Fuel oil atomization characteristic analysis method based on PLIF-Mie dual-spectrum optical measurement

Abstract

The invention provides a fuel oil atomization characteristic analysis method based on PLIF-Mie dual-spectrum optical measurement, and relates to the technical field of fuel oil atomization characteristics. After fuel oil is sprayed into the atomization characteristic visual measurement system through a centrifugal nozzle, laser is adjusted by using the PLIF-Mie dual-spectrum optical measurement system, and the two-dimensional distribution condition of the average particle size value is obtained at the same time through a method of measuring an LIF signal and a Mie scattering signal at the same time. The PLIF-Mie dual-spectrum optical measurement technology is adopted to comprehensively analyze the fuel oil atomization process of the combustion chamber in the limited space, the high-speed camera shooting and synchronous triggering system can capture the fuel oil atomization process and transient flow field characteristics which change rapidly, the high-precision measurement requirement is met, and the device is suitable for an aero-engine combustion chamber and also suitable for a combustion chamber of an aero-engine. And the method can also be applied to research and optimization of other combustion systems and industrial combustion equipment, and has wide application prospects and remarkable technical advantages in the aspects of improving the combustion efficiency and reducing pollutant emission.

Description

Technical Field

[0001] The invention relates to the technical field of fuel atomization characteristics, and in particular to a fuel atomization characteristics analysis method based on PLIF-Mie dual-spectrum optical measurement. Background Art

[0002] With the rapid development of the aviation industry, military aircraft have put forward higher requirements for excellent combat performance such as tactical maneuverability, short-distance takeoff, and supersonic cruise, while civil aircraft are developing in the direction of low cost, high cleanliness, and high reliability. In order to meet the development requirements of military and civil aircraft, it has become an inevitable trend for aircraft engines to develop in the direction of high thrust-to-weight ratio, high pressure ratio, high temperature rise, and low pollution. The combustion process in the combustion chamber is completed in a very short time by a series of steps including fuel atomization and evaporation, mixing of fuel and air after evaporation, ignition of combustible mixed gas, and oxidation combustion reaction. As the pre-step of the entire combustion process, the quality of fuel atomization and the flow field morphology of the oil-gas mixture have a decisive influence on the combustion process in the combustion chamber.

[0003] In previous studies, laser Doppler velocimeters, phase Doppler particle analyzers, phase Doppler anemometers and other laser equipment were usually used in combination with high-speed cameras to photograph the atomization morphology of the fuel nozzle, collect the oil mist information in the fog cone area and on a certain line at a certain distance from the fuel nozzle outlet, and analyze the influence of factors such as fuel physical properties, fuel nozzle design parameters and aerodynamic parameters on the distribution characteristics of liquid film breakage, atomized oil droplet size, size distribution and atomization cone angle. It was found that when the above method was used to test the atomization characteristics of the fuel in the combustion chamber, the test results could only obtain the characteristic parameters of a certain point or a certain line in the atomization field, and it was difficult to obtain multiple key parameters at the same time, which limited the comprehensive understanding of the fuel atomization process and lacked research on the overall atomization field characteristics of the combustion chamber. At the same time, it is difficult to obtain high-resolution atomization characteristics and flow field characteristics data when conducting experimental tests in confined spaces, especially in complex combustion chambers. In addition, the consistency and repeatability of the measurement results are greatly affected by changes in nozzle design, fuel type and operating conditions. High temperature and high pressure also bring great challenges to the use of traditional measurement equipment. In addition, these technologies usually require complex data processing and analysis processes, which increases the workload of researchers and the uncertainty in the data processing process. Therefore, the existing single optical measurement technology has obvious limitations when studying the fuel atomization characteristics in confined spaces, and a more comprehensive and accurate measurement technology is needed to solve these problems. Summary of the invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies of the above-mentioned prior art and to provide a fuel atomization characteristic analysis method based on PLIF-Mie dual-spectrum optical measurement. Through laser excitation and detection at different wavelengths, multiple key parameters such as oil mist concentration, temperature and droplet size in the fuel atomization process can be simultaneously obtained, thereby ensuring transient capture and high-resolution imaging of the fuel atomization process.

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

[0006] A fuel atomization characteristic analysis method based on PLIF-Mie dual-spectrum optical measurement, after the fuel is sprayed into the atomization characteristic visualization measurement system through a centrifugal nozzle, the laser is adjusted by using the PLIF-Mie dual-spectrum optical measurement system, and the two-dimensional distribution of the average particle size value is obtained by simultaneously measuring the LIF signal and the Mie scattering signal; when the laser is irradiated to the fuel atomization area, the atoms in the fuel are excited by the laser irradiation to produce energy level transition, and the photons generated in the process of decaying from the excited state to the low energy level are fluorescence; through the planar array detector in the PLIF optical test system, optical information on the two-dimensional plane is obtained, including the fuel component concentration, temperature, speed, pressure and density; at the same time, the scattering of the laser by the droplet generates the Mie scattered light signal to generate the scattering spectrum; through the relationship that the intensity of Mie scattering is proportional to the square of the droplet particle size, the two signals are comprehensively analyzed to finally obtain the average fuel concentration and the distribution of the droplet particle size;

[0007] The atomization characteristic visualization measurement system includes an air source, a digital acquisition and control system, a test bench, a PLIF-Mie dual-spectrum optical measurement system, and an integrated fuel control test system. The PLIF-Mie dual-spectrum optical measurement system includes a laser generator, a filter system, a sheet light shaping system, a laser detector, and a digital delay generation controller; lasers of different wavelengths are generated by adjusting the laser generator; the laser is expanded by a concave cylindrical lens in the filter system, and then converged into a sheet laser by a plano-convex mirror; the sheet laser is shot into the visualized atomization field in the test bench through the sheet light shaping system to keep it parallel to the side window of the test piece, and finally outputs a thin sheet laser with a width of 100 mm and a thickness of about 50 μm; the delay of the laser generator and the laser detector is adjusted by the digital delay generation controller to ensure the synchronization of all equipment; the entire process of fuel atomization is photographed by the laser detector.

[0008] Furthermore, the specific steps of adjusting the laser using the PLIF-Mie dual-spectrum optical measurement system are as follows:

[0009] S1: Use DG645 digital delay generation controller to externally trigger the laser generator and laser detector. According to the corresponding relationship between delay and laser energy, the test is carried out under the condition that the delay of the laser and the detector is 215μs in the digital delay generation controller to ensure the synchronization of all devices.

[0010] S2: Generate line lasers with wavelengths of 1064nm, 532nm, and 266nm in the laser generator system;

[0011] S3: By adjusting the combination of high-reflection and high-lens filters in the filter system, the combined beams are finally output with 266nm and 532nm wavelength lasers, and the output spot diameters are both 9mm; the 266nm wavelength laser is used to excite kerosene fluorescence, and the 532nm wavelength laser is used to excite Mie scattering signals;

[0012] S4: In the sheet light shaping system, the beam shaping part is fixed on the frame. In order to facilitate the lateral adjustment of the optical path and large-range measurement, the reflector frame is fixed on the one-dimensional moving stage. The one-dimensional moving stage uses the frame as the base to realize the excitation and measurement of different longitudinal sections of the sheet light in the test section. The line laser is expanded by a concave cylindrical lens and then converged into a sheet laser by a plano-convex mirror. The sheet laser enters the atomization field through a reflector and remains parallel to the side window. Finally, a thin sheet laser with a width of 100 mm and a thickness of about 50 μm is output.

[0013] S5: The laser detector part is composed of a high-resolution industrial camera with a resolution of 2336×1728@10Hz and a high-gain intensifier;

[0014] S6: The air inlet direction is defined as the Y axis, the vertical direction is defined as the Z axis, the direction perpendicular to the view is defined as the positive direction of the X axis, the origin of the coordinate is the center of the cyclone outlet, and the shooting area is 120×75mm;

[0015] S7: The fuel droplets in the atomized field are excited by the laser, inducing fluorescence and scattered light; the scattered light signal is captured by the 532nm / 10nm bandpass filter in the filter system, and the fluorescence signal is captured by the UG5 filter in the filter system;

[0016] S8: The laser detector uses a CCD camera and an ICMOS camera to capture the entire process of fuel atomization.

[0017] Furthermore, the specific numerical calculations for adjusting the laser include:

[0018] The Mie scattered light intensity S of each illuminated droplet M (D) is proportional to the surface area of ​​the droplet:

[0019] S M (D) = aM D 2

[0020] Among them, S M (D) represents the intensity of Mie scattered light; a M represents a constant; D represents the droplet diameter;

[0021] The fluorescence intensity S of each illuminated droplet is F (D) is proportional to the droplet volume:

[0022] S F (D) = a F D 3

[0023] Among them, S F (D) represents the fluorescence intensity of kerosene; a F Represents a constant;

[0024] The Sauter mean diameter SMD of the droplet size distribution is defined as:

[0025]

[0026] Where K represents the SMD calibration parameter; dN(D) represents the distribution probability of droplets in the atomization field;

[0027] Kerosene fluorescence intensity S k It is expressed by the following formula:

[0028]

[0029] Among them, η opt It represents the total efficiency of the detector system; E represents the energy density of a single laser pulse, in mJ / cm 2 ; hc / λ represents the energy value of a single photon with wavelength λ, in mJ; V c Indicates the laser irradiation volume in cm 3 ; k represents the kerosene concentration in %; k represents the Boltzmann constant in J / K; σ represents the absorption cross section in cm 2 / molecule; T is temperature, in Kelvin; P is pressure, in Pa; Φ is fluorescence quantum yield; χ q represents the quenching gas concentration;

[0030] The above formula of kerosene fluorescence intensity S k Simplified to the following formula:

[0031] S k =C o χ k

[0032] Among them, C o represents the experimental constant; this formula shows that the kerosene concentration distribution is proportional to the detected fluorescence signal intensity, so the intensity of the fluorescence signal is used to qualitatively represent the kerosene distribution.

[0033] The beneficial effects of adopting the above technical solution are: the fuel atomization characteristic analysis method based on PLIF-Mie dual-spectrum optical measurement provided by the present invention adopts PLIF-Mie dual-spectrum optical measurement technology to analyze the fuel atomization process in the combustion chamber, which can realize the simultaneous measurement of multiple parameters of the overall atomization process in the model combustion chamber in a confined space. At the same time, high spatial resolution can be applied to more complex combustion chamber model research, and high-speed camera and synchronous trigger system can capture rapidly changing fuel atomization process and transient flow field characteristics to meet high-precision measurement requirements. This technology is not only suitable for aircraft engine combustion chambers, but can also be applied to the research and optimization of other combustion systems and industrial combustion equipment. It has broad application prospects and significant technical advantages in improving combustion efficiency and reducing pollutant emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a visual measurement system for atomization characteristics provided by an embodiment of the present invention;

[0035] Figure 2 A schematic diagram of the structure of a PLIF-Mie dual-spectrum optical measurement system provided in an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of the output of a laser generator provided in an embodiment of the present invention;

[0037] Figure 4 A schematic diagram of the structure of a light sheet shaping system provided in an embodiment of the present invention;

[0038] Figure 5 A schematic diagram of a calibration test bench provided in an embodiment of the present invention;

[0039] Figure 6 A calibration test shot provided by an embodiment of the present invention;

[0040] Figure 7 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =2g / s when the SMD distribution diagram of the fuel atomized droplets of cyclone A under different pressure losses;

[0041] Figure 8 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =4.15g / s fuel atomized droplet SMD distribution diagram of cyclone A under different pressure losses;

[0042] Fig. 9The main and auxiliary oil circuits provided in the embodiment of the present invention supply oil simultaneously and the fuel flow rate W f1 =72.5g / s, W f2 =6.4g / s fuel atomized droplet SMD distribution diagram of cyclone A under different pressure losses;

[0043] Fig.10 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =2g / s SMD distribution diagram of fuel atomized droplets in cyclone B under different pressure losses;

[0044] Fig.11 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =4.15g / s SMD distribution diagram of fuel atomized droplets in cyclone B at different pressure losses;

[0045] Fig.12 The main and auxiliary oil circuits provided in the embodiment of the present invention supply oil simultaneously and the fuel flow rate W f1 =72.5g / s, W f2 =6.4g / s fuel atomized droplet SMD distribution diagram of cyclone B under different pressure losses;

[0046] Fig.13 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =2g / s fuel atomization concentration distribution diagram of cyclone A under different pressure losses;

[0047] Fig.14 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =4.15g / s distribution diagram of fuel atomization concentration in cyclone A under different pressure losses;

[0048] Fig.15 The main and auxiliary oil circuits provided in the embodiment of the present invention supply oil simultaneously and the fuel flow rate W f1 =72.5g / s, W f2 =6.4g / s fuel atomization concentration distribution diagram of cyclone A under different pressure losses;

[0049] Fig.16 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =2g / s fuel atomization concentration distribution diagram of cyclone B under different pressure losses;

[0050] Fig.17 The embodiment of the present invention provides that only the auxiliary oil circuit supplies oil and the fuel flow rate W f2 =4.15g / s fuel atomization concentration distribution diagram of cyclone B under different pressure losses;

[0051] Fig.18The main and auxiliary oil circuits provided in the embodiment of the present invention supply oil simultaneously and the fuel flow rate W f1 =72.5g / s, W f2 =6.4g / s fuel atomization concentration distribution diagram of cyclone B under different pressure losses;

[0052] Fig.19 A schematic diagram of atomization cone angle recognition provided by an embodiment of the present invention;

[0053] Fig. 20 A fuel concentration distribution diagram under different pressure losses when the fuel temperature is 0°C provided in an embodiment of the present invention;

[0054] Fig.21 A fuel concentration distribution diagram under different pressure losses when the fuel temperature is -20°C provided in an embodiment of the present invention;

[0055] Fig. 22 The fuel concentration distribution diagram under different pressure losses when the fuel temperature is -40°C provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0056] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0057] This embodiment provides a method for analyzing the atomization characteristics of fuel in a combustion chamber in a confined space based on the PLIF-Mie dual-spectrum optical measurement technology. Based on the characteristics that kerosene is prone to produce fluorescence and scattering spectra when excited by laser, and the relationship that the Mie scattering intensity is proportional to the square of the droplet size, by simultaneously measuring the LIF signal and the Mie scattering signal, the distribution of fuel concentration and droplet size can be obtained at the same time. When the laser is irradiated to the fuel atomization area, the molecules in the fuel are excited to produce fluorescence, and at the same time, the scattering of the laser by the droplets produces Mie scattered light signals. Detecting the fluorescence signal can obtain the concentration and temperature distribution of the fuel, and detecting the Mie scattering signal can obtain the droplet size distribution. By comprehensively analyzing these two signals, the atomization characteristics of the fuel can be accurately measured.

[0058] PLIF (Planar Laser Induced Fluorescence) technology uses a planar array detector to obtain high-resolution image information on a two-dimensional plane, combined with a high-speed camera and a synchronous trigger system, it can capture the rapidly changing atomization process in real time. The high-performance data processing system performs analysis and imaging, providing comprehensive fuel atomization characteristic data, which is not only used to study the basic scientific issues of fuel atomization, but also provides important reference for combustion efficiency optimization and pollutant emission reduction in the combustion chamber.

[0059] Atomization characteristics visual measurement system Figure 1As shown, it includes gas source, digital acquisition and control system, test bench, PLIF-Mie dual-spectrum optical measurement system and comprehensive fuel laser test system. Among them, the test section includes the combustion chamber head swirl nozzle, air curtain device, visual high temperature and high pressure resistant organic glass on the wall, nozzle mounting seat and air inlet interface of the air curtain device. The visual high temperature and high pressure resistant organic glass is the window, which is used for optical testing through laser and imaging shooting; the air curtain device is to ensure that oil mist or tracer particles are prevented from accumulating on the window surface during measurement, causing shooting errors. The exhaust section is connected to a transmitter for outlet pressure measurement, which is used to record the combustion chamber outlet state parameters. The air enters the combustion chamber from the intake section through the opening on the cap cover through the swirler. The nozzle is a dual oil circuit centrifugal nozzle. The swirler adopts a two-stage axial anti-swirl structure. The two types of swirlers are replaced by matching mounting bushings. The end face of the combustion chamber head mounting plate is 85.5mm away from the intake end flange, the entire cavity is 410mm long, and the nozzle outlet is 1mm away from the outlet end face of the swirler blade.

[0060] The PLIF-Mie dual-spectrum optical measurement system includes a laser generator, a filter system, a light shaping system, a laser detector, and a digital delay generation controller. Figure 2 As shown. The intake air flow is regulated and controlled by the digital acquisition and control system, and the fuel flow and temperature are regulated by the integrated fuel laser test system and the temperature controller. Lasers of different wavelengths are generated by adjusting the laser generator. The laser is expanded by the concave cylindrical lens in the filter system, and then converged into a sheet laser by the plano-convex mirror; the sheet laser is shot into the visualized atomization field in the test bench through the sheet light shaping system to keep it parallel to the side window of the test piece, and finally output a thin sheet laser with a width of 100mm and a thickness of about 50μm. The digital delay generation controller is used to adjust the delay of the laser and the detector to ensure the synchronization of all equipment. The fuel droplets in the atomization field are excited by the sheet laser, which will induce fluorescence and scattered light, and are imaged by the ICMOS camera at the same time through the separated optical path.

