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Experimental and numerical study on oxidation deposition properties of aviation kerosene Xinyan Pei, Lingyun Hou, and William L. Roberts Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01250 • Publication Date (Web): 08 Jun 2018 Downloaded from http://pubs.acs.org on June 8, 2018
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Energy & Fuels
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Experimental and Numerical Study on Oxidation Deposition
2
Properties of Aviation Kerosene
3
Xinyan Peia†, Lingyun Hou*b‡, William L. Robertsa†
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a
Clean Combustion Research Center, King Abdullah University of Science and Technology Thuwal 23955-6900, Saudi Arabic b
6 7 8 9
School of Aerospace Engineering, Tsinghua University Beijing 100084, China
Tel.+86-10-62772157. E-mail:
[email protected]. Abstract
10
In the fuel cooling system of the engine, the heating of aviation kerosene exhibits complicated,
11
unsteady physicochemical processes and forms the undesirable coke deposition. To understand
12
these processes better, we investigated the coupling relationship between turbulent flow, heat
13
transfer, autoxidation, and deposition reactions of fuel in a cooling heat exchanger. The experiments
14
were performed to investigate the whole process within 105 min, separated into five continuous
15
phases of 20 min, 40 min, 60 min, 80 min and 105 min, with a heat flux of 38.6 kW/m2. Based on
16
the experimental results, we established a three-dimensional model to study the influence of
17
kerosene’s heat-transfer process on oxidation deposition in a long, straight, horizontal pipe under
18
supercritical pressure condition. A modified six-step, pseudo-detailed chemical kinetic and global
19
deposition mechanism has been incorporated into the numerical model with particular attention to
20
temperature variation. The model was validated based on the quantity of deposition and dissolved
21
oxygen consumption rate under different experimental temperatures and heating times. We then
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analyzed the fluid dynamics profiles and physical parameters of density, specific heat, viscosity and
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Reynold number, species, and deposition rates along the reactor, micrographs and surface elements
24
of deposition at various temperatures to understand the coupling effect between heat transfer and
25
coke deposition. Results indicated that supercritical characteristics of both the fuel and deposition
26
affect the local heat-transfer characteristics, resulting in some instabilities in the wall temperature
27
distribution. The fuel temperature determines the regime of the chemical reactions in the flow and
28
that the flow conditions and wall temperature determine the deposition rate at the local position of
29
the inner surface.
30
Nomenclature Pre-exponential factor A Specific heat at constant pressure Cp d E
Diameter Activation energy for the reaction
r Ji
Diffusion flux of species i
p
Effective conductivity Pressure
Qr
Heat of the surface reaction
R
Universal gas constant
SE
Heat source term
Si
Species source term
T x
Temperature Axial coordinate
Yi
Mass fraction of species i
r v
Velocity vector
ke
__
Pa
J/kmol∙°C
°C m
m/s
τ
Stress tensor
ρ
Density Temperature exponent
β
J/kg∙°C m J/kmol
kg/m3
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Energy & Fuels
ω& r ,s 31
Rate of the surface reaction
1. .Introduction
32
With advances in the power of aircraft, gas turbine engines must now operate at a higher
33
compression ratio and higher turbine inlet temperatures. Aircraft engines therefore experience
34
greater heat load and operate in complex thermal environments that include heat effects from the
35
combustion system, aerodynamics, hydraulics, and electronics. These engines require elaborate
36
cooling systems to deal with the heat load. Fuel-cooled technologies can be used in an indirect
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cooling system, such as a cooling cooled air (CCA) system,1 the cooled air takes the heat from the
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hot parts, passes it to the fuel and then cools other thermal components. In comparison with air-
39
cooling systems, fuel-cooled cooling systems are more efficient due to the supercritical
40
characteristic of aviation kerosene and the heated fuel from the fuel-cooled system can also return
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thermal energy to the engine’s thermodynamic cycle after being burnt in the combustor. However,
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when hydrocarbon fuel is heated, it experiences deposition reactions that form insoluble particles on
43
surfaces, which can decrease the heat transfer and even block the cooling passage. Hydrocarbon
44
fuels follow two processes during thermal decomposition, including autoxidation and pyrolysis.
