A constant volume combustion device and method for discriminating flame flow states

Abstract

The present invention relates to the technical field of flame combustion, and discloses a constant-volume combustion device and method for discriminating flame flow states. The device includes a constant-volume combustion bomb cylinder pressure acquisition system and a flame schlieren image acquisition system. The refined pressure fluctuation state in the combustion cylinder is used as a new evaluation index, and then compared and analyzed with the flame front obtained under different working conditions according to the characteristic parameters of the flame flow state, so as to better quantify the influence of pressure fluctuation on the flame development process during flame propagation, and then make a detailed classification of the flame flow state changes due to fluid instability and heat-mass instability. Finally, it can lay a foundation for quantifying the influence of instability on flame propagation during flame propagation, and provide certain theoretical support for subsequent research on the basic theory of flame combustion.

Description

Technical Field

[0001] The present invention relates to the technical field of flame combustion, and specifically to a constant - volume combustion device and method for discriminating flame flow states. Background Art

[0002] In the traditional combustion mode, the initial flame formed after the ignition of the premixed fuel is the premixed laminar flame. As the flame develops, due to being extremely sensitive to changes in stretching and pressure, the flame will gradually transition from a laminar flame to a turbulent flame. The earliest turbulent flame is a highly wrinkled laminar flame affected by the action of stretching and pressure. Although the turbulent combustion speed is affected by many complex factors such as gas flow disturbance and in - cylinder turbulent intensity, under the same intake mode and turbulent intensity, the turbulent combustion speed depends on the chemical and physical properties of different fuels, that is, the laminar combustion characteristics of the fuels. Therefore, the laminar combustion theory is the basis for studying the turbulent combustion theory.

[0003] In the actual flame propagation process, due to the differences in the physical and chemical properties of fuels and the imperfection of research methods, the current division of flame flow states is still very rough. Only some flame front characteristic parameters or large - amplitude fluctuations of the overall in - cylinder pressure can be used to characterize the flame flow state, but it is impossible to effectively make a more refined division and judgment of the flame flow state. Thus, it is impossible to effectively evaluate the influence and error brought by different initial conditions and different influencing factors on the change of the flame flow state. Facing the problem that the flame flow state cannot be finely discriminated by the previous methods, it is very necessary to propose a new method and device for evaluating the flame flow state, reduce the errors caused by theoretical limitations of the previous research methods, and at the same time improve the experimental device to obtain more refined experimental data to fill the huge gap still existing in the field of flame combustion flame flow state discrimination. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a constant - volume combustion device and method for discriminating flame flow states, better determine the boundary ranges of each flame flow state, thereby obtaining more accurate combustion characteristic parameters under each flame flow state, and providing data support for subsequent research on the physical and chemical properties of fuels. The technical solutions are as follows:

[0005] A constant - volume combustion device for discriminating flame flow states includes an in - cylinder pressure acquisition system of a constant - volume combustion bomb and a flame schlieren image acquisition system;

[0006] The pressure collection system in the cylinder of the constant volume combustion bomb comprises a constant volume combustion bomb body and a pressure sensor probe; the combustion bomb body is provided with a plurality of probe holes, one end of the pressure sensor probe is provided with a signal transmission line, the other end is inserted into the probe hole and the probe hole is sealed, and the end of the probe points to the geometric center of the inner cavity of the combustion bomb; a plurality of pressure sensors are installed on the pressure sensor probe at a certain interval from the end of the probe outward, which are used to detect the pressure fluctuation data at different positions in the direction in which the pressure sensor probe points; the detected pressure fluctuation data is transmitted to an external charge amplifier through the signal transmission line, and the pressure signal is converted into an electrical signal after conditioning by the charge amplifier and enters the acquisition card and the electronic control unit; after the acquisition card records the data, the electronic control unit controls to end the experiment;

[0007] The flame schlieren picture acquisition system comprises a schlieren picture shooting optical path composed of a plurality of reflectors, and a high-speed camera; the high-speed camera records the flame propagation situation inside the constant volume combustion bomb body through the schlieren picture shooting optical path.

