Simplified Chemical Reaction Mechanism for Surrogate Fuel of

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A simplified chemical reaction mechanism for surrogate fuel of aviation kerosene and its verification Yingwen Yan, Yunpeng LIU, Dong DI, Chao Dai, and Jinghua Li Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01852 • Publication Date (Web): 24 Oct 2016 Downloaded from http://pubs.acs.org on November 6, 2016

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A simplified chemical reaction mechanism for surrogate fuel of aviation kerosene and its verification Yingwen YAN, Yunpeng LIU, Dong DI, Chao DAI, Jinghua LI∗

Jiangsu Province Key Laboratory of Aerospace Power Systems, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China

Abstract: In order to investigate the combustion performance of RP-3 aviation kerosene, n-decane was chosen as a one-component surrogate fuel. Sensitivity analysis and the reaction-path analysis method were used to simplify the detailed reaction mechanism of n-decane, and a simplified mechanism including 36 species and 62 elementary reaction steps was obtained. A Bunsen burner for the combustion of premixed, pre-evaporated RP-3 aviation kerosene was designed to verify the simplified mechanism, and the temperature and gas component concentrations in the axial and radial directions at different heights were measured. The combustion process of the premixed, pre-evaporated RP-3 aviation kerosene in the Bunsen burner was also simulated based on the simplified mechanism, and the numerical results were compared with the experimental data. The results show that the simulated distributions of temperature and O2 concentration are in good agreement with the experimental data in all cases. In addition, the simulated distribution of CO2 concentration is in general agreement with the experimental data. Thus, the simplified mechanism can accurately predict the trend in CO2 concentration near the outer flame. Therefore, n-decane can be used as a one-component surrogate fuel for RP-3 aviation kerosene, and the simplified mechanism of n-decane with 36 species and 62 elementary reaction steps can accurately predict the

∗

Corresponding author: Dr. Jinghua LI, E-mail: [email protected], Tel: +86-18751986782

1 ACS Paragon Plus Environment

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combustion performance of RP-3 aviation kerosene over a wide range of conditions.

Keywords: sensitivity analysis, simplified mechanism, n-decane, Bunsen burner, temperature, gas component.

An aircraft engine combustor is one of the three core parts of a gas turbine; its main function is to mix the fuel and air, form the fuel and gas mixture, and then combust and convert the chemical energy of the fuel into the heat energy of the high-temperature gas. The spray combustion reactions of liquid fuel in gas turbine combustors are complex and include turbulent mixing and combustion processes controlled by chemical kinetics. In order to accelerate the development of gas turbine combustors and the optimization of combustor design, complicated phenomena such as air flow, heat exchange, and combustion need to be investigated. Therefore the Computational Fluid Dynamics (CFD) of combustion phenomena is an important tool, but the chemical kinetics of fuel combustion is the basis of accurate numerical simulation for two-phase spray combustion processes in gas turbine combustors. However, the chemical kinetics of hydrocarbon fuels and oxygen are very complex as they are affected by hundreds of components and thousands of elementary reactions (1). The detailed chemical kinetics is too complex to be applied to simulate the spray combustion process in a gas turbine combustor at the current calculation level. In addition, due to the lack of studies on the chemical kinetics of aviation kerosene, C12H23 is generally used as a single-component surrogate fuel for aviation kerosene, and a single- or multi-step simplified chemical reaction mechanism is commonly employed (2). Although the temperature and the temperature difference between the inlet and outlet of the combustor can be predicted, the fuel ignition process, along with the important intermediate combustion products, cannot be accurately simulated, especially when concentrated OH is used to estimate the positions of the flame front and the maximum combustion temperature. Therefore, in order to numerically simulate the combustion process in a gas turbine combustor accurately, a simplified chemical


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mechanism for aviation kerosene needs to be found (3).