[0061] In the preliminary test, it was found that the 266nm wavelength would cause the excited MIE scattering signal to be weak. It may be that the high fuel concentration caused a large degree of absorption on the propagation path, which interfered with the detection of Mie scattering signals and thus affected the accuracy of the test measurement results. Therefore, the laser transmission was optimized by adjusting the combination of high-reflection and high-lens sheets to finally output 266nm and 532nm wavelength lasers. The 266nm wavelength laser was used to excite kerosene fluorescence, and the 532nm wavelength laser was used to excite Mie scattering signals. Figure 3 shown.

[0062] According to the above laser output scheme, the stable output of 266nm and 532nm lasers was achieved, and the output spot diameter was 9mm. According to the corresponding relationship between delay and laser energy, as shown in Table 1, the experiment was carried out under the condition of delay of 215μs.

[0063] Table 1 Delay and corresponding laser energy

[0064] Delay(μs) 266nm laser energy (mJ) 532nm laser energy (mJ) 200 9.33 4.91 210 11.5 18.4 215 16.2 28.8 220 18 41

[0065] Light sheet shaping system Figure 4 The beam shaping part is fixed on the frame. In order to facilitate the lateral adjustment of the optical path and large-range measurement, the reflector frame is fixed on a one-dimensional moving stage. The moving stage uses the frame as a base to realize the excitation and measurement of different longitudinal sections of the light sheet in the test section.

[0066] The system uses a high-resolution industrial camera with a resolution of 2336×1728@10Hz and a high-gain enhancer, which together form the detector part. In order to increase the light collection efficiency and reduce the detection depth of field, achieve better noise suppression, and thus improve the image signal-to-noise ratio, a CCD camera is used in combination with an ICMOS camera (large aperture UV lens). The scattered light signal is captured by the 532nm / 10nm bandpass filter in the filter system, and the fluorescence signal is captured by the UG5 filter in the filter system. The timing control system uses a DG645 digital delay generator to perform external trigger control on the laser and detector, and adjust the delay between the two to ensure the synchronization of all devices.

[0067] The specific steps of laser adjustment are as follows:

[0068] S1: Use DG645 digital delay generation controller to perform external trigger control on the laser and detector. According to the corresponding relationship between delay and laser energy, the test is carried out under the condition that the delay of the laser and the detector is 215μs in the digital delay generation controller to ensure the synchronization of all equipment.

[0069] S2: Generate line lasers with wavelengths of 1064nm, 532nm, and 266nm in the laser generator system.

[0070] S3: By adjusting the combination of high-reflection and high-lens filters in the filter system, the combined beams are finally output with 266nm and 532nm wavelength lasers, and the output spot diameters are both 9mm. The 266nm wavelength laser is used to excite kerosene fluorescence, and the 532nm wavelength laser is used to excite Mie scattering signals.

[0071] S4: In the sheet light shaping system, the beam shaping part is fixed on the frame. In order to facilitate the lateral adjustment of the optical path and large-range measurement, the reflector frame is fixed on the one-dimensional moving stage. The moving stage uses the frame as the base to realize the excitation and measurement of different longitudinal sections of the sheet light in the test section. The line laser is expanded by a concave cylindrical lens and then converged into a sheet laser by a plano-convex mirror. The sheet laser enters the atomization field through a reflector and remains parallel to the side window. Finally, a thin sheet laser with a width of 100 mm and a thickness of about 50 μm is output.

[0072] S5: The laser detector part is composed of a high-resolution industrial camera with a resolution of 2336×1728@10Hz and a high-gain enhancer.

[0073] S6: The Y axis is defined along the air inlet direction, the Z axis is defined as the vertical direction, the X axis (positive direction) is perpendicular to the viewing direction, the origin of the coordinate is the center of the cyclone outlet, and the shooting area is 120×75 mm.

[0074] S7: The fuel droplets in the atomization field are excited by the laser, inducing fluorescence and scattered light, where the scattered light signal is captured by the 532nm / 10nm bandpass filter in the filter system, and the fluorescence signal is captured by the UG5 filter in the filter system.

[0075] S8: The laser detector uses a CCD camera and an ICMOS camera to capture the entire process of fuel atomization, which is used to increase the light collection efficiency and reduce the detection depth of field, achieve better noise suppression effects, and thus improve the image signal-to-noise ratio.

[0076] In this embodiment, the PLIF-Mie dual-spectrum optical measurement technology is used to test the atomization characteristics of the swirler in the combustion chamber of a certain aircraft engine model under normal temperature and pressure and low temperature conditions, and the influence of the fuel supply method, fuel flow rate, swirler design parameters and temperature on the atomization characteristics of this type of swirler is analyzed.

[0077] The design parameters of two cyclones selected in this embodiment are shown in Table 2. Table 3 is a table of normal temperature and pressure test parameters of cyclone A and cyclone B and a table of low temperature test parameters of cyclone A.

[0078] Table 2 Design parameters of two cyclones

[0079]

[0080]

[0081] Table 3 Cyclone A and Cyclone B normal temperature and pressure test parameters

[0082]

[0083] The distribution characteristics of SMD are as follows.

[0084] First, a calibration test is performed.

[0085] The relationship between the intensity ratio of the fluorescence and scattered light of the laser-irradiated droplets and the droplet diameter is the basis of the PLIF-Mie technique, which is specifically expressed as the Mie scattered light intensity S of each irradiated droplet. M (D) is proportional to the surface area of ​​the droplet, as shown in formula (1):

[0086] S M (D) = a M D 2 (1)

[0087] Among them, S M (D) represents the intensity of Mie scattered light; a M represents a constant; D represents the droplet diameter.

[0088] The fluorescence intensity S of each illuminated droplet is F (D) is proportional to the droplet volume, as shown in formula (2):

[0089] S F (D) = a F D 3 (2)

[0090] Among them, S F (D) represents the fluorescence intensity of kerosene; a F Represents a constant.