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Autoxidation reactions require dissolved oxygen in the fuel and occur at or above 150°C. When the
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temperature increases above 450°C, pyrolysis reactions dominate, involving the breakdown and
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recombination of hydrocarbon chains.2, 3
48
Many experimental
4-6
and numerical investigations
7-10
have been performed with the aim of
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understanding the deposit formation and oxidation processes of hydrocarbon fuels. The formation
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of deposition coke in fuel during the heat-transfer. In general, amount of dissolved oxygen,11, 12
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cooling channel geometries,13-15 operational conditions,16,
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transfer characteristics,19 additives,6 heating time,5,
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characteristics of a system. In a limited oxidation deposition mechanism study, a nine-step model
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was developed by Katta et al.22. Ervin et al.23 modified this model by focusing on surface
55
deposition in the cooled regions. Zabarnick et al.24 and Ervin et al.25 further extended the model to a
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17-step, pseudo-detailed mechanism by considering the effects of oxygen consumption on
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deposition. To improve dissolved-oxygen consumption predictions, Doungthip et al.26 calculated
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catalytic deposition reactions into the mechanism. Kuprowicz et al.27 refined the model to include
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21 steps by including reactions of sulfur species, phenols, hydroperoxides and dissolved metals.
20
17
fluid dynamics,13 buoyancy,18 heat
and temperature,4,
21
affect coking
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Most studies, including mechanisms investigation, of the thermal stability of hydrocarbon fuels
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are conducted under isothermal conditions. However, the fuel coolant passes through various
62
geometries and thermal conditions in the fuel supply and cooling system. Under conditions of
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incomplete oxygen consumption and non-thermal equilibrium, the interactions among the
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consumed dissolved oxygen, heat transfer and deposition rate are complex but knowledge of these
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interactions, especially when coupled with temperature, is necessary to design fuel cooling systems.
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Therefore experimentally and numerically studies were conducted to investigate the coupling
67
effects between heat transfer process and autoxidation in the coke deposition formation under
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different heating times and temperatures. In the experimental study, these processes were
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investigated coupling fluid flow dynamics, heat transmission, autoxidation chemical reactions, and
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oxidation deposition over 105 min. Then, our experimental results were used to compute a three-
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dimensional simulation of the fluid dynamics and heat-transfer characteristics of fuel in a circular
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tube under supercritical pressure condition. The global autoxidation mechanism and the kinetic
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deposition model were developed to simulate the oxidation deposition process of aviation kerosene.
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2. Experimental Apparatus
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In Table 1, Chinese No. 3 aviation kerosene (RP-3) was used as the fuel in our experiments.28
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A small-scale test rig was designed to heat the fuel through a heat-exchanger under different
77
temperatures and heating times, which was to stimulate the heat transfer process in the cooling
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passage.
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In Figure 1, the present experimental system includes a fuel supply subsystem with a fuel
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container and a plunger metering pump, a heating subsystem, a parameter control and measurement
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subsystem, and an online sampling analysis subsystem. The detailed experimental parameters are
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given in Table 2.The inlet mass flow rate was kept constant at 1 g/s for all conditions. The SS316
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tube (the inner diameter of 2 mm, the wall thickness of 0.5 mm, the total length of 450 mm) was
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applied as the heat exchanger and reaction section in the experiment. The tube was prepared to be
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flushed by the water and N2 and dried before the experiment to clean manufacturing residues. The
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test tube was in the horizontal arrangement, and an indirect electrical heater simulated the heat flux. 5 ACS Paragon Plus Environment
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The following fuel pressure was monitored by two pressure gauges at inlet and outlet of the test
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section and maintained using a pressure damper and a backpressure regulator at 3 MPa under the
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supercritical pressure condition. The outer-wall temperatures of the pipe were measured using 18 K-
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type thermocouples spot-welded at 2.5 cm intervals along the tube. The fuel temperatures of inlet
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and outlet were measured using K-type thermocouples inserted into the center of the tube. The
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dissolved oxygen concentration was measured and monitored before and after the tests via two
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continuous oxygen sensors (InPro 6850i) based on the polarographic method with the accuracy of
94
±1 % +6 ppb.11, 29 The oxygen sensor was separated from the sample by a membrane, which was
95
only permeable to oxygen but prevented detrimental components from affecting the measurement.
