A Plug Flow Reactor for studying fuel autoignition chemistry at pressures of up to 50 bar
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A Plug Flow Reactor for studying fuel autoignition chemistry at pressures of up to 50 bar

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Description

In this thesis, a High Pressure Flow Reactor (HPFR) is designed to study the combustion chemistry of conventional and alternative fuels over a wide range of conditions. The facility can operate at pressures of up to 50 bar and temperatures of up to 1000 K. At these conditions, the reactor was designed such that it meets the most recent Australian Standards (AS) and University of Melbourne safety requirements. The design methodology is divided in four step:
1. reaction rate calculations to set the design constraints
2. sizing, structural dimensioning and CAD modelling of the pressure vessel
3. characterisation and development of the static in-line coaxial mixer
4. accuracy and efficiency numerical estimation of the mixer within the reactor
The chemical kinetics calculations were conducted using Chemkin software. At the heart of the PFR is a 1 m quartz tube with an internal diameter of 25 mm. The entire length of the tube is considered as the test section and is maintained isothermal to within 5 K using four insulated ceramic fibre heaters. The mixing section consist in a series of parallel injectors used to supply the fuel and the oxidiser to the flow reactor. For a better understanding of the reactions in the HPFR, a model was developed using Comsol Multiphysics , which couples the injection process and the mixing reaction mechanism using a three-dimensional turbulent jet in a coaxial flow model. The injector configuration in the PFR was chosen to minimise the time to mix the injected fuel with the hot cross-flow of air.

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Published 13 October 2013
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Document size 13 MB
A Plug Flow Reactor for studying fuel autoignition chemistry at pressures of up to 50 bar
by
Julien Cochet
Submitted to the Department of Mechanical Engineering in partial fulfilment of the requirements for the degree of
Master of Engineering in Mechanical Engineering
at the
UNIVERSITY OF MELBOURNE
July 2013
 Cochet, MMXIII. All rights reserved.c Julien
The author hereby grants to UNIMELB permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created.
Author
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Department of Mechanical Engineering September 13, 2013
Certified by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yi Yang Senior Lecturer Thesis Supervisor
Accepted by . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Michael Brear Associate Professor
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Abstract
A Plug Flow Reactor for studying fuel autoignition chemistry at pressures of up to 50 bar by
Julien Cochet
Submitted to the Department of Mechanical Engineering on September 13, 2013, in partial fulfilment of the requirements for the degree of Master of Engineering in Mechanical Engineering
In this thesis, a High Pressure Flow Reactor (HPFR) is designed to study the combustion chemistry of conventional and alternative fuels over a wide range of conditions. The facility can operate at pressures of up to 50 bar and temperatures of up to 1000 K. At these conditions, the reactor was designed such that it meets the most recentAustralian Standards(AS) and University of Melbournedesign methodology is divided in four step:safety requirements. The
1.
2.
3.
reaction rate calculations to set the design constraints
sizing, structural dimensioning and CAD modelling of the pressure vessel
characterisation and development of the static in-line coaxial mixer
4. accuracy and efficiency numerical estimation of the mixer within the reactor
The chemical kinetics calculations were conducted using Chemkin software. At the heart of the PFR is a 1 m quartz tube with an internal diameter of 25 mm. The entire length of the tube is considered as the test section and is maintained isothermal to within±5 K using four insulated ceramic fibre heaters. The mixing section consist in a series of parallel injectors used to supply the fuel and the oxidiser to the flow reactor. For a better understanding of the reactions in the HPFR, a model was developed using Comsol MultiphysicsR, which couples the injection process and the mixing reaction mechanism using a three-dimensional turbulent jet in a coaxial flow model. The injector configuration in the PFR was chosen to minimise the time to mix the injected fuel with the hot cross-flow of air.