[0008] A flame flow pattern identification method comprises the following steps:

[0009] Step 1: Under initial experimental conditions, the fuel is ignited by the ignition system of the constant volume combustion device to generate a flame, and a high-speed camera is used to obtain flame front images at different times;

[0010] Step 2: While the experiment is being carried out in step 1, the in-cylinder pressure data collected by the pressure sensors at different positions in all directions of the pressure sensor probes inserted during the experiment at different times are obtained through the constant volume combustion bomb in-cylinder pressure collection system;

[0011] Step 3: Summarize the flame front images and cylinder pressure data obtained from steps 1 and 2, and construct a three-dimensional pressure distribution surface based on the pressure data;

[0012] Step 4: Match the cylinder pressure data at different times with the flame front image;

[0013] Step 5: Calculate the center and radius in each direction of each flame front image obtained in step 2, and on this basis, rematch the flame radius data in the direction of the pressure sensor probe at different times with the cylinder pressure data measured by the pressure sensor at different positions at different times in the corresponding direction;

[0014] Step 6: Based on the flame radius in each direction at different times obtained in step 5, the flame front image data before and after are compared by the following formula to calculate the flame propagation speed in each direction at different times:

[0015] S n =dr u / dt

[0016] In the formula, S n is the stretching flame propagation speed in a certain direction; r u is the flame radius at a certain moment in the same direction;

[0017] Step 7: Calculate the propagation speed of the pressure fluctuation and draw a trend chart of the change of the pressure wave in the three-dimensional space;

[0018] Step 8: Determine the flame flow state according to the change law of the pressure wave of the in-cylinder pressure data and the flame radius data

[0019] Furthermore, before the said Step 7, it also includes: adjusting the probe position of the pressure regulating sensor to make the probe positions of the two times symmetrical about the central plane of the inner cavity of the spherical bomb, repeating the experiment under exactly the same initial conditions, measuring the influence deviation on the propagation of the pressure wave, and correcting the measured in-cylinder pressure data with this.

[0020] Furthermore, the said Step 4 includes:

[0021] Step 41: Determine the reference moment of the change of the flame front as the shooting moment of the flame front picture;

[0022] Step 42: Obtain the response time when the in-cylinder pressure sensor senses the change of the in-cylinder pressure under this model according to the model of the pressure sensor installed in the experimental device;

[0023] Step 43: Obtain the delay time t1 from shooting the flame front to the in-cylinder pressure sensor collecting the corresponding data according to the response time of the pressure sensor;

[0024] Step 44: Obtain the shooting frequency f1 of the high-speed camera and the measurement frequency f2 of the cylinder pressure sensor;

[0025] Step 45: Define the corresponding ratio k = f2 / f1, where k represents the number of in-cylinder pressure data collected by the pressure sensor during the shooting interval between two consecutive flame front pictures;

[0026] Step 46: Select a picture before the appearance of the flame front from the flame front pictures at different moments obtained in Step 1 as the background picture, and define this moment as the starting point of the ignition moment;

[0027] Step 47: Extract the in-cylinder pressure data at different positions in each direction at the starting point of the ignition moment from the data summarized in Step 3, and find the in-cylinder pressure data closest to the starting point of the ignition moment after acquisition delay according to the said delay time t1;

[0028] Step 48: Obtain the mean value of all pressure data in the direction of a certain pressure sensor probe before the ignition moment through the following formula and determine the mean value with this The in-cylinder pressure data at the ignition moment in this direction;

[0029]

[0030] where P j is the pressure data measured by one of the pressure sensors in the probe direction of a certain pressure sensor at each moment before the ignition moment; N is the number of pressure sensors installed on a certain pressure sensor probe;

[0031] Step 49: According to the search method and the corresponding ratio k in Step 47, taking the starting point of the ignition moment as the benchmark, sequentially match each flame front image with the in-cylinder pressure data measured at its corresponding shooting moment, and summarize the matching results.

[0032] Furthermore, the said Step 7 includes:

[0033] Step 71: Select the pressure data collected by the pressure sensor that shows obvious pressure data fluctuations and is the farthest from the flame center on the pressure sensor probes in different directions as the pressure data fluctuations in the adjacent shooting time intervals;

[0034] Step 72: Extract the flame front radius data at different moments and the in-cylinder pressure data in the corresponding measurement directions after matching, and obtain the change amount ΔP i of the pressure data in different measurement directions within a certain adjacent shooting interval, where i = 1, 2,... m; here, i represents the in-cylinder pressure data measured by the pressure sensors on the i-th pressure sensor probe installed on the combustion bomb body, and m represents the number of pressure sensor probes installed inside the constant volume combustion bomb body;

[0035] Step 73: According to the data matching result in Step 5, extract the front and rear flame front radius data R i1 and R i2 in the corresponding direction of the i-th pressure sensor probe within a certain adjacent shooting time interval. At the same time, according to the spacing between the pressure sensors on the i-th pressure sensor probe, obtain the distance d i of the pressure sensor from the combustion bomb body in this direction;

[0036] Step 74: Obtain the distances r i1 and r i2 from the pressure sensor to the flame front within a certain adjacent shooting time interval before and after, as well as the change amount Δr i of the distance from the flame front to the in-cylinder pressure sensor:

[0037]

[0038] Δr i = r i2-r i1

[0039] where D is the inner cavity diameter of the incendiary bomb, and R it is the data of the flame front radius before and after in the corresponding direction of the i-th pressure sensor probe within a certain adjacent shooting time interval. t = 1 represents the previous shooting moment, and t = 2 represents the subsequent shooting moment;

[0040] Step 75: Calculate the change rate S of the change in the in-cylinder pressure data measured by the target pressure sensor with respect to the change in the flame front radius data in the corresponding direction of the i-th pressure sensor probe within a certain adjacent shooting interval i , which is used to represent the relative velocity of the pressure wave during the flame propagation process;

[0041] S i = ΔP i / Δr i

[0042] Step 76: By summarizing the data of the relative velocity S i , according to the distribution of the pressure sensor probes and the pressure sensors, establish a trend graph of the change in the relative velocity of the equivalent pressure wave in the three-dimensional space during the flame propagation process.

[0043] Furthermore, the said Step 8 includes:

[0044] Step 81: Obtain the average propagation velocity of the pressure wave measured by the in-cylinder pressure sensors in different directions within a certain adjacent shooting interval in the entire three-dimensional space through the following formula

[0045]

[0046] Step 82: Comparing the entire experimental recording process, when the propagation velocities of the pressure waves in different directions in the three-dimensional space all satisfy for the first time within M consecutive shooting intervals after the ignition of the experimental system, it is regarded that the influence of the initial ignition energy of the flame on the flame propagation has been eliminated, and the flame changes in a spherical-like manner in all directions. At this time, the flame development enters the laminar flame propagation stage;

[0047] Step 83: After the flame has entered the laminar flame propagation stage, when the propagation velocities of the pressure waves in different directions in the three-dimensional space no longer satisfy within M consecutive shooting intervals, the unstable phenomenon of the flame front begins to appear during the flame propagation process, and the flame begins to enter the transition stage between the laminar flame and the turbulent flame;

[0048] Step 84: Starting from the node where the instability phenomenon of the flame front determined in Step 83 begins to appear, analyze the flame front of the flame pictures after this node, and extract the cracks that appear in the flame front during the transition stage between laminar flame and turbulent flame, as well as the cellular structure of the flame front pictures after the cellular structure.

[0049] Step 85: Based on the cellular structure of the flame front pictures obtained, use the equivalent circle area method and the distance formula to calculate the area S of each cellular structure of the flame. n And the length L of each crack m , as well as the total area S of the flame front at this shooting moment.

[0050] Step 86: When there is a situation where exists in the pressure wave propagation speeds in different directions in three-dimensional space within M consecutive shooting intervals, and or L m ≥R i appears at M / 2 consecutive shooting moments, the flame flow regime officially enters the turbulent flame propagation state; where R i is the equivalent flame radius at this moment.

[0051] The beneficial effects of the present invention are:

[0052] The present invention can better quantify the influence of pressure fluctuations on the flame development process during flame propagation based on the improved constant volume combustion device and the determination method of flame flow regime, and then make a detailed division of the changes in the flame flow regime due to fluid instability and thermal-mass instability. Finally, it can lay a foundation for quantifying the influence of instability on flame propagation during flame propagation and provide certain theoretical support for subsequent research on the basic theory of flame combustion. Description of the Drawings

[0053] Figure 1 is the working flow chart of the in-cylinder pressure acquisition system and the flame schlieren picture acquisition system of the constant volume combustion bomb of the present invention.

[0054] Figure 2 is the processing flow chart of the pressure fluctuation data and the flame schlieren pictures of the present invention.

[0055] Figure 3 is the schematic diagram of the installation of the pressure sensor probe on the body of the new constant volume combustion bomb.

[0056] Figure 4 is the schematic diagram of the flame front and the pressure wave propagation process.

[0057] Figure 5 are the flame schlieren pictures corresponding to the in-cylinder pressure flow regime.

[0058] In the figure: 1 - Constant - volume combustion bomb body; 2 - Pressure sensor probe; 3 - Pressure sensor; 4 - Flame front; 5 - Ignition electrode. Specific implementation mode

[0059] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0060] The present invention designs a new type of constant - volume combustion experimental device, takes the refined pressure fluctuation state in the combustion cylinder as a new evaluation index, and then conducts a comparative analysis with the flame front obtained under different working conditions according to the characteristic parameters of the flame flow state.

