CN112697443B - Experimental device and method for simulating transient change of exhaust flow under engine starting and accelerating conditions - Google Patents
Experimental device and method for simulating transient change of exhaust flow under engine starting and accelerating conditions Download PDFInfo
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Abstract
The invention relates to an experimental device and a method for simulating transient change of exhaust flow of engine starting and accelerating working conditions.A gas outlet of an air compressor at the upstream of a gas circuit is connected to a gas inlet of a tee joint through a primary gas tank and a first valve in sequence; a first air outlet of the tee joint is connected to a first air inlet of the secondary air tank sequentially through the second valve, the primary air tank, the fourth valve and the first spray pipe; a second air outlet of the tee joint is connected to a second air inlet of the secondary air tank through a third valve; and the air outlet of the secondary air tank is connected to the air inlet of the second spray pipe through a fifth valve, and the air outlet of the second spray pipe is the air outlet of the whole device. The invention utilizes the principle that the critical flow of the spray pipe is only related to the stagnation pressure, so that the flow of the secondary gas tank is larger than the flow of the discharged gas, the pressure of the secondary gas tank is promoted to be gradually increased, and the flow of the outlet spray pipe is gradually increased, thereby realizing the simulation of the gradually increased exhaust flow under the working conditions of starting and accelerating the engine, and having the characteristics of convenient operation, strong consistency and the like.
Description
Technical Field
The invention relates to the technical field of automobile engine experiments, in particular to an experimental device and method for simulating transient change of exhaust flow under the working conditions of engine starting and acceleration.
Background
The design and research and development of the automobile engine do not leave experimental tests, and the experimental test result can provide important basis for the selection of engine parameters and help to improve various performances of the engine. In the experimental process, some parts or systems needing important research are often extracted from the whole engine, the experimental model is simplified under reasonable conditions, and a special experimental platform is built, so that the research and development cost is reduced, the experimental efficiency is improved, and the method is suitable for carrying out long-term deep research. The engine after-treatment system can greatly reduce the pollutant emission of the engine under the condition of less sacrifice of power performance and economy, and improve the environmental protection performance of the engine. In the relevant experiment of the post-processing device, the post-processing device is often extracted from the whole engine system, and a corresponding experiment platform is independently established. In these experimental platforms, it is necessary to simulate the working conditions of the experimental objects, i.e. the components of the aftertreatment system, such as the particulate trap, SCR, DOC, etc., such as the working temperature, pressure, incoming flow rate and composition, etc. The simulation of the flow of the exhaust incoming flow usually adopts an air compressor, a blower and the like as air sources, and controls the flow by using a valve and a flowmeter. However, because the control principle of these conventional flow control devices is simple, most of them can only provide steady-state gas flow, and cannot realize accurate simulation of the changing flow, so that they can only be used for experimental tests when the engine is operated under steady-state working conditions.
Nowadays, with the stricter emission regulations of automobiles, the emission control of automobile engines is not only satisfied with the stable working condition of the engines after starting, but also the transient working condition such as starting and accelerating is gradually the key point to have to be strictly controlled. The starting and accelerating working conditions of the engine are worse than the emission conditions of the engine during steady-state running, and the running time of the engine occupies a huge proportion in the whole life running period of the engine, so in order to improve the working performance of the aftertreatment device under the transient working condition, the working characteristics of each aftertreatment emission reduction device under the starting working condition of the engine need to be researched, and an optimization scheme is further provided. When the post-treatment device is subjected to experimental research under transient working conditions, corresponding exhaust flow simulation needs to be carried out on an experimental platform of the post-treatment device. There is therefore a need for a gas supply device that can provide transient and gradual rise in gas flow to simulate exhaust flow for engine start-up and acceleration conditions, and which requires greater stability and convenience to ensure reliable and repeatable testing.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide an experimental apparatus for simulating transient changes of exhaust flow rate under engine starting and acceleration conditions, which solves the problem of transient flow rate supply that is difficult to achieve in the past, and provides a transient flow rate supply apparatus with convenient operation, easy control, and strong consistency for a post-treatment experimental bench. The technical scheme is as follows:
an experimental device for simulating transient change of exhaust flow of an engine under starting and accelerating working conditions is characterized in that an air compressor is arranged at the most upstream of an air path, and an air outlet of the air compressor is connected to an air inlet of a tee joint through a primary air tank and a first valve in sequence; a first air outlet of the tee joint is connected to a first air inlet of the secondary air tank sequentially through the second valve, the primary air tank, the fourth valve and the first spray pipe; a second air outlet of the tee joint is connected to a second air inlet of the secondary air tank through a third valve; the second valve and the third valve are adjustable pressure valves; the gas outlet of the secondary gas tank is connected to the gas inlet of the second spray pipe through a fifth valve, and the gas outlet of the second spray pipe is the gas outlet of the whole device.
