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1.2 Aviation Fuel Autoxidation Behaviour of Hydrocarbons in the Context of Conventional and Alternative Aviation Fuels Detlev Conrad Mielczarek Submitted in accordance with the requirements for the degree of Doctor of Philosophy. The University of Leeds, The School of Chemical and Process Engineering July 2015 The candidate confirms that the work submitted is his own, except where work which has formed part of jointly authored publications has been included. The contribution of the candidate and the other authors to this work has been explicitly indicated below. The candidate confirms that appropriate credit has been given within the thesis where reference has been made to the work of others. Some of the work in Chapter 5 was presented at IASH 2013. D. C. Mielczarek, S. Blakey, K. J. Hughes, D. B. Ingham, M. Pourkashanian, C. W. Wilson, Experimental and Theoretical Investigation of Pathways to Deposit Formation in THermally Stressed Aviation Fuel in the Presence of Nitrogenous Additives, the 13th International Conference on Stability, Handling and Use of Liquid Fuels, Rhodes, Greece, 2013. The work presented in the presentation and included in the thesis is attributable to the author of this thesis. The co-authors provided experimental data and observations that formed the basis for the work as well as contributed to the discussion of the work carried out. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. The right of Detlev Conrad Mielczarek to be identified as Author of this work has been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. ©2015 The University of Leeds and Detlev Conrad Mielczarek. Acknowledgements My thanks go to Dr. Kevin Hughes whose patience as well as help and support in chemistry were invaluable for the completion of this PhD. This PhD would not have been possible without the help from the University of Sheffield and the Low Carbon Combustion Centre. My thanks go to Dr. Simon Blakey whose help was invaluable in obtaining experimental data as well as Dr. Ehsan Alborzi who offered valuable suggestions and the opportunity for interesting discussions and further collaboration. Work for this PhD also depended on the support team at the LCCC. My thanks also go to Simon Thorpe at the University of Sheffield for introducing me to a gas chromatograph and making his analytical lab available to me. Further thanks belong Professor Pourkashanian and Professor Ingham who arranged the position and funding at the University of Leeds for my PhD. Abstract This PhD aspired to a develop greater insight into the fundamentals of hydrocarbon autoxidation processes in the context of thermal stability of aviation fuels. A number of approaches to develop a better understanding of the observed processes have been considered. This covers establishing the suitability of an automated reaction mecha- nism generator to develop autoxidation reaction mechanism as well as manipulating the resultant schemes, for example by lumping species and their associated reactions as well as reaction rate based mechanism reduction. Further a number of postulated interactions between contaminants in fuel and oxidised products in thermally stressed hydrocarbons employing ab initio quantum chemistry methods were examined. Finally a set of systematic experiments was carried out to obtain quantitative data of the effect of a number of additives on the stability of thermally stressed hydrocarbons. These tests employed a small scale test device, the PetroOxy which provides reliable and repro- ducible experimental data under well defined test conditions. The PetroOxy enabled the collection of samples of the deposition products on metal foils for further analysis under a scanning electron microscope with x-ray dispersive spectroscopy for elemental analysis. This provided both the morphology as well as the elemental distribution of the deposits formed on the foils, offering a first hand look at the differences between deposits formed from different additives. This thesis shows that automated mechanism generation is a suitable method when de- scribing the initial steps of autoxidation processes without any additives. It further shows that the PetroOxy is a very useful tool for obtaining systematic, reliable, experimental data for further analysis. Contents Abstract vi Table of Contents xi List of Figures xvii List of Tables xxi Nomenclature xxviii 1 Introduction 1 1.1 Energy - A Historic Perspective . .1 1.2 Aviation Fuel . .2 1.3 Objective of this Thesis . .4 1.4 Outline of this Thesis . .6 1.4.1 Chapter 1 . .6 1.4.2 Chapter 2 . .6 1.4.3 Chapter 3 . .6 1.4.4 Chapter 4 . .6 1.4.5 Chapter 5 . .6 1.4.6 Chapter 6 . .7 1.4.7 Chapter 7 . .7 2 Background and Literature Review 9 2.1 Background Details on Aviation Fuel . .9 2.1.1 Aviation Fuel Properties and Requirements . .9 2.1.2 Synthetic Fuels - Fischer Tropsch Fuels . 