Prediction model and prediction method for oxidation coking reaction of hydrocarbon fuel

Abstract

A prediction model and a prediction method for an oxidation coking reaction of a hydrocarbon fuel relate to the field of hydrocarbon fuels, and the prediction method comprises the following steps: simplifying an oxidation coking process of the hydrocarbon fuel into a two-step reaction: 1, simplifying a chain free radical reaction of the hydrocarbon fuel into a total inclusion reaction for directly generating a coking precursor by the hydrocarbon fuel; in the second step, the carbon precipitation reaction of the coking precursor on the wall surface and the deposition process of the coke are simplified into a wall surface reaction of directly generating the coke on the wall surface by the coking precursor; the reaction rates of the two-step reaction are given in the form of an Arrhenius formula; unknown parameters in a reaction rate calculation formula are solved based on a quasi-infinitesimal method, a prediction model of the hydrocarbon fuel oxidation coking reaction is obtained, and the prediction model is embedded into a CFD solver for hydrocarbon fuel oxidation coking reaction prediction. According to the method, only two chemical reaction processes are included, the prediction precision is improved by 20%, and accurate prediction of hydrocarbon fuel oxidation coking at low calculation cost is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of hydrocarbon fuels, and in particular to a prediction model and a prediction method for an oxidation coking reaction of hydrocarbon fuels. Background Art

[0002] Hypersonic vehicles have high flight speeds and wide flight envelopes, and are of great significance in the fields of national defense, economy, science and technology. With the continuous increase in flight Mach number, the temperature of the combustion chamber wall continues to increase, and the thermal protection problem has become the key to inhibiting the further development of hypersonic vehicles. The regenerative cooling technology that uses the hydrocarbon fuel of the hypersonic vehicle to cool the outer wall of the combustion chamber can not only use the high heat sink of the hydrocarbon fuel to meet the cooling needs, but also preheat the hydrocarbon fuel to improve the combustion efficiency. It is an effective means to solve the thermal protection problem of hypersonic aircraft. However, during the heat exchange and heating process of the hydrocarbon fuel, when the temperature reaches above 150℃, the hydrocarbon fuel will undergo an oxidation and coking reaction, generating a coke layer with low thermal conductivity attached to the wall, causing heat exchange deterioration and increased flow resistance, and even causing channel blockage and leading to local over-temperature and over-limit. Therefore, the accurate prediction of the oxidation and coking reaction of hydrocarbon fuel is related to the successful realization of regenerative cooling technology and is of great significance to the design of cooling schemes for hypersonic aircraft.

[0003] The oxidation coking reaction of hydrocarbon fuels contains hundreds of elementary chemical reactions. The main method for predicting the oxidation coking of hydrocarbon fuels is to use a simplified kinetic model embedded in CFD (Computational Fluid Dynamics) calculation. Existing models that can accurately predict the oxidation coking reaction generally contain more than 6 chemical reactions, such as the model disclosed in reference Ⅰ (Pei X, Hou L, Ren Z. Kinetic modeling of thermal oxidation and coking deposition in aviation fuel. Energy Fuels 2017; 31: 1399-1405.) contains 6 reactions, and the model disclosed in reference Ⅱ (Liu Z, Tang S, Li Z, Qiu Z, Qin Z, Yuan S, et al. An improved kinetic model for deposition by thermal oxidation of aviation hydrocarbon fuels. Fuel 2019; 258: 116139.) contains 34 reactions, which is cumbersome and consumes a lot of computing resources. Summary of the invention

[0004] In order to solve the problems of the existing hydrocarbon fuel oxidation coking prediction kinetic model in the actual prediction process, such as the large number of chemical reactions, cumbersome process and large consumption of computing resources, the present invention provides a prediction model and prediction method for hydrocarbon fuel oxidation coking reaction. The prediction method for hydrocarbon fuel oxidation coking reaction provided by the present invention only includes two chemical reaction processes, realizes the accurate prediction of hydrocarbon fuel oxidation coking at low computing cost, and has important theoretical guiding significance for the design of regenerative cooling scheme for hypersonic aircraft.