96
The oxygen was electrochemically measured as a current to calculate the oxygen partial pressure at
97
the cathode. The current output is proportional to the concentration of oxygen. A polarization
98
voltage was applied between the anode and the cathode to obtain the entirely linear relationship
99
over the whole measurement range from 0 to 100% oxygen concentrations.
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After heating, the fuel was cooled using a counter-flow water-fuel exchanger and collected for
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GC/MS analysis. The tube was blown by nitrogen to clean the residual fuel in all pipes before
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drying. After each experiment, the tube of the reaction part was cut into 11 equal sections by a wire-
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electrode cutting for weighing the deposition. The repeatability test and the more detailed
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experimental setup information can be referred to our previous work.11, 15
105
In the heat-transfer experiments, the fuel reached thermal equilibrium after some time.
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Therefore, five heating times was performed at different times to guarantee the flow to heat balance
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and sufficient deposit sample for the test. For the investigation of the effect of heat transfer process
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on the deposition process, five heating times, i.e., 0-20 min, 0-40 min, 0-60 min, 0-80 min and 0-
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105 min, were conducted in our experiments. The selection of heating time was based on our
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previous heat transfer experiments that the fuel comes to be thermal equilibrium after 105 min
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under the same conditions in Table 2.30
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For all the experiments, the inlet mass flow rate was set at 1 g/s; the initial fuel temperature
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was 20°C; the dissolved oxygen concentration was 10 ppm; the heat flux was 38.6 kW/m2. These
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parameters remained the same under the supercritical pressure of 3 MPa for all heating times. In
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this way, each heating time corresponded to a specific outlet fuel temperature listed in Table 2. We
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used a scanning electron microscope (SEM, FEICO95-001) to study the deposition microstructure
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morphologies of samples from each experiment, and an X-ray photoelectron spectroscopy (XPS,
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Thermo Fisher ESCALAB 250Xi) to measure the surface elements of the coke deposits, and gas
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chromatography/mass spectrometry (GC/MS, Agilent 7890B–5975A) to determine the composition
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of the residual fuel. Results of the error analysis on the measured parameters and transfer formula
121
are presented in Table 3.
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3. Numerical Methods
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The Ansys Fluent package 31 was used in conjunction with a user-defined function to simulate
124
the fluid-thermal-solid interactions coupled with chemical reactions. The governing equation in the
125
fluid region is: 7 ACS Paragon Plus Environment
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r ∂ ( ρφ ) (1) + div(ρ uφ )=div(Γφ gradφ )+Sφ ∂t where φ are generalized variables, which can stand for a variety of physical quantities, such as
127
velocity, enthalpy, and turbulence parameters. Γφ is the generalized diffusion coefficient and a
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representation for the transport properties such as viscosity or conductivity. And Sφ is the
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generalized source term such as heat generation in a fluid, production of a chemical species in a
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reaction, and the generation of turbulence kinetic energy.32 In the solid region, the thermal
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conduction equation is solved as ∇⋅ (λ∇T ) = 0 . The surface boundary conditions of the species and
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energy equations are set as follows: ρ Di
λs
∂Yi ∂n
∂T ∂n
= Wi ∑ (bir − air )ω& r ,s
(2)
= ∑ Qrω& r ,s
(3)
r
w
w
r
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The temperature-dependent thermal properties of the fuel were defined by the three-component
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surrogate model,28, 30 including density, specific heat (Cp), viscosity and thermal conductivity. The
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convection terms were discretized in a second-order upwind scheme. The RNG k-ε model,33 was
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used for simulation of the turbulent flow, which predicted the convective heat transfer under
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supercritical conditions well.34, 35 In Figure 2a, the inner diameter of the circular reactor tube is 2
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mm with a wall thickness of 0.5 mm and the total length of the tube is 450 mm. The outer wall
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temperature profiles obtained from the experiments were used as the outer surface boundary
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condition along the tube, and the inner surface was set as a no-slip wall. The mesh of the cross-
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section is shown in Figure 2b with the compressed mesh in the solid region, as the oxidation
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deposition is produced on the inner surface of the tube. The total number of the mesh cells is