In recent years, in an attempt to obtain this, many types of single-component and multi-component surrogate fuels have been proposed along with their detailed chemical reaction mechanisms, and combustion experiments have been carried out to verify the related chemical reaction mechanism of aviation kerosene. Wenxuan Huang et al.(4) suggested a method to develop a universal chemical mechanism for kerosene. The reduced mechanism is constructed based on the reduction process of principal component analysis to reducesome unimportant reactions. The numerical simulation results show that the simplified mechanism agrees well with the detailed mechanism during a wide range under different initial reaction conditions. Wei Yao et al.(5)obtained a skeletal mechanism consisting of 39 species/153 elemental reactions for RP-3 aviation kerosene by simplifyingfrom the detailed reaction mechanism. The flame temperature, total heat release and ignition delay time of the simplified reaction mechanism have a good agreement with the detailed reaction mechanism. Then the simplified mechanism and the Detached Eddy Simulation modeling were used to simulate the full-scale scramjet combustor, the numerical results have a good accordance with the experimental data. Jeong-Yeol Choi et al.(6) proposed a multi-step quasiglobal mechanism about the kerosene. The reaction constants of the mechanism were determined by the experimental data. The mechanism will be used tonumerically simulatethe kerosene/oxygen shear coaxial injector. Meredith B. Colket et al.(7) investigated the flame thickness, laminar flame speed and the reaction zone thickness of the fuel premixed flame about the surrogate kerosene fuel by using the detailed chemical mechanism. The correlations were developed for the flame speeds, flame thicknesses and reaction zone thicknesses as a function of temperature, pressure and equivalence ratio. N.Slavinskaya et al.(8) investigated the kinetic model formulation for synthetic Gas-To-Liquid (GTL) kerosene. The proposed surrogate fuel consists of 17% of 2, 7-dimethyloctane, 32% of 2-methyldecane, 15% of n-propylcyclohexane and 36% of n-decane. The simplified surrogate composed of ndecane, n-propylcyclohexane and iso-octane had been suggested and used as a reference model. The ignition


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delay time of GTL kerosene was modeled using the simplified surrogates and the numerical results were compared with the experimental data.

In this work, numerical simulations of surrogate fuels for aviation kerosene were summarized and analyzed; after a comprehensive comparison, n-decane was selected to be the one-component surrogate fuel for aviation kerosene. By referencing the detailed chemical reaction mechanism of Bikas(9), eliminating low-temperature reactions and the reaction mechanism of benzene, and referring to the detailed mechanism of Huiru et al.(10), the simplified mechanism of surrogate fuel(n-decane) was obtained from sensitivity analysis (11) and response flow analysis. Because the numbers of the intermediate components and elementary reactions can be sharply decreased, the computational cost can be reduced largely. A combustion test using premixed, pre-evaporated fuel in a Bunsen burner was then carried out to study the combustion flame of RP-3 aviation kerosene; the temperature and gas component concentrations in the axial and radial directions at different heights were measured. In addition, a numerical simulation model of the premixed flame of the Bunsen burner was built, and the resulting numerical simulation results were compared with the experimental data to verify the correctness of the simplified mechanism. Therefore, the simplified mechanism is the result of a trade-off between mechanism complexity, mechanism accuracy and range of applicability.

1.Surrogate fuels of aviation kerosene and the simplified mechanism

In recent years, a large quantity of research has been conducted with the aim of finding surrogate fuels for aviation kerosene, and many single- or multi-component surrogate fuels have been proposed (Table 1).Huiru et al. (10) applied n-decane as a single-component surrogate fuel for aviation kerosene; Table 1 shows that n-decane is often found in large proportions in surrogate fuels. Both the physical and chemical properties of n-decane are similar to those of aviation kerosene. Additional equations are needed in reacting flows for all species in


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Computational Fluid Dynamics (CFD), therefore the number of component equations increases sharply with the increase of the number of components in a surrogate fuels. Considering the computing costs, the number of components in a surrogate fuel cannot be too large. In this paper, having considered all of the above factors, ndecane was chosen as the single-component surrogate fuel for aviation kerosene.