[0005] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0006] The present invention provides a method for predicting a hydrocarbon fuel oxidation coking reaction, comprising the following steps:

[0007] The hydrocarbon fuel oxidation coking process is simplified into two-step reactions. The first step is a total package space reaction, that is, the chain radical reaction of hydrocarbon fuel is simplified to a total package reaction in which hydrocarbon fuel directly generates coking precursors. The second step is a wall reaction, that is, the carbon deposition reaction of the coking precursor at the wall and the coke deposition process are simplified to a wall reaction in which the coking precursor directly generates coke at the wall. The reaction rates of the above two-step reactions are given in the form of Arrhenius formula. The unknown parameters in the reaction rate calculation formula are solved by a quasi-element method to obtain a prediction model for the hydrocarbon fuel oxidation coking reaction, and the prediction model for the hydrocarbon fuel oxidation coking reaction is embedded in a CFD solver to predict the hydrocarbon fuel oxidation coking reaction.

[0008] Further, the reaction equation of the two-step reaction is:

[0009]

[0010]

[0011] Formula (1) is the reaction equation of the first step reaction, and formula (2) is the reaction equation of the second step reaction, where F represents hydrocarbon fuel, α represents oxygen concentration index, O2 represents dissolved oxygen, P represents coking precursor, IN represents insoluble intermediate product, and D represents coke; τ represents reaction time; k′1 represents the reaction rate constant of the first step reaction; k1 represents the reaction rate constant of the first step reaction after ignoring the change in the concentration of hydrocarbon fuel itself; and k2 represents the reaction rate constant of the second step reaction.

[0012] Furthermore, the reaction rate is calculated as follows:

[0013]

[0014] Wherein, k1 represents the reaction rate constant of the first step reaction, A1 represents the pre-exponential factor of the first step reaction, and represents the effect of hydrocarbon fuel density on the transport process of coking precursor to the wall; ρ b Represents the average density of hydrocarbon fuel; E a1 represents the activation energy of the first step reaction; R represents the molar gas constant; t b represents the qualitative temperature of hydrocarbon fuel; k2 represents the reaction rate constant of the second step reaction; A2 represents the pre-exponential factor of the second step reaction; E a2 represents the activation energy of the second step reaction; represents the effect of wall temperature gradient on coke deposition process, where T w represents the wall temperature, and B represents a dimensionless parameter used to reflect the influence of the wall.

[0015] Furthermore, the specific process of solving the unknown parameters in the reaction rate calculation formula by the method based on the quasi-element method is:

[0016] Carry out hydrocarbon fuel oxidation coking experiments under different flow pipeline lengths, ensure that other conditions remain unchanged, first measure the hydrocarbon fuel composition and concentration at the pipeline outlet; then regard the hydrocarbon fuel composition and concentration at the short pipeline outlet as the hydrocarbon fuel composition and concentration at the middle of the long pipeline, and obtain the hydrocarbon fuel composition and concentration at each position in the middle of the pipeline; finally, solve the unknown parameters by solving the reaction process at different positions in the long pipeline, and obtain the prediction model of hydrocarbon fuel oxidation coking reaction.

[0017] Furthermore, the specific process of embedding the prediction model of hydrocarbon fuel oxidation coking reaction into the CFD solver to predict the hydrocarbon fuel oxidation coking reaction is as follows:

[0018] Within a time step, for a grid, determine whether it belongs to the coking temperature range. If not, do not solve the oxidation coking reaction and end directly; if it does, start solving the first step reaction, read the local aviation kerosene concentration, dissolved oxygen concentration and temperature of the grid, solve the coking precursor concentration, and then determine whether the grid belongs to the near-wall grid. If not, end directly; if it does, start solving the second step reaction, read the local coking precursor concentration, temperature and temperature gradient of the grid, solve the coke formation rate, and further solve the coke formation mass and thickness; further read the coke formation thickness and use the node spring method to realize grid movement to simulate the coke layer formation and deposition, and finally achieve accurate prediction of the hydrocarbon fuel oxidation coking process at low computational cost.

[0019] Furthermore, the specific method for further solving the coke generation mass and thickness is to calculate the coke generation mass by integrating the coke generation rate, and then calculate the coke generation thickness by dividing the coke generation mass by the coke density.