[0061] The present invention provides a constant - volume combustion bomb in - cylinder pressure acquisition system, which includes a constant - volume combustion bomb body, a constant - volume combustion bomb in - cylinder pressure acquisition device, an in - cylinder pressure sensor matched with the in - cylinder pressure acquisition device, and an electronic control unit. In addition, a corresponding flame schlieren image acquisition system and a method for synchronizing the pressure acquisition signal and the schlieren image are required.

[0062] The working flow chart of the constant - volume combustion bomb in - cylinder pressure acquisition system and the flame schlieren image acquisition system is as Figure 1 shown, and the processing flow chart of the pressure fluctuation data and the flame schlieren images obtained therefrom is as Figure 2 shown.

[0063] As Figure 3 shown, several small holes for installing and accommodating the pressure sensor probe are distributed symmetrically at different angles with the geometric center of the inner cavity of the spherical - shaped bomb body of the constant - volume combustion bomb as the center. The constant - volume combustion bomb in - cylinder pressure acquisition device is a pressure sensor probe of a unified specification. The pressure sensor probe is inserted into the small holes on the constant - volume combustion bomb body and fixed to seal the small holes. The end of the probe is inserted into the inner cavity of the spherical constant - volume combustion bomb and points to the geometric center; several pressure sensors are installed on the pressure sensor probe at a certain interval from the end of the probe outward, and the pressure fluctuation data at different positions in the direction pointed by the pressure sensor probe can be detected.

[0064] The pressure fluctuation data collected by the pressure sensor is transmitted to an external charge amplifier through a signal transmission line connected to the pressure sensor probe outside the constant - volume combustion bomb. After being conditioned by the charge amplifier, the pressure signal is converted into an electrical signal and enters the acquisition card and the electronic control unit. After the acquisition card records the data, the electronic control unit controls the end of the experiment.

[0065] The flame schlieren image acquisition system consists of a light source, a schlieren image shooting optical path composed of several reflectors, and a high - speed camera. The high - speed camera records the flame propagation situation inside the constant - volume combustion bomb body through the schlieren image shooting optical path.

[0066] The installed pressure sensor probe should not affect the normal observation of the constant - volume combustion optical path.

[0067] According to the requirements of the experimental method for this device, before the start of the experiment, the inner diameter D of the spherical cavity of the constant volume combustion bomb and the distance d from each pressure sensor on the pressure sensor probe to the bomb body i (i = 1, 2, … m) can be measured, and the response time t1 of the selected pressure sensor model to the change in the in-cylinder pressure can be obtained;

[0068] The method for the present invention to discriminate the flame flow state includes the following steps:

[0069] Step 1: Under certain initial experimental conditions, the fuel is ignited by the ignition system of the constant volume combustion experiment system to generate a flame, and high-speed cameras are used to obtain flame front pictures at different times.

[0070] Step 2: While the experiment in Step 1 is being carried out, through the in-cylinder pressure acquisition system of the constant volume combustion bomb, the in-cylinder pressure data collected by the pressure sensors at different positions in different directions of the pressure sensor probe inserted during the experiment are obtained at different times.

[0071] Step 3: The flame front pictures at different times obtained from Step 1 and the in-cylinder pressure data measured by the pressure sensors at different positions and different times are summarized, and a three-dimensional pressure distribution surface is constructed based on the pressure data.

[0072] Among them, the three-dimensional pressure distribution surface is drawn by using the mesh function of MATLAB software for the pressure data in different directions in the three-dimensional space at a certain moment.

[0073] Step 4: Match the in-cylinder pressure data at different times with the flame front pictures.

[0074] Step 41: Since the propagation time of light in the flame shooting path can be ignored compared with the response time of the in-cylinder pressure sensor to the pressure change, the shooting moment of the flame front picture can be regarded as the reference moment for the change of the flame front.

[0075] Step 42: According to the model of the pressure sensor installed in the experimental device, the response time of the in-cylinder pressure sensor of this model to the change in the in-cylinder pressure is obtained.

[0076] Step 43: According to the definition in Step 41 and the response time of the cylinder pressure sensor obtained in Step 42, the delay time t1 from the moment when the flame front is photographed to the moment when the in-cylinder pressure sensor collects the corresponding data can be obtained.

[0077] Step 44: Based on Steps 1 and 3, the shooting frequency f1 of the high-speed camera and the measurement frequency f2 of the cylinder pressure sensor can be obtained.

[0078] Step 45: On the basis of Step 44, define the corresponding ratio k = f2 / f1, where k represents the number of in-cylinder pressure data collected by the pressure sensor within the time interval between the shootings of the front and rear flame front pictures.

[0079] Step 46: On the basis of obtaining the flame front pictures at different moments in Step 1, select the picture before the appearance of the flame front as the background picture, and define this moment as the starting point of the ignition moment.

