Design and Development of an Apparatus to Study Aviation Jet Fuel Thermal Stability

100 Pages·2010·4.98 MB·English

by  Owen Wong

Design and Development of an Apparatus to Study Aviation
Jet Fuel Thermal Stability
by
Owen Wong
A thesis submitted in conformity with the requirements
for the degree of Master of Applied Science and Engineering
Graduate Department of Institute for Aerospace Studies
University of Toronto
Copyright (cid:13)c 2010 by Owen Wong
Abstract
Design and Development of an Apparatus to Study Aviation Jet Fuel Thermal Stability
Owen Wong
Master of Applied Science and Engineering
Graduate Department of Institute for Aerospace Studies
University of Toronto
2010
A single tube flow heat exchanger was designed and built to thermally stress Jet A-1
with air-saturated and deoxygenated levels of dissolved oxygen over a range of fuel tem-
peratures, pressures, and flow rates. Liquid samples of thermally degraded Jet A-1 were
analyzed using various physical and optical methods to determine which methods were
sensitive enough to measure compositional changes in thermally degraded liquid fuel and
to correlate these changes to the measured amount of deposits produced. Temperature
programmed oxidation (TPO) was shown to be successful in measuring deposit quantity
and structure, while UV-visible absorption and UV-visible fluorescence were sensitive
enough to quickly measure the relative population growth of large aromatic compounds
that lead to deposit formation in thermally stressed Jet A-1.
ii
Acknowledgements
¨
I am thankful for Dr. Omer L. Gu¨lder for giving me this opportunity to work on this
project and learn from him over the last three years. He patiently supported and guided
me through the good and difficult times during this project and I am grateful for that.
He taught me an important life lesson in his third year undergraduate combustion course
that has helped me always to strive to be better.
Thank you to Pratt & Whitney Canada for funding this project and giving me this
opportunity to transform this apparatus from a paper drawing to a functional machine.
Also, I am thankful for my fellow students and co-workers Frank, Gorngrit, Ivo, and
Mario for their help and guidance. I am especially grateful for all the times when Frank
patiently helped me with my project, especially at the beginning where he taught me
how everything in the lab worked.
Lastly, I am thankful for my family and friends for their continual love, patience, and
support throughout this three year journey.
iii
Contents
1 Introduction 1
1.1 Aviation Jet Fuel in High-Speed Aircrafts . . . . . . . . . . . . . . . . . 1
1.2 Motivation for Aviation Fuel Thermal Stability Research . . . . . . . . . 2
1.3 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Literature Review 5
2.1 Modern Aviation Fuels In North America . . . . . . . . . . . . . . . . . . 5
2.2 Thermal Degradation Temperature Regimes . . . . . . . . . . . . . . . . 7
2.3 Autoxidation Temperature Regime . . . . . . . . . . . . . . . . . . . . . 8
2.3.1 Effect of Dissolved Oxygen on Autoxidation . . . . . . . . . . . . 8
2.3.2 Jet Fuel Autoxidation Reaction Mechanisms . . . . . . . . . . . . 11
2.4 Transition Temperature Regime . . . . . . . . . . . . . . . . . . . . . . . 16
2.5 Pyrolytic Temperature Regime . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5.1 Jet Fuel Pyrolytic Reaction Mechanisms . . . . . . . . . . . . . . 18
2.5.2 Supercritical Jet Fuel . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.6 Effect of Pressure on Surface Deposition . . . . . . . . . . . . . . . . . . 21
2.7 Effect of Jet Fuel Chemical Composition on
Surface Deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.7.1 Deposit Formation . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.8 Surface Deposit Morphology . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.8.1 Surface Deposit Size and Composition . . . . . . . . . . . . . . . 29
2.8.2 Surface Deposit Structures . . . . . . . . . . . . . . . . . . . . . . 30
3 Experimental Apparatus and Analytical Techniques 32
3.1 Past Experimental Apparatuses . . . . . . . . . . . . . . . . . . . . . . . 32
3.2 Single Tube Heat Exchanger Apparatus . . . . . . . . . . . . . . . . . . . 34
iv
3.2.1 Gas Sparging Vessel . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2.2 Dissolved Oxygen Sensor . . . . . . . . . . . . . . . . . . . . . . . 39
3.2.3 Single Tube Heat Exchanger . . . . . . . . . . . . . . . . . . . . . 42
3.2.4 Fuel Cooling Coil . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.2.5 Operating Conditions and Procedure . . . . . . . . . . . . . . . . 49
3.3 Analytical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.3.1 Quantitative Measurement Techniques . . . . . . . . . . . . . . . 51
3.3.2 Qualitative Measurement Techniques . . . . . . . . . . . . . . . . 54
4 Results and Discussion 63
4.1 TPO Deposit Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.1.1 Total Amount of Carbon Deposits . . . . . . . . . . . . . . . . . . 63
4.1.2 Carbon Deposit Structures . . . . . . . . . . . . . . . . . . . . . . 65
4.2 UV-Visible Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
4.2.1 UV-Visible Absorption of Autoxidative Products . . . . . . . . . 69
4.3 UV-Visible Fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4.4 NMR Spectroscopy of Jet Fuel . . . . . . . . . . . . . . . . . . . . . . . . 70
4.5 Instrumental and Systematic Error . . . . . . . . . . . . . . . . . . . . . 75
5 Conclusion 79
5.1 Suggestions for Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 80
Bibliography 81
A Jet Fuel Composition and Properties 90
v
List of Tables
2.1 Dissolved oxygen concentration measurements for air-saturated fuel . . . 10
2.2 Oxidation temperatures of carbon deposit structures . . . . . . . . . . . 31
3.1 Fuel flow conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2 Refractive index measurements of thermally stressed jet fuel . . . . . . . 61
4.1 Calculated amounts of carbon deposit and deposition rates in 4 hour ex-
periments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
A.1 Physical and chemical properties of JP-8 . . . . . . . . . . . . . . . . . . 90
A.2 Jet A-1 fuel specifications . . . . . . . . . . . . . . . . . . . . . . . . . . 91
A.3 1H-NMR spectroscopy of thermally stressed jet fuel . . . . . . . . . . . . 92
vi
List of Figures
1.1 Autoxidation and pyrolytic temperature regimes . . . . . . . . . . . . . . 2
2.1 Deposition trend within the three temperature regimes . . . . . . . . . . 8
2.2 JP-8 axial deposition quantity along a heated tube . . . . . . . . . . . . 9
2.3 Deposition rate as a function of dissolved oxygen concentration . . . . . . 10
2.4 Taylor’s two-step autoxidation mechanism for deposit formation . . . . . 12
2.5 Six-step basic autoxidation mechanism . . . . . . . . . . . . . . . . . . . 13
2.6 Simplified SMORS mechanism for autoxidation deposit formation . . . . 15
2.7 Deposition pathways from insoluble particle to surface deposit . . . . . . 17
2.8 Amount of surface deposit at various pressures within both autoxidation
and pyrolytic regimes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1 Photograph of experimental setup . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Detailed layout of dynamic flow setup . . . . . . . . . . . . . . . . . . . . 36
3.3 Detailed layout of carbon burn-off setup . . . . . . . . . . . . . . . . . . 37
3.4 Oxygen-diffusive membrane . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.5 Detailed layout of the nitrogen sparging system . . . . . . . . . . . . . . 40
3.6 Dissolved oxygen concentration during nitrogen sparging . . . . . . . . . 41
3.7 Effect of volumetric flow rate on surface deposit . . . . . . . . . . . . . . 45
3.8 Temperature differences between tube wetted wall and fuel in PSU’s flow
reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.9 Temperatureprofilesofthefuelatfurnaceoutlet,tubesurface,andfurnace
heaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.10 Design drawing of cooling coil . . . . . . . . . . . . . . . . . . . . . . . . 49
3.11 Variation in TPO deposit profiles . . . . . . . . . . . . . . . . . . . . . . 53
3.12 UV-visible fluorescence Jablonski diagram . . . . . . . . . . . . . . . . . 57
3.13 Fluorescence emission wavelengths of some aromatic hydrocarbons . . . . 58
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4.1 Calculated amounts of carbon deposit in 4 hour experiments . . . . . . . 64
4.2 TPO carbon dioxide profiles . . . . . . . . . . . . . . . . . . . . . . . . . 67
4.3 UV-visible absorption spectra of unstressed Jet A-1 . . . . . . . . . . . . 68
4.4 Additional UV-visible absorption at higher fuel temperatures and flow rates 68
4.5 Excess absorption caused by autoxidation products. . . . . . . . . . . . . 70
4.6 Excess UV-visible absorption caused by autoxidation products. . . . . . . 71
4.7 SchematicofUV-visibleexcitationandemissionwavelengthsforPAHcom-
pounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
4.8 UV-visible 3-D EEMF spectra of unstressed Jet A-1 . . . . . . . . . . . . 72
4.9 UV-visible EEMF spectra contour plots of thermally stressed Jet A-1. . . 73
4.9 UV-visible EEMF spectra contour plots of thermally stressed Jet A-1. . . 74
4.10 1H-NMR spectra of Jet A-1 thermally stressed to 400 ◦C . . . . . . . . . 76
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Chapter 1
Introduction
1.1 Aviation Jet Fuel in High-Speed Aircrafts
Thermal heat management of aircraft jet engines is important since new engines are
designed to be more powerful, fuel efficient, and environmentally friendly [1,2]. Modern
engines operate at higher temperatures for increased efficiency, and therefore generate
more waste heat that needs to be removed. The past few decades have shown an ex-
ponential increase in the cooling requirements of aircrafts and this trend is expected to
continue [3]. The three most common methods to cool an engine and dissipate heat
are to use a mechanical cooling unit, forced air cooling, or jet fuel as a liquid coolant.
Mechanical cooling units are undesirable because of their large size and weight, which
are two aspects that cost a premium in an aircraft [2,4]. Forced air cooling is difficult
at higher air speeds because the ram inlet air temperature increases and does not pro-
vide sufficient cooling. Thus, the best option is to use circulating fuel as a heat sink for
high-speed flight.
Fuel cooling is further categorized as either direct or indirect [2]. Direct cooling has
the fuel-cooled heat exchanger in direct contact with the hot component. In contrast,
indirect cooling uses the fuel to cool a stream of air, and then the air cools the hot
component. Indirect cooling is the preferred choice because it allows a greater increase of
an engine’s pressure ratio, which consequentially increases the engine’s thrust-to-weight
ratio and thermal efficiency.
1
Chapter 1. Introduction 2
1.2 Motivation for Aviation Fuel Thermal Stability
Research
The problem with using jet fuel as a coolant is that the fuel begins to break down
and change its chemical structure above 150 ◦C by a process called autoxidation, which
involves fuel, oxygen, and free radical chain mechanisms in oxidation reactions (Figure
1.1) [5, p.7-8][6, p.72][7, p.1]. As the temperature is increased, the fuel continues to
change and solid particles can precipitate out of the liquid fuel. The temperature range
between 150 ◦C to 350 ◦C is called the autoxidation regime [8,9]. The transition regime
exists between 350 ◦C and 400 ◦C. Above 400 ◦C is the pyrolytic regime, where fuel
pyrolysis occurs and the fuel degradation process is called thermal decomposition. Ther-
mal stability research encompasses all the chemical and physical changes of the fuel and
deposit formation within all three temperature regimes. Currently, the United States
Air Force (USAF) has set a maximum fuel temperature of 163 ◦C (325 ◦F) at the inlet
to the fuel nozzles and a 205 ◦C (400 ◦F) maximum wetted wall temperature to prevent
fuel degradation [10–12]. Research has been attempting to push this limit up to 480 ◦C
to handle the expected increase in heat produced by the engines.
Figure 1.1: Autoxidation and pyrolytic temperature regimes with schematic representations of the de-
position rates as functions of temperature within each regime [5, p.8].
The particles that form within the fuel affect the performance of a jet engine as well
as other aircraft systems where the fuel is used as a coolant, such as the hydraulics, gear