[0020] The present invention provides a prediction model for the oxidation coking reaction of hydrocarbon fuels, including a reaction equation for a two-step reaction and a calculation formula for the reaction rate. The reaction equation for the two-step reaction is:

[0021]

[0022]

[0023] The calculation formula of the reaction rate is:

[0024]

[0025] Formula (1) is the reaction equation of the first step reaction, and formula (2) is the reaction equation of the second step reaction, where F represents hydrocarbon fuel, α represents oxygen concentration index, O2 represents dissolved oxygen, P represents coking precursor, IN represents insoluble intermediate product, and D represents coke; τ represents reaction time; k'1 represents the reaction rate constant of the first step reaction; k1 represents the reaction rate constant of the first step reaction after ignoring the change in the concentration of hydrocarbon fuel itself; A1 represents the pre-exponential factor of the first step reaction, which represents the effect of hydrocarbon fuel density on the transport process of coking precursor to the wall; ρ b Represents the average density of hydrocarbon fuel; E a1 represents the activation energy of the first step reaction; R represents the molar gas constant; t b represents the qualitative temperature of hydrocarbon fuel; k2 represents the reaction rate constant of the second step reaction; A2 represents the pre-exponential factor of the second step reaction; E a2 represents the activation energy of the second step reaction; represents the effect of wall temperature gradient on coke deposition process, where T w represents the wall temperature, and B represents a dimensionless parameter used to reflect the influence of the wall.

[0026] The beneficial effects of the present invention are:

[0027] The present invention provides a prediction method for hydrocarbon fuel oxidation coking reaction, which includes only two chemical reaction processes. Under 15 different working conditions within the range of Reynolds number 5000-50000, pressure 2.5-3.5MPa, temperature 200-450°C, and dissolved oxygen concentration 2-20ppm, the deviation between the predicted value of the coking amount and the experimental value does not exceed 10%. Compared with the existing hydrocarbon fuel oxidation coking kinetics prediction model, the prediction accuracy of the present invention is improved by 20%, and the accurate prediction of hydrocarbon fuel oxidation coking reaction is achieved with low computing resource consumption. The prediction efficiency is improved while ensuring the prediction accuracy, which has important theoretical guiding significance for the design of regenerative cooling schemes for hypersonic aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The invention discloses a solution path diagram for a prediction model of a hydrocarbon fuel oxidation coking reaction.

[0029] Figure 2 The figure is a comparison chart of the prediction results of the model of the present invention, the prediction results of the existing model and the experimental values ​​under 15 different working conditions. DETAILED DESCRIPTION

[0030] In a first aspect, the present invention provides a method for predicting the oxidation coking reaction of hydrocarbon fuels.

[0031] A prediction method for the oxidation coking reaction of hydrocarbon fuels of the present invention has the following specific implementation process:

[0032] Step S1: constructing a prediction model for the oxidation coking reaction of hydrocarbon fuels;

[0033] S1.1: Simplified steps of the hydrocarbon fuel oxidation coking process;

[0034] Firstly, the oxidation coking process of hydrocarbon fuel is simplified into two steps. The first step is a total package space reaction, that is, the chain radical reaction of hydrocarbon fuel is simplified to a total package reaction in which hydrocarbon fuel directly generates coking precursor; the second step is a wall reaction, that is, the carbon deposition reaction of coking precursor at the wall and the coke deposition process are simplified to a wall reaction in which coking precursor directly generates coke at the wall.

[0035] The reaction equations for the above two-step reaction are as follows:

[0036]

[0037]

[0038] Formula (1) is the reaction equation of the first step reaction, and formula (2) is the reaction equation of the second step reaction. Among them, F represents hydrocarbon fuel, α represents oxygen concentration index, O2 represents dissolved oxygen, P represents coking precursor, IN represents insoluble intermediate product, D represents coke; τ represents reaction time; k1 represents the reaction rate constant of the first step reaction after ignoring the change of hydrocarbon fuel concentration itself; k2 represents the reaction rate constant of the second step reaction.

[0039] The reaction rates of the above two-step reactions are given in the form of the Arrhenius formula, and the specific calculation formula is as follows:

[0040]

[0041] Wherein, k1 represents the reaction rate constant of the first step reaction, A1 represents the pre-exponential factor of the first step reaction, and represents the effect of hydrocarbon fuel density on the transport process of coking precursor to the wall; ρ bRepresents the average density of hydrocarbon fuel; E a1 represents the activation energy of the first step reaction; R represents the molar gas constant; t b represents the qualitative temperature of hydrocarbon fuel; k2 represents the reaction rate constant of the second step reaction; A2 represents the pre-exponential factor of the second step reaction; E a2 represents the activation energy of the second step reaction; represents the effect of wall temperature gradient on coke deposition process, where T w represents the wall temperature, and B represents a dimensionless parameter used to reflect the influence of the wall.