[0080] Step 47: Extract the in-cylinder pressure data at different positions in different directions between the background picture and the starting point of the ignition moment summarized in Step 3, and obtain the in-cylinder pressure data measured by the pressure sensors at different positions on the pressure sensor probes in each direction that is closest to the starting point of the ignition moment after acquisition delay through the delay time t1 from the flame front to the corresponding data collected by the in-cylinder pressure sensor obtained in Step 43.

[0081] Step 48: Considering the change of the in-cylinder pressure before the ignition moment, the mean value of the pressure data in a certain direction before the ignition moment is obtained through the following formula, and this is regarded as the in-cylinder pressure data at the ignition moment in this direction.

[0082]

[0083] where P j is the pressure data measured by the first pressure sensor in a certain direction of a cylinder pressure sensor probe at each moment before the ignition moment.

[0084] Step 49: Using the data search method in Step 47 and the corresponding ratio k defined in Step 45, with the starting point of the ignition moment as the reference, match the flame front pictures obtained in Steps 1 and 2 with the in-cylinder pressure data measured by the pressure sensors at different positions on the pressure sensor probes in each direction at the shooting moments of each flame front picture in turn.

[0085] Step 410: Summarize the matched flame front pictures and the in-cylinder pressure data measured by the pressure sensors at different positions on the pressure sensor probes in each direction at the shooting moments of each flame front picture through the above steps.

[0086] Step 5: Use the existing flame front picture processing technology to calculate the center and radii in each direction of each flame front picture obtained in Step 2, and on the basis of Step 5, match the flame radius data at different moments in the direction where the pressure sensor probe is installed with the in-cylinder pressure data measured by the pressure sensors at different positions and different moments in the corresponding direction again.

[0087] Step 6: On the basis of the flame radii in each direction at different moments obtained in Step 5, through the formula S n = dr u / dt, compare the front and rear flame front image data, and calculate the propagation speed of the flame in each direction at different times.

[0088] Step 7: Since the presence of the pressure sensor probe will affect the propagation process of the pressure wave during the flame propagation, a comparative experiment needs to be carried out. By adjusting the probe position, repeat the experiment under two sets of exactly the same initial conditions in such a way that the probe positions in the two experiments are symmetric about the central plane of the inner cavity of the spherical bomb, measure the influence deviation on the pressure wave propagation, and use this to correct the measured in-cylinder pressure data.

[0089] Step 8: Based on Steps 4, 5, and 7, calculate the propagation speed of the pressure fluctuation and draw a trend diagram of the change of the pressure wave in three-dimensional space.

[0090] Step 81: Since the pressure propagation speed inside the bomb is usually faster than the flame development speed, select the pressure data collected by the in-cylinder pressure sensor that has obvious pressure data fluctuations and is the farthest from the flame center on the pressure sensor probes in different directions as the pressure data fluctuation for this adjacent shooting time interval.

[0091] Step 82: Through Steps 4, 5, and 81, extract the matched flame front radius data at different times and the in-cylinder pressure data measured by the pressure sensors at different positions on the pressure sensor probes in the corresponding measurement directions of the cylinder pressure sensor. The change amount ΔP of the in-cylinder pressure data measured by the selected pressure sensors in different measurement directions within a certain adjacent shooting interval can be obtained. i (i = 1, 2, … m), where i represents the in-cylinder pressure data measured by the pressure sensor on the i-th pressure sensor probe installed on the combustion bomb body, and m represents the number of pressure sensor probes installed inside the constant volume combustion bomb body.

[0092] Step 83: Based on Step 5, obtain the front and rear flame front radius data R at the corresponding angle of the i-th pressure sensor probe within a certain adjacent shooting time interval selected in Step 82. i1 and R i2 , and at the same time, according to the spacing of the pressure sensors distributed on the selected pressure sensor probe, the distance d from the pressure sensor on the pressure sensor probe in this direction to the bomb body can be obtained. i (i = 1, 2, … m).

[0093] Step 84: Based on Step 83, obtain the distances r from the pressure sensor to the flame front before and after within a certain adjacent shooting time interval through the distance formula. i1 and r i2 , as well as the change amount Δr of the distance from the flame front to the in-cylinder pressure sensor. i (i = 1, 2, … m)

[0094]

[0095] Δr i = r i2 - r i1

[0096] where D is the inner cavity diameter of the incendiary bomb, and R it is the data of the flame front radius before and after in the corresponding direction of the i-th pressure sensor probe within a certain adjacent shooting time interval. t = 1 represents the previous shooting moment, and t = 2 represents the subsequent shooting moment.

