An experimental method for obtaining the critical conditions of gaseous fuel autoignition

Abstract

The present invention discloses an experimental method for obtaining the critical conditions for self-ignition of a gaseous fuel, comprising: determining the proportions of the components of a gaseous fuel mixture, preparing the mixture, and allowing it to stand; charging the gaseous fuel mixture into a combustion chamber; recording the changes in light intensity and pressure of the mixture in the combustion chamber during compression, and determining whether the mixture self-ignites under these conditions; repeating the above steps, and if the gaseous fuel mixture does not self-ignite, further varying the combustion chamber length and air intake, observing the ignition situation, and obtaining the self-ignition critical temperature when the temperature difference between the two is less than 10K; obtaining the self-ignition critical temperature at different compression end pressures, and establishing a self-ignition critical spectrum of the gaseous fuel mixture; if the obtained self-ignition critical ignition simulation value is well consistent with the experimental value in the self-ignition critical spectrum, it indicates that the prediction of the gaseous fuel chemical reaction kinetic mechanism is accurate; otherwise, there are deficiencies. The present invention can accurately determine whether ignition or non-ignition occurs.

Description

Technical Field

[0001] The present invention belongs to the field of gas-phase combustion chemical reaction kinetics, and specifically relates to an experimental method for obtaining the critical conditions for gas-phase fuel self-ignition, which is used to study the boundary conditions between ignition and non-ignition of gas-phase fuel and verify the kinetic mechanism model. Background Art

[0002] The combustion chemistry of gaseous fuels has been a research hotspot this year. The experimental and mechanistic development of small molecule fuels is relatively mature, especially the diversification of experimental techniques, mainly including shock tubes, rapid compressors, constant volume combustion bombs, jet agitators, etc. Among them, rapid compressors are typical devices for obtaining ignition delay data of gaseous fuels at medium-low temperature and high pressure. Rapid compressors compress the gaseous mixture in the combustion chamber, record the pressure changes, and obtain its ignition delay through pressure to verify the developed chemical reaction kinetic model. The existing experimental methods have the following problems: (1) the experimental data obtained are single and cannot be verified by other means. The existing kinetic mechanism model; (2) the detection means are single and cannot capture the boundary between ignition and non-ignition through microscopic detection means. Summary of the Invention

[0003] The present invention aims to provide an experimental method for determining the critical conditions for gaseous fuel autoignition. This method, based on a rapid compressor device and supplemented with an optical signal acquisition channel, produces a light intensity curve. This method can accurately determine ignition and non-ignition conditions and is used to validate kinetic mechanism models, making the mechanism more precise and rational.

[0004] The present invention is achieved by adopting the following technical solutions:

[0005] An experimental method for obtaining critical conditions for autoignition of gaseous fuel comprises the following steps:

[0006] 1) Determine the proportions of the components of the gaseous fuel mixture, prepare the mixture using the gas distribution system, and let it sit in the mixing tank for 2-3 hours;

[0007] 2) Determine the length of the combustion chamber, evacuate the combustion chamber using a vacuum pump, and fill the combustion chamber with a fixed amount of p0 gaseous fuel mixture;

[0008] 3) The compressed gas in the high-pressure mixing tank compresses the gaseous fuel mixture in the combustion chamber. The light intensity and pressure changes of the mixture in the combustion chamber during the compression process are recorded by the optical signal and pressure acquisition system. The temperature and pressure at the top dead center of compression are recorded as T1 and p1, and it is determined whether the mixture self-ignites under these conditions.

[0009] 4) If self-ignition occurs, increase the combustion chamber length, reduce the compression ratio, increase the intake volume of the combustion mixture, ensure that the pressure is consistent with that in step 3), and the temperature T2 is lower than T1, repeat step 3), if the gaseous fuel mixture does not self-ignite, then the self-ignition critical temperature of the gaseous mixture at the pressure p1 is between T1 and T2, continue to change the combustion chamber length and intake volume, make the compression top dead center temperature T3 between T1 and T2, observe the ignition situation, when the temperature difference between the two is less than 10K, the self-ignition critical temperature is obtained as (T i +T j ) / 2;

[0010] 5) Repeat steps 3) and 4) to obtain different compression end pressures p k The critical temperature of self-ignition T k , and establish the critical spectrum of gas phase fuel mixture autoignition;

[0011] 6) Input the gas-phase fuel chemical reaction kinetic mechanism file into the Chemkin-Pro software, select the zero-dimensional homogeneous reactor model, and input the boundary conditions to carry out simulation calculations; if the obtained self-ignition critical ignition simulation value is consistent with the experimental value in the self-ignition critical pulse spectrum, it means that the gas-phase fuel chemical reaction kinetic mechanism prediction is accurate; otherwise, there are deficiencies.