Further, pressure gauges are arranged in the primary air tank, the primary air tank and the secondary air tank.
Further, the minimum section diameter of the first spray pipe and the second spray pipe is 0.8-6mm.
Further, the primary and secondary gas tanks have a volume of 8-100L.
Furthermore, the outlet flow of the second spray pipe is 10-400L/min.
An experimental method for simulating transient changes of exhaust flow under starting and accelerating conditions of an engine comprises the following steps:
s1: performing initial pressure boosting of the primary and secondary gas tanks:
s11: setting preset pressure values of the second valve and the third valve, and closing the fourth valve, the fifth valve and the second valve;
s12: opening the first valve and the third valve to charge and pressurize the secondary gas tank; when the pressure of the secondary gas tank reaches the preset pressure value of the third valve, no gas enters the secondary gas tank due to the pressure regulating effect of the third valve, and the opening state of the third valve is maintained;
s13: keeping the first valve open, and opening the second valve to start to charge and boost the primary gas tank; when the pressure of the primary air tank reaches the preset pressure value of the second valve, the pressure of the primary air tank is kept unchanged due to the pressure regulating effect of the second valve;
s2: directly starting the occurrence of transient flow:
keeping the first valve and the second valve open, closing the third valve, and simultaneously opening the fourth valve and the fifth valve; at the moment, the first spray pipe and the second spray pipe simultaneously have airflow to pass through and reach critical flow at the position of the minimum section; the pressure of the primary gas tank is kept unchanged under the control of the second valve with adjustable pressure, the flow of the first spray pipe is also kept unchanged, and stable gas flow can be continuously provided for the secondary gas tank; the pressure of the secondary gas tank is gradually increased because the flow of the first spray pipe is greater than that of the second spray pipe, namely the inflow flow is greater than the outflow flow, so that the flow of the second spray pipe is gradually increased, and the aim of transient change is fulfilled.
Replacing the S2 with: firstly, steady-state flow is continued for a period of time, and then transient flow is generated:
the fourth valve is not opened, the first valve, the second valve and the third valve are kept opened, the fifth valve is opened firstly, and at the moment, airflow begins to pass through the second spray pipe and critical flow is achieved at the position of the minimum cross section; the pressure of the secondary gas tank is kept unchanged under the control of the third pressure-adjustable valve, so that the critical flow of the second spray pipe is kept unchanged along with the pressure of the secondary gas tank, namely the flow at the outlet of the secondary spray pipe is in steady-state flow; when the transient flow needs to be started, the third valve is closed and the fourth valve is opened at the same time, so that the change of the flow which is firstly steady and then raised in a transient state is realized.
The invention has the beneficial effects that:
1) The invention utilizes the principle that the critical flow of the spray pipe is only related to the stagnation pressure, and in the using process, the flow entering the secondary gas tank is larger than the flow of the exhaust gas tank, so that the pressure of the secondary gas tank is gradually increased, and the flow of the outlet spray pipe is gradually increased, thereby realizing the simulation of the gradually increased exhaust flow under the working conditions of starting and accelerating the engine, and having the characteristics of convenient operation, strong consistency and the like.