[0042] S1.2: Solve the unknown parameters in the reaction rate calculation formula to obtain the prediction model of hydrocarbon fuel oxidation coking reaction;

[0043] The reaction rate calculation formula given above contains unknown pre-exponential factors, activation energy and reactant concentration exponents, which can be solved by a method based on the quasi-differential method. The specific solution steps are as follows: carry out hydrocarbon fuel oxidation coking experiments under different flow pipeline lengths, ensure that other conditions remain unchanged, first measure the hydrocarbon fuel composition and concentration at the pipeline outlet; then regard the hydrocarbon fuel composition and concentration at the short pipeline outlet as the hydrocarbon fuel composition and concentration at the middle position of the long pipeline, and obtain the hydrocarbon fuel composition and concentration at each position in the middle of the pipeline; finally, solve the unknown parameters by solving the reaction process at different positions in the long pipeline, and obtain a prediction model for the hydrocarbon fuel oxidation coking reaction.

[0044] Step S2: prediction step of hydrocarbon fuel oxidation coking reaction;

[0045] The prediction model of hydrocarbon fuel oxidation coking reaction finally obtained above is embedded in the CFD solver, and its solution path is as follows: Figure 1 As shown, within a time step, for a grid, it is determined whether it belongs to the coking temperature range. If not, the oxidation coking reaction is not solved and the process ends directly. If it does, the first step of the reaction is solved, the local aviation kerosene concentration, dissolved oxygen concentration and temperature of the grid are read, the coking precursor concentration is solved, and then it is determined whether the grid belongs to a near-wall grid. If not, the process ends directly. If it does, the second step of the reaction is solved, the local coking precursor concentration, temperature and temperature gradient of the grid are read, the coke formation rate is solved, and the coke formation mass and thickness are further solved. Specifically, the coke formation mass can be calculated by integrating the coke formation rate, and the coke formation thickness can be calculated by dividing the coke formation mass by the coke density. The coke formation thickness is further read and the node spring method is used to realize the mesh movement simulation of the coke layer formation and deposition, which can ultimately achieve accurate prediction of the oxidation coking process of hydrocarbon fuels at a low computational cost.

[0046] In a second aspect, the present invention provides a prediction model for the oxidation coking reaction of hydrocarbon fuels.

[0047] The prediction model of the hydrocarbon fuel oxidation coking reaction of the present invention specifically includes a reaction equation of a two-step reaction and a calculation formula of a reaction rate. The reaction equation of the two-step reaction is:

[0048]

[0049]

[0050] The reaction rate is calculated as:

[0051]

[0052] Formula (1) is the reaction equation of the first step reaction, and formula (2) is the reaction equation of the second step reaction, where F represents hydrocarbon fuel, α represents oxygen concentration index, O2 represents dissolved oxygen, P represents coking precursor, IN represents insoluble intermediate product, and D represents coke; τ represents reaction time; k′1 represents the reaction rate constant of the first step reaction; k1 represents the reaction rate constant of the first step reaction after ignoring the change in the concentration of hydrocarbon fuel itself; A1 represents the pre-exponential factor of the first step reaction, which represents the effect of hydrocarbon fuel density on the transport process of coking precursor to the wall; ρ b Represents the average density of hydrocarbon fuel; E a1 represents the activation energy of the first step reaction; R represents the molar gas constant; t b represents the qualitative temperature of hydrocarbon fuel; k2 represents the reaction rate constant of the second step reaction; A2 represents the pre-exponential factor of the second step reaction; E a2 represents the activation energy of the second step reaction; represents the effect of wall temperature gradient on coke deposition process, where T w represents the wall temperature, and B represents a dimensionless parameter used to reflect the influence of the wall.

[0053] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0054] Specifically for RP-3 aviation kerosene, oxidation coking experiments were carried out with a pipeline length of 600mm-1000mm (one group every 50mm). Other conditions were as follows: inlet oil temperature 20℃, system pressure 3MPa, mass flow rate 1g / s, average actual heating heat flux density 206kW / m 2, the inlet oxygen concentration is 10ppm, the experimental time is 2h, and the two-step oxidation coking reaction prediction model is solved, where the reaction rate dimension of the first step reaction is (mol / L) -0.91 / s, the oxygen concentration index is 1.634, and the pre-exponential factor is 8.45×10 7 , the activation energy is 8.44×10 4 J / mol; the reaction rate of the second step reaction is kg / (m 2 ·s) / (mol / L), the temperature gradient exponent is 0.0769, and the pre-exponential factor is 1.08×10 2 , the activation energy is 1.29×10 5 J / mol, as shown in Table 1.

