Design Method of an Injection Diluter for Ultra-Fine Particle Dilution in Vehicles

Abstract

The present invention discloses a design method for an injection diluter for vehicle ultrafine particle dilution, including: selecting relevant factors affecting the dilution ratio of the diluter; according to the injection dilution principle, deriving using the continuity equation and the Bernoulli total flow equation, and determining the design factors of the exhaust end and the air end of the injection diluter among the relevant factors; constructing a simulation model of the diluter, and according to the design factors, using CFD simulation software, corresponding simulation conditions and simulation schemes to simulate the internal flow field of the diluter to obtain simulation conclusions; according to the relationship between some data in the design factors and the dilution ratio, randomly combining some data in the design factors to obtain diluters with any dilution ratio. This method can realize the optimal design of the internal structure parameters of the injection diluter, which helps to directly build a PFSS dilution system on the laboratory engine bench to test the dilution ratio under different working conditions; and helps to accurately measure the ultrafine particles in vehicle exhaust.

Description

Technical Field

[0001] The present invention relates to the technical field of the design of injection dilutors, and particularly to a design method for an injection dilutor for diluting ultrafine particles of a vehicle. Background Art

[0002] Atmospheric fine particulate matter (PM 2.5 ) has become the primary pollutant of air pollution in China, and the control of PM 2.5 pollution has a long way to go. Among them, the emission of ultrafine particles from motor vehicles (generally referring to particles with a particle size ≤ 100 nm) accounts for a small mass percentage in PM 2.5 , but the number concentration percentage is as high as over 90%. On the one hand, the number concentration and surface area of ultrafine particles are high, and the chemical composition is complex, which has important impacts on human health, atmospheric visibility, global climate, etc.; on the other hand, a large number of ultrafine particles will absorb moisture and grow under certain atmospheric environmental conditions, directly forming haze or even heavy haze pollution. Therefore, the accurate measurement of ultrafine particles emitted from motor vehicles is particularly important, and the monitoring results can provide an effective basis for motor vehicle emission assessment, research on the particle growth mechanism, and formulation of refined control measures, etc.

[0003] Due to the high temperature of motor vehicle exhaust gas, conventional particulate matter monitoring equipment cannot directly measure it. The U.S. Environmental Protection Agency (EPA) first proposed diluting the exhaust gas first and then sