A simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3 as an alternative fuel for internal combustion engines

Abstract

The invention discloses a simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3, an alternative fuel for internal combustion engines, and adopts a direct relationship diagram method, a sensitivity analysis method and an isomerism method reaction mechanism simplification method to obtain this simplified model. Starting from the detailed chemical reaction mechanism model of the mixing mechanism of dimethyl ether-polyoxymethylene dimethyl ether 3, an alternative fuel for internal combustion engines, a simplified chemical reaction model of dimethyl ether-polyoxymethylene dimethyl ether 3 mixed internal combustion engine alternative fuel is given and constructed. The simplified model of the combustion chemical reaction mechanism of alternative fuel dimethyl ether-polyoxymethylene dimethyl ether 3 for internal combustion engine numerical simulation constructed by the present invention has high calculation efficiency and accurate results. It can be directly used in the numerical simulation of the combustion flow field of dimethyl ether-polyoxymethylene dimethyl ether 3 mixed fuel, an alternative fuel for internal combustion engines, and provides effective technical support for the numerical analysis of internal combustion engines.

Description

Technical Field

[0001] The invention relates to the technical field of computer simulation of internal combustion engine combustion process, and in particular to a simplified method for a reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3, an alternative fuel for internal combustion engines. Background Art

[0002] At present, the research method for internal combustion engine emissions and combustion efficiency is mainly to conduct numerical simulation of the internal combustion engine working process, because this method can significantly shorten the product development cycle, reduce the number of actual machine tests, and reduce product development costs compared to experiments. It is an important research method. However, there is a problem of low computational efficiency when numerically simulating the combustion process involving multiple components and a large number of elementary reactions. Therefore, the simplification of the combustion mechanism of hydrocarbon fuels has become an important research direction in the field of combustion. In terms of hydrocarbon fuels, engines fueled by DME show the characteristics of smokeless combustion, low hydrocarbons (HC) and CO, and slightly higher nitrogen oxide emissions, which are very friendly to the environment. However, some characteristics of DME, such as low bulk modulus, low calorific value and viscosity, are not conducive to its application in diesel engines. Its bulk modulus and viscosity values ​​are much lower than those of diesel, resulting in higher pressure in the fuel supply system (high-pressure pump, common rail, injector), and large pressure fluctuations leading to steam leakage. Therefore, using DME as the fuel of the engine will consume a large amount of lubricating additives, increase NOx emissions, and even black smoke emissions. This situation can be improved significantly if the higher viscosity polyoxymethylene dimethyl ether (DMMn) is mixed with dimethyl ether, especially with DMM3 fuel.

[0003] At present, there are mainly simplified mechanisms of DME and DMM3, and the simplified mechanism of mixing has not been studied. Although the simplified method of DME and DMM3 combustion mechanism in the existing technology can greatly reduce the mechanism of combustion reaction, it has not yet been involved in the calculation of DME-DMM3 mixed mechanism. In this case, it is necessary to effectively simplify the DME-DMM3 mixed mechanism and finally obtain the best simplified mechanism model. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a simplified method for the reaction mechanism model of dimethyl ether (DME)-polyoxymethylene dimethyl ether 3 (DMM3) as an alternative fuel for internal combustion engines. This simplified mechanism model of DME-DMM3 mixed fuel reduces the number of components and elementary reactions while ensuring calculation accuracy, thereby improving the numerical calculation efficiency of the internal combustion engine working process. This is of great significance for shortening the development cycle of internal combustion engine products and reducing development costs, has good market application prospects, and fills in the gaps in the field.

