Design and Development of an Experimental Apparatus to Study Jet Fuel Coking in Small Gas ...

87 Pages·2013·6.06 MB·English

Design and Development of an Experimental Apparatus to
Study Jet Fuel Coking in Small Gas Turbine Fuel Nozzles
by
Jason Jian Liang
A thesis submitted in conformity with the requirements
for the degree of Master of Applied Science
Graduate Department of Aerospace Science and Engineering
University of Toronto
©
Copyright 2013 by Jason Jian Liang
Abstract
Design and Development of an Experimental Apparatus to Study Jet Fuel Coking in
Small Gas Turbine Fuel Nozzles
Jason Jian Liang
Master of Applied Science
Graduate Department of Aerospace Science and Engineering
University of Toronto
2013
An experimental apparatus was designed and built to study the thermal autoxidative
carbon deposition, or coking, in the fuel injection nozzles of small gas turbine engines.
The apparatus is a simplified representation of an aircraft fuel system, consisting of a
preheating section and a test section, which is a passage that simulates the geometry,
temperatures, pressures and flow rates seen by the fuel injection nozzles. Preliminary
experiments were performed to verify the functionality of the apparatus. Pressure drop
across the test section was measured throughout the experiments to monitor deposit
buildup, and an effective reduction in test section diameter due to deposit blockage was
calculated. The preliminary experiments showed that the pressure drop increased more
significantly for higher test section temperatures, and that pressure drop measurement
is an effective method of monitoring and quantifying deposit buildup.
ii
Acknowledgements
Setting up a test rig comes with a steep learning curve, as I have come to realize. How-
ever, I am thankful that many people where there to help make it easier. First, many
¨
thanks to Dr. Omer Gu¨lder, for providing me with valuable guidance and advice, and for
entrusting me with major project decisions; to Pratt & Whitney Canada, for providing
funding and feedback for the project.
I want to give thanks to Ivo Fabris, who patiently taught me to operate the equipment
and answered my many questions; to Owen Wong, who put together the previous test
rig, without which my task would have been much more difficult.
I am thankful for Frank Yuen, whose expertise and assistance in troubleshooting, equip-
ment purchasing and safety were most valuable; for John Liu, who provided important
numerical simulation data and covered my lunch breaks during the long test runs; for
Leon Li and the Flow Control and Experimental Turbulence lab at UTIAS, for loaning
me testing equipment and helping me to set up data acquisition.
Lastly, to my parents, and Jessie, who kept me going through rain and shine, I am always
grateful.
iii
Contents
1 Introduction 1
1.1 Jet Fuel and Aircraft Thermal Management . . . . . . . . . . . . . . . . 1
1.2 Jet Fuel Thermal Stability . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Project Definition 4
2.1 Fuel Injector Coking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 General Experimental Approach . . . . . . . . . . . . . . . . . . . . . . . 5
3 Background and Literature Review 10
3.1 Thermal Stability of Jet Fuels . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Mechanics and Chemistry of Thermal Stability . . . . . . . . . . . . . . . 11
3.2.1 Autoxidation Mechanism . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.2 Pyrolysis Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3 Factors that Affect Thermal Stability . . . . . . . . . . . . . . . . . . . . 12
3.3.1 Dissolved Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.2 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.3.3 Flow Rate and Residence Time . . . . . . . . . . . . . . . . . . . 14
3.4 Past Experimental Studies and Apparatuses . . . . . . . . . . . . . . . . 14
3.4.1 Dynamic Flow Tests . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.4.2 Fuel Injector Studies . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.5 Analytical Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
iv
3.5.1 Temperature Programmed Oxidation . . . . . . . . . . . . . . . . 16
3.5.2 Pressure Drop Measurement . . . . . . . . . . . . . . . . . . . . 17
3.5.3 Spectroscopic Techniques for Chemical Analysis . . . . . . . . . . 19
3.6 Jet Fuel Thermal Stability Research at UTIAS . . . . . . . . . . . . . . 20
4 Experimental Apparatus 22
4.1 Overview of the Experimental Apparatus . . . . . . . . . . . . . . . . . 23
4.2 Fuel Pump and Back Pressure Regulator . . . . . . . . . . . . . . . . . . 27
4.2.1 Syringe Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.2 Back Pressure Regulator . . . . . . . . . . . . . . . . . . . . . . . 27
4.3 Fuel Preheater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.3.1 Oil Bath for Preheating . . . . . . . . . . . . . . . . . . . . . . . 29
4.3.2 Silicone Bath Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.4 Test Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.4.1 Test Section Design Drivers . . . . . . . . . . . . . . . . . . . . . 31
4.4.2 Test Section Designs . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.5 Test Section Heater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.5.1 Brass Heating Block . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.5.2 Band Heater and Temperature Controller . . . . . . . . . . . . . 37
4.6 Pressure Drop Measurements . . . . . . . . . . . . . . . . . . . . . . . . 37
4.7 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.8 Other Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5 Experimental Methodology and Procedures 44
5.1 Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2 Numerical Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.3 Description of Experimental Procedures . . . . . . . . . . . . . . . . . . 46
5.3.1 Preparation and Set Up . . . . . . . . . . . . . . . . . . . . . . . 46
v
5.3.2 Run Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.3 Heat-Up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.3.4 Steady State Operation . . . . . . . . . . . . . . . . . . . . . . . . 49
5.3.5 Shutdown and Purging . . . . . . . . . . . . . . . . . . . . . . . . 51
5.3.6 Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
6 Results and Discussion 54
6.1 Fuel Batch and Jet Fuel Thermal Oxidation Tester (JFTOT) Results . . 54
6.2 Apparatus Verification Experiment Conditions . . . . . . . . . . . . . . . 55
6.3 Pressure Drop Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.3.1 Test Section Temperature Measurement and Profiles . . . . . . . 62
6.4 Pressure Drop Dependence on Temperature . . . . . . . . . . . . . . . . 62
6.4.1 Viscosity as a Function of Temperature . . . . . . . . . . . . . . . 62
6.4.2 Handbook Viscosity Data . . . . . . . . . . . . . . . . . . . . . . 64
6.4.3 Semi-Empirical Approximation . . . . . . . . . . . . . . . . . . . 64
6.4.4 Effect on Pressure Drop Measurements . . . . . . . . . . . . . . . 65
6.5 Sources of Experimental Error . . . . . . . . . . . . . . . . . . . . . . . . 68
7 Conclusion 71
7.1 Recommendations and Future Work . . . . . . . . . . . . . . . . . . . . . 72
Bibliography 74
vi
List of Tables
2.1 Commercial aircraft fuel environment . . . . . . . . . . . . . . . . . . . . 7
3.1 Overview of paraffin autoxidation mechanism . . . . . . . . . . . . . . . 11
4.1 Commercial stainless steel tubing sizes . . . . . . . . . . . . . . . . . . . 33
5.1 Revised Pratt & Whitney Canada test matrix for fuel temperature tests . 45
5.2 Revised Pratt & Whitney Canada test matrix for wetted wall temperature
tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.3 Oil bath temperature settings for various test section inlet temperatures . 49
6.1 Measured steady state T and T . . . . . . . . . . . . . . . . . . . . . 63
in out
6.2 Comparison of pressure drop measurement against literature . . . . . . . 69
vii
List of Figures
3.1 Temperature regimes of jet fuel deposit formation . . . . . . . . . . . . . 13
3.2 Schematic of UTIAS single tube flow test apparatus . . . . . . . . . . . . 21
4.1 Photograph of the experimental apparatus . . . . . . . . . . . . . . . . . 24
4.2 Experimental apparatus overview . . . . . . . . . . . . . . . . . . . . . . 25
4.3 Insulation for non-heated components . . . . . . . . . . . . . . . . . . . . 25
4.4 Nitrogen purging schematic diagram . . . . . . . . . . . . . . . . . . . . 26
4.5 Memmert ONE 45 oil bath . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.6 EDM test section example (0.009 in.) . . . . . . . . . . . . . . . . . . . . 33