[0091] a in formula (1) and formula (2) M with a F The two constant values ​​are related to factors such as the sensitivity of the imaging camera, the characteristics of the optical system, and the image magnification, and are the signal transmission characteristic coefficients of the measurement system.

[0092] The Sotel mean diameter (SMD) of the droplet size distribution is defined as follows:

[0093]

[0094] Where K represents the SMD calibration parameter; dN(D) represents the distribution probability of droplets in the atomization field.

[0095] K in formula (3) is a calibration parameter that converts the PLIF-Mie intensity ratio into the SMD of the measured droplet. This number is related to factors such as the position of the imaging camera relative to the laser sheet, the wavelength (i.e., intensity) of the laser sheet, and the focal length of the imaging camera. When the characteristics of the components of the measurement system, the relative positions between the components, and the relative positions between the measurement object and the measurement system remain unchanged, the K value is a constant. The K value can be determined by measuring the SMD value and the known ratio of the droplet fluorescence and scattered light intensity, or by using a monodisperse droplet generator to generate a single uniform droplet to calibrate the K value.

[0096] According to the above, the calibration test was finally carried out on an open nozzle atomization test bench using PDPA as the standard source. The schematic diagram is shown in the figure. Figure 5 shown.

[0097] PLIF-Mie takes 100 images simultaneously, and uses the PDPA system to measure the SMD values ​​at three locations, A, B, and C, on the outside of the fog cone at 10mm, 20mm, and 30mm below the nozzle, and takes the average value as the parameter for calibrating the system. Figure 6 The calibration results are shown in Table 4. The mean value of the calibration coefficient is 24.96, and the error range of the atomized particle size is 2.3% to 5.1%.

[0098] Table 4 PDPA test calibration results

[0099] Axial distance from nozzle mm SMDμm Calibration coefficient K 10 29.8 26.71 20 24.1 24.05 30 22.5 24.12

[0100] The analysis of the SMD distribution within the atomization field is as follows.

[0101] Figure 7 , Figure 8 , Fig. 9 The figure shows the SMD distribution of fuel atomized droplets of cyclone A under normal temperature and pressure conditions and different fuel flow rates and pressure loss conditions. Figure 7 and Figure 8 The figure shows that only the auxiliary oil circuit supplies oil, and the oil mist shows an obvious hollow cone distribution shape. When the fuel flow rate is low, the number of oil droplets is small and concentrated in the fog cone area on the upper and lower sides, among which the large-size oil droplets are mainly distributed in the lower fog cone area. At this time, the maximum SMD is about 10μm; there are a small number of small-size oil droplets in the center of the fog cone. As the fuel flow rate increases, the SMD gradually increases, and the maximum SMD is about 20μm; the oil droplets are still concentrated in the fog cone area on the upper and lower sides, and the SMD on both sides of the fog cone gradually decreases. The oil droplets on the upper and lower sides are unevenly distributed, and the large-size oil droplets are mainly distributed in the lower fog cone; the range of the fog cone increases, indicating that the number of oil droplets increases; the number of oil droplets in the center of the fog cone increases.

[0102] Figure 7 and Figure 8This indicates that when only the secondary oil circuit supplies oil, the fuel flow is too low, resulting in a small number of oil droplets in the flame tube. The fuel droplets formed after the primary atomization by the central nozzle are secondary atomized under the shear force of the primary swirl airflow, and expand outward in combination with the secondary swirl airflow, and finally appear in the form of a hollow cone at the swirler outlet. However, at a lower fuel flow rate, the primary atomization effect of the central nozzle is dominant. As the pressure loss increases, the gas flow rate increases, which reduces the relative velocity between the gas and liquid phases, resulting in a reduction in the shear effect of the secondary atomization, resulting in the phenomenon that the SMD increases instead of decreases.

[0103] Fig. 9 The figure shows the SMD distribution cloud diagram when the main and auxiliary oil circuits are supplying oil at the same time. Under low pressure loss conditions, due to the low gas flow rate and the sudden increase in fuel flow, the effect of the secondary swirl airflow on the outward diffusion of the oil mist is weakened, resulting in the oil mist at the cyclone outlet forming an atomization form with concentrated oil droplets and a small fog cone angle. At this time, the maximum SMD is about 20μm. As the pressure loss increases to 4.5%, the oil mist at the cyclone outlet can form a standard hollow fog cone shape; the increase in the main and secondary swirl intensity promotes the expansion of the central recirculation area, thereby causing the oil droplets at the cyclone outlet to diffuse to both sides; at this time, the large-size oil droplets are concentrated in the fog cone areas on the upper and lower sides, and some oil droplets are broken into small-size droplets due to the entrainment of the central recirculation area and exist in the central area of ​​the fog cone.

[0104] Fig.10 , Fig.11 , Fig.12 The figure shows the SMD distribution of fuel atomized droplets of cyclone B under normal temperature and pressure conditions and different fuel flow rates and pressure loss conditions. Fig.10 and Fig.11 The figure shows that only the auxiliary oil circuit supplies oil. When the fuel flow rate is small, the number of oil droplets in the combustion chamber is small and concentrated on the upper and lower sides of the middle area of ​​the combustion chamber. The maximum SMD is about 10μm. When the fuel flow rate increases, the number of oil droplets in the combustion chamber increases, and the oil droplets are randomly distributed in the entire shooting area. The maximum SMD is about 20μm, and the oil droplets with the largest SMD value are mainly distributed on the upper and lower sides of the shooting area. At the same time, with the increase of pressure loss, the SMD value gradually decreases, and the number of droplets with large SMD values ​​also gradually decreases, and the large-diameter oil droplets gradually move to the downstream area of ​​the combustion chamber.