12 2.2 Development of Stability and Deposition Research . 13 2.2.1 Deposit Modelling Methodology . 13 2.2.2 Theoretical Approaches to Stability . 20 2.2.2.1 Pseudo-Detailed Reaction Schemes . 21 2.2.2.2 Reduced Detailed Reaction Schemes . 23 vii viii CONTENTS 2.2.2.3 Combined Pseudo-Detailed as well as Detailed Reaction Schemes . 23 2.2.2.4 Surrogate Models . 24 2.2.3 Experimental Investigations into Thermal Stability . 27 2.3 Additives . 31 2.4 Stability Limits . 35 2.5 Thermal Stability Conclusion . 35 3 Software Tools and Theory 39 3.1 Chemical Kinetics . 39 3.1.1 Description of Chemical Kinetics . 39 3.1.2 Stoichiometric Equations . 39 3.1.3 Elementary Reactions and Reaction Rates . 40 3.1.3.1 Elementary Reactions . 40 3.1.3.2 Reaction Rates . 40 3.1.4 Arrhenius Equation . 41 3.1.5 Thermodynamics . 42 3.1.6 Ideal Gas Law . 43 3.2 Employing and Handling Kinetics . 44 3.2.1 Background for Employing Time Dependent Chemical Kinetics . 44 3.2.1.1 Basic Introduction to Differencing Schemes . 44 3.2.1.2 Translating Chemical Reactions to Differential Equations 46 3.2.2 Existing Software for Time Dependent Chemical Kinetics . 47 3.2.2.1 Chemkin . 47 3.2.2.2 SPRINT . 51 3.2.3 A New Chemical Kinetics Solver . 54 3.2.3.1 Basic Use . 55 3.2.3.2 Mechanism Reduction . 55 3.2.3.3 PetroOxy Pressure Drop . 62 3.2.3.4 Creating an Analytical Jacobian . 66 3.3 RMG Usage and Findings . 67 3.3.1 Initial Settings . 67 3.3.1.1 Temperature and Pressure . 69 3.3.1.2 Liquid Phase Kinetics in RMG . 69 3.3.1.3 Reactants and Concentrations . 70 3.3.1.4 Error Tolerance, Pruning - Controlling Mechanism Size 71 3.3.1.5 Termination Criteria - Species Conversion or Reaction Time . 72 3.3.1.6 Databases . 73 3.3.2 Influencing Models - Observations . 74 3.3.2.1 Effects of the Error Tolerance . 74 CONTENTS ix 3.3.2.2 Effects of the RMG Database . 74 3.3.3 Computational Requirements . 75 3.3.4 Potential Difficulties . 75 3.4 Computational Chemistry . 76 3.4.1 Choosing Appropriate Methods . 76 3.4.1.1 Basis Sets . 77 3.4.1.2 Computational Method - Level of Theory . 77 3.4.2 Geometry - Creating Structures . 77 3.4.3 Searching For Transition States . 78 3.4.3.1 Finding Transition State - QST2 . 78 3.4.3.2 Finding Transition State - QST3 . 78 3.4.3.3 Finding Transition State - Opt=TS . 79 3.4.3.4 Verifying The Transition State . 79 3.4.3.5 Solvation . 79 4 Reaction Mechanism Generation 81 4.1 Initial Evaluation of RMG Models . 81 4.1.1 Criteria for RMG Evaluation . 81 4.1.2 Heptane Autoignition Delay Times . 81 4.1.2.1 Comparison of Product Species after Combustion . 83 4.1.3 Initial Conclusion on the Validity of RMG Models . 85 4.2 Developing a Good RMG Scheme . 85 4.2.1 RMG Sensitivity . 85 4.2.1.1 Termination Criteria - Reaction Time . 86 4.2.1.2 Single Reaction Temperature . 88 4.2.1.3 Single or Multiple Temperatures . 89 4.2.1.4 Solvation - Solvent Type and Viscosity . 89 4.2.2 Chosen Models to Describe Autoxidation Behaviour with RMG . 95 4.3 Mechanism Reduction . 99 4.4 Modelling the PetroOxy with RMG . 102 4.5 Antioxidant Speculation . 106 4.6 Closer Scheme Inspection . 109 4.6.1 Difference Between Iso and Normal Paraffinic Scheme . 109 4.6.2 Hydroperoxide Decomposition Speculation . 110 4.7 RMG Conclusions . 115 5 Deposits and Precursors in the HiReTS 119 5.1 The HiReTS . 120 5.1.1 Specifications . 120 5.1.2 Test Methodology . 121 5.1.3 Known Issues . 123 x CONTENTS 5.2 Precursor Concentration and Deposit Formation in HiReTS . 124 5.3 Application - Electrophilic Aromatic Substitution . 125 5.4 Amine Alkene Reaction . 130 5.5 Surface Effects . 130 5.6 Deposition Process - Initial Conclusion . 133 5.7 HiReTS Experimental Work . 134 5.8 HiReTS Conclusion . 134 6 Assessing Thermal Stability with the PetroOxy 137 6.1 The PetroOxy - A Look at the Device . 137 6.2 Experimental Methodology . 137 6.2.1 Sample Preparation . 137 6.2.2 PetroOxy Usage . 138 6.3 Test Series . 139 6.4 Experimental Results and Observations . 141 6.4.1 Repeatability of the PetroOxy . 141 6.4.2 Neat Fuels . 142 6.4.3 Addition of Amines . 142 6.4.4 Addition of Aromatic Species . 146 6.4.5 Addition of Aromatic Species and Butylamine . ..
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