Bikas and Peters (9) compiled a chemical reaction mechanism for the combustion of n-decane, and experimentally validated the chemical reaction mechanism for a wide range of conditions. Due to the large number of reactions, the computing cost is very high when the chemical reaction mechanism is applied to numerically simulate the combustion process of gas turbine combustors. Based on the detailed chemical reaction mechanism of Bikas and Peters (9), sensitivity analysis and reaction-path analysis were used to simplify the detailed chemical reaction mechanism according to the combustion temperature and the reaction components.

In order to establish the simplified mechanism, the Chemkin was used. Sensitivity analysis was carried out in a closed homogeneous reactor according to the steady-state temperature for an equivalent ratio of 1.0, a pressure of 0.5MPa, and initial temperatures of 1300, 1400, 1500, 1600 and 1700 K. The threshold of the temperature sensitivity coefficient was 1.0; thus, elementary reactions with sensitivity coefficients greater than 1.0 were retained, while the others were deleted. At the same time, the sensitivity analysis was carried out according to the mole concentration of each reactant with an equivalent ratio of 1.0, a temperature of 1500 K, and a pressure of 0.1MPa. The threshold of concentration sensitivity coefficient was 0.1; thus, elementary reactions with sensitivity coefficients greater than 0.1 were retained, while the others were deleted. Finally, the reaction-path analysis method was used to further improve the simplification process; in this method the temperature was 1500 K, the pressure was 1atm, and the equivalent ratio was 1.0. The reactions with net generation rates exceeding 1.0e5

mol/(cm3.s) were retained.


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1.1 Analysis of simplification results

Figure 1 shows the variation in the top ten highest temperature sensitivity coefficient with time for an initial temperature of 1500 K and a pressure of 5 atm. The ten most important elementary reactions, involving about 344 steps, in the detailed chemical reaction mechanism(9) are shown. The sensitivity coefficients change as the reaction progresses. The absolute values of the temperature sensitivity coefficient are larger when the time of the chemical reaction is near the ignition delay time; however, the temperature sensitivity coefficient tends to zero quickly prior to the ignition or after reaction completion. Thus, the time at which the temperature sensitivity coefficient is at its maximum can be considered to be the ignition delay time.

Figure 2 shows the top ten highest temperature sensitivity coefficient of elementary reactions for different initial temperatures. Figures 2 (a)–(e) show the values of the temperature sensitivity coefficient for the ten most important elementary reactions at different temperatures. The temperature sensitivity coefficient becomes smaller with increasing initial temperature. The reason is that most elementary reactions can reach the activation energy at high temperature; thus, they become less and less sensitive to temperature. As the main reaction to produce OH (H + O2OH + O) is highly sensitive to temperature, and the temperature sensitivity increases with increasing initial temperature, this demonstrates that OH is a sign of the development of ignition and combustion.

Figure 3 lists some of the elementary reactions that are closely related to the molar concentration sensitivity coefficients of O2 and OH at an initial temperature of 1500 K, a pressure of 1 atm, and an equivalent ratio of 1.0. Comparing Figure 3 with Figure 2, the top ten highest molar concentration sensitivity coefficients of elementary reactions are basically consistent with the top ten highest temperature sensitivity coefficients; this shows that both the concentration of important components and the reaction temperature are important for the fuel combustion process. Figures 3 (a) and (b) show that the molar concentration sensitivity coefficients of O2 and OH are similar,


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but the values are the opposite. The reaction CH3+ HO2CH3O + OH plays an important role in the oxidation process of CH3. The superoxide acid mainly comes from the oxidation of H radicals by O2, which has extremely strong oxidizability. Figure 4 shows the contribution of OH generation and consumption in every elementary reaction. The reaction H + O2OH + O is the most important branch of the chain reaction and playsan important part in OH production. The consumption of OH is mainly through reactions with C1–C3 compounds to generate H2O and the reactants of the next reaction are obtained. Hence, the entire reaction is accelerated.

1.2 Simplified mechanism

Based on above sensitivity analysis and the reaction-path analysis methods, the detailed chemical reaction mechanism containing 344 steps was simplified to a mechanism comprising 36 species and 62 steps; thus, the simplified chemical reaction mechanism of n-decane was established. The elementary reactions are shown in Table 2. At the same time, the comparison of the ignition delay time for the simplified mechanism with the detailed chemical reaction mechanism is shown as Fig.5. When the pressure is 5atm and the equivalent ratio is 1, the ignition delay time of simplified mechanism has a good accordance with that of the detailed mechanism, especially for the high temperature.