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488,920 and the boundary layer of the inter-surface between solid and liquid zone uses 100,076 8 ACS Paragon Plus Environment
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cells. Steady simulation results at different times were used to describe the whole heat-transfer and
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deposition process. The residence time and the heat-transfer process indicated by thermal
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conductivity of the tube wall in the experiments are given in Figure 3. The thermal conductivities
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were calculated from the experimental data such as fuel and wall temperatures and heat flux. Then
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the calculated thermal conductivities were utilized in the setting of the boundary conditions of the
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tube interface for the heat-transfer simulation between the inner surface and the fuel. In Figure 3,
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the residence time of the fuel in the tube gradually decreases as the temperature increases. The
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density of the fuel decreases as the fuel temperature increases, which increases the velocity of the
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fuel in the tube. In addition, the residence time is also affected by the thickness of the deposition
153
layer increasing with the heating time due to the change of the inner diameter. But the effects of the
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deposits on the flow were neglected since the thickness of the deposition layer were very thin,
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which was observed in the morphological investigation on deposition.13, 19 The difference in the
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wall thermal conductivity between the ideal condition of Stainless Steel 316 and that at the end of
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the experiment indicates the accumulated effect of deposition on heat transfer.
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The composition of the kerosene is very complicated, and the detailed reaction process is not
159
very clear at present. The modified pseudo-detailed deposition mechanism model of supercritical
160
RP-3, based on our previous mechanism,9 is given in Table 4, where fuel, precursor, bulk solubles,
161
bulk insolubles, and deposition represent five pseudo components. Dissolved oxygen (O2)
162
stimulates the oxidation chain reactions. The detailed kinetic parameters of the model are listed in
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Table 4. The main modification is focused on the temperature exponent. The reaction rate constant
164
is based on the Arrhenius expression of k = AT β exp( - E ) at each component step, and β is the
165
temperature exponent.
RT
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During the heat-transfer process, the fluid fuel experiences a range of different liquid and wall
167
temperatures. Thus, the model in this study was developed with particular focus on temperature by
168
adding the temperature exponent in the reaction-rate expression comparing to the previous model.
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The mechanism was divided into three bulk fuel reactions that occur in the liquid phase and three
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surface reactions at the wall. The total deposition rate was calculated by adding the three wall
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reactions together.
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4. Results and Discussion
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The numerical simulation model is verified by assessing the experimental results capturing the
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total mass of the deposition and the dissolved oxygen concentration at the outlet in relation to the
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variation in fuel temperature in Figure 4. The numerical results based on the reaction mechanism
176
described here are compared with a previous model. In comparison with the previous model, the
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modified model focuses on temperature by adding the temperature exponent in the reaction-rate
178
expressions. In this way, we found that the consumption of dissolved oxygen is sensitive to changes
179
in temperature in the modified model. The predicted results with the modified model follow the
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same trend as the experimental data. The total mass of the deposition follows a nonlinear increasing
181
trend with increasing fuel temperature in both the measured and predicted results. The dissolved 10 ACS Paragon Plus Environment
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oxygen concentration in the fuel follows a decreasing trend with increasing fuel temperature due to
183
continued consumption during deposition reactions. This oxygen consumption profile means that
184
the increased oxygen consumption rate enhances the rate of autoxidation reactions in the liquid
185
phase. Nearly 70% of dissolved oxygen is consumed when heating time lasts 105 min. The
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concentration of oxygen stimulates the chain-reaction oxidation processes. The fuel molecules react
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with dissolved oxygen to form alkyl-peroxides, and in turn, these alkyl-peroxides develop into
188
deposition precursor species. Ultimately the precursor grows into particles that form deposits. The
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deposition rate and oxygen consumption both sharply increase above 300°C at 60 min due to the
190
effects of temperature and the supercritical properties of the fuel as it will be discussed later while
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looking on the computed fuel properties.