[0097] Step 84: Obtain the change amount ΔP of the in-cylinder pressure data in different directions within a certain adjacent shooting time interval in Steps 83 and 84 i and the change amount Δr of the radius data from the flame front to the target pressure sensor at the angle corresponding to the i-th pressure sensor probe i Based on this, the change rate S of the change amount of the in-cylinder pressure data measured by the target pressure sensor at the angle corresponding to the i-th pressure sensor probe within a certain adjacent shooting interval with respect to the change amount of the flame front radius data i = ΔP i / Δr i (i = 1, 2, … m) is used to represent the relative velocity of the pressure wave during the flame propagation process; as Figure 4 shown in the schematic diagram of the flame front and the pressure wave propagation process.

[0098] Step 85: Summarize the data of the relative velocity S of the pressure wave during the flame propagation process obtained in Step 84 i According to the distribution of the pressure sensor probes in the bomb and the in-cylinder pressure sensors on the pressure sensor probes, establish a trend chart of the relative velocity change of the equivalent pressure wave in the three-dimensional space during the flame propagation process.

[0099] Step 9: Determine the flame flow state based on the pressure wave change law of the in-cylinder pressure data and the flame radius data.

[0100] Step 91: Based on Step 83, the average propagation velocity of the pressure wave measured by the in-cylinder pressure sensors in different directions within a certain adjacent shooting interval in the entire three-dimensional space can be obtained through the following formula

[0101]

[0102] Step 92: Based on the average propagation velocity of the pressure wave measured by the in-cylinder pressure sensors in different directions found in Step 91, compare the entire experimental recording process. When, after the ignition of the experimental system, for the first time within twenty consecutive shooting intervals, the pressure wave propagation velocities in different directions in the three-dimensional space all satisfy When this occurs, it is considered that the influence of the initial ignition energy of the flame on flame propagation has been eliminated, and the flame changes in a spherical-like manner in all directions. At this time, the flame development enters the laminar flame propagation stage.

[0103] Step 93: Based on the calculation of the average propagation speed of the pressure wave in Step 91, after the flame has entered the laminar flame propagation stage, when the propagation speeds of the pressure waves in different directions in the three-dimensional space no longer satisfy during twenty consecutive shooting intervals, it indicates that the propagation speed of the pressure wave is no longer uniform and the instability of the flame front will start to appear during the subsequent flame propagation process. The flame begins to enter the transition stage between laminar flame and turbulent flame.

[0104] Step 94: At the node where the instability of the flame front determined in Step 93 begins to appear, analyze the flame front of the flame pictures after this node. Using the image recognition function based on MATLAB software, extract the cellular structure of the flame front picture after cracks and cellular structures appear in the transition stage between laminar flame and turbulent flame.

[0105] Step 95: Based on the cellular structure of the flame front picture obtained in Step 94, the area S of each cellular structure of the flame can be calculated using the equivalent circle area method and the distance formula n (n = 1, 2, 3,... n), the lengths L of each crack m (m = 1, 2, 3,... m), and the total area S of the flame front at this shooting moment.

[0106] Step 96: On the basis of the above steps, when there is in the propagation speeds of the pressure waves in different directions in the three-dimensional space during twenty consecutive shooting intervals and or L m ≥ R i appears at ten consecutive shooting moments, where R i is the equivalent flame radius at this moment, it indicates that the flame flow regime officially enters the turbulent flame propagation state at this moment.

[0107] Step 10: Under the method of Step 9, by continuously changing the initial conditions of the experiment, calculate and summarize the boundary conditions of the flame flow regimes under different working conditions, and conduct quantitative analysis on the variation laws of the boundaries of laminar flames under different initial conditions.

[0108] As Figure 5 shown, the schlieren pictures of the flame corresponding to the in-cylinder pressure flow regime. No flame front appears before the ignition moment, and there are small-amplitude pressure fluctuations in the bomb body of the constant volume bomb. Therefore, the mean value of the pressure data in a certain direction before the ignition moment It is recognized as the in-cylinder pressure data at the ignition moment. After ignition, a kernel of flame is formed at the ignition center, and the flame front is formed and propagates outward. Since the volume covered by the flame front is not large compared to the volume of the constant-volume combustion bomb body, the in-cylinder pressure only shows a small increase, and at this time the flame is in the laminar combustion state. As the flame continues to propagate, the volume ratio between the burned area and the unburned area continuously increases, the in-cylinder pressure distribution gradually becomes disordered, causing the flame front to start showing unstable phenomena, and the pressure in the bomb body increases significantly, and the flame begins to enter the transition stage between laminar flame and turbulent flame. After that, with the further deepening of the flame instability, the overall combustion begins to intensify, the flame completely enters the turbulent flame stage, and the pressure in the bomb body begins to rise sharply.