2. Experimental test of the combustion of premixed, pre-evaporation aviation kerosene in a Bunsen burner

In order to accurately verify the simplified chemical reaction mechanism of the surrogate fuel of RP-3 aviation kerosene, the test system should be simple to reduce the influence of outside factors, thus making the data more reliable. In this paper, a Bunsen burner experiment was designed to combust premixed, pre-evaporated RP-3 aviation kerosene (Figures 6 and 7). RP-3 kerosene was extracted from the fuel tank by an oil pump with a controlled flow rate. The liquid kerosene was injected into a quartz glass tube and heated by a set of electric heaters which were situated outside of the quartz glass tube. The heating temperature was controlled by adjusting


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the voltage of the electric heater. The liquid kerosene then becomes aviation kerosene steam. Fresh air was supplied by the air pump at a flow rate controlled by the rotor flow meter. Air was flowed into another quartz glass tube and heated by a set of electric heaters outside of the quartz glass tube. The heated kerosene steam and fresh air were flowed into the bottom of the Bunsen burner and mixed in the duct of the Bunsen burner, and the inlet temperature of combustible gas was measured by the thermocouple. Then, after flowing from the Bunsen burner nozzle jet, the mixed gas was ignited, and the pre-evaporated, premixed combustion flame of kerosene was formed. The flame temperature was measured using a single point of a double platinum rhodium thermocouple. The sample gas was collected using a single point sampling tube and cooled rapidly to stop the chemical reaction. The gas concentration was measured using gas analyzer. By moving the 3D coordinate frame, the temperature and gas concentration distribution in the axial and radial directions at different heights were measured. Gas temperature was measured using a platinum-30% rhodium/platinum-6% rhodium thermocouple, and its measuring range is 270K to 2200K, and the measuring error is ±10K, that is, the measuring error level is 0.45%. The volume concentrations of O2 and CO2 are measured by the SIEMENS U23 infrared continuous gas analyzer through gas sampling, and the sampling pipe is electrically heated to assure the measurement accuracy. The measuring range of CO2 volume concentration is 0 to 10%, and the measuring lever is 1%. And the measuring range of O2 volume concentration is 0 to 25%, and the measuring lever is 0.5%.

3. Numerical simulation method A 3D numerical simulation model was established according to the proportion of 1:1 for the experimental Bunsen burner, and an imaginary cylinder chimney with a height of 600 mm and a diameter of 350 mm was added outside the combustion flame (Figure 8).The unstructured grid is used, the local grid near the outlet of Bunsen burner is refined, and the grid independence is verified, finally the total number of mesh is 1394786. The working conditions of the experiment and the numerical simulation are the same and shown in Table 3.


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Fluent 12.0 was used to simulate the combustion process of Bunsen burner. The mass flow inlet boundary condition was applied for the combustible gas inlet of the Bunsen burner. The pressure inlet boundary condition was used for the outer ring of the Bunsen burner inlet, and the pressure outlet boundary condition was adopted for the outlet of the Bunsen burner (Figure 7). The standard k-ε turbulence mode, component transport model, and Eddy Dissipation Concept(EDC) mode were used to simulate the combustion. Second-order upwind scheme was applied for the discretization of the pressure equation, and Quadratic Upwind Interpalation (QUICK) scheme was used for the discretization of the momentum equations, turbulence kinetic energy and its dissipation rate, energy equation and components equation. The employed convergence criterion was that the import and export flow relative errors were less than 1%, and all residual error was less than 1.0e-3. 4. Analysis of Bunsen flame results