[0005] In order to solve the problems of the prior art, the technical solution adopted by the present invention is:

[0006] A simplified method for a reaction mechanism model of dimethyl ether (DME)-polyoxymethylene dimethyl ether 3 (DMM3) as an alternative fuel for internal combustion engines comprises the following steps:

[0007] Step 1, according to the detailed reaction mechanism model of DME-DMM3, by using the direct relationship diagram method, the non-important reactions in the detailed reaction mechanism model are deleted to obtain a simplified mechanism model of the primary mixed fuel of DME-DMM3 containing 82 components and 587 reaction equations;

[0008] Step 3, based on the secondary simplified mechanism model obtained in step 2, further simplifying it by isomerization method, further obtaining a DME-DMM3 three-stage mixed fuel simplified mechanism model with 65 components and 308 reaction equations;

[0009] Step 3, based on the simplified mechanism model of the secondary mixed fuel obtained in step 2; further simplifying it by isomerization method, further obtaining the simplified mechanism model of the DME-DMM3 tertiary mixed fuel with 65 components and 308 reaction equations;

[0010] Step 4, based on the simplified mechanism model of the DME-DMM3 three-stage mixed fuel obtained in step 3, respectively make a comparison between the laminar flame and ignition delay time data obtained by the simplified mechanism model of the DME-DMM3 mixed fuel and the detailed reaction mechanism models of DME and DMM3 under the same conditions, and check whether the trends presented in the data graphs are the same and whether the error is within 15%. If so, the simplified reaction mechanism model of the DME-DMM3 mixed fuel obtained is desirable; if not, return to step 1, adjust the threshold, and repeat steps 1-3 until the final simplified mechanism model of the DME-DMM3 mixed fuel is obtained.

[0011] As an improvement, the specific steps of the direct relationship diagram method in step 1 are: first set the threshold value, set DME-DMM3, O2, and N2 as starting substances; take the equivalent ratio Phi as 0.5~2.0, the temperature as 600K~1600K, and the pressure as 1atm~50atm, determine the degree of coupling between the two components of DME and DMM3 by the direct relationship diagram method, and judge the coupling relationship between the intermediate product and the starting substance by the relationship between these starting substances, finally retain the coupled components, remove the uncoupled components, and obtain a simplified mechanism model of the first-level mixed fuel DME-DMM3 containing 82 components and 587 reaction equations.

[0012] As an improvement, the specific steps of the sensitivity analysis method assisted by the direct relationship diagram in step 2 are as follows: using the simplified mechanism model of the primary mixed fuel of DME-DMM3 obtained in step 1, the sensitivity analysis method is used to simplify it at an equivalence ratio Phi of 0.5 to 2.0, a temperature of 600K to 1600K, and a pressure of 1atm to 50atm, and the reactions with poor sensitivity are removed. The standard of poor sensitivity is that the reaction is less than 30% of the maximum sensitivity in the sensitivity data, thereby obtaining a simplified mechanism model of the secondary mixed fuel of DME-DMM3 with 71 components and 416 reaction equations.

[0013] As an improvement, the specific steps of the isomerization method described in step 3 are: using a simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3, an alternative fuel for internal combustion engines, obtained in step 2, setting the equivalence ratio Phi to 0.5-2.0, the temperature to 600K-1600K, and the pressure to 1atm-50atm in the Chemkin software, and selecting the isomerization method for simplification, thereby obtaining a simplified mechanism model of the DME-DMM3 three-stage mixed fuel with 65 components and 308 reaction equations.

[0014] As an improvement, the specific steps of step 4 are:

[0015] The first step is to import the file of DME-DMM3 three-stage mixed fuel simplified mechanism model into Chemkin's reactor;

[0016] In the second step, the temperature was set to 600-1600K, the pressure was set to 1-50atm, the equivalence ratio was set to 0.5-2.0, the combustion materials were set to DME / O2 / N2 and DMM3 / O2 / N2, respectively, and the laminar flame and ignition delay data were obtained by running in Chemkin;

[0017] The third step is to import the detailed mechanism files of DME and DMM3 into the Chemkin reactor;

[0018] Step 4: Set the temperature, pressure, and equivalence ratio, and run the obtained laminar flame and ignition delay data in Chemkin;

[0019] The fifth step is to check whether the trends presented by the data graphs are the same and whether the error is within 15%. If so, the simplified reaction mechanism model of DME-DMM3 obtained is desirable; if not, return to step 1, adjust the threshold, and repeat steps 1-3 until the final simplified mechanism model of DME-DMM3 mixed fuel is obtained.