2) The invention can simulate the transient change of the exhaust flow of the engine under the starting and accelerating working conditions, and has the characteristics of convenient operation, easy control, strong repeatability and the like; determining corresponding specific flow change curves by adjusting the pressures in the two gas tanks at the initial moment of the volume or flow of the gas tanks; the cluster number of the flow change curve can be increased by changing the size of the spray pipe so as to enlarge the coverage range of the curve, and therefore high-precision simulation of the transient exhaust flow of the engine is achieved. The invention makes up the defect that the simulation of the exhaust flow under the transient working condition of the engine is difficult to realize in the past, provides the experimental conditions corresponding to the transient working condition of the engine for the research of each aftertreatment device, and is favorable for the deeper transient performance research.
Drawings
FIG. 1 is a schematic structural diagram of an experimental device for simulating transient changes of exhaust flow under engine starting conditions according to the present invention.
FIG. 2 is a graph showing the change of the flow rate in example 1 of the present invention.
FIG. 3 is a graph showing the change in flow rate in example 2 of the present invention.
FIG. 4 is a graph showing the variation of the flow rate at the outlet of the apparatus according to different system parameters in example 3 of the present invention; (a) d1=3.4mm; (b) d1=3.2mm; (c) d1=3mm.
In the figure: 1-an air compressor; 2-connecting a pipeline; 3-a primary gas tank; 4-a first valve; 5-a tee joint; 6-primary gas tank; 7-a second valve; 8-a fourth valve; 9-a third valve; 10-a first nozzle; 11-a fifth valve; 12-a secondary gas tank; 13-second nozzle.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments.
As shown in figure 1, the experimental device for simulating the transient change of the exhaust flow of the engine under the starting and accelerating working conditions of the engine is characterized in that an air compressor 1 is arranged at the most upstream of an air path, and an air outlet of the air compressor 1 is connected to an air inlet of a tee joint 5 through a primary air tank 3 and a first valve 4 in sequence; a first air outlet of the tee joint 5 is connected to a first air inlet of a secondary air tank 12 through a second valve 7, a primary air tank 6, a fourth valve 8 and a first spray pipe 10 in sequence; a second air outlet of the tee joint 5 is connected to a second air inlet of the secondary air tank 12 through a third valve 9; the air outlet of the secondary air tank 12 is connected to the air inlet of the second spray pipe 13 through the fifth valve 11, and the air outlet of the second spray pipe 13 is the air outlet of the whole device, namely the air flow providing transient change for the downstream experimental device.
The device of the invention realizes the control of the flow of the spray pipe by controlling the gas pressure at the front end of the spray pipe by utilizing the principle that the critical flow of the spray pipe is only related to the gas stagnation pressure.
The second valve 7 and the third valve 9 are pressure-adjustable valves, so that the pressure behind the valves can be kept at a preset value, and the pressure of the valves can be adjusted in the using process to control the pressure of the inlet and the outlet of the first spray pipe and the pressure of the outlet of the second spray pipe, so that the two spray pipes reach the critical flow.
The primary gas tank 3, the primary gas tank 6 and the secondary gas tank 12 are all gas tanks provided with pressure gauges, and the pressure of the gas tanks can be read in real time; and the volumes of the primary and secondary gas tanks 6 and 12 are in the range of 8-100L.
The minimum section diameter of the first spray pipe 10 and the second spray pipe 13 is in the range of 0.8-6mm, the outlet flow of the second spray pipe 13 is in the range of 10-400L/min, the change time from the lowest flow to 95% of the highest flow is in the range of 2-80s, and the flow change is approximately in a linear growth relationship.
In the case of a subsonic initial flow rate of the gas, when the ratio of the pressures at the inlet and outlet of the nozzle reaches or exceeds the critical pressure ratio of the gas, a critical flow of the gas is achieved at the minimum section of the nozzle, where the flow rate of the nozzle is proportional to the stagnation pressure of the accelerated gas, i.e. in the present invention, proportional to the gas pressure in the gas tank in front of the nozzle.
