A Study on the Sooting Tendency of Jet Fuel Surrogates Using the Threshold Soot Index

Open Access
- Author:
- Mensch, Amy
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Robert John Santoro, Thesis Advisor/Co-Advisor
Robert John Santoro, Thesis Advisor/Co-Advisor
Thomas Litzinger, Thesis Advisor/Co-Advisor - Keywords:
- surrogate
smoke point
TSI
JP-8 - Abstract:
- Currently, modeling the combustion of aviation turbine fuels is not feasible due to the complexity and variation of real fuels. Surrogates, created out of a few pure hydrocarbon compounds, are a key step toward modeling new engines and new fuels. For the surrogate to simulate the real fuel, the composition must be designed to reproduce certain pre-designated parameters. In the present research, instead of attempting to match distillation curves or estimates of the composition of the real fuel, three combustion related parameters including hydrogen to carbon (H/C) ratio, cetane number, and sooting tendency are to be reproduced. The objective of this thesis is to characterize the sooting tendency. The tendency of a fuel to produce soot in the combustor is relevant because it affects flame radiation as well as emissions. Parameters which characterize sooting tendency include hydrogen content, H/C ratio, smoke point, Threshold Soot Index (TSI), Yield Sooting Index (YSI), and others. In this work, TSI, which is derived from the smoke point measurement, is used. Previous data on TSI had been scaled inconsistently, and widely differing values for some compounds had been reported. In addition, the TSI for a key iso-alkane, iso-cetane, had not been measured. Therefore this work sought to provide a complete and consistent set of TSI values for surrogate components. Smoke point heights of sixteen compounds were measured according to ASTM D1322, and TSI values were derived from these measurements. The soot threshold and soot yield (YSI) data from prior studies were rescaled with a correlation to the TSI values from the current study. The magnitude of the correlation coefficient was used to determine whether the data set was used in the final average TSI values. Results showed that the differences in TSI values were significantly reduced by scaling all the data sets in this manner. Once individual TSI values are known, the resulting TSI when components are mixed together can be predicted. Previous researchers tested a mixture rule, which was shown to hold for the mixtures investigated. In this work, it was found that six additional binary mixtures and four multi-component mixtures follow the same mixture rule. A method of calculating the TSI of a single component from the mixture TSI was used to obtain a TSI value for iso-cetane, which could not otherwise be measured, and to verify the TSI value for 1-methylnaphthalene. Due to the complex molecular structures of aromatics, it is one of the hydrocarbon classes for which developing chemical kinetic models is difficult. Among the hydrocarbon families, aromatics also have the highest sooting tendencies, and their presence has the most effect on TSI. Due to inadequate development of some chemical kinetic models, certain aromatic compounds may need to be replaced with others for which models exist. The TSI values of three mixtures were tested to show that TSI can be replicated using different combinations of compounds for the aromatic fraction of the mixture. The methodology of designing surrogates based on TSI was applied to JP-8, the USAF jet fuel. The smoke point height of JP-8 was measured, and the TSI was obtained using an estimated molecular weight. A surrogate, created to match the JP-8 TSI, produced the same value within the estimated uncertainty. The formation of a set of TSI values for individual compounds and the verification of a mixture rule showed that TSI can be used as a sooting tendency parameter for designing surrogate composition.