[0012] A further improvement of the present invention is that the gas distribution system includes an intake pipe, an exhaust pipe, an intake valve, an exhaust valve, a gas mixing tank, a pressure gauge and a vacuum pump.

[0013] A further improvement of the present invention is that the combustion chamber is composed of stainless steel segments of different lengths of 1 mm, 2 mm, 5 mm, 10 mm, 40 mm and 50 mm, so that the length of the combustion chamber is adjustable from 10 to 100 mm in steps of 1 mm.

[0014] A further improvement of the present invention is that the judgment of whether the mixture has self-ignited is based on whether the light signal curve and the pressure curve have a sharp rise after the compression top dead center. If the light intensity or pressure rises sharply, it means that self-ignition has occurred, otherwise it means that self-ignition has not occurred.

[0015] A further improvement of the present invention is that the self-ignition critical temperature refers to the average value of the lowest temperature at which the gas phase mixture can self-ignite and the highest temperature at which it cannot self-ignite under a fixed pressure.

[0016] A further improvement of the present invention is that the self-ignition critical spectrum diagram is a statistical diagram of ignition and non-ignition conditions under temperature and pressure coordinates.

[0017] A further improvement of the present invention is that the chemical reaction kinetic mechanism file includes elementary reactions and thermodynamic parameter files.

[0018] A further improvement of the present invention is that the boundary conditions input to the zero-dimensional homogeneous reactor model include the initial temperature and initial pressure of the gaseous fuel in the combustion chamber, the heat dissipation curve of the combustion chamber, and the composition of the gaseous fuel mixture.

[0019] The present invention has at least the following beneficial technical effects:

[0020] 1) Through optical signal acquisition and pressure signal acquisition, the critical conditions for gaseous fuel self-ignition can be obtained more accurately, providing a reference for its safe use and avoiding accidental fires that cause loss of life and property.

[0021] 2) The obtained autoignition critical temperature and pressure data can be used to verify the developed kinetic mechanism model, increase the ways to verify the kinetic mechanism, and make the model more reliable and accurate.

[0022] 3) The combustion chamber length is continuously adjustable from 10mm to 100mm, which can obtain experimental data under a wide range of working conditions. The experimental operation is simple and the cost is low.

[0023] 4) Using the controlled variable method, that is, keeping the pressure constant and changing the temperature to obtain the critical conditions for self-ignition. This method is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A flow chart for obtaining critical conditions for self-ignition of gaseous fuel is provided in an embodiment of the present invention.

[0025] Figure 2 1 is the light intensity and pressure curve of the embodiment of the present invention at 45 bar and 1204.25K.

[0026] Figure 3 1 is the light intensity and pressure curve of the embodiment of the present invention at 45 bar and 1192.25K.

[0027] Figure 4 1 is the light intensity and pressure curve of the embodiment of the present invention at 45 bar and 1185.9 K.

[0028] Figure 5 1 is the light intensity and pressure curve of the embodiment of the present invention at 45 bar and 1175.8K.

[0029] Figure 6 These are the critical conditions and mechanism simulation values of self-ignition obtained in the embodiments of the present invention. DETAILED DESCRIPTION