4.1. Temperature distributions

Figure 9 and Figure 10 show the velocity contour and temperature contour at central axial section. The combustible gas injects into the static atmosphere from the Bunsen burner nozzle, because of the entrainment of the jet, the surrounding air is sucked in, therefore, the width of jet gradually increases firstly and then decreases, but the velocity of jet gradually decreases. When the mixed gas was ignited at the outlet of Bunsen burner nozzle, the pre-evaporated, premixed combustion flame of kerosene was formed, the temperature reaches a maximum near the flame front, then the temperature decreases. Figure 11 compares the temperature distributions of numerical simulation and experiment on the central axis of the Bunsen flame under three conditions. Figure 11 shows that the numerical simulation results are in good agreement with the experimental results for the temperature distributions. The temperature rises sharply behind the Bunsen burner inlet, forming a hightemperature zone, and then reaches the maximum near the position for the distance to the inlet of 0.02m. As


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distance increases, the cold air is entrained into the jet flame, and the fuel is consumed; therefore, the fuel/air ratio gradually decreases, the combustion intensity weakens, and the flame temperature gradually decreases and finally tends to the ambient temperature when the measuring position is far from the inlet of the Bunsen burner. With decreasing fuel/air ratio (Case 1 to Case 3), the position of maximum temperature gradually moves to the inlet of Bunsen burner. In all cases, the results of simulating the 62 steps of the simplified mechanism are in good agreement with experimental data, especially when the fuel/air is equivalent (Case 2) or lean (Case 3), the predicted flame temperature on the axis is more accurate. When the fuel/air is rich, the flame temperature distribution in the central position agrees well with the experimental data; however, there are some differences in the inner flame zone of Bunsen burner. Figure 12 shows the temperature distribution in the radial direction at different heights in Case 2. On the flame section near the Bunsen burner inlet (Figure 12(a)), the fuel is rich and the air is lean in the center which is called the inner flame, combustion is not complete, therefore the temperature is low. With increasing of radius, the cold air is entrained into the jet flame and takes part in the combustion, and the temperature rises and reaches its maximum on the flame front where the fuel/air ratio is equivalent. At the outer flame, the air is excessive and fuel is lean, and the cold air takes away a lot of heat through convection, so the temperature decreases with the increase of radius. The simulation results for the 62 steps of the simplified mechanism are in good agreement with the experimental data, with some small differences at the flame edge. The simulated temperature is slightly higher than the experimental data at the center of the flame; however, the temperature decreases moving outward from the center, which is in good agreement with the experimental data.

4.2 O2 concentration

Figure 13 compares the simulated and experimental O2 concentration distributions under three conditions. The simulation and experimental results basically show the same trend. In all cases, at the inner flame zone, the


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numerical simulation results are in good agreement with the experimental results for the oxygen concentration. But at the outer flame zone, due to the entrainment of cold air, the oxygen concentration of experimental measurement is larger than that of the simulation results of the 62 steps mechanism, especially for the rich fuel case (Case 1). However, the O2 concentration agrees well with the experimental data for the lean fuel case (Case 3) and could be used to predict the ignition delay very well. Figure 14 shows the O2 concentration distribution in the radial direction at different heights for case 3. In all cases, the trend in O2 concentration distribution is the same at different heights. The temperature is the highest at the flame front position (Figure 12(a)) or the central position (Figure 12(b) or Figure 12(c)); thus, the combustion is the most violent at this position, which consumes a large amount of O2 consumption, resulting in the lowest O2 concentration. With increasing radius, fuel becomes less, temperature drops, and O2 concentration increases sharply. The simulated results show good agreement with the experimental data (Figure 14(a) and Figure 14(b)). However, at the flame tail (Figure 14(c)), with the mixing of cold air, the O2 concentration increases rapidly, and the calculated and experimental results are quite different.