[0055] Table 1 Parameters of the prediction model for two-step oxidation coking reaction

[0056]

[0057] The above two-step oxidation coking reaction prediction model was embedded in ANSYS Fluent software using the User Defined Function method to carry out transient simulation of the oxidation coking process of RP-3 aviation kerosene. The specific simulation process is as follows: meshing the model; setting the CFD solver solution method, turbulence model and boundary conditions; and mounting UDF to solve the transient oxidation coking process. The UDF solution path for the oxidation coking process is as follows: within a time step, for a grid, determine whether it belongs to the coking temperature range (150℃-450℃). If not, do not solve the oxidation coking reaction and end directly; if it does, start solving the first step reaction, read the local RP-3 aviation kerosene concentration, dissolved oxygen concentration and temperature of the grid, solve the coking precursor concentration, and then determine whether the grid belongs to the near-wall grid. If not, end directly; if it does, start solving the second step reaction, read the local coking precursor concentration, temperature and temperature gradient of the grid, solve the coke generation rate, and further solve the coke generation mass and thickness. Specifically, the coke generation mass can be calculated by integrating the coke generation rate, and then the coke generation thickness can be calculated by dividing the coke generation mass by the coke density; further read the coke generation thickness and use the node spring method to realize grid movement to simulate the generation and deposition of the coke layer.

[0058] Fifteen different working conditions were selected for prediction within the range of Reynolds number 5000-50000, pressure 2.5-3.5MPa, temperature 200-450℃, and dissolved oxygen concentration 2-20ppm. The results are as follows Figure 2((a) is the prediction result of coking amount under different dissolved oxygen concentrations, (b) is the prediction result of coking amount under different imported hydrocarbon fuel mass flow rates, (c) is the prediction result of coking amount under different pressures, and (d) is the prediction result of coking amount under different heat flux densities) as shown in the figure, the deviation between the predicted value of coking amount and the experimental value does not exceed 10%, which is 20% higher than the prediction result of the calculation model in reference Ⅰ (Pei X, Hou L, Ren Z. Kinetic modeling of thermal oxidation and coking deposition in aviation fuel. Energy Fuels 2017; 31: 1399-1405.).

[0059] The present invention discloses a prediction model and prediction method for the oxidation coking reaction of hydrocarbon fuels. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The products of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the products described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

Claims

1. A method for predicting the oxidation coking reaction of hydrocarbon fuels, characterized in that: The following steps are involved: The hydrocarbon fuel oxidation coking process is simplified into two-step reactions. The first step is a total package space reaction, that is, the chain radical reaction of hydrocarbon fuel is simplified to a total package reaction in which hydrocarbon fuel directly generates coking precursors. The second step is a wall reaction, that is, the carbon deposition reaction of the coking precursor at the wall and the coke deposition process are simplified to a wall reaction in which the coking precursor directly generates coke at the wall. The reaction rates of the above two-step reactions are given in the form of Arrhenius formula. The unknown parameters in the reaction rate calculation formula are solved by a quasi-element method to obtain a prediction model for the hydrocarbon fuel oxidation coking reaction, and the prediction model for the hydrocarbon fuel oxidation coking reaction is embedded in a CFD solver to predict the hydrocarbon fuel oxidation coking reaction.

2. The method for predicting the oxidation coking reaction of hydrocarbon fuels according to claim 1, characterized in that: The reaction equation of the two-step reaction is: Formula (1) is the reaction equation of the first step reaction, and formula (2) is the reaction equation of the second step reaction, where F represents hydrocarbon fuel, α represents oxygen concentration index, O2 represents dissolved oxygen, P represents coking precursor, IN represents insoluble intermediate product, and D represents coke; τ represents reaction time; k'1 represents the rate constant of the first step reaction; k1 represents the reaction rate constant of the first step reaction after ignoring the change in the concentration of hydrocarbon fuel itself; and k2 represents the reaction rate constant of the second step reaction.