The principle of the device is that the gas in the spray pipe is subjected to critical flow, the flow of the spray pipe is indirectly controlled by the pressure of the gas tank at the front end of the spray pipe, namely the flow of the first spray pipe 10 is indirectly controlled by the pressure of the primary gas tank 6, and the flow of the second spray pipe 13 is indirectly controlled by the pressure of the secondary gas tank 12; and the flow rate of the gas flowing into the secondary gas tank 12 is larger than the flow rate of the gas flowing out, so that the pressure of the gas is gradually increased, the flow rate of the second spray pipe 13 is gradually increased, and the simulation of transient change of the exhaust flow rate of the engine starting working condition is realized.
The following is a specific description of the use of the device:
when the device is used, the initial pressure increasing stage of the primary air tank 6 and the secondary air tank 12 is firstly carried out. Firstly, setting preset pressure values of a second valve 7 and a third valve 9 with adjustable pressure, closing a fourth valve 8, a fifth valve 11 and the second valve 7, opening a first valve 4 and the third valve 9 with adjustable pressure to charge and pressurize a secondary gas tank 12, when the pressure of the secondary gas tank 12 reaches the preset pressure value of the third valve 9, no gas enters the secondary gas tank 12 due to the pressure regulation function of the third valve 9, and at the moment, the opening state of the third valve 9 can be kept; and then, starting to charge and boost the primary gas tank 6, keeping the first valve 4 open, opening the second valve 7 to start charging, and keeping the pressure of the primary gas tank 6 unchanged due to the pressure regulating effect of the second valve 7 when the pressure of the primary gas tank 6 reaches the preset pressure value of the second valve 7. At this point both the primary and secondary gas tanks 6, 12 have completed pre-inflation.
And then, the generation of the transient flow can be directly started, or the generation of the steady-state flow and then the generation of the transient flow can be started, which can be determined according to the experimental needs.
If the transient flow is to be started directly, the first valve 4 and the second valve 7 are kept open, the third valve 9 is closed, the fourth valve 8 and the fifth valve 11 are opened, at the same time, the first nozzle 10 and the second nozzle 13 simultaneously have airflow passing through and reach critical flow at the minimum cross section, the pressure of the primary gas tank 6 is kept unchanged by the control of the second valve 7 with adjustable pressure, the flow of the first nozzle 10 is kept unchanged, and stable airflow can be continuously provided for the secondary gas tank 12, the pressure of the secondary gas tank 12 is gradually increased because the flow of the first nozzle 10 is greater than that of the second nozzle 13, namely, the inflow flow is greater than the outflow, and therefore, the flow of the second nozzle 13 is gradually increased, so that the purpose of transient change is achieved.
If the steady-state flow is continued for a period of time and then the transient flow is generated, the fourth valve 8 is not opened, the first valve 4, the second valve 7 and the third valve 9 are kept opened, the fifth valve 11 is opened first, the second nozzle 13 starts to have airflow passing through and reaches critical flow at the minimum cross section, and the pressure of the secondary gas tank 12 is kept unchanged under the control of the third valve 9 with adjustable pressure, so the critical flow of the second nozzle 13 is also kept unchanged along with the pressure of the secondary gas tank 12, that is, the flow at the outlet of the secondary nozzle is steady-state flow, and the steady-state flow can be used for exhaust flow simulation of the steady-state working condition of the engine and can also be used as a preparation stage for the generation of the transient flow. When the transient flow needs to be started, the third valve 9 is closed and the fourth valve 8 is opened at the same time, and the flow change situation at the moment is the same as the situation of the direct transient occurrence, so that the change of the flow which is firstly steady and then rises in a transient state can be realized.
It should be added that when the pressure of the secondary gas tank 12 rises to a certain value, the first nozzle 10 will not perform critical flow any more due to the reduction of the pressure ratio before and after the first nozzle 10, but the inflow flow rate of the secondary gas tank 12 is still greater than the outflow flow rate, so that the pressure of the secondary gas tank 12 can still be increased until the inflow and outflow flow rates of the secondary gas tank 12 reach the equilibrium, and the flow rate at the outlet of the second nozzle 13 will not increase any more.