4.7 Brass block with thermocouple probes . . . . . . . . . . . . . . . . . . . 38
4.8 Thermocouple contact mechanism in brass heater block . . . . . . . . . . 39
4.9 Test section heater wiring diagram . . . . . . . . . . . . . . . . . . . . . 40
4.10 Placement of pressure taps for pressure drop measurement . . . . . . . . 41
4.11 Overpressure protection valve . . . . . . . . . . . . . . . . . . . . . . . . 41
5.1 Temperature-time profile of steady state operation . . . . . . . . . . . . . 50
6.1 Pressure drop data for Run 2 . . . . . . . . . . . . . . . . . . . . . . . . 60
6.2 Pressure drop data for Run 3 . . . . . . . . . . . . . . . . . . . . . . . . 61
6.3 Axial temperature profiles . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.4 Viscosity-temperature curve comparison . . . . . . . . . . . . . . . . . . 66
6.5 Geometry for calculating pressure drop . . . . . . . . . . . . . . . . . . . 67
viii
Chapter 1
Introduction
1.1 Jet Fuel and Aircraft Thermal Management
Jet fuel is the source of power for many types of aircraft, from small turboprops to
heavy jet aircraft. Jet fuel is a middle-distillate product of the crude oil refinery process.
The most common commercial jet fuel in North America are Jet A and Jet A-1, which
are kerosene-type jet fuels. JP-8 is the primary fuel of the U.S. Air Force [1], and it is
essentially Jet A with additives added to improve lubricity, and thermal stability. These
fuels are composed of many different types of compounds, but primarily of hydrocarbons
with carbon numbers from C to C [1], with the most prevalent being C [2]. Other
8 16 11
compounds, such as dissolved oxygen, metals, sulfur are present in the fuel in minute
amounts, but play a significant role in the thermal stability of the fuel.
In addition to powering the aircraft, one very important function of jet fuel is its
ability to be used as a heat sink. Many aircraft systems generate large quantities of heat
and require cooling [3]. On modern aircraft, these cooling demands are ever increasing.
For example, modern engines operate at very high combustion temperatures to increase
efficiency, and their lubrication systems require cooling as well [4]. In addition, there are
ever more avionics and electronic equipment that generate an excessive amount of waste
1
Chapter 1. Introduction 2
heat that must be removed [5].
Using the fuel system as a heat sink offers several advantages as compared to another
coolingmethod,whichusesenginebleedair[6]orramair[7]asthecoolingmedium. First,
jet fuel has a greater heat sink capacity under a wider range of operating conditions than
air cooling. The disadvantage to using air as a coolant is that as flight speeds increase,
the stagnation temperature of the air rises as well, thus decreasing the effectiveness of the
heat sink. Jet fuel, on the other hand, is not as restricted by operating conditions. Fuel
° °
temperatures in aircraft fuel tanks stay relatively cool, ranging from 40 F to 120 F
−
° °
( 40 C to 49 C) [8]. Another advantage of fuel cooling is that it is weight-saving. Air
−
cooling requires heavy equipment to be installed, and may incur drag penalties [5]. With
jet fuel, the cooling infrastructure can be designed into an aircraft’s fuel system and does
not require a separate system, reducing weight penalties. Yet another advantage to a fuel
cooling is that during the cooling process, the jet fuel is heated, resulting in an elevated
fuel temperature entering the combustion chamber, which leads to more efficient fuel
burn and reduced fuel consumption [5].
1.2 Jet Fuel Thermal Stability
While jet fuel is an effective cooling medium, its heat sink capabilities are limited,
primarily by the property known as thermal stability. When fuel is heated to high
temperatures, which is referred to as being thermally stressed, chemical reactions take
place in the fuel that break it down and form solid precipitates that are eventually
deposited onto the walls of the fuel lines in a process referred to as coking. If left
unchecked, this could not only result in severe damage to engine components, but also
reduce the effectiveness of heat transfer in the heat exchangers between the fuel and
engine components [8, p. 2-3].
Many factors affect the thermal stability of jet fuel and coking, such as the dissolved