[0105] Fig.10 and Fig.11This shows that when only the secondary oil circuit of the dual oil circuit centrifugal nozzle is working, the primary atomization quality of the fuel is poor due to factors such as low fuel flow, insufficient fuel oil pressure and small fuel spray angle. At the same time, some fuel oil droplets do not touch the inner wall of the venturi tube to form an oil film, but directly enter the combustion chamber in the form of larger particles, and collide with the oil droplets that are thrown to both sides by the centrifugal force of the primary and secondary swirl airflows, resulting in concentrated distribution of oil droplets on the upper and lower sides of the combustion chamber and a large SMD value. With the increase of pressure loss, the flow rate of the primary and secondary swirl airflows increases, which increases the tangential kinetic energy between the two-stage swirl airflows, strengthens the crushing effect on the oil droplets, and reduces the SMD in the flame tube.

[0106] Fig.12 The figure shows the SMD distribution cloud map when the main and auxiliary oil circuits are supplying oil at the same time. At this time, the oil droplets with large SMD in the combustion chamber are mainly concentrated on the upper and lower sides of the fog cone, with the maximum SMD being about 20μm. The SMD of the oil droplets in the center of the fog cone is reduced and evenly distributed. With the increase of pressure loss, the SMD in the flame tube decreases, but the distribution of the oil droplets does not change significantly. When the dual oil circuits supply oil at the same time, the primary atomization quality of the fuel is improved, so that the particle size of the oil droplets in the combustion chamber is more uniform without large differences, which is conducive to improving the subsequent ignition efficiency and ignition stability. At the same time, the increase in pressure loss enhances the shearing effect of the main and auxiliary swirl airflows, and the secondary atomization quality of the oil droplets is improved, resulting in a reduction in SMD.

[0107] Comprehensive comparison Figure 7-Figure 12 It can be seen that the increase in the swirl number of the cyclone weakens the central jet effect, reduces the axial velocity at the cyclone outlet, increases the airflow expansion angle, and also promotes the diffusion of high-speed airflow to both sides. In this way, the oil droplets are more easily sucked to the outside by the swirl airflow, so that the oil mist quickly diffuses to both sides. Therefore, cyclone A is more likely to form a hollow mist cone with a certain opening angle than cyclone B. At the same time, under the same working conditions, the shearing effect between the primary and secondary airflows of the high-speed swirl is enhanced, making the secondary atomization effect of cyclone A better and the SMD smaller.

[0108] The distribution characteristics of fuel concentration are analyzed as follows.

[0109] In the kerosene laser induced fluorescence theory, the energy density of the excitation light is in the linear excitation region of kerosene fluorescence, so the kerosene fluorescence intensity S obtained by using the PLIF technique is k Expressed by formula (4):

[0110]

[0111] Among them, η opt It represents the total efficiency of the detector system; E represents the energy density of a single laser pulse, in mJ / cm 2; hc / λ represents the energy value of a single photon with wavelength λ, in mJ; V c Indicates the laser irradiation volume in cm 3 ; k represents the kerosene concentration in %; k represents the Boltzmann constant in J / K; σ represents the absorption cross section in cm 2 / molecule; T is temperature, in Kelvin (K); P is pressure, in Pa; Φ is fluorescence quantum yield; χ q represents the quenching gas concentration.

[0112] As can be seen from formula 4, the intensity of the fluorescence signal captured by the detector is closely related to multiple variables, which makes it difficult to quantitatively measure the kerosene concentration distribution. However, under specific test conditions, it can be assumed that the physical variables remain unchanged, so formula (4) is simplified to the following formula:

[0113] S k =C o χ k (5)

[0114] Among them, C o = represents the experimental constant. Equation (5) indicates that the kerosene concentration distribution is proportional to the intensity of the detected fluorescence signal, so the intensity of the fluorescence signal is used to qualitatively represent the kerosene distribution.

[0115] Fig.13 , Fig.14 , Fig.15 The figure shows the fuel atomization concentration distribution of cyclone A under normal temperature and pressure conditions and different fuel flow rates and pressure loss conditions. Fig.13 and Fig.14 The figure shows that only the auxiliary oil circuit supplies oil. When the fuel flow rate is low, the fuel concentration distribution is in the form of a hollow cone, but the oil mist distribution is relatively dispersed. When the fuel flow rate increases, the oil mist concentration increases, mainly distributed on the upper and lower sides of the hollow cone. The center area of ​​the fog cone has some low-concentration oil mist and the distribution gradually becomes uniform. When the fuel flow rate is constant, as the pressure loss increases, the flow rate of the swirl gas also increases, causing the oil mist hollow cone to expand to both sides with the swirl airflow, and the fuel concentration in the center area of ​​the fog cone decreases.

[0116] Fig.15 The main and auxiliary dual oil circuits are shown, and the hollow cone shape of the oil mist is clearer at this time. Similar to the SMD distribution, when the pressure loss is 1.5%, the oil mist is over-concentrated, resulting in too high a concentration in the center of the combustion chamber. At this time, ignition is prone to cause local over-temperature in the combustion chamber, uneven temperature distribution in the combustion area, and other undesirable phenomena. When the pressure loss increases to 4.5%, the swirl gas flow rate increases, causing the atomization cone angle to expand outward, and the high-concentration oil mist is concentrated on the upper and lower sides of the hollow mist cone, while the concentration in the center area is low but evenly distributed.

[0117] Fig.16 , Fig.17 , Fig.18 The figure shows the fuel atomization concentration distribution of cyclone B under normal temperature and pressure conditions and different fuel flow rates and pressure loss conditions. Fig.16 and Fig.17 The figure shows that only the auxiliary oil circuit supplies oil. When the fuel flow rate is low, the fuel concentration in the combustion chamber is low and the distribution is relatively uniform, but no obvious hollow fog cone shape is formed; when the fuel flow rate increases, the oil mist concentration in the combustion chamber increases, and the higher concentration of oil mist is mainly distributed near the fog cone opening angle at the cyclone outlet, but it still does not present a hollow cone shape. When the fuel flow rate is constant, under low pressure loss conditions, due to the low flow velocity in the combustion chamber, the phenomenon of local concentration of fuel occurs, resulting in a higher fuel concentration in the area near the cyclone outlet; when the pressure loss increases to 4.5%, the flow velocity in the flow field increases, causing the oil mist to accumulate in the middle and downstream areas of the combustion chamber.