When the device is used for transient flow, the initial conditions of the device are only the pressure of two stages of gas tanks except for geometric parameters such as the volume of the gas tank, the diameter of the minimum section of the spray pipe and the like, so that when the geometric parameters are fixed, a unique transient flow change curve can be determined by the initial pressures of the two gas tanks, the device is convenient and easy to control in use, and accurate repeated experiments can be carried out. In addition, the change of the spray pipes with different geometric parameters can change the curve change condition under the same pressure parameter, and the cluster number of the flow change curve is increased, so that the coverage range of the flow change curve is enlarged, and the high-precision simulation of the transient change of the exhaust flow under the engine starting working condition is realized.
The technical result achieved by the device of the present invention is further illustrated by the following specific examples.
[ example 1 ]
The following is a simulation of exhaust flow for a cylindrical diesel particulate trap 50mm in diameter and 150mm in length at engine start-up conditions. Because diesel particulate traps are typically larger, smaller volume test samples are often used in simulation experiments to simplify the bench. The experimental object is obtained by reducing the actual engine post-treatment device according to a certain proportion, so that the exhaust flow passing through the experimental object is obtained by converting the equivalent space velocity (the amount of gas flowing through the experimental device per unit volume in unit time) of the actual post-treatment device, and the experimental object is ensured to be consistent with the actual working condition.
A diesel engine with a displacement of 2.77L and a particle trap with a diameter of 170mm and a length of 200mm is taken as a simulation object, the initial rotating speed of the starting working condition is about 160 rpm, the idle rotating speed after the starting is finished is about 800 rpm, and the time consumed by the starting process, namely the time required by the engine to rise from the starting rotating speed to the idle rotating speed, is generally 2-3s. The initial and final exhaust flow of the engine starting working condition is 221.6L/min and 1108L/min respectively, the corresponding volume airspeed of the particulate trap is 2930.4/h and 14651.9/h respectively, and further the volume of the experimental object selected according to the embodiment is calculated, and the initial flow and the final flow of the experimental object in the experiment simulating the engine starting working condition are 14.4L/min and 71.9L/min respectively.
Next, the change of the gas flow rate from 14.4L/min to 71.9L/min in a transient state and the change completion time within 2-3s was simulated based on the above calculation results.
After the parameters of the invention are debugged, when the parameters of the invention are as follows: the initial pressure of the primary gas tank 6 is 1.0MPa, the initial pressure of the secondary gas tank 12 is 0.19MPa, the minimum section diameter of the first spray pipe 10 is 5.1mm, the minimum section diameter of the second spray pipe 13 is 0.93mm, and the volume of the secondary gas tank 12 is 12L, so that the experimental post-treatment device can be accurately simulated in the exhaust flow under the starting working condition, and the flow change condition is shown in figure 2 and table 1.
TABLE 1 flow Change
As can be seen from the graph data, the flow change curves of the four conditions have higher linear degree, the initial flow of each group is 14.49L/min, the time for the flow to rise to 71.9L/min is within the range of 2.3-2.6s, the degree of coincidence with the actual change condition of the exhaust flow of the engine starting condition is higher, and the flow change condition required by the starting condition experiment of the selected experimental object in the embodiment can be met. Comparing the four sets of data, it can be found that the larger the minimum diameter of the first nozzle 10 is, the shorter the change completion time is, and the length of the change completion time can be controlled by selecting the sizes of the nozzles with different diameters, so that the change completion time is closer to the actual situation.
[ example 2 ]
The following is a description of the simulation of the exhaust gas flow rate under the engine acceleration condition for the test subjects selected in example 1. In the embodiment, the simulation data of the two cases of rapid acceleration and slow acceleration are respectively shown, wherein the slow acceleration case is a simulation of the typical acceleration condition of the automobile, and the rapid acceleration case is a case of verifying the limit condition of the flow change generated by the invention by using the acceleration as large as possible, that is, the flow rate increase rate as large as possible is achieved. In the embodiment, a speed interval that the automobile speed is accelerated from 32km/h to 45km/h is selected, the corresponding engine rotating speeds are 1600 revolutions per minute and 2250 revolutions per minute respectively, and the engine exhaust flow and the particle trap volume airspeed at the two rotating speeds are calculated to be 203L/min, 292L/min, 29303.8/h and 41208.4/h respectively according to the displacement and the rotating speed of the engine. The acceleration of the slow acceleration working condition simulation of the automobile is 0.2m/s respectively 2 And 0.3m/s 2 Under the two acceleration conditions, the acceleration time of the automobile is respectively 18s and 12s, and the simulated acceleration under the rapid acceleration condition is respectively 0.8m/s 2 And 1.0m/s 2 The acceleration time of the automobile under the two accelerations is 4.5s and 3.2s respectively.