[0030] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0031] like Figure 1 As shown, the present invention provides an experimental method for obtaining the critical conditions for gaseous fuel self-ignition. The experimental process for obtaining the critical conditions for gaseous combustion self-ignition is as follows: first, prepare a gaseous fuel mixture, let it stand in a mixing tank for 2-3 hours, use a vacuum pump to evacuate the gas in the combustion chamber, and use the gas distribution system to fill the combustion chamber with a certain amount of gaseous fuel mixture. The pressure differential between the high-pressure gas tank and the combustion chamber rapidly compresses the piston-connecting rod mechanism from the bottom dead center to the top dead center. At this time, the mixture is in a high-temperature and high-pressure environment. The optical signal and pressure acquisition system records the changes in the mixture in the combustion chamber in real time. By observing the changes in light intensity and pressure in the combustion chamber, it is determined whether the mixture has self-ignited. If the light intensity and pressure rise sharply after the compression to the top dead center, it indicates that the gaseous fuel mixture has self-ignited. It is necessary to increase the combustion chamber length and reduce the compression ratio. A second experiment is performed to ensure that the pressure remains unchanged and the temperature is reduced. The light intensity and pressure changes are similarly observed. If ignition occurs, the combustion chamber length is further increased and the compression ratio is reduced to obtain light intensity and pressure changes at a lower temperature to determine whether self-ignition has occurred. If the first misfire occurs, the critical temperature for autoignition at a specific pressure can be obtained. Similarly, if the light intensity and pressure do not rise sharply after compression top dead center, it indicates that the mixture has not self-ignited. The combustion length needs to be reduced, the compression ratio needs to be increased, and a second experiment needs to be conducted until the first self-ignition occurs. The critical temperature for autoignition at a specific pressure can be obtained. After obtaining the critical conditions for autoignition, the 0-D homogeneous reactor model in Chemkin-Pro software is used to simulate the autoignition of the gaseous fuel mixture. The kinetic mechanism model and boundary conditions are input to obtain the simulated value of the pressure change to determine whether autoignition occurs. The critical temperature for autoignition of the mixture at a specific pressure is found by changing the initial boundary conditions. This is compared with the experimental value to determine the accuracy and reliability of the kinetic mechanism simulation.

[0032] Example 1:

[0033] First, the research object is determined to be a gas phase mixture of ethylene / nitrous oxide / argon (0.25% C2H4 / 3% N2O / 96.75% Ar). The mixture is prepared using the gas distribution system and left to stand for 2-3 hours. The combustion chamber length is selected to be 34mm. Then, the combustion chamber is evacuated using a vacuum pump. At this time, the pressure gauge reading is 0.0026bar. The combustion chamber is filled with a 1.9494bar mixture. The compressed air in the high-pressure mixed gas tank is used to push the piston connecting rod mechanism to the top dead center. The light signal and pressure acquisition system records the light intensity and pressure changes during the compression process, such as Figure 2 As shown in the figure, 30ms after compression top dead center, both the pressure and light intensity curves show a steep rise, indicating that the gas phase fuel mixture has self-ignited at 45 bar and 1204.25K.

[0034] In order to find the critical temperature of autoignition of ethylene / nitrous oxide / argon mixture at 45 bar, the combustion chamber length was increased to 35 mm, its compression ratio was reduced, the combustion chamber was evacuated to 0.0026 bar, a mixture of 1.9692 bar was filled into the combustion chamber, the piston connecting rod mechanism was compressed to the bottom dead center, and the changes in the optical signal and pressure curve were observed, as shown in FIG. Figure 3 As shown in Figure 2, both the pressure and light intensity curves show a steep rise 60ms after compression top dead center, indicating that the gas-phase fuel mixture has self-ignited at 45 bar and 1192.25 K.

[0035] Further increase the length of the combustion chamber to 37mm, evacuate the combustion chamber to 0.0027bar, fill the combustion chamber with 2.019bar mixed gas, compress the piston connecting rod mechanism to the bottom dead center, and observe the changes in the light signal and pressure curve, such as Figure 4 As shown in the figure, the pressure and light intensity curves rise but are relatively gentle 100ms after the compression top dead center, indicating that the gas-phase fuel mixture self-ignites at 45 bar and 1185.9 K, but the ignition is weak.

[0036] Further increase the length of the combustion chamber to 38mm, evacuate the combustion chamber to 0.0027bar, fill the combustion chamber with 2.0612bar mixed gas, compress the piston connecting rod mechanism to the bottom dead center, and observe the changes in the light signal and pressure curve, such as Figure 5 As shown in the figure, both the pressure and light intensity curves increase after the compression top dead center, indicating that the gaseous fuel mixture does not self-ignite at 45 bar and 1175.8 K.

[0037] Therefore, the autoignition critical temperature of the ethylene / nitrous oxide / argon mixture at 45 bar can be obtained as (1185.9+1175.8) / 2=1180.85K.

[0038] The critical ignition conditions of ethylene / nitrous oxide / argon gas phase reaction at 45 bar were simulated using the kinetic mechanism. First, the kinetic mechanism file and thermodynamic file were input into the Chemkin-Pro software. At the same time, the composition, temperature, pressure, heat dissipation of the combustion chamber, etc. of the mixture were also input into the software as boundary conditions. The ignition conditions at the above-mentioned temperatures of 1204.25K, 1192.25K, 1185.9K and 1175.8K were simulated. The results showed that the critical self-ignition temperature occurred between 1185.9K and 1175.8K. The boundary conditions were further changed to find the determined critical self-ignition temperature of 1181K, which is consistent with the experimental value.