[0118] Fig.18 The main and auxiliary dual oil circuits are used to supply oil. At this time, the angle boundary and shape of the atomized fuel cone can be clearly seen. The high-concentration oil mist is mainly distributed on the upper and lower sides of the atomized fuel cone, and the low-concentration oil mist is distributed more evenly in the central area. As the pressure loss increases, the oil mist concentration on the upper and lower sides of the atomized fuel cone decreases.

[0119] Comprehensive comparison Figure 13-Figure 18 It can be seen that the increase in the swirl number enhances the primary and secondary swirl effects, and the oil mist diffuses to both sides with the swirl airflow, and the oil mist concentration is concentrated on both sides of the hollow cone. Therefore, the oil mist of cyclone A has a more obvious hollow cone shape, and the concentration is significantly higher than that of cyclone B.

[0120] The analysis of atomization cone angle is as follows.

[0121] After the dual oil circuit centrifugal nozzle is combined with the two-stage axial cyclone, due to the effect of swirling air, there are also a small amount of oil droplets at the boundary of the atomization cone angle, making the boundary no longer clear. Therefore, according to the maximum fuel concentration, the coordinates of the corresponding fog cones on both sides are extracted, and the points are drawn to fit the straight line. The angle between the two straight lines is the atomization cone angle. The measurement diagram is shown as follows: Fig.19 The color image of the fuel atomization concentration distribution is grayed out, and a threshold with a higher brightness is selected for binarization. The scatter plot obtained after binarization is fitted into a straight line using Hough transform, and the angle value of the atomization cone angle is obtained by calculating the slope of the straight line.

[0122] Table 5 shows the atomization cone angle of cyclone A under normal temperature and pressure, different fuel flow rates and pressure loss conditions. It can be seen from the table that when the fuel is supplied by a single oil circuit, the atomization cone angle decreases slightly with the increase of fuel flow rate; when the fuel is supplied by two oil circuits, the atomization cone angle decreases significantly. And with the increase of inlet and outlet pressure loss, the oil mist diffuses to both sides under the action of pneumatics, and the atomization cone angle shows an increasing trend.

[0123] Table 5 Atomization cone angle of cyclone A under normal temperature and pressure conditions

[0124] <![CDATA[Fuel flow rate (W f1 / W f2 ) g / s]]> 0 / 2 0 / 4.15 72.5 / 6.4 Pressure loss: 1.5% 76.91℃ 74.1℃ 38.41℃ Pressure loss: 4.5% 81.90℃ 80.45℃ 55.12℃

[0125] Table 6 shows the atomization cone angle of cyclone B under normal temperature and pressure, different fuel flow rates and pressure loss conditions. It can be seen from the table that when the fuel is supplied by a single oil circuit, the atomization cone angle increases significantly with the increase of fuel flow rate; while when the fuel is supplied by two oil circuits, the atomization cone angle decreases. With the increase of pressure loss, the atomization cone angle shows an increasing trend, but under the condition of low fuel flow rate when the fuel is supplied by a single oil circuit, the atomization cone angle decreases instead.

[0126] Table 6 Atomization cone angle of cyclone B under normal temperature and pressure conditions

[0127] <![CDATA[Fuel flow rate (W f1 / W f2 ) g / s]]> 0 / 2 0 / 4.15 72.5 / 6.4 Pressure loss: 1.5% 63.83℃ 73.49℃ 69.20℃ Pressure loss: 4.5% 59.58℃ 83.83℃ 70.00℃

[0128] The atomization characteristics under low temperature conditions are analyzed as follows.

[0129] In order to control the temperature of low-temperature fuel, a low-temperature fuel supply system is selected to provide low-temperature conditions for the test. The system mainly includes insulated fuel tanks, high-pressure gas cylinders, valves, instruments, etc. Before the test, the fuel tank is placed in a freezer to freeze to the lowest test temperature. During the test, dry ice is used for insulation to maintain the temperature required for the test conditions. The high-pressure gas cylinder is used as the power supply to avoid the use of an oil pump that causes temperature rise and affects the test results.

[0130] Fig. 20 , Fig.21 , Fig. 22 The figure shows the fuel concentration distribution of cyclone A under different low temperature conditions. It can be seen from the figure that the oil mist concentration distribution under low temperature conditions is more uniform than that under normal temperature conditions, and there is almost no hollow cone shape. As the temperature drops to -40°C, the phenomenon is more obvious. The oil mist in the entire combustion chamber is evenly distributed, and its distribution shape is almost invisible. Under low temperature conditions, the oil mist at low pressure loss mainly accumulates near the cyclone outlet. As the pressure loss increases, the oil mist is entrained by the airflow to the middle and downstream areas of the combustion chamber. Low temperature increases the viscosity of the fuel liquid. At this time, the influence of the liquid viscosity on atomization plays a dominant role. Therefore, the oil droplets formed by the fuel breakage are larger in size, and the atomization process is seriously affected, resulting in a decrease in atomization quality.

[0131] The same measurement method as that of the atomization cone angle under normal temperature and pressure conditions is used, and the coordinate points with the maximum fuel concentration on both sides of the atomization cone are fitted into a straight line to obtain the atomization cone angle under low temperature conditions. As shown in Table 7, low temperature has little effect on the atomization cone angle, and the fluctuation is smaller than that at normal temperature.