Thesis Supervisor: Yi Yang Title: Senior Lecturer
iii
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When we finally got down to something, which the individual says he really wants to do, I will say to him, you do that ; and forget the money. Because, if you say that getting the money is the most important thing, you will spend your life completely wasting your time. You’ll be doing things you don’t like doing in order to go on living, that is to go on doing things you don’t like doing, which is stupid. Better to have a short life that is full of what you like doing than a long life spent in a miserable way.
What If Money Was No Object? Alan Wilson Watts
v
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Preface
It must be mentioned that the design of a chemical reactor is no routine matter, and many alternatives are probable for each process. In searching for the optimal solution, it is not just the cost of the reactor that determines our decision, since one design may have the lowest reactor cost, but the materials leaving the unit may be such that the treatment requires a much higher cost than alternative solutions.
Reactor design uses information, knowledge and experience from a variety of chemical engineering areas: thermodynamics, chemical kinetics, fluid mechanics, heat transfer, mass transfer and finally economics. Hence, when making these important decisions, I have come to rely on several individuals for guidance and support.
In particular, I would like to thank my thesis advisor, Dr. Yi Yang without whom this project would have never seen the light. His insight and influence have always kept me pointed in the right direction. When this project seemed to be at a standstill for extended periods of time, he was understanding and patient. I have vast respect for him and am thankful to have had the opportunity to work with him.
One person deserves a special recognition, although he was not here the full time, he was vital from the very beginning of this work. Rhys Frazer passed on many of his insight and was one of the guiding force in the modelling of the High Pressure Flow Reactor. Thank you Rhys.
I would also like to express my heartfelt gratitude to Kai Morganti, Ashley Wiese, Peter Dennis and Matthew Blom for their availability, kindness and dedication in contributing their time and advice to assist me. They have shown more diligence in sharing their outstanding knowledge that was intended to be only temporary, than anybody else in the thermodynamics laboratory.
My family has been unconditionally supportive of my academic and non-academic exploits over the years. I am grateful to have such a caring family. Thank you Mom and Dad. AndthankyouM´elanie.
Finally, I want to dedicate this thesis to my soon to be born nephew. I hope that in some way, this accomplishment can serve as an inspiration for him to chase his dreams and achieve his goals.
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2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8
Overview 2.1 Air delivery and heating . . . . . . . 2.1.1 Air mass flow requirements . 2.1.2 Compressor selection . . . . . 2.1.3 Air heater . . . . . . . . . . . 2.2 Fuel delivery system . . . . . . . . . Fuel mass flow requirements Fuel supply . . . . . . . . . . Fuel flow control . . . . . . . Fuel heater calculations . . . Fuel vaporisation . . . . . . . Nitrogen supply . . . . . . . Nitrogen heater . . . . . . . . Mixing device . . . . . . . . .
Experimental apparatus 3.1 Flow reactor system . . . . . . . . . . 3.1.1 Quartz tube . . . . . . . . . . 3.1.2 Wall heater . . . . . . . . . . 3.1.2.1 Power requirements 3.1.2.2 Application . . . . . 3.1.3 Insulation . . . . . . . . . . .
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Abstract
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Contents
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Background
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List of Symbols
List of Figures
List of Tables
Preface
Contents
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1.1 Introduction . . . . . . . . 1.2 Motivation . . . . . . . . . 1.2.1 Generalities . . . . 1.2.2 Octane index . . . 1.3 Objectives . . . . . . . . .
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3.1.5 3.1.6 3.1.7
Pressurised vessel . . . . . 3.1.4.1 Stress calculation . 3.1.4.2 Material selection Pipe flange . . . . . . . . . . Ring seal . . . . . . . . . . . Radial thermal expansion .
