimental data with AAD% < 8%. Experimental uncertainties caused by sample injection, detector linearity, mobile phase mean velocity, and column orientation were extensively discussed. A dimensionless parameter φ was proposed to characterize the effect of the injection volume, and a new D12-U pattern diagram was generalized based on current results to describe the impact of mobile phase mean velocity on diffusivity measurements.

The effects of temperature, residence time and CO2 on thermal stability of diesel fuel at high temperatures were investigated by both batch and continuous thermal stressing experiments. Results showed that thermal stability of diesel fuel decreased as temperature and residence time increased. 400-420 °C was found to be the optimal temperature range where supercritical fuel delivery and combustion could work. The presence of 10 wt% CO2 reduced accumulation of solid deposits due to enhanced solvent capacity. However, CO2 was not likely to have the ability to chemically prevent fuel coking. Solid deposits of different sizes, morphologies and structures were observed at 300 - 440 °C, which implies different deposit formation mechanisms.

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Open Access

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