4.3 CO2 concentration

Figure 15 compares the simulated and experimental CO2 concentration distributions under three conditions. The trends in CO2 concentration in the axial direction are the same. At the inlet of the Bunsen burner, the flame front is formed with intense burning, and CO2 concentration increases until it reaches a maximum to form a highconcentration zone. Then, as combustion intensity weakens, CO2 gas diffuses and mixes with the surrounding air, the concentration drops rapidly. The simulated concentrations are always higher than the experimental ones, especially in the rising stage. The simulated position of maximum CO2 concentration is 0.04m, while the experimental value is 0.07m (Figure 15(a)). During the decline in CO2 concentration, the simulated results show good agreement with the experimental data, especially for the equivalent or lean fuel/air ratio. Figure 16 shows


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the CO2 concentration distribution at the radial direction at different heights for Case 1. Figure 16(a) shows that the O2 is lacking at the inner flame, and combustion is not sufficient; thus, significant amounts of CO are produced, and CO2 concentration is low at the center. Radiating outward from the center, O2 is supplied from surrounding environment, prompting the reaction of CO to form CO2, and the high-CO2-concentration area is formed. Then, as CO2 diffuses, its concentration decreases along the radial direction. It can be seen that in the decline stage, simulation results of the 62 steps mechanism is basically consistent with experiment data; however, there are certain differences in center zone. In addition, at the outer flame zone, O2 is available in sufficient quantities, and combustion is complete; therefore, the CO2 concentration is the highest at the center of the flame and decreases outwards in the radial direction. The CO2 concentration in the radial direction is largely in agreement with the experimental data; thus, the numerical simulation is highly accurate.

5. Conclusions

1) The n-decane was chosen as the single component surrogate fuel for RP-3 aviation kerosene, and a simplified mechanism comprising 36 species and 62 steps was obtained based on detailed mechanism.

2) A Bunsen burner experiment was designed to combust premixed, pre-evaporated RP-3 aviation kerosene, and the temperature and gas composition concentrations in the axial and radial directions at different heights were measured seperately.

3) The simplified mechanism was used to simulate the combustion process for the Bunsen burner, and the simulated temperature, O2 and CO2 concentrations in the axial and radial directions at different heights have a good agreement with the experimental results under different working conditions.

4) The numbers of the intermediate components and elementary reactions are largely cut down for the simplified mechanism, and the computational time and computational resources can decrease sharply. Therefore,


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the simplified mechanism can be used to simulate the real combustion process of the gas turbine combusting RP-3 aviation kerosene.

Acknowledgments This work received funding from National Natural Science Foundation of China (No.51676097) and the Fundamental Research Funds for the Central Universities (No.NJ20140023).

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Table captions

Table 1 Surrogate fuels of aviation kerosene in numerical simulation Table 2 Simplified chemical reaction mechanism of n-decane Table 3 Experimental and numerical simulation conditions Figure captions

Figure 1 Variation in the temperature sensitivity coefficient with time about partial reactions(T0= 1500 K, P＝ 5atm, TOP 10) Figure 2 Temperature sensitivity coefficient of partial reactions at different temperatures Figure 3 OH and O2 sensitivity coefficients of partial reactions Figure 4 Contribution of every reaction to the rate of OH production Figure 5 Ignition delay time of simplified and detailed mechanism (equivalent ratio=1) Figure 6 Diagram of the experimental Bunsen burner combustion system Figure 7 Photo of the experimental system Figure 8 Calculation model Figure 9 Velocity contour at central axial section Figure 10 Temperature contour at central axial section Figure 11 Comparison of temperature distributions on the central axis Figure 12 Temperature distributions in the radial direction at different heights (Case 2) Figure13 Comparison of O2 concentration distributions on the central axis Figure 14 O2 concentration distributions on the radius direction at different heights (case 3) Figure 15 Comparison of CO2 concentration distributions on the central axis Figure 16 CO2 concentration distributions in the radial direction at different heights (Case 1)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 1 Alternative fuels of aviation kerosene in numerical simulation Kerosene type RP-3 Baoguo et al. [14]

Alternative fuels 79% n-decane, 13% trimethyl-cyclohexane

Reaction mechanism 109 species, 946 steps

16% ethylbenzene Huiru et al. [10]

RP-3

n-decane

388 species, 2226 steps

32.6% n-decane Montgomery[15]

