A device and method for testing the fire extinguishing efficiency of ultrafine dry powder fire extinguishing agent

Abstract

The present invention discloses a device and method for testing the fire extinguishing efficiency of an ultrafine dry powder fire extinguishing agent. The device includes an air intake system, an aerosol generating system, a device supporting system, a cup burner, a laser measuring system, an exhaust gas collecting and processing system, and a calibration system. The method includes the calibration of the laser system and the measurement of the laser system. Compared with the existing technology, the device can form a stable, uniform, and dispersed solid aerosol in the cup burner, solving the problem of large critical fire extinguishing concentration measurement error caused by uneven dust distribution. The method can be used to evaluate the fire extinguishing performance of existing ultrafine dry powder fire extinguishing agents, and can also be used for the formulation design optimization of new ultrafine powders.

Description

Technical Field

[0001] The invention relates to the field of fire extinguishing efficiency testing of ultra-fine dry powder fire extinguishing agents, and in particular to a fire extinguishing efficiency testing device and method for ultra-fine dry powder fire extinguishing agents. Background Art

[0002] Halon fire extinguishing agent was once the main fire extinguishing product. It is widely used in civil airliners, computer rooms, cultural relics protection units, large ships and warships due to its fast fire extinguishing speed, high efficiency, non-conductivity and no residue after fire extinguishing. However, since the 1970s, scientists have discovered that the ozone in the earth's ozone layer is constantly decreasing, and that the halon fire extinguishing agent used in large quantities in the firefighting industry exists in the atmosphere for a long time after release. When the residual substances in the atmosphere drift to the stratosphere, they are decomposed by ultraviolet UV-C to produce Cl· or Br· free radicals, which participate in the consumption of the ozone layer. Based on this, in 1987, the United Nations Environment Program (UNEP) formulated the Montreal Protocol on Substances that Deplete the Ozone Layer. To date, halon fire extinguishing agents have been banned in developed countries, and other developing countries have also included them in the list of obsolete substances.

[0003] Ultrafine dry powder fire extinguishing agent is a kind of solid aerosol fire extinguishing agent, which refers to the particle size D 90 Fire extinguishing agents with a (90% particle size) less than or equal to 20um can be used as a good substitute for halon. When extinguishing a fire, it can spread to the fire area in a very short time, bypass obstacles and retain a longer residence time in the fire space, and protect the protected space for a long time. Ultrafine dry powder particles have a small particle size, a large specific surface area, high fire extinguishing efficiency and low concentration. It can be used to extinguish Class A / B mixed fires, Class B and Class C fires in fully and semi-enclosed spaces. It is 5 to 9 times more effective than ordinary dry powder fire extinguishing and 2-3 times more effective than halon fire extinguishing agents.

[0004] However, due to the influence of different ultra-fine dry powder fire extinguishing agent formula components and particle size, the fire extinguishing performance of products from different manufacturers will lead to differences, that is, the minimum fire extinguishing efficiency of each manufacturer is different. In the current powder fire extinguishing agent product standards, more fire models close to the actual fire scale are used to qualitatively evaluate whether the fire extinguishing performance of existing ultra-fine dry powder fire extinguishing agents or fire extinguishing systems can meet the relevant requirements. For example, GB4066-2004 "Dry Powder Fire Extinguishing Agent" uses a portable fire extinguisher (3kg) to extinguish the local fire extinguishing test model of the oil pan fire, and GA 578-2005 "Ultra-fine Dry Powder Fire Extinguishing Agent" uses a 100m 3 The full flooding fire extinguishing test model in the fire extinguishing room. Due to the lack of quantitative experiments, it is impossible to give specific critical fire extinguishing parameters of ultrafine dry powder fire extinguishing agents, which also brings difficulties to the formulation development of ultrafine dry powder fire extinguishing agents and the industrial application of fire extinguishing technology.

[0005] In order to evaluate the fire extinguishing performance of ultrafine dry powder fire extinguishing agents with different raw materials and particle sizes, and accurately test the critical fire extinguishing parameters of different ultrafine dry powder fire extinguishing agents, a scientific and effective ultrafine dry powder fire extinguishing agent fire extinguishing efficiency test device is urgently needed. Among the existing technologies, researchers from the Tianjin Fire Protection Research Institute proposed a method for testing the fire extinguishing performance of ultrafine dry powder fire extinguishing agents (CN 203376300 U ultrafine dry powder fire extinguishing agent fire extinguishing performance test device), which uses a spiral propulsion method to transport powder and mix it with dry air to form an aerosol for fire extinguishing testing. However, the inhomogeneity of the formed aerosol will make it difficult to measure the critical fire extinguishing concentration of the powder, the most important of which is that it is difficult to observe the critical extinction characteristics of the flame.

