Date of Award

Spring 2021

Document Type

Open Access Thesis

Department

Mechanical Engineering

First Advisor

Sang Hee Won

Abstract

As combined cycle gas turbines for power generation operating on light distillate fuels provide a sufficient energy, there is a global trend in using heavy liquids (e.g. HFO, crude oils) for direct-firing in gas turbine. However, using these heavy fuels imposes many challenges due to their wide range of physical/chemical properties, which control near-limit combustion behaviors, such lean blow-out and flashback. In addition, the ignition propensity of these heavy fuels is not reported in crude assays, and utilizing a simple, with small sample, and quick methodology to characterize the ignition propensity is important in determining the fuel quality.

In this work, the derived cetane number (DCN) of whole crudes and their distillation cuts are measured. Four crudes were distilled into four fractions as reported in crude assays: light naphtha, heavy naphtha, kerosene, and light gas oil. The DCN of each fraction was measured and compared using an ignition quality tester (IQT), where the DCN values for all the crude cuts increase from 23-35 for lighter fractions to 50-60 for heaver one. This variation of DCN values over their distillation curves was observed before (for distillate fuels, e.g. Petroleum-derived fuels) to be linked to strongly influence near limit combustion behaviors (e.g. LBO) through preferential vaporization, which suggests that preferential vaporization will play a significant role when using whole crudes in gas turbine applications. To further analyze such a behavior, 1H and 13C NMR spectra were acquired to characterize the chemical functional groups controlling the DCN and their distinctive influence. Based on a chemical functional groups approach, A QSPR regression model was developed indicating that the n-paraffinic CH2 group has the most influence in determining the global ignition propensity of crude oils. The analysis also suggests that chemical reactivity (DCN) of crude oils can be roughly estimated based on key-functional groups determined from 1H and 13C NMR analysis.

Finally, to investigate the impact of preferential vaporization on flame flashback, a spray burner was developed which has the ability to control the extent of fuel vaporization. Experiment was first conducted at burner temperature of 700 K with various n-alkanes and iso-alkanes, where two distinct flame flashback behaviors were observed, propagation and ignition-driven flashback. Two binary mixture were formulated that have identical chemical reactivity for fully vaporized fuel/air mixture but exhibit a drastic difference of ignition propensity under partially vaporized conditions. To observe the role of preferential vaporization effectively, the experiment was conducted at 450 K using those two mixtures. One of the Crude oils was used to investigate crude oil flashback behaviors in the spray burner.

Rights

© 2021, Ayuob Al wahaibi

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