[0020] As a further improvement, the specific parameters of the fourth step are a temperature of 600 to 1600 K, a pressure of 1 to 50 atm, and an equivalence ratio of 0.5 to 2.0.

[0021] Beneficial effects: Compared with the prior art, the present invention provides a simplified method for the reaction mechanism model of dimethyl ether (DME)-polyoxymethylene dimethyl ether 3 (DMM3), an alternative fuel for internal combustion engines. The invention combines multiple simplified methods to simplify the detailed mechanism model of the mixed fuel DME-DMM3, which can avoid the phenomenon of inaccurate deletion of components in the simplification process of the traditional single method. The components in the DME-DMM3 fuel are identified, screened, and unimportant files are eliminated through the direct relationship diagram chemical reaction mechanism simplification method, so that the model is simplified to the greatest extent, and a simplified mechanism model of the first-level mixed fuel DME-DMM3 containing 82 components and 587 reaction equations is obtained. Then, the global sensitivity analysis of the primitives is obtained through the sensitivity analysis method chemical mechanism simplification method, and a simplified mechanism model of the third-level mixed fuel DME-DMM3 containing 71 components and 416 reaction equations is obtained. Combined with the isomerism method, the number of components in the reaction can be minimized to the greatest extent, so that the error between the results of the simplified model and the results of the detailed mechanism model can be minimized, and the final simplified mechanism model of the DME-DMM3 three-stage mixed fuel with 65 components and 308 reaction equations is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flowchart of a simplified method for a reaction mechanism model of dimethyl ether (DME)-polyoxymethylene dimethyl ether 3 (DMM3) as an alternative fuel for internal combustion engines according to the present invention;

[0023] Figure 2 It is a typical relationship diagram between species in the direct relationship diagram method (DRG);

[0024] Figure 3 The ignition delay comparison diagram of the simplified mechanism model of DME-DMM3 three-stage mixed fuel and DME experiment under the same conditions, (a) is the equivalence ratio of 0.5, the pressure of 11bar and 25bar, (b) is the equivalence ratio of 1, the pressure of 11bar and 25bar, (c) is the equivalence ratio of 2, the pressure of 11bar and 25bar;

[0025] Figure 4 The ignition delay comparison diagram of the simplified mechanism model of DME-DMM3 three-stage mixed fuel and the detailed mechanism model of DMM3 and the experiment under the same conditions, (a) is the equivalence ratio of 0.5, the pressure of 1Mpa and 1.5Mpa, (b) is the equivalence ratio of 1, the pressure of 1Mpa and 1.5Mpa; (c) is the equivalence ratio of 1.5, the pressure of 1Mpa and 1.5Mpa;

[0026] Figure 5This is a comparison chart of the laminar flame of the simplified mechanism model of DME-DMM3 three-stage mixed fuel and the experimental value of DME under the same conditions;

[0027] Figure 6 It is a comparison diagram of the simplified mechanism model of DME-DMM3 three-stage mixed fuel and the detailed mechanism and experimental values ​​of DMM3 under the same laminar flame conditions; DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific implementation described herein is only used to explain the present invention, but not to limit the present invention.

[0029] The embodiment of the present invention simplifies the detailed mechanism of the combustion reaction of the internal combustion engine alternative fuel DME-DMM3. Through the analysis of this embodiment, the present invention is explained in detail.

[0030] A simplified method for a reaction mechanism model of dimethyl ether (DME)-polyoxymethylene dimethyl ether 3 (DMM3) as an alternative fuel for internal combustion engines comprises the following steps:

[0031] Step 1: According to the detailed reaction mechanism model of DME-DMM3, the non-important reactions in the detailed reaction mechanism model are deleted by using the direct relationship diagram method to obtain a simplified mechanism model of the primary mixed fuel of DME-DMM3 containing 82 components and 587 reaction equations. The specific steps are as follows:

[0032] Determine the acceptable error, set the threshold, set DME / O2 / N2 and DMM3 / O2 / N2 as the starting materials respectively; take the equivalent ratio Phi to 0.5-2.0, the temperature to 600K-1600K, and the pressure to 1atm-50atm. In the reaction, we compare the contribution rate of each component. Delete the reaction formula with low contribution rate. Component A and component B are the substances in the reactor during the reaction process, not specific substances. For example, the contribution rate of O2 to the reaction of DME, or the contribution rate of N2 to the reaction of DME, etc. The contribution rate rAB of component B to the generation of component A can be expressed as:

[0033]

[0034]

[0035]

[0036] k fi =[A i T ni exp(-E i / RT)]F i

[0037] Wherein, the subscripts i and j represent the i-th elementary reaction and the j-th species, respectively. A,i is the stoichiometric coefficient of A, R A is the generation rate factor of A, ω i is the production rate, k fi and k bi are the forward and reverse reaction rates, respectively, and C j is the molar concentration, v' ij ,v" ij The stoichiometric coefficients of the forward and reverse reactions, A i is the frequency factor, T ni is the thermometric coefficient under the ith elementary reaction, R is the temperature factor, T is the temperature, and E i is the activation energy of the chemical reaction, F i is the correction factor, δ Bi The values ​​are:

[0038]

[0039] Compare the coupling relationships and delete those with less influence. The coupling relationships are as follows: Figure 2 As shown, these starting materials are used to determine the coupling relationship between other intermediates and the starting materials, and finally the uncoupled components are removed to obtain a simplified mechanism model of the primary mixed fuel of DME-DMM3.

[0040] Step 2: We use the simplified mechanism model of the first-stage mixed fuel of DME-DMM3 obtained in step 1, with an equivalence ratio Phi of 0.5 to 2.0, a temperature of 600K to 1600K, and a pressure of 1atm to 50atm. We simplify it using the sensitivity analysis method, and perform a sensitivity analysis on the ignition delay. The sensitivity coefficient of the uncertainty component is calculated as

[0041]

[0042] Where: To simplify the ignition delay time of the mechanism obtained by deleting the i-th component in the uncertain component under the j-th condition in the mechanism, θ j (d) is the ignition delay time of the detailed mechanism under the jth operating condition. It is not an important reaction and can be eliminated from the reaction system to obtain the simplified mechanism model of DME-DMM3 secondary mixed fuel;

[0043] Step 3, according to step 2, a simplified mechanism model of DME-DMM3 two-stage mixed fuel is obtained, with an equivalence ratio Phi of 0.5 to 2.0, a temperature of 600K to 1600K, and a pressure of 1atm to 50atm. The model is imported into Chemkin software, simplified by isomerism method, and the isomer part is removed. After simplification, a simplified mechanism model of DME-DMM3 three-stage mixed fuel with 65 components and 308 reaction equations is further obtained;

[0044] Step 4: The specific steps are as follows:

[0045] The first step is to import the DME-DMM3 three-stage mixed fuel simplified mechanism model file into the Chemkin reactor;

[0046] In the second step, the temperature was set to 600-1600K, the pressure was set to 1-50atm, the equivalence ratio was set to 0.5-2.0, and DME / O2 / N2 and DMM3 / O2 / N2 were set as the starting materials respectively; the laminar flame and ignition delay data of the simplified mechanism models of DME and DMM3 were obtained by running the analysis in Chemkin;

[0047] The third step is to import the detailed mechanism files of DME and DMM3 into the Chemkin reactor;

[0048] Step 4: Set the temperature to 600-1600K, the pressure to 1-50atm, the equivalence ratio to 0.5-2.0, and run the obtained laminar flame and ignition delay data in Chemkin;

[0049] Step 5, based on the obtained simplified mechanism model of DME-DMM3 three-stage mixed fuel, the laminar flame and ignition delay time data under the conditions of DME / O2 / N2 and DMM3 / O2 / N2 as the starting materials are respectively compared with the detailed mechanism data to check whether the trends presented by the data are the same and whether the error is within 15%. If so, the obtained simplified mechanism model of DME-DMM3 three-stage mixed fuel is desirable; if not, return to step 1, adjust the threshold, and repeat steps 1-3 until the final simplified mechanism model of DME-DMM3 mixed fuel is obtained.