After the parameters of the invention are debugged, when the parameters of the invention are as follows: the initial pressure of the primary gas tank 6 is 0.8MPa, the initial pressure of the secondary gas tank 12 is 0.19MPa, the minimum section diameter of the second spray pipe 13 is 3.4mm, the volume of the secondary gas tank 12 is 30L, and the minimum section diameter of the first spray pipe 10 is 2.2mm, 2.3mm, 2.9mm and 3.1mm respectively, the change of the outlet flow from 203L/min to 292L/min can be realized, and the change completion time is 18s, 12.2s and 4 s respectively6s and 3.5s, the automobile acceleration of the experimental post-processing device can be respectively 0.2m/s 2 、0.3m/s 2 、0.8m/s 2 、1.0m/s 2 The exhaust flow of the acceleration condition is simulated, and the flow change conditions of four conditions are shown in figure 3.
The flow curves show that the flow of the four conditions gradually rises along with time and has higher linear degree, and the change conditions of the exhaust flow during the acceleration of the automobile are met. Note that the four sets of flow acceleration completion times have a small difference from the previously calculated theoretical acceleration completion time, but the error is small in a controllable range, and thus can be ignored. In addition, in an actual transient experiment, experimental characteristics under certain typical working conditions only need to be qualitatively researched, so that the repeatability of experimental conditions in the experiment only needs to be ensured, and the method can meet the requirement of repeated operation.
Comparing the system parameters corresponding to the four sets of data in this embodiment, it can be found that, under the condition that other system parameters are not changed, the flow rate change rate can be changed by adjusting the minimum cross-sectional diameter of the first nozzle 10 (in the actual experiment operation, only nozzles of different sizes are replaced), so as to realize the exhaust flow simulation of the automobile under acceleration conditions of different accelerations.
[ example 3 ]
Several cases of slow exhaust flow growth are listed below, providing examples of flow changes over longer time spans, and verifying the effect of various system parameters on flow change slopes, ranges, durations, etc. The system parameters are respectively as follows: the volume of the secondary gas tank 12 is 80L, the initial pressure is 0.19MPa, the minimum diameter of the second spray pipe 13 is 1.6mm, the minimum diameter of the first spray pipe 10 is 3mm, 3.2mm and 3.4mm respectively, the initial pressure of the primary gas tank 6 is 0.8MPa, 0.9MPa and 1.0MPa respectively, and the flow change condition of the outlet of the second spray pipe is shown in a figure 4 and a table 2. It should be noted that, as can be seen from the curve in fig. 4, the flow rate changes under various conditions, the flow rate changes at the early stage with a high linearity, and the flow rate increase at the later stage gradually slows down. Table 2 shows the initial flow rate, the first 100s flow rate change rate, the 95% maximum flow rate and the time taken to reach the 95% maximum flow rate for the above three cases, and since the flow rate increase rate becomes gradually slow in the later period and the flow rate change in this period is hardly used in the actual experiment, the 95% maximum flow rate and the time taken to reach the 95% maximum flow rate are selected as the reference.