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Mixing device 4.1 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Chocked flow . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1.1 Critical static pressure . . . . . . . . . . . . . . . . 4.2.1.2 Maximum mass flow rate . . . . . . . . . . . . . . 4.2.2 Hole distribution . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2.1 Configuration . . . . . . . . . . . . . . . . . . . . 4.2.2.2 Nitrogen nozzles diameter . . . . . . . . . . . . . 4.2.2.3 Pitch of the holes . . . . . . . . . . . . . . . . . . . 4.2.2.4 Nitrogen inlet depth . . . . . . . . . . . . . . . . . 4.2.3 Air hole diameters . . . . . . . . . . . . . . . . . . . . . . . 4.3 Material selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Stress calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Data input . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1.1 Simulation mode . . . . . . . . . . . . . . . . . . . 4.4.1.2 Elements . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Results and discussion . . . . . . . . . . . . . . . . . . . . . 4.4.3.1 Thermal expansion . . . . . . . . . . . . . . . . . 4.4.3.2 Stress . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3.3 Orifice plate lifetime . . . . . . . . . . . . . . . . . 4.4.4 Thickness of the plate . . . . . . . . . . . . . . . . . . . . . 4.5 Diffuser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . .
Mixing efficiency 5.1 Flow problem formulation . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Geometry and flow model . . . . . . . . . . . . . . . . . . . 5.1.2 Governing equations . . . . . . . . . . . . . . . . . . . . . . 5.1.2.1 Turbulent flow . . . . . . . . . . . . . . . . . . . . 5.1.2.2 Mass balance . . . . . . . . . . . . . . . . . . . . . 5.2 Boundary conditions . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Initial conditions . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Diffusion coefficient . . . . . . . . . . . . . . . . . . . . . . 5.2.3 Schmidt number . . . . . . . . . . . . . . . . . . . . . . . . 5.2.4 Symmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 CFD modelling strategy . . . . . . . . . . . . . . . . . . . . . . . . 5.3.1 Mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3.2 Solver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Validation and verification . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Description . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Jet entry length . . . . . . . . . . . . . . . . . . . . . . . . .
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5.4.4 Comparisons of the results . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.1 Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.1.1 Recirculation zone . . . . . . . . . . . . . . . . . . 5.5.1.2 Turbulence kinetic energy . . . . . . . . . . . . . 5.5.2 Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.3 Evolution of concentration . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusion 6.1 Specifications . . . . . . . . . . . . . . . 6.2 Notable achievements . . . . . . . . . . 6.2.1 Overall design . . . . . . . . . . 6.2.2 Fuel-oxidiser mixer . . . . . . . . 6.3 Further work . . . . . . . . . . . . . . . .
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Calculations A.1 Chemkin fuel consumption simulations . . . . . . . . . . . . . . . . . . . . . . A.2 Fuel flow calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.2.1 air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.2.2 ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.2.3 iso-octane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.2.4 n-heptane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.2.5 toluene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.3 Nitrogen flow calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.4 Nitrogen supply calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.5 Fuel/Nitrogen vessel mixing calculations . . . . . . . . . . . . . . . . . . . . . A.6 Pressure loss calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6.1 Orifice plate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6.2 Quartz tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6.2.1 Friction factor . . . . . . . . . . . . . . . . . . . . . . . . . . . A.6.2.2 Newton-Raphson . . . . . . . . . . . . . . . . . . . . . . . . . A.7 Thermal-Stress analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Drawings B.1 Detailed drawings of the mixing section . . . . . . . . . . . . . . . B.2 Details of the parts contained within the injector . . . . . . . . . . B.3 Main dimensions of the orifice plate . . . . . . . . . . . . . . . . .
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CFD analysis process C.1 Details of the CFD domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.2 Computational mesh . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.3 Smith et al. numerical results . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.3.1 Side view concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . C.3.2 Cross sectional concentration . . . . . . . . . . . . . . . . . . . . . . . . C.4 CFD results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C.4.1 Air mass flow rate: 12 g/s . . . . . . . . . . . . . . . . . . . . . . . . . . C.4.2 Air mass flow rate: 60 g/s . . . . . . . . . . . . . . . . . . . . . . . . . . C.4.3 Cross sectional nitrogen/air axis velocity profiles . . . . . . . . . . . . C.4.4 Turbulent kinetic energy . . . . . . . . . . . . . . . . . . . . . . . . . . .
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