34.7% n-dodecane JP-8

16.7% trimethylcyclohexane

90 species, 573 steps

16% butylbenzene 79% n-decane， Gueret [16] Jet A-1

10% npropylcyclohexane， 11% 1,2,4trimethylbenzene

Luche [17] Jet A-1

Global reaction mechanism

n-decane，

134 species,

n-propylbenzene,

1220 steps

n-propylcyclohexane 74% n-decane,

Dagaut[18]

15% n-propylbenzene， Jet A-1

Honnet[19]

11% npropylcyclohexane

Jet A-1

80% n-decane， 20% 1,2,4trimethylbenzene

Vovelle [20]

Cook[21]

Kyne[22]

Jet A-1

JP-8

209 species, 1673 steps 118 species, 914 steps

90% n-decane,

39 species,

10% toluene

207 steps

n-decane, n-dodecane, n-hexadecane, xylenes, decaline, tetraline

221 species,

89% n-decane,

84 species,

11% tobulene

440 steps

Jet A-1


5032 steps

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 38

Table 2 Simplified chemical reaction mechanism of n-decane k = A / NO.

Reaction

A

n

E(J/mol)

1

N-C10H22+OH=>T-C10H21+H2O

1.00E+14

0

47630

2

N-C10H22+OH=>S-C10H21+H2O

1.00E+14

0

49000

3

N-C10H22+H=>T-C10H21+H2

4.50E+07

2

4995.22

4

N-C10H22+H=>S-C10H21+H2

4.50E+07

2

4995.22

5

T-C10H21=>P-C6H13+P-C4H8

1.50E+13

0

28274.38

6

S-C10H21=>P-C7H15+C3H6

1.50E+13

0

28274.38

7

P-C7H15=>P-C4H9+C3H6

2.00E+13

0

28776.29

8

P-C7H15=>P-C4H8+N-C3H7

2.00E+13

0

28776.29

9

P-C7H15=>P-C5H10+C2H5

4.00E+13

0

28776.29

10

P-C6H13=>P-C4H9+C2H4

2.50E+13

0

28776.29

11

P-C5H10=>C2H5+C3H5

3.16E+16

0

80901

12

P-C4H9C2H5+C2H4

2.50E+13

0

28824.09

13

C3H5+CH3P-C4H8

1.00E+13

0

0

14

C3H8+HN-C3H7+H2

1.30E+14

0

9703.63

15

C2H5+CH3C3H8

7.00E+12

0

0

16

N-C3H7CH3+C2H4

9.60E+13

0

31022.94

17

N-C3H7H+C3H6

1.25E+14

0

37021.99

18

C3H6+OHC3H5+H2O

7.90E+12

0

0


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Energy & Fuels

19

C3H5+H=> C3H4+H2

3.33E+12

0

0

20

C3H4+OH=>C3H3+H2O

2.00E+07

2

998.71

21

C3H3+OC2H2+CO+H

1.40E+14

0

0

22

C2H6+OHC2H5+H2O

7.20E+06

2

860.42

23

C2H6+HC2H5+H2

1.40E+09

1.5

7433.08

24

C2H5+O2C2H4+HO2

1.02E+10

0

-2186.18

25

C2H4+OCH3+HCO

1.36E+07

1.88

178.78

26

C2H4+OHC2H3+H2O

3.00E+13

0

3011.47

27

C2H4+HC2H3+H2

5.40E+14

0

14913.96

28

C2H3+O2C2H2+HO2

5.19E+15

-1.26

3307.84

29

C2H3+O2CH2O+HCO

1.70E+29

-5.31

6493.79

30

C2H2+OHCCO+H

5.06E+06

2.1

1570.27

31

C2H2+OT-CH2+CO

2.17E+06

2.1

1570.27

32

HCCO+O22CO+OH

8.13E+11

0

855.64

33

HCCO+O2HCO+CO2

8.13E+11

0

855.64

34

HCCO+HP-CH2+CO

1.50E+14

0

0

35

CH4+OHCH3+H2O

1.56E+07

1.83

2772.47

36

CH4+OCH3+OH

7.23E+08

1.56

8484.7

37

CH4+HCH3+H2

1.30E+04

3

8030.59

38

CH3O+M=>CH2O+H+M

5.42E+13

0

13503.82


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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39