[0006] Based on this, the device of the present invention proposes a new critical fire extinguishing efficiency testing device for ultra-fine dry powder fire extinguishing agent. Summary of the invention

[0007] In order to accurately test the critical fire extinguishing concentration of ultrafine dry powder fire extinguishing agents with different raw materials and particle size distributions, the present invention proposes a fire extinguishing efficiency testing device and method for ultrafine dry powder fire extinguishing agents.

[0008] The technical solution adopted by the present invention is a device for testing the fire extinguishing efficiency of an ultrafine dry powder fire extinguishing agent, the device comprising: an air intake system, an aerosol generating system, a device support system, a laser measurement system, a cup burner, an exhaust gas collection and processing system and a calibration system (7).

[0009] The air intake system delivers dry and clean compressed air to the aerosol generation system, forming a stable aerosol that is delivered to the cup burner. By adjusting the air flow of the air intake system and the powder feeding rate of the aerosol generation system, the concentration of the generated aerosol can be accurately controlled. By adjusting the aerosol concentration, the flame of the cup burner gradually detaches from the bottom of the flame from a stable state, generating flame pulsation, that is, the critical extinction phenomenon of the flame. This concentration is detected by a laser measurement system, which is the critical extinguishing concentration of the corresponding fire extinguishing agent.

[0010] The air intake system includes an air compression pump, a water and oil removal filter and an air flow controller.

[0011] The aerosol generating system uniformly mixes air and ultrafine powder to form a stable polydisperse solid aerosol;

[0012] The device supporting system is used for supporting and fixing the main body testing device.

[0013] The laser measurement system can measure the change of powder concentration in real time. The laser measurement system includes a laser transmitting end and a receiving end. Before use, the laser measurement system is calibrated in a calibration system. The calibration system includes a gas source part, an aerosol generator, a balance, a calibration section, a data acquisition system, a test pipeline, a powder capture system, and an air pipe. The gas source part includes a controller that can be used to adjust the gas flow rate Q, which can be adjusted by the gas flow rate. The aerosol generator fully mixes the powder sample with the airflow to form a polydisperse aerosol. The aerosol generator is transported to the rotating brush through the piston, and the rotating brush will accurately transport a certain amount of sample to the diffusion head. At the diffusion head, the airflow will be accelerated by the acceleration of the nozzle. The high-speed airflow provides the necessary turbulence and shear force for the full dispersion of the powder. The agglomerated particles are finally dispersed and output, and the output aerosol is polydisperse. The generated aerosol enters the test pipeline, and after a distance of uniform diffusion, the particle speed of particles of different particle sizes finally reaches stability and moves downward at a constant speed. The balance measures the mass loss of the powder in the aerosol generator in real time, and the data is collected and processed by the data acquisition system.

[0014] The cup burner comprises a gravity oil supply device, a connection port, a combustion cup, an aerosol connection port, a metal diffusion section, an observation section, a metal connection cylinder, a rectifying screen, and an experimental measurement section.

[0015] The gravity oil supply device is connected to the combustion cup through a pipeline, and the communicating vessel principle is used to ensure the constancy of the liquid level of the combustion cup during the combustion process. Preferably, the ratio between the surface area S1 of the gravity oil supply device and the surface area S2 of the combustion cup, i.e., S1:S2>100; the connection port not only supports connection with the gravity oil supply device, but also can be connected with the combustible gas pipeline; the aerosol generated by the aerosol generating system passes through the aerosol connection port, the metal diffusion section, the observation section, the metal connection cylinder and the rectifying screen to reach the experimental measurement section;

[0016] The exhaust gas treatment system is used to collect the generated aerosol.

[0017] A method for testing the fire extinguishing efficiency of an ultrafine dry powder fire extinguishing agent, the steps comprising:

[0018] Step S1), place the laser measurement system in the calibration system, adjust the air source volume to Q, set the feed rate of the aerosol generator, and use a balance to weigh the mass loss M' of the aerosol generating system in real time. The concentration in the cavity can be calculated to be C=M' / Q.