[0039] Repeat the above steps to experimentally measure the critical temperature of ethylene / nitrous oxide / argon mixture at 20 bar, 25 bar, 30 bar, 35 bar and 40 bar, and simulate the mechanism. It is found that the simulation results of the mechanism are good over a wide pressure range, such as Figure 6 shown.

[0040] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. An experimental method for obtaining the critical conditions for self-ignition of gaseous fuel, characterized in that: The following steps are involved: 1) Determine the proportions of the components of the gaseous fuel mixture, prepare the mixture using the gas distribution system, and let it sit in the mixing tank for 2-3 hours; 2) Determine the length of the combustion chamber, evacuate the combustion chamber using a vacuum pump, and fill the combustion chamber with a fixed amount of p0 gaseous fuel mixture; 3) The compressed gas in the high-pressure mixing tank compresses the gaseous fuel mixture in the combustion chamber. The light intensity and pressure changes of the mixture in the combustion chamber during the compression process are recorded by the optical signal and pressure acquisition system. The temperature and pressure at the top dead center of compression are recorded as T1 and p1, and it is determined whether the mixture self-ignites under these conditions. 4) If self-ignition occurs, increase the combustion chamber length, reduce the compression ratio, increase the intake volume of the combustion mixture, ensure that the pressure is consistent with that in step 3), and the temperature T2 is lower than T1, repeat step 3), if the gaseous fuel mixture does not self-ignite, then the self-ignition critical temperature of the gaseous mixture at the pressure p1 is between T1 and T2, continue to change the combustion chamber length and intake volume, make the compression top dead center temperature T3 between T1 and T2, observe the ignition situation, when the temperature difference between the two is less than 10K, the self-ignition critical temperature is obtained as (T i +T j ) / 2; 5) Repeat steps 3) and 4) to obtain different compression end pressures p k The critical temperature of self-ignition T k , and establish the critical spectrum of gas phase fuel mixture autoignition; 6) Input the gas-phase fuel chemical reaction kinetic mechanism file into the Chemkin-Pro software, select the zero-dimensional homogeneous reactor model, and input the boundary conditions to carry out simulation calculations; if the obtained self-ignition critical ignition simulation value is consistent with the experimental value in the self-ignition critical pulse spectrum, it means that the gas-phase fuel chemical reaction kinetic mechanism prediction is accurate; otherwise, there are deficiencies.

2. The experimental method for obtaining the critical conditions for gaseous fuel autoignition according to claim 1, characterized in that: The gas distribution system includes an intake pipe, an exhaust pipe, an intake valve, an exhaust valve, a gas mixing tank, a pressure gauge and a vacuum pump.

3. The experimental method for obtaining the critical conditions for gaseous fuel autoignition according to claim 1, characterized in that: The combustion chamber is composed of stainless steel segments of different lengths, such as 1 mm, 2 mm, 5 mm, 10 mm, 40 mm and 50 mm, so that the length of the combustion chamber is adjustable from 10 to 100 mm in steps of 1 mm.

4. The experimental method for obtaining the critical conditions for gaseous fuel autoignition according to claim 1, characterized in that: The judgment of whether the mixture has self-ignited is based on whether the light signal curve and the pressure curve have a steep rise after the compression top dead center. If the light intensity or pressure rises sharply, it means that self-ignition has occurred, otherwise it means that self-ignition has not occurred.

5. The experimental method for obtaining the critical conditions for gaseous fuel autoignition according to claim 1, characterized in that: The self-ignition critical temperature refers to the average value of the lowest temperature at which a gaseous mixture can self-ignite and the highest temperature at which it cannot self-ignite under a fixed pressure.

6. The experimental method for obtaining the critical conditions for gaseous fuel autoignition according to claim 1, characterized in that: The self-ignition critical spectrum diagram is a statistical diagram of ignition and non-ignition conditions under temperature and pressure coordinates.

7. The experimental method for obtaining the critical conditions for gaseous fuel autoignition according to claim 1, characterized in that: The chemical reaction kinetic mechanism file includes elementary reactions and thermodynamic parameter files.

8. The experimental method for obtaining the critical conditions for autoignition of gaseous fuel according to claim 1, characterized in that: The boundary conditions input into the zero-dimensional homogeneous reactor model include the initial temperature and initial pressure of the gaseous fuel in the combustion chamber, the heat dissipation curve of the combustion chamber, and the composition of the gaseous fuel mixture.

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