[0132] Table 7 Atomization cone angle under low temperature conditions

[0133] Temperature ℃ normal temperature 0 -20 -40 Pressure loss: 1.5% 63.91° 62.51° 59.83° 62.57° Pressure loss: 4.5% 51.97° 55.51° 59.99° 55.54°

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A fuel atomization characteristics analysis method based on PLIF-Mie dual-spectrum optical measurement, characterized in that: After the fuel is sprayed into the atomization characteristics visualization measurement system through a centrifugal nozzle, the laser is adjusted using the PLIF-Mie dual-spectrum optical measurement system. By simultaneously measuring the LIF signal and the Mie scattering signal, the two-dimensional distribution of the average particle size value is obtained. When the laser is irradiated to the fuel atomization area, the atoms in the fuel are excited by the laser irradiation to produce energy level transitions, and the photons generated in the process of decaying from the excited state to the low energy level are fluorescence. The planar array detector in the PLIF optical test system is used to obtain optical information on the two-dimensional plane, including the concentration, temperature, velocity, pressure and density of the fuel components. At the same time, the scattering of the laser by the droplets generates Mie scattered light signals to generate scattering spectra. The intensity of Mie scattering is proportional to the square of the droplet size, and the two signals are comprehensively analyzed to finally obtain the average fuel concentration and the distribution of the droplet size. The atomization characteristic visualization measurement system includes an air source, a digital acquisition and control system, a test bench, a PLIF-Mie dual-spectrum optical measurement system and an integrated fuel control test system; wherein the PLIF-Mie dual-spectrum optical measurement system includes a laser generator, a filter system, a sheet light shaping system, a laser detector, and a digital delay generation controller; lasers of different wavelengths are generated by adjusting the laser generator; the laser is expanded by a concave cylindrical lens in the filter system, and then converged into a sheet laser by a plano-convex mirror; the sheet laser is shot into a visualized atomization field in the test bench through the sheet light shaping system to keep it parallel to the side window of the test piece, and finally a thin sheet laser with a width of 100 mm and a thickness of about 50 μm is output; the delay of the laser generator and the laser detector is adjusted by the digital delay generation controller to ensure the synchronization of all equipment; and the entire process of fuel atomization is photographed by the laser detector.

2. The fuel atomization characteristic analysis method based on PLIF-Mie dual spectrum optical measurement according to claim 1 is characterized in that: The specific steps of adjusting the laser using the PLIF-Mie dual-spectrum optical measurement system are as follows: S1: Use DG645 digital delay generation controller to externally trigger the laser generator and laser detector. According to the corresponding relationship between delay and laser energy, the test is carried out under the condition that the delay of the laser and the detector is 215μs in the digital delay generation controller to ensure the synchronization of all devices. S2: Generate line lasers with wavelengths of 1064nm, 532nm, and 266nm in the laser generator system; S3: By adjusting the combination of high-reflection and high-lens filters in the filter system, the combined beams are finally output with 266nm and 532nm wavelength lasers, and the output spot diameters are both 9mm; the 266nm wavelength laser is used to excite kerosene fluorescence, and the 532nm wavelength laser is used to excite Mie scattering signals; S4: In the sheet light shaping system, the beam shaping part is fixed on the frame. In order to facilitate the lateral adjustment of the optical path and large-range measurement, the reflector frame is fixed on the one-dimensional moving stage. The one-dimensional moving stage uses the frame as the base to realize the excitation and measurement of different longitudinal sections of the sheet light in the test section. The line laser is expanded by a concave cylindrical lens and then converged into a sheet laser by a plano-convex mirror. The sheet laser enters the atomization field through a reflector and remains parallel to the side window. Finally, a thin sheet laser with a width of 100 mm and a thickness of about 50 μm is output. S5: The laser detector part is composed of a high-resolution industrial camera with a resolution of 2336×1728@10Hz and a high-gain intensifier; S6: The air inlet direction is defined as the Y axis, the vertical direction is defined as the Z axis, the direction perpendicular to the view is defined as the positive direction of the X axis, the origin of the coordinate is the center of the cyclone outlet, and the shooting area is 120×75mm; S7: The fuel droplets in the atomized field are excited by the laser, inducing fluorescence and scattered light; the scattered light signal is captured by the 532nm / 10nm bandpass filter in the filter system, and the fluorescence signal is captured by the UG5 filter in the filter system; S8: The laser detector uses a CCD camera and an ICMOS camera to capture the entire process of fuel atomization.

3. The fuel atomization characteristic analysis method based on PLIF-Mie dual spectrum optical measurement according to claim 2 is characterized in that: The specific numerical calculations based on which the laser is adjusted include: The Mie scattered light intensity S of each irradiated droplet M (D) is proportional to the surface area of ​​the droplet: S M (D)=a M D 2 Among them, S M (D) represents the intensity of Mie scattered light; a M represents a constant; D represents the droplet diameter; The fluorescence intensity S of each illuminated droplet is F (D) is proportional to the droplet volume: S F (D)=a F D 3 Among them, S F (D) represents the fluorescence intensity of kerosene; a F Represents a constant; The Sauter mean diameter SMD of the droplet size distribution is defined as: Where K represents the SMD calibration parameter; dN(D) represents the distribution probability of droplets in the atomization field; Kerosene fluorescence intensity S k It is expressed by the following formula: Among them, η opt It represents the total efficiency of the detector system; E represents the energy density of a single laser pulse, in mJ / cm 2 ; hc / λ represents the energy value of a single photon with wavelength λ, in mJ; V c Indicates the laser irradiation volume in cm 3 ; k represents the kerosene concentration in %; k represents the Boltzmann constant in J / K; σ represents the absorption cross section in cm 2 / molecule; T is temperature, in Kelvin; P is pressure, in Pa; Φ is fluorescence quantum yield; χ q represents the quenching gas concentration; The above formula of kerosene fluorescence intensity S k Simplified to the following formula: S k =C o x k Among them, C o represents the experimental constant; this formula shows that the kerosene concentration distribution is proportional to the detected fluorescence signal intensity, so the intensity of the fluorescence signal is used to qualitatively represent the kerosene distribution.

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