[0019] Step S2), before measuring, measure the initial signal I0 of the laser measurement system. Collect the signal of the laser measurement system in real time, and select the average value I' of the stable section to obtain the transmittance T=I' / I0. Plot the square of the transmittance T 2The corresponding curve of concentration C is obtained by fitting the curve to obtain the corresponding fitting formula f(x).

[0020] Step S3), add fuel (n-heptane, gasoline, diesel, aviation kerosene, etc.) to the gravity fuel supply device, adjust the position of the gravity fuel supply device, so that the fuel level of the combustion cup is within 5mm~10mm from the top of the cup. Turn on the exhaust gas collection device and the air compression pump, adjust the air flow rate to 10L / min, ignite the fuel, and pre-burn for 60s. You can also connect the fuel pipe to perform an ignition test on the combustible gas.

[0021] Step S4), turn on the aerosol generator, gradually adjust the powder feeding rate from slow to fast, and when the flame is observed to be suspended in the air and pulsating continuously from the stable state, record the concentration value q measured by the laser measurement system. The experiment can be repeated many times, and finally the critical fire extinguishing concentration of the specified ultrafine dry powder fire extinguishing agent is obtained as:

[0022] ,

[0023] Among them, q' represents the average value of the measured concentration, q i represents the concentration value measured for the i-th time, and n represents the total number of measurements.

[0024] The advantages of the present invention compared with the prior art are:

[0025] (1) The present invention adopts a dust aerosol generator and arranges a diffusion section and a screen at the inlet end of the cup burner, thereby solving the problem of uneven distribution of ultrafine dry powder fire extinguishing agent in the cup burner;

[0026] (2) The calibration system of the present invention is designed by utilizing the free settling characteristics of powders, so the test environment is uniform and the calibration error is low;

[0027] (3) The device of the present invention can accurately observe the critical characteristics of flame extinction and obtain a relatively accurate critical fire extinguishing concentration of ultra-fine dry powder fire extinguishing agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of a fire extinguishing efficiency test device for an ultra-fine dry powder fire extinguishing agent according to the present invention;

[0029] Figure 2 The schematic diagram of the air intake system is shown in FIG.

[0030] Figure 3 It is a schematic diagram of the cup burner structure;

[0031] Figure 4 To calibrate the system;

[0032] Figure 5A schematic diagram of the diffusion of dust aerosol in a test chamber for one embodiment of a calibration test;

[0033] Figure 6 A curve showing the change of the photoelectric signal over time in one embodiment of the calibration test;

[0034] Figure 7 It is the real-time curve of mass variation over time used for calibration test;

[0035] Figure 8 is the calibration fitting curve.

[0036] The meanings of the figures in the figure are marked as follows: 1 is the air intake system, 2 is the aerosol generation system, 3 is the device support system, 4 is the laser measurement system, 5 is the cup burner, 6 is the exhaust gas collection and treatment system, and the calibration system 7. Among them, 11 is an air compression pump, 12 is a water and oil removal filter, 13 is an air flow controller; 51 is a gravity oil supply device, 52 is a connection port, 53 is a combustion cup, 54 is an aerosol connection port, 55 is a metal diffusion section, 56 is an observation section, 57 is a metal connection cylinder, 58 is a rectifier screen, 59 is an experimental measurement section, 71 is an air source part, 72 is an aerosol generator, 73 is a balance, 74 is a calibration section, 75 is a data acquisition system, 76 is a test pipeline, 77 is a powder capture system, and 78 is an air pipe. DETAILED DESCRIPTION

[0037] The following embodiments are further descriptions of the content of the present invention as an explanation of the technical content of the present invention, but the essential content of the present invention is not limited to the following embodiments. Ordinary technicians in this field can and should know that any simple changes or replacements based on the essential spirit of the present invention should fall within the scope of protection required by the present invention.

[0038] like Figure 1 As shown, the present invention provides a fire extinguishing efficiency testing device for ultrafine dry powder fire extinguishing agent, comprising: an air intake system 1, an aerosol generating system 2, a device supporting system 3, a laser measuring system 4, a cup burner 5, an exhaust gas collecting and processing system 6, and a calibration system 7.