[0050] We compared the simplified mechanism model of DME-DMM3 three-stage mixed fuel obtained by the above method, such as Figure 3(a), 3(b), 3(c), the data obtained by using the simplified mechanism of mixed fuel under the conditions of DME / O2 / N2 reaction fuel are compared with the DME experimental data of Lun 2015. It is found that the maximum error between the simplified mechanism of mixed fuel and the experimental mechanism occurs under the conditions of φ=2, pressure P=1.1MPa, P=2.5MPa, and temperature around 800K, and the error is within 15%.

[0051] like Figure 4 (a), 4(b), 4(c), under the conditions of DME / O2 / N2 reaction fuel, the data obtained by using the simplified mechanism of mixed fuel were compared with the experimental data of DMM3 from He et al. of Tsinghua University. It was found that the maximum error occurred under the conditions of φ=1.0, P=1.0MPa, and temperature around 1200K. The ignition delay time of the simplified mechanism was in good agreement with the experimental data under the conditions of φ=1.5, P=1MPa and 1.5MPa. The overall ignition delay of the two mechanisms was well simulated with the time trend, and the error was controlled within 15%, which can well reproduce the ignition characteristics of the detailed mechanism.

[0052] like Figure 5 , the data obtained by using the simplified mechanism of mixed fuel under the conditions of DME / O2 / N2 reaction fuel and the experimental data are from RJ. Under standard atmospheric pressure, the initial temperature is set to 300K, 400K, 500K, 600K, 650K and the laminar flame speed of DME under different equivalence ratios (0.7-1.4, time interval is 0.1). It can be seen from the figure that the combustion increases with the increase of temperature. At different temperatures, a bell-shaped curve can be seen. Even at higher temperatures, the mixed fuel always maintains the maximum combustion speed. The laminar flame speed reaches a peak at Ф=1.1, and then the laminar flame speed decreases with the increase of equivalence ratio. Compared with the simplified mechanism, the simplified mechanism predicts the laminar combustion speed more accurately at temperatures of 300K, 400K, 500K, and 600K. For the temperature of 650K, the simplified mechanism overestimates the laminar combustion speed, and the maximum error is at Ф=1.4, but the overall trend is more accurate and the error is within an acceptable range.

[0053] like Figure 6, the data obtained by using the simplified mechanism of mixed fuel under the conditions of DME / O2 / N2 reaction fuel and the experimental data of Sun et al. of DMM3 were found to be the laminar flame speed of DMM3 under different equivalence ratios (0.7-1.5, time interval of 0.1) with the initial temperature set to 408K. The laminar flame speed increases with the increase of equivalence ratio, reaches a peak value at Ф=1.2, and then decreases with the increase of equivalence ratio. Compared with the experiment, the maximum error is at Ф=1.4, which overestimates the laminar flame speed. Compared with the simplified mechanism of Lin and Ren et al., the laminar flame speed is underestimated, but it is generally more accurate, and the overall simulation trend meets the requirements, with an error within 15%, which is within the acceptable range.

[0054] The above is only a preferred specific implementation manner of the present invention, and the protection scope of the present invention is not limited thereto. Any simple change or equivalent replacement of the technical solution that can be obviously obtained by any technician familiar with the technical field within the technical scope disclosed in the present invention falls within the protection scope of the present invention.