3. The prediction method of a hydrocarbon fuel oxidation coking reaction according to claim 1, characterized in that: The calculation formula of the reaction rate is: Wherein, k1 represents the reaction rate constant of the first step reaction, A1 represents the pre-exponential factor of the first step reaction, and represents the effect of hydrocarbon fuel density on the transport process of coking precursors to the wall; ρ b Represents the average density of hydrocarbon fuel; E a1 represents the activation energy of the first step reaction; R represents the molar gas constant, t b represents the qualitative temperature of hydrocarbon fuel; k2 represents the reaction rate constant of the second step reaction; A2 represents the pre-exponential factor of the second step reaction; E a2 represents the activation energy of the second step reaction; represents the effect of wall temperature gradient on coke deposition process, where T w represents the wall temperature, and B represents a dimensionless parameter used to reflect the influence of the wall.

4. The method for predicting the oxidation coking reaction of hydrocarbon fuels according to claim 1, characterized in that: The specific process of solving the unknown parameters in the reaction rate calculation formula by the method based on the quasi-element method is: Carry out hydrocarbon fuel oxidation coking experiments under different flow pipeline lengths, ensure that other conditions remain unchanged, first measure the hydrocarbon fuel composition and concentration at the pipeline outlet; then regard the hydrocarbon fuel composition and concentration at the short pipeline outlet as the hydrocarbon fuel composition and concentration at the middle of the long pipeline, and obtain the hydrocarbon fuel composition and concentration at each position in the middle of the pipeline; finally, solve the unknown parameters by solving the reaction process at different positions in the long pipeline, and obtain the prediction model of hydrocarbon fuel oxidation coking reaction.

5. The method for predicting the oxidation coking reaction of hydrocarbon fuels according to claim 1, characterized in that: The specific process of embedding the prediction model of hydrocarbon fuel oxidation coking reaction into the CFD solver to predict the hydrocarbon fuel oxidation coking reaction is as follows: Within a time step, for a grid, determine whether it belongs to the coking temperature range. If not, do not solve the oxidation coking reaction and end directly; if it does, start solving the first step reaction, read the local aviation kerosene concentration, dissolved oxygen concentration and temperature of the grid, solve the coking precursor concentration, and then determine whether the grid belongs to the near-wall grid. If not, end directly; if it does, start solving the second step reaction, read the local coking precursor concentration, temperature and temperature gradient of the grid, solve the coke formation rate, and further solve the coke formation mass and thickness; further read the coke formation thickness and use the node spring method to realize grid movement to simulate the coke layer formation and deposition, and finally achieve accurate prediction of the hydrocarbon fuel oxidation coking process at low computational cost.

6. The method for predicting the oxidation coking reaction of hydrocarbon fuels according to claim 5, characterized in that: The specific method for further solving the coke generation mass and thickness is to calculate the coke generation mass by integrating the coke generation rate, and then calculate the coke generation thickness by dividing the coke generation mass by the coke density.

7. A prediction model for the oxidation coking reaction of hydrocarbon fuels, characterized in that: The reaction equation of the two-step reaction and the calculation formula of the reaction rate are included, and the reaction equation of the two-step reaction is: The calculation formula of the reaction rate is: Formula (1) is the reaction equation of the first step reaction, and formula (2) is the reaction equation of the second step reaction, where F represents hydrocarbon fuel, α represents oxygen concentration index, O2 represents dissolved oxygen, P represents coking precursor, IN represents insoluble intermediate product, and D represents coke; τ represents reaction time; k'1 represents the reaction rate constant of the first step reaction; k1 represents the reaction rate constant of the first step reaction after ignoring the change in the concentration of hydrocarbon fuel itself; A1 represents the pre-exponential factor of the first step reaction, which represents the effect of hydrocarbon fuel density on the transport process of coking precursor to the wall; ρ b Represents the average density of hydrocarbon fuel; E a1 represents the activation energy of the first step reaction; R represents the molar gas constant, t b represents the qualitative temperature of hydrocarbon fuel; k2 represents the reaction rate constant of the second step reaction; A2 represents the pre-exponential factor of the second step reaction; E a2 represents the activation energy of the second step reaction; represents the effect of wall temperature gradient on coke deposition process, where T w represents the wall temperature, and B represents a dimensionless parameter used to reflect the influence of the wall.

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