[0039] The air intake system 1 delivers dry and clean compressed air to the aerosol generating system 2, forming a stable aerosol that is delivered to the cup burner 5. By adjusting the air flow of the air intake system 1 and the powder feeding rate of the aerosol generating system 2, the concentration of the generated aerosol can be accurately controlled. By adjusting the aerosol concentration, the flame of the cup burner gradually detaches from the bottom of the flame from a stable state, generating flame pulsation, that is, the critical extinction phenomenon of the flame. The laser measurement system 4 is used to detect this concentration, which is the critical extinguishing concentration of the corresponding fire extinguishing agent.

[0040] The air intake system 1 includes an air compression pump 11 , a water and oil removal filter 12 and an air flow controller 13 .

[0041] The aerosol generating system 2 uniformly mixes air and ultrafine powder to form a stable polydisperse solid aerosol;

[0042] The device support system 3 is used to support and fix the main body testing device.

[0043] The laser measurement system 4 can measure the change of powder concentration in real time. The laser measurement system 4 includes a laser transmitting end and a receiving end. Before use, the laser measurement system is calibrated in the calibration system 7. The calibration system 7 includes a gas source part 71, an aerosol generator 72, a balance 73, a calibration section 74, a data acquisition system 75, a test pipeline 76, a powder capture system 77, and an air pipe 78. The gas source part 71 includes a controller that can be used to adjust the gas flow rate Q, which can be adjusted by the gas flow rate. The aerosol generator 72 fully mixes the powder sample with the airflow to form a polydisperse aerosol. The aerosol generator is transported to the rotating brush through the piston, and the rotating brush will accurately transport a certain amount of sample to the diffusion head. At the diffusion head, the airflow will be accelerated by the acceleration of the nozzle. The high-speed airflow provides the necessary turbulence and shear force for the full dispersion of the powder. The agglomerated particles are finally dispersed and output, and the output aerosol is polydisperse. The generated aerosol enters the test pipeline 76, and after a certain distance of uniform diffusion, the particle speed of particles of different particle sizes finally reaches stability and moves downward at a constant speed. The balance 73 measures the mass loss of the powder in the aerosol generator in real time, and the data is collected and processed by the data acquisition system 75 .

[0044] The cup burner 5 includes a gravity oil supply device 51, a connection port 52, a combustion cup 53, an aerosol connection port 54, a metal diffusion section 55, an observation section 56, a metal connection cylinder 57, a rectifying screen 58, and an experimental measurement section 59.

[0045] The gravity oil supply device 51 is connected to the combustion cup 53 through a pipeline, and the communicating vessel principle is used to ensure the constant liquid level of the combustion cup 53 during the combustion process. Preferably, the ratio between the surface area S1 of the gravity oil supply device 51 and the surface area S2 of the combustion cup, i.e., S1:S2>100; the connecting port 52 not only supports connection with the gravity oil supply device 51, but also can be connected with the combustible gas pipeline; the aerosol generated by the aerosol generating system 2 passes through the aerosol connecting port 54, the metal diffusion section 55, the observation section 56, the metal connecting cylinder 57 and the rectifying screen 58 to reach the experimental measurement section 59;

[0046] The waste gas collection and treatment system 6 is used to collect the generated aerosol.

[0047] A method for testing the fire extinguishing efficiency of an ultrafine dry powder fire extinguishing agent, the steps comprising:

[0048] Step S1), place the laser test system in the calibration system, and adjust the air source volume to , set the feed rate of the aerosol generator, and use a balance 73 to weigh the mass loss of the aerosol generating system in real time The concentration in the cavity can be calculated .

[0049] Step S2), before measuring, measure the initial signal I0 of the laser measurement system. Collect the signal of the laser measurement system in real time and select the average value of the stable segment , we can get the transmittance T= / I0. Plot the square of transmittance T 2 The corresponding curve of concentration C is obtained by fitting the curve to obtain the corresponding fitting formula f(x).

[0050] Step S3), add fuel (n-heptane, gasoline, diesel, aviation kerosene, etc.) to the gravity fuel supply device, adjust the position of the gravity fuel supply device, so that the fuel level of the combustion cup is within 5mm~10mm from the top of the cup. Turn on the exhaust gas collection device and the air compression pump, adjust the air flow rate to 10L / min, ignite the fuel, and pre-burn for 60s. You can also connect the fuel pipe to perform an ignition test on the combustible gas.