[0109] In short, the present invention can better determine the boundary ranges of each flame flow regime, thereby obtaining more accurate combustion characteristic parameters under each flame flow regime, and providing data support for subsequent research on the physical and chemical properties of fuels.

Claims

1. A method for discriminating flame flow states by a constant volume combustion device for discriminating flame flow states, characterized in that, The constant volume combustion device includes a constant volume combustion cylinder pressure acquisition system and a flame pattern image acquisition system; The constant volume incendiary bomb cylinder pressure acquisition system comprises a spherical constant volume incendiary bomb body (1) and a pressure sensor probe (2); the constant volume incendiary bomb body (1) is provided with a plurality of probe holes, one end of the pressure sensor probe (2) is provided with a signal transmission line, the other end is inserted into the probe hole and the probe hole is sealed, and the end of the probe points to the geometric center of the constant volume incendiary bomb cavity; a plurality of pressure sensors (3) are installed on the pressure sensor probe (2) at a certain interval from the end of the probe outward, and are used to detect pressure fluctuation data at different positions in the direction in which the pressure sensor probe (2) points; the detected pressure fluctuation data is transmitted to an external charge amplifier through the signal transmission line, and the pressure signal is converted into an electrical signal after conditioning by the charge amplifier and enters the acquisition card and the electronic control unit; After the data is recorded by the acquisition card, the electronic control unit controls the end of the experiment; The flame schlieren picture acquisition system includes a schlieren picture shooting optical path composed of a number of reflectors, and a high-speed camera; The high-speed camera records the flame propagation inside the constant volume combustion bomb through the schlieren image shooting light path; The flame flow pattern discrimination method comprises the following steps: Step 1: Under initial experimental conditions, the fuel is ignited by the ignition system of the constant volume combustion device to generate a flame, and a high-speed camera is used to obtain flame front images at different times; Step 2: While the experiment is being carried out in step 1, the in-cylinder pressure data collected by the pressure sensors at different positions in all directions of the pressure sensor probes inserted during the experiment at different times are obtained through the constant volume combustion bomb in-cylinder pressure collection system; Step 3: Summarize the flame front images and cylinder pressure data obtained from steps 1 and 2, and construct a three-dimensional pressure distribution surface based on the pressure data; Step 4: Match the cylinder pressure data at different times with the flame front image; The step 4 comprises: Step 41: identifying the shooting time of the flame front image as the reference time of the flame front change; Step 42: According to the model of the pressure sensor installed in the experimental device, the response time of the in-cylinder pressure sensor sensing the change of the in-cylinder pressure under the model is obtained; Step 43: according to the response time of the pressure sensor, obtain the delay time t1 from photographing the flame front to the cylinder pressure sensor collecting the corresponding data; Step 44: obtaining the shooting frequency f1 of the high-speed camera and the measuring frequency f2 of the cylinder pressure sensor; Step 45: define a corresponding ratio k=f2 / f1, where k represents the number of cylinder pressure data collected by the pressure sensor within the interval between the two flame front images; Step 46: From the flame front images at different times obtained in step 1, select a picture before the flame front appears as the background picture, and define this moment as the starting point of the ignition moment; Step 47: extracting the in-cylinder pressure data at different positions in all directions of the ignition start point from the data collected in step 3, and finding the in-cylinder pressure data closest to the ignition start point after the collection delay according to the delay time t1; Step 48: Obtain the mean value of all pressure data in the direction of a certain pressure sensor probe before the ignition moment by the following formula and determine the mean value as the in-cylinder pressure data at the ignition moment in this direction; where P j is the pressure data measured by one of the pressure sensors in the probe direction of a certain pressure sensor at each moment before the ignition moment; N is the number of pressure sensors installed on the probe of a certain pressure sensor; Step 49: Based on the search method and the corresponding ratio k in Step 47, taking the starting point of the ignition timing as the reference, successively match each flame front image with the in-cylinder pressure data measured at its corresponding shooting time, and summarize the matching results; Step 5: Calculate the centers and radii in various directions of each flame front image obtained in Step 2, and on this basis, re-match the flame radius data in the direction of the pressure sensor probe at different times with the in-cylinder pressure data measured by the pressure sensors at different positions in the corresponding direction at different times; Step 6: Based on the flame radii in various directions at different times obtained in Step 5, compare the data of the front and rear flame front images through the following formula to calculate the flame propagation speeds in various directions at different times: S n = dr u / dt where S n is the stretching flame propagation speed in a certain direction; r u is the flame radius at a certain moment in the same direction; Step 7: Calculate the propagation speed of the pressure fluctuation and draw a trend chart of the change of the pressure wave in the three-dimensional space; Step 8: Determine the flame flow state based on the pressure wave change law and the flame radius data of the in-cylinder pressure data.