192
Temperature is a critical factor in the autoxidation process including both fuel and wall
193
temperatures, which in turn affect oxidation deposition reactions. However, the influence of
194
temperature on the deposition process is very complicated because the temperature simultaneously
195
affects the flow conditions and the fuel’s properties and compositions. There is a strong coupling
196
relationship between oxidation deposition and convection heat transfer in the presence of chemical
197
reactions. Profiles of the wall and fuel temperatures along the reactor in relation to heating time are
198
given in Figure 5 to demonstrate the influence of temperature on deposition during the heat-transfer
199
process. The simulated fuel temperatures at the outlet at different times are in acceptable agreement
200
with the measured data within about 1% error. The centerline fuel temperatures are almost identical
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to the bulk average temperatures of the cross-section of the tube and are significantly lower than the
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measured wall temperatures. This result indicates the different heat-transfer characteristics of the
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fluid in different locations. The wall temperatures rapidly increase within 50 mm from the inlet.
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However, the fuel temperature remains relatively low. At 150 mm from the inlet, the outer wall
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temperatures increase only a little along the axis of the test section in all cases, but the fuel
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temperature continuously increases along the tube and follows a similar trend in each case. The only
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difference is the rate of increase over time. Wall temperatures along the tube rise gradually to the
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thermal equilibrium in relation to the heating time. The supercritical characteristics of the fuel and
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deposition affect the local heat-transfer characteristics, resulting in some fluctuation in the
210
distribution of the wall temperature.11 Therefore, the fuel temperature defines the regime of the
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chemical reactions in the flow and the flow conditions and wall temperature define the deposition
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rate at a specific location at the inner surface of the tube.
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As discussed above, the consumption of dissolved oxygen can reflect changes in autoxidation
214
and deposition processes. In addition, the precursor is critical to the formation of deposits10. The
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profiles of oxygen and the deposition precursor are shown in Figure 6a. It is noted that by
216
comparing Figure 4 and Figure 6a that the oxygen consumption rate is not directly correlated with
217
the temperature. Low oxygen consumption rates near the inlet (within 150 mm) are reasonable since
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temperatures in this location are lower than the autoxidation temperature range for all cases. The
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low oxygen consumption rate and the low precursor production rate at 20 min corresponding to the
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outlet fuel temperature at 160°C are expected because the temperature is at an initial temperature of
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the autoxidation regime. The consumption of oxygen gradually becomes evident after 40 min. The
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autoxidation reaction rate depends on both amounts of the radical species and temperature. Rapid
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oxidation occurs as the number of radical species becomes substantial. These results indicate that
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the oxygen concentration and the amount of precursor are in a trend of a slow reaction rate followed
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by a gradually fast oxidation rate along the axial direction of the tube. The oxygen is consumed with
226
an increase in the precursor. The deposition precursor is believed to form solubles at higher
227
temperatures and only starts to precipitate from the bulk fuel onto the wall as it reaches a specific
228
temperature. The profile of precursor at 105 min become gradual after 350 mm at the axial of the
229
tube.