[0051] Step S4), turn on the aerosol generator, gradually adjust the powder feeding rate from slow to fast, and when the flame is observed to be suspended in the air and pulsating continuously from the stable state, record the concentration value q measured by the laser measurement system. The experiment can be repeated many times, and finally the critical fire extinguishing concentration of the specified ultrafine dry powder fire extinguishing agent is obtained as:

[0052] ,

[0053] in, represents the average value of the measured concentration values, represents the concentration value measured for the i-th time, and n represents the total number of measurements.

[0054] Before the test begins, the laser measurement system 4 needs to be calibrated first. The laser measurement system 4 includes a laser emitting end and a laser receiving end, with an angle of 180°. In some embodiments, the laser measurement and laser emitting ends are arranged at the same end or at other angles. What is measured here is the transmission signal of light. In some embodiments, the scattering and diffraction signals of the powder can also be measured. The specific calibration process is as follows:

[0055] The gas source part 71 includes a controller that can be used to adjust the gas flow rate Q, and the gas flow rate can be adjusted. In some embodiments, the gas source part 71 can be high-purity nitrogen, dry air, or a device or system that provides related gases. This depends on the measurement environment and the usage scenario. The aerosol generator 72 fully mixes the powder sample with the airflow to form a polydisperse aerosol. In some embodiments, the aerosol generator uses the RGB-1000 model produced by PALAS in Germany. The system can diffuse the mass flow rate with the highest level of metered constancy, ranging from about 10 mg / h–430 g / h. The aerosol generator is delivered to the rotating brush through the piston, and the rotating brush will accurately deliver a certain amount of sample to the diffusion head. At the diffusion head, the airflow will be accelerated by the acceleration of the nozzle, and the high-speed airflow provides the necessary turbulence and shear force for the full dispersion of the powder. The agglomerated particles are finally dispersed and output, and the output aerosol is polydispersed.

[0056] Place the laser test system in the calibration system and adjust the air volume to , set the feed rate of the aerosol generator, and use a balance 73 to weigh the mass loss of the aerosol generating system in real time The concentration in the cavity can be calculated .

[0057] Before measuring, measure the initial signal I0 of the laser measurement system. Collect the signal of the laser measurement system in real time and select the average value of the stable segment. , we can get the transmittance T= / I0. Plot the square of transmittance T 2 The corresponding curve of concentration C is fitted to obtain the corresponding fitting formula. , with a maximum error of -17%.

[0058] Add fuel (n-heptane, gasoline, diesel, aviation kerosene, etc.) to the gravity fuel supply device, and adjust the position of the gravity fuel supply device so that the fuel level in the combustion cup is within 5mm~10mm from the top of the cup. Turn on the exhaust gas collection device and the air compressor pump, adjust the air flow rate to 10L / min, ignite the fuel, and pre-burn for 60s; in some embodiments, gas can also be used as fuel to measure the critical fire extinguishing concentration of the fire extinguishing agent for a certain gas fuel.

[0059] Turn on the aerosol generator and gradually adjust the powder feeding rate from slow to fast. When the flame is observed to be suspended in the air and pulsating continuously from a stable state, record the concentration value q measured by the laser measurement system. The experiment can be repeated many times, and the critical fire extinguishing concentration of the specified ultrafine dry powder fire extinguishing agent is finally obtained as:

[0060] ,

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A fire extinguishing efficiency test device for ultra-fine dry powder fire extinguishing agent, characterized in that: The device comprises: an air intake system (1), an aerosol generating system (2), a device supporting system (3), a laser measuring system (4), a cup burner (5), an exhaust gas collecting and processing system (6) and a calibration system (7), wherein: The air intake system (1) delivers dry and clean compressed air to the aerosol generating system (2), forming a stable aerosol which is delivered to the cup burner (5). By adjusting the air flow rate of the air intake system (1) and the powder feeding rate of the aerosol generating system (2), the concentration of the generated aerosol can be accurately controlled. By adjusting the aerosol concentration, the flame of the cup burner gradually separates from the bottom of the flame from a stable state, generating flame pulsation, i.e., the critical extinction phenomenon of the flame. The laser measurement system (4) detects this concentration, which is the critical extinguishing concentration of the corresponding fire extinguishing agent. The air intake system (1) comprises an air compression pump (11), a water and oil removal filter (12) and an air flow controller (13); The aerosol generating system (2) uniformly mixes air and ultrafine powder to form a stable polydisperse solid aerosol; The device support system (3) is used to support and fix the main body test device; The laser measurement system (4) can measure the change of powder concentration in real time. The laser measurement system (4) includes a laser transmitting end and a receiving end. Before use, the laser measurement system is calibrated in a calibration system (7); the calibration system (7) includes an air source part (71), an aerosol generator (72), a balance (73), a calibration section (74), a data acquisition system (75), a test pipeline (76), a powder capture system (77) and an air pipe (78); the air source part (71) includes a controller that can be used to adjust the gas flow rate Q, and can adjust the gas flow rate; the aerosol generator (72) fully mixes the powder sample with the air flow to form a plurality of Dispersible aerosol; the aerosol generator is transported to the rotating brush through the piston, and the rotating brush will accurately transport a certain amount of sample to the diffusion head. At the diffusion head, the airflow will be accelerated by the acceleration of the nozzle, and the high-speed airflow provides the necessary turbulence and shear force for the full dispersion of the powder. The agglomerated particles are finally dispersed and output, and the output aerosol is polydispersed; the generated aerosol enters the test pipe (76), and after a certain distance of uniform diffusion, the speed of particles of different particle sizes finally reaches stability and moves downward at a constant speed; the balance (73) measures the mass loss of the powder in the aerosol generator in real time, and collects and processes the data through the data acquisition system (75); The cup burner (5) comprises a gravity oil supply device (51), a connection port (52), a combustion cup (53), an aerosol connection port (54), a metal diffusion section (55), an observation section (56), a metal connection tube (57), a rectifying screen (58) and an experimental measurement section (59); wherein the gravity oil supply device (51) and the combustion cup (53) are connected via a pipeline, and the communicating vessel principle is used to ensure that the liquid level of the combustion cup (53) remains constant during the combustion process, and the ratio of the surface area S1 of the gravity oil supply device (51) to the surface area S2 of the combustion cup, i.e., S1:S2>100; the connection port (52) not only supports connection with the gravity oil supply device (51), but also can be connected with a combustible gas pipeline; the aerosol generated by the aerosol generating system (2) reaches the experimental measurement section (59) through the aerosol connection port (54), the metal diffusion section (55), the observation section (56), the metal connection tube (57) and the rectifying screen (58); The waste gas collection and treatment system (6) is used to collect the generated aerosol.

2. The fire extinguishing efficiency testing device of an ultra-fine dry powder fire extinguishing agent according to claim 1, characterized in that: The ratio between the surface area S1 of the gravity oil supply device (51) and the surface area S2 of the combustion cup, i.e. S1:S2>100.

3. A method for testing the fire extinguishing efficiency of an ultrafine dry powder fire extinguishing agent, based on the device of claim 1, characterized in that: The method steps include: Step S1) placing the laser test system in the calibration system, adjusting the air source volume to Q, setting the feed rate of the aerosol generator, and using a balance (73) to weigh the mass loss M' of the aerosol generating system in real time, and calculating the concentration C=M' / Q in the cavity; Step S2) Before measuring, the initial signal I0 of the laser measurement system is measured, the signal of the laser measurement system is collected in real time, and the average value I' of the stable section is selected to obtain the transmittance T=I' / I0, and the square of the transmittance T is plotted. 2 and the corresponding curve of concentration C, and fitting the curve to obtain the corresponding fitting formula f(x); Step S3) Add fuel to the gravity fuel supply device, adjust the position of the gravity fuel supply device so that the fuel level in the combustion cup is within 5 mm to 10 mm from the top of the cup, turn on the exhaust gas collection device and the air compression pump, adjust the air flow rate to 10 L / min, ignite the fuel, pre-combust for 60 seconds, and also connect the fuel pipe to perform an ignition test on the combustible gas; Step S4) Turn on the aerosol generator and gradually adjust the powder feeding rate from slow to fast. When the flame is observed to be suspended in the air and pulsating continuously from a stable state, record the concentration value q measured by the laser measurement system. The experiment can be repeated many times, and the critical fire extinguishing concentration of the specified ultrafine dry powder fire extinguishing agent is finally obtained as: ， q' represents the average value of the measured concentration values, q i represents the concentration value measured for the i-th time, and n represents the total number of measurements.

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