2. The flame flow state discrimination method according to claim 1, characterized in that Before Step 7, it further includes: adjusting the position of the pressure sensor probe so that the positions of the two probes are symmetric about the central plane of the inner cavity of the spherical bomb, repeating the experiment under exactly the same initial conditions, measuring the influence deviation on the pressure wave propagation, and correcting the measured in-cylinder pressure data based on this.

3. The method for discriminating the flame flow state according to claim 1, characterized in that Step 7 includes: Step 71: Select the pressure data collected by the pressure sensor that has obvious pressure data fluctuations on the pressure sensor probes in different directions and is the farthest from the flame center as the pressure data fluctuation in the adjacent shooting time interval; Step 72: Extract the data of the flame front radius at different times that have been matched and the in-cylinder pressure data in the corresponding measurement directions, and obtain the change amount ΔP of the pressure data in different measurement directions within a certain adjacent shooting interval. i , where i = 1, 2, … m; here, i represents the in-cylinder pressure data measured by the pressure sensor on the i-th pressure sensor probe installed on the combustion bomb body, and m represents the number of pressure sensor probes installed inside the constant volume combustion bomb body. Step 73: According to the data matching result in Step 5, extract the front and rear flame front radius data R in the corresponding direction of the i-th pressure sensor probe within a certain adjacent shooting time interval i1 and R i2 , and at the same time, according to the spacing of the pressure sensors distributed on the i-th pressure sensor probe, obtain the distance d of the pressure sensor from the combustion bomb body in this direction i ; Step 74: Obtain the distance r from a pressure sensor to the flame front before and after a certain adjacent shooting time interval through the following distance formula i1 and r i2 , and the change amount Δr of the distance from the flame front to the in-cylinder pressure sensor i : where D is the inner cavity diameter of the incendiary bomb, and R it is the data of the flame front radius before and after in the corresponding direction of the i-th pressure sensor probe within a certain adjacent shooting time interval. t = 1 represents the previous shooting moment, and t = 2 represents the subsequent shooting moment; Step 75: Calculate the change rate S of the change in the in-cylinder pressure data measured by the target pressure sensor with respect to the change in the flame front radius data in the direction corresponding to the i-th pressure sensor probe within a certain adjacent shooting interval, which is used to represent the relative velocity of the pressure wave during the flame propagation process; i , which is used to represent the relative velocity of the pressure wave during the flame propagation process; S i = ΔP i / Δr i Step 76: By summarizing the relative velocity S i data, according to the distribution of the pressure sensor probes and the pressure sensors, establish a trend graph of the relative velocity change of the equivalent pressure wave in the three-dimensional space during the flame propagation process.

4. The flame flow regime discrimination method according to claim 3, characterized in that Step 8 includes: Step 81: Obtain the average propagation velocity of the pressure wave measured by the in-cylinder pressure sensors in different directions within a certain adjacent shooting interval in the entire three-dimensional space through the following formula Step 82: Compare the entire experimental recording process. When the pressure wave propagation speeds in different directions in three-dimensional space all satisfy for the first time within M consecutive shooting intervals after the experimental system ignites, it is considered that the influence of the initial ignition energy of the flame on flame propagation has been eliminated, and the flame changes in a spherical-like manner in all directions. At this time, the flame development enters the laminar flame propagation stage; Step 83: After the flame has entered the laminar flame propagation stage, when the propagation speeds of the pressure waves in different directions in the three-dimensional space no longer satisfy during consecutive M shooting intervals, the instability phenomenon of the flame front begins to appear during the flame propagation process, and the flame begins to enter the transition stage between the laminar flame and the turbulent flame; Step 84: Through the node at which the unstable phenomenon of the flame front determined in Step 83 begins to appear, analyze the flame front of the flame image after this node, and extract the cracks that appear in the flame front during the transition stage between the laminar flame and the turbulent flame, as well as the flame cellular structure in the flame front image after the cellular structure. Step 85: Based on the cellular structure of the obtained flame front image, use the equivalent circle area method and the distance formula to calculate the area S of each cellular structure of the flame n and the length L of each crack m , and the total area S of the flame front at this moment of shooting; Step 86: When there exists in the pressure wave propagation speeds in different directions in the three-dimensional space within M consecutive shooting intervals, and or L m ≥R i occurs at M / 2 consecutive shooting moments, the flame flow regime officially enters the turbulent flame propagation state; where R i is the equivalent flame radius at this moment.

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