Claims

1. A simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3 as an alternative fuel for internal combustion engines, characterized in that: The following steps are involved: Step 1, according to the detailed reaction mechanism model of DME-DMM3, by using the direct relationship diagram method, the non-important reactions in the detailed reaction mechanism model are deleted to obtain a simplified mechanism model of the primary mixed fuel of DME-DMM3 containing 82 components and 587 reaction equations; Step 2, based on the simplified mechanism model of the primary mixed fuel obtained in step 1, further simplify it by using the sensitivity analysis method assisted by the direct relationship diagram, judge its sensitivity, delete the reaction formula with poor sensitivity, and further obtain the simplified mechanism model of the DME-DMM3 secondary mixed fuel with 71 components and 416 reaction equations; Step 3, based on the secondary simplified mechanism model obtained in step 2, further simplifying it by isomerization method, further obtaining a DME-DMM3 three-stage mixed fuel simplified mechanism model with 65 components and 308 reaction equations; Step 4, according to the simplified mechanism model of the DME-DMM3 three-stage mixed fuel obtained in step 3, respectively make a comparison of the data of the laminar flame and ignition delay time obtained by the simplified mechanism model of the DME-DMM3 mixed fuel and the detailed reaction mechanism model of DME and DMM3 under the same conditions, check whether the trends presented by the data graphs are the same, and whether the error is within 15%. If so, the simplified reaction mechanism model of the DME-DMM3 mixed fuel obtained is desirable; if not, return to step 1, adjust the threshold, and repeat the operations of steps 1-3 until the final simplified mechanism model of the DME-DMM3 mixed fuel is obtained, wherein the specific steps are as follows: the first step, import the file of the simplified mechanism model of the DME-DMM3 three-stage mixed fuel into the Chemkin reactor; In the second step, the temperature was set to 600 ~ 1600 K, the pressure was set to 1 ~ 50 atm, the equivalence ratio was set to 0.5 ~ 2.0, the combustion materials were set to DME / O2 / N2 and DMM3 / O2 / N2 respectively, and the laminar flame and ignition delay data were obtained by running in Chemkin; The third step is to import the detailed mechanism files of DME and DMM3 into the Chemkin reactor; Step 4: Set the temperature to 600 ~ 1600 K, the pressure to 1 ~ 50 atm, and the equivalence ratio to 0.5 ~ 2.0, and run the obtained laminar flame and ignition delay data in Chemkin; The fifth step is to check whether the trends presented by the data graphs are the same and whether the error is within 15%. If so, the obtained simplified mechanism model of the DME-DMM3 three-stage mixed fuel is desirable; if not, return to step 1, adjust the threshold, and repeat steps 1-3 until the final simplified mechanism model of the DME-DMM3 mixed fuel is obtained.

2. A simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3 as an alternative fuel for internal combustion engines according to claim 1, characterized in that: The specific steps of the direct relationship diagram method in step 1 are as follows: first, set the threshold value, set DME-DMM3, O2, and N2 as starting substances; take the equivalent ratio Phi as 0.5~2.0, the temperature as 600K~1600K, and the pressure as 1atm~50atm, and determine the degree of coupling between the two components of DME and DMM3 through the direct relationship diagram method, and judge the coupling relationship between the intermediate product and the starting substance through the relationship between these starting substances, and finally retain the coupled components and remove the uncoupled components, thereby obtaining a simplified mechanism model of the first-level mixed fuel DME-DMM3 containing 82 components and 587 reaction equations.

3. A simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3 as an alternative fuel for internal combustion engines according to claim 1, characterized in that: The specific steps of the sensitivity analysis method assisted by the direct relationship diagram in step 2 are as follows: Using the simplified mechanism model of the primary mixed fuel of DME-DMM3 obtained in step 1, the sensitivity analysis method is used to simplify it under the conditions of an equivalence ratio Phi of 0.5~2.0, a temperature of 600K~1600K, and a pressure of 1atm~50atm, and the reactions with poor sensitivity are removed. The standard of poor sensitivity is that the reaction is less than 30% of the maximum sensitivity in the sensitivity data, thereby obtaining a simplified mechanism model of the secondary mixed fuel of DME-DMM3 with 71 components and 416 reaction equations.

4. A simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3 as an alternative fuel for internal combustion engines according to claim 1, characterized in that: The specific steps of the isomerization method described in step 3 are: using a simplified method for the reaction mechanism model of dimethyl ether-polyoxymethylene dimethyl ether 3 for internal combustion engine alternative fuel obtained in step 2, setting the equivalence ratio Phi to 0.5~2.0, the temperature to 600K~1600K, and the pressure to 1atm~50atm in Chemkin software, and selecting the isomerization method for simplification, thereby obtaining a simplified mechanism model of DME-DMM3 three-stage mixed fuel with 65 components and 308 reaction equations.

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