TABLE 2 variation of the flow at the outlet of the device under different pressures and geometric parameters
As can be seen from each flow change curve, the exhaust flow flowing out of the air outlet of the device still approximately linearly rises, and the purposes of changing the flow change slope and the maximum flow can be achieved by changing the initial pressure of the primary air tank 6 and the minimum section diameter of the first spray pipe 10; under the same other parameters, the larger the initial pressure of the primary gas tank 6 is, the larger the first 50s flow change slope and 95% maximum flow are; under the same other parameters, the larger the minimum section diameter of the first nozzle 10 is, the larger the first 50s flow change slope is, but the 95% maximum flow has no obvious change, that is, the change of the minimum section diameter of the first nozzle 10 can increase the flow change slope under the condition of keeping the maximum flow without great change. Compared with the embodiment 1, the embodiment can also find that the time span of flow change, the flow change range and the like can be adjusted by changing the volume of the secondary gas tank 12, the minimum section of the second spray pipe 13 and other parameters, so that richer experimental working conditions are met.
Claims (2)
1. An experimental method adopting an experimental device for simulating transient changes of exhaust flow under the starting and accelerating conditions of an engine is characterized in that,
the experimental device comprises: an air compressor (1) is arranged at the most upstream of the air path, and an air outlet of the air compressor (1) is connected to an air inlet of the tee joint (5) through the primary air tank (3) and the first valve (4) in sequence; a first air outlet of the tee joint (5) is connected to a first air inlet of the secondary air tank (12) through a second valve (7), the primary air tank (6), a fourth valve (8) and the first spray pipe (10) in sequence; a second air outlet of the tee joint (5) is connected to a second air inlet of the secondary air tank (12) through a third valve (9); the second valve (7) and the third valve (9) are adjustable pressure valves; the air outlet of the secondary air tank (12) is connected to the air inlet of a second spray pipe (13) through a fifth valve (11), and the air outlet of the second spray pipe (13) is the air outlet of the whole device;
the experimental method comprises the following steps:
s1: performing an initial pressure increase of the primary gas tank (6) and the secondary gas tank (12):
s11: setting preset pressure values of a second valve (7) and a third valve (9) and closing a fourth valve (8), a fifth valve (11) and the second valve (7);
s12: opening the first valve (4) and the third valve (9) to charge and pressurize the secondary gas tank (12); when the pressure of the secondary gas tank (12) reaches the preset pressure value of the third valve (9), no gas enters the secondary gas tank (12) due to the pressure regulating effect of the third valve (9), and the opening state of the third valve (9) is maintained at the moment;
s13: keeping the first valve (4) open, and opening the second valve (7) to start to charge and boost the primary gas tank (6); when the pressure of the primary air tank (6) reaches the preset pressure value of the second valve (7), the pressure of the primary air tank (6) is kept unchanged due to the pressure regulating effect of the second valve (7);
s2: directly starting the occurrence of transient flow:
keeping the first valve (4) and the second valve (7) open, closing the third valve (9), and simultaneously opening the fourth valve (8) and the fifth valve (11); the first spray pipe (10) and the second spray pipe (13) simultaneously have airflow passing through and reach critical flow at the position of the minimum section; the pressure of the primary air tank (6) is kept constant under the control of the second valve (7) with adjustable pressure, the flow of the first spray pipe (10) is kept constant, and stable air flow can be continuously provided for the secondary air tank (12); the pressure of the secondary gas tank (12) is gradually increased because the flow rate of the first spray pipe (10) is greater than that of the second spray pipe (13), namely the inflow flow rate is greater than the outflow flow rate, so that the flow rate of the second spray pipe (13) is gradually increased, and the purpose of transient change is achieved.
2. The experimental method according to claim 1, characterized in that said S2 is replaced by: firstly, steady-state flow is continued for a period of time, and then transient flow is generated:
without opening the fourth valve (8), the fifth valve (11) is first opened, keeping the first valve (4), the second valve (7) and the third valve (9) open, at which time the second nozzle (13) starts to have a flow through it and reaches a critical flow at the minimum cross-section; because the pressure of the secondary gas tank (12) is kept unchanged under the control of the third pressure-adjustable valve (9), the critical flow of the second spray pipe (13) is kept unchanged along with the pressure of the secondary gas tank (12), namely the flow at the outlet of the secondary spray pipe (13) is in steady-state flow; when the transient flow needs to be started, the third valve (9) is closed and the fourth valve (8) is opened at the same time, so that the change of the flow which is firstly in a steady state and then in a transient rise is realized.
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