CH3+HO2CH3O+OH

3.78E+13

0

0

40

CH3+OCH2O+H

8.43E+13

0

0

41

OH+CH3P-CH2+H2O

2.50E+13

0

0

42

2CH3C2H5+H

0.2677

1821.91

43

CH2O+OH=>HCO+H2O

3.43E+09

1.18

-454.11

44

CH2O+H=>HCO+H2

1.26E+08

1.62

2165.39

45

P-CH2+CO2CO+CH2O

1.40E+13

0

0

46

P-CH2+C2H4C3H6

9.64E+13

0

0

47

2CH3+M=>C2H6+M

0

0

48

P-CH2+MT-CH2+M

1.50E+13

0

0

49

T-CH2+O2=>CO2+H2

1.20E+13

0

1481.84

50

T-CH2+O2=>CO+OH+H

1.30E+13

0

1481.84

51

T-CH2+CH3C2H4+H

4.22E+13

0

0

52

HCO+OHCO+H2O

1.02E+15

0

0

53

HCO+MCO+H+M

7.00E+14

0

16802.1

54

CO+OHCO2+H

8.97E+06

1.5

-740.92

55

H+O2OH+O

9.76E+13

0

14842.26

56

O+H2OH+H

5.12E+04

2.67

6285.85

57

OH+H2H2O+H

1.02E+08

1.6

3298.28

58

2OHH2O+O

1.51E+09

1.14

100.38

3.16E+13

1.81E+13


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Energy & Fuels

59

H+O2+MHO2+M

3.54E+18

-0.8

0

60

HO2+H2OH

1.69E+14

0

874.76

61

HO2+HH2+O2

4.28E+13

0

1410.13

62

HO2+HH2O+O

3.01E+13

0

1720.84


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 38

Table 3 Experimental and numerical simulation conditions Pipe

Case

diameter/mm

Fuel flow ml/h

Air flow L/h

Inlet

Fuel/air

Reynolds

temperature/K

ratio

numbers

1

90

650

430

0.0835

1540

2

90

800

430

0.0678

1875

3

90

900

430

0.0603

2098

12


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Energy & Fuels

Figure 1 Variation in the temperature sensitivity coefficient with time about partial reactions (T0= 1500 K, P＝5atm, TOP 10)


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

（a） T0=1300K

Page 24 of 38

（b）T0=1400K

（c）T0=1500K

（d）T0=1600K

（e）T0=1700K

Figure 2 Temperature sensitivity coefficient of partial reactions at different temperatures


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Energy & Fuels

(a) OH

(b) O2

Figure 3 OH and O2 sensitivity coefficients of partial reactions


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4 Contribution of every reaction to the rate of OH production


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Energy & Fuels

Figure 5 Ignition delay time of simplified and detailed mechanism (equivalent ratio=1)


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 6 Diagram of the experimentalBunsen burner combustion system


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Energy & Fuels

Figure 7 Photo of the experimental system


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8 Calculation model


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure 9 Velocity contour at central axial section


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 10 Temperature contour at central axial section


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a) Case 1

(b) Case 2

(c) Case 3 Figure 11 Comparison of temperature distributions on the central axis


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) h=0.008m

(b) h=0.024m

(c) h=0.042m Figure 12 Temperature distributions in the radial directionat different heights (Case 2)


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Energy & Fuels

(a) Case 1

(b) Case 2

(c) Case 3 Figure 13 Comparison of O2 concentration distributions on the central axis


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) h=0.017m

(b) h=0.035m

(c) h=0.065m Figure 14 O2 concentration distributions on the radius direction at different heights (case 3)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a) Case 1

(b) Case 2

(c) Case 3 Figure 15 Comparison of CO2 concentration distributions on the central axis


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a) h=0.022m

(b) h=0.048m

(c) h=0.088m Figure 16 CO2 concentration distributions in the radial direction at different heights (Case 1)


Page 38 of 38

Simplified Chemical Reaction Mechanism for Surrogate Fuel of

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