230
The physical properties of fuel under supercritical pressure determine the distribution of species
231
and affect the deposition. The properties of the supercritical fluid are sensitive to temperature,
232
especially in the pseudo-critical region. In Figure 6b, the specific heat of the fuel increases at 105
233
min and the fuel temperature increases to the pseudo-critical temperature zone. The heat transfer of
234
the flow increases significantly after 350°C. The Reynolds number was mainly defined by the basis
235
of the viscosity coefficient and density with the variation of fuel temperature in Figure 5. As
236
presented in Figure 6c, the viscosity profiles decrease and the Reynold numbers of the flow increase
237
along the axial of the tube for all cases with increasing temperature. The flow is laminar within 60
238
mm of the axial of the tube. After 20 min, the flow is fully developed and mainly turbulent as the
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heating process. The Reynold number at 105 min increases sharply at 300 mm of the tube and
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reaches more than 40,000 at the exit of the tube with significant changes in the density and viscosity
241
because the fuel temperature reaches the pseudo-critical value.
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After each experiment, the residual fuel was collected at the outlet of the tube. And
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compositions of the residual fuel samples, analyzed by GC/MS, at different temperatures are given
244
in Figure 7. The composition of original RP-3 can be divided into four typical classes as straight-
245
chain alkanes (54.4 wt%), cycloalkanes (21.3 wt%), aromatic hydrocarbons (21.5 wt%) and others
246
(2.7 wt%). As the fuel temperature increases into autoxidation-reaction range, the amount of straight
247
chain alkanes decreases by nearly 50% in all cases. There are no significant changes in the
248
proportion of aromatic hydrocarbons, cycloalkanes, and olefins with different fuel temperatures. In
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general, naphthenic compounds have higher thermal stability compared with other components.
250
Moreover, hydrogen donors such as naphthalene compounds are considered as high-temperature
251
thermal stabilizers in jet fuel. There is a significant increase in oxygen-containing compounds in all
252
cases in comparison with the original RP-3. Most of the straight chain alkanes are transformed into
253
oxygen-containing compounds. In the detailed classification of components, these oxygen-
254
containing compounds consist of acid esters, alcohols and ketones. In the autoxidation process,
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oxygen-containing compounds are critical in chain-propagation reactions and forming precursor
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species. In addition, it should be noted that fuel degeneration reactions do not influence deposit
257
formation. Autoxidation and pyrolysis reactions occur in the liquid phase of fuel. Only a relatively
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Energy & Fuels
small quantity of fuel involves in oxidation reactions that finally form insoluble and solid deposits.
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In Figure 8, the deposition rates in all locations of the test section increase with heating time.
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The higher amounts of deposition near the inlet are ascribed to the entrance effect that is determined
261
by the temperature gradient and boundary layer.11 In the surface elemental analysis by XPS in
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Figure 9, there are relatively high levels of carbon and oxygen, which account for 70-80% and 20-
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30%, respectively. The proportions of other elements are tiny and do not change much respecting
264
temperature. Furthermore, there are similar apparent changes from 310°C to 360°C in the residual
265
fuel composition as indicated in the SEM analysis during deposition due to the supercritical
266
properties of the fuel.
267
SEM micrographs of deposition samples at the same position of the test section (x=325 mm from
268
the inlet) corresponding to different heating times are presented in Figure 10. The inner surface of
269
the experiment at 0 min exhibits random ravines and embossments. The complicated structures
270
enlarge the contact surface area and promote deposition from the fuel. The deposition at 20 min and
271
40 min is not recognizable in the SEM images. The deposit obtained from a long heating time is
272
denser than that from a short one. After 60 min, deposits significantly increase in the micrographs
273
and are composed of amorphous and flocculent particles. Similar fluffy, cauliflower-like deposits
274
were also observed by Ervin25 and Tao36. The deposition rate visibly accelerates from 60 min to 80
275
min. The significant increases in the deposition rate and oxygen consumption after 60 min in Figure
276
4 correspond to the slight increase in the oxygen-containing compounds with the decrease in the
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straight-chain alkanes in the residual fuel at 360°C. These results indicate that the morphology of
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deposited carbon is strongly affected by the operating temperature.
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5. .Conclusions
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Detailed experimental and numerical studies of the oxidation deposition characteristics of
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aviation kerosene during the heat-transfer process were conducted to evaluate the critical effects of
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the temperature and heating time. The CFD model with a modified six-step autoxidation deposition
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mechanism, considering flow dynamics, heat-transfer process, chemical reactions of the fuel and
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the heat conduction in the tube wall, was used to obtain detailed information about the flow field
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and species distribution along the tube. The predicted fuel temperatures, total amount of deposits,
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and dissolved oxygen consumption during the heat-transfer process are conforming to the
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experimental results. The wall thermal conductivity and Reynolds number of the flow are
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significantly increased above a temperature of 360°C at 80 min due to the coke deposition and the
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properties of the supercritical fuel. Both the deposition rate and oxygen consumption rate sharply
290
increase above a temperature of 300°C at 60 min. An apparent turning point is found in the
291
micrographs and surface elements of deposition. Although the wall temperatures after 60 min are
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out of the range of oxidation reactions, the deposition process falls in oxidation deposition reaction
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regime, which is demonstrated by the SEM micrographs of the deposition and residual fuel
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components. Therefore, the regime of the chemical reactions in the flow depends on the fuel’s
295
temperature. The flow conditions and wall temperature determine the deposition rate at specific
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locations.
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Acknowledgment
298
This research described in this paper was supported by King Abdullah University of Science
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and Technology (KAUST). In addition, financial assistance provided by the National Natural
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Science Foundation of China (91641114) is gratefully acknowledged.
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References
302
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Table 1 Properties of Aviation Kerosene.28
380
Properties Critical pressure Critical temperature Density Values
2.39 MPa
372.5°C
Flash point Distillation range Relative molecular weight
0.7913 g/cm3(20°C)
50°C
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163-212°C
148.33 g/mol
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Table 2 Experimental Parameters. Heating Time (min)
Outlet Fuel Operation Heat Flux Mass Flow Temperature (°C) Pressure (MPa) (kW/m2) Rate (1g/s)
Inlet Dissolved Oxygen (ppm)
20 40 60 80 105
160 260 310 360 410
10
3
38.6
1
384 385
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Inlet Fuel Temperature (°C)
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Table 3 Error Analysis. Items Error (%) Heat Flux 5.1 Temperature Difference 7.1 Mass Flow Rate 0.2 Pressure 1 Deposition Rate 6.6
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Table 4 Kinetic Parameters of the Oxidation Deposition Reactions of RP-3. Reaction No. Pre-Exponential A Activation Energy E Reaction Order α Bulk Fuel Reactions Wall Reactions
3
k1
1.8e-05
5e+07
[T] [F][O2]
k2 k3 k4
500 2 2e-11
4.1861e+07 8.4e+06 8.6e+06
[P] [P] [F][dT/dX]
k5
10
5e+07
[T]
k6
480
8.5e+07
[T]
0.04
[IN]
0.015
[P]
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0.7
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Figure1. Schematic Diagram of the Experiment.
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Figure 2. (a) Computational Configuration of Convection Heat Transfer with Oxidation Deposition of RP-3 (Left) and (b) Cross-Section of the Grid (Right).
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Figure 3. Residence Time and Thermal Conductivity of the Tube in Relation to Temperature.
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Figure 4. Comparison between Experimental and Numerical Results of the Total Mass of Deposition and Dissolved Oxygen Concentration.
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Figure 5. Comparison of Experimentally and Numerically Derived Wall and Fuel Temperatures.
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Figure 6. Profiles of Simulation Results along the Axial of the Tube with Time: (a) Precursor and O2; (b) Cp and Density; (c) Viscosity and Re.
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Figure 7. Variation in Residual Fuel Components in Relation to Temperatures Determined by GC/MS.
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Figure 8. Experimental Deposition Rates along the Axial in Relation to Time and Temperature.
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Figure 9. Surface Deposition of Coke Elements Variation in Relation to Temperature.
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437 438 439
20 min
40 min
60 min 80 min 105 min Figure 10. SEM Micrographs at Different Heating times.
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