Experimental and Numerical Study on Oxidation Deposition Properties

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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

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Properties of Aviation Kerosene

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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

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In the fuel cooling system of the engine, the heating of aviation kerosene exhibits complicated,

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unsteady physicochemical processes and forms the undesirable coke deposition. To understand

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these processes better, we investigated the coupling relationship between turbulent flow, heat

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transfer, autoxidation, and deposition reactions of fuel in a cooling heat exchanger. The experiments

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were performed to investigate the whole process within 105 min, separated into five continuous

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phases of 20 min, 40 min, 60 min, 80 min and 105 min, with a heat flux of 38.6 kW/m2. Based on

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the experimental results, we established a three-dimensional model to study the influence of

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kerosene’s heat-transfer process on oxidation deposition in a long, straight, horizontal pipe under

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supercritical pressure condition. A modified six-step, pseudo-detailed chemical kinetic and global

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deposition mechanism has been incorporated into the numerical model with particular attention to

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temperature variation. The model was validated based on the quantity of deposition and dissolved

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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

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of deposition at various temperatures to understand the coupling effect between heat transfer and

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coke deposition. Results indicated that supercritical characteristics of both the fuel and deposition

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affect the local heat-transfer characteristics, resulting in some instabilities in the wall temperature

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distribution. The fuel temperature determines the regime of the chemical reactions in the flow and

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that the flow conditions and wall temperature determine the deposition rate at the local position of

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the inner surface.

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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

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With advances in the power of aircraft, gas turbine engines must now operate at a higher

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compression ratio and higher turbine inlet temperatures. Aircraft engines therefore experience

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greater heat load and operate in complex thermal environments that include heat effects from the

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combustion system, aerodynamics, hydraulics, and electronics. These engines require elaborate

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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-

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cooling systems, fuel-cooled cooling systems are more efficient due to the supercritical

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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

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surfaces, which can decrease the heat transfer and even block the cooling passage. Hydrocarbon

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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

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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

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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

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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

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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

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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

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±1 % +6 ppb.11, 29 The oxygen sensor was separated from the sample by a membrane, which was

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only permeable to oxygen but prevented detrimental components from affecting the measurement.

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The oxygen was electrochemically measured as a current to calculate the oxygen partial pressure at

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the cathode. The current output is proportional to the concentration of oxygen. A polarization

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voltage was applied between the anode and the cathode to obtain the entirely linear relationship

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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

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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

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the fluid-thermal-solid interactions coupled with chemical reactions. The governing equation in the

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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

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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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Energy & Fuels

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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

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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

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very clear at present. The modified pseudo-detailed deposition mechanism model of supercritical

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RP-3, based on our previous mechanism,9 is given in Table 4, where fuel, precursor, bulk solubles,

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bulk insolubles, and deposition represent five pseudo components. Dissolved oxygen (O2)

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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

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is based on the Arrhenius expression of k = AT β exp( - E ) at each component step, and β is the

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temperature exponent.

RT

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During the heat-transfer process, the fluid fuel experiences a range of different liquid and wall

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temperatures. Thus, the model in this study was developed with particular focus on temperature by

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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

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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

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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

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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

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continued consumption during deposition reactions. This oxygen consumption profile means that

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the increased oxygen consumption rate enhances the rate of autoxidation reactions in the liquid

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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

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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

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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.

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Temperature is a critical factor in the autoxidation process including both fuel and wall

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temperatures, which in turn affect oxidation deposition reactions. However, the influence of

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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

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reactions. Profiles of the wall and fuel temperatures along the reactor in relation to heating time are

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given in Figure 5 to demonstrate the influence of temperature on deposition during the heat-transfer

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process. The simulated fuel temperatures at the outlet at different times are in acceptable agreement

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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

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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

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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

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comparing Figure 4 and Figure 6a that the oxygen consumption rate is not directly correlated with

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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

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an increase in the precursor. The deposition precursor is believed to form solubles at higher

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temperatures and only starts to precipitate from the bulk fuel onto the wall as it reaches a specific

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temperature. The profile of precursor at 105 min become gradual after 350 mm at the axial of the

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tube.

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The physical properties of fuel under supercritical pressure determine the distribution of species

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and affect the deposition. The properties of the supercritical fluid are sensitive to temperature,

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especially in the pseudo-critical region. In Figure 6b, the specific heat of the fuel increases at 105

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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

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presented in Figure 6c, the viscosity profiles decrease and the Reynold numbers of the flow increase

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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

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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

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in Figure 7. The composition of original RP-3 can be divided into four typical classes as straight-

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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.

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Moreover, hydrogen donors such as naphthalene compounds are considered as high-temperature

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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-

263

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.

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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

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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

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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

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and are composed of amorphous and flocculent particles. Similar fluffy, cauliflower-like deposits

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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

281

aviation kerosene during the heat-transfer process were conducted to evaluate the critical effects of

282

the temperature and heating time. The CFD model with a modified six-step autoxidation deposition

283

mechanism, considering flow dynamics, heat-transfer process, chemical reactions of the fuel and

284

the heat conduction in the tube wall, was used to obtain detailed information about the flow field

285

and species distribution along the tube. The predicted fuel temperatures, total amount of deposits,

286

and dissolved oxygen consumption during the heat-transfer process are conforming to the

287

experimental results. The wall thermal conductivity and Reynolds number of the flow are

288

significantly increased above a temperature of 360°C at 80 min due to the coke deposition and the

289

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

292

out of the range of oxidation reactions, the deposition process falls in oxidation deposition reaction

293

regime, which is demonstrated by the SEM micrographs of the deposition and residual fuel

294

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.

297

Acknowledgment

298

This research described in this paper was supported by King Abdullah University of Science

299

and Technology (KAUST). In addition, financial assistance provided by the National Natural

300

Science Foundation of China (91641114) is gratefully acknowledged.

301

References

302

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3 surface coke deposition under stable and vibration conditions. Energy & Fuels 2015, 29, (3), 2006-2013.

34. Li, X. F.; Huai, X. L.; Cai, J.; Zhong, F. Q.; Xuejun, F.; Zhixiong, G., Convective heat transfer 15), 2360-2366.

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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

381 382


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


Inlet Fuel Temperature (°C)

20

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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

387 388


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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]

390 391


0.7

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392 393

Figure1. Schematic Diagram of the Experiment.

394 395


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Energy & Fuels

Figure 2. (a) Computational Configuration of Convection Heat Transfer with Oxidation Deposition of RP-3 (Left) and (b) Cross-Section of the Grid (Right).

400 401


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402 403

Figure 3. Residence Time and Thermal Conductivity of the Tube in Relation to Temperature.

404 405


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Figure 4. Comparison between Experimental and Numerical Results of the Total Mass of Deposition and Dissolved Oxygen Concentration.

409 410


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411 412

Figure 5. Comparison of Experimentally and Numerically Derived Wall and Fuel Temperatures.

413 414


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416

417 418 419

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.

420 29 ACS Paragon Plus Environment

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421

422 423 424

Figure 7. Variation in Residual Fuel Components in Relation to Temperatures Determined by GC/MS.

425 426


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Energy & Fuels

Figure 8. Experimental Deposition Rates along the Axial in Relation to Time and Temperature.

430 431


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432 433 434

Figure 9. Surface Deposition of Coke Elements Variation in Relation to Temperature.

435 436


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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.


Experimental and Numerical Study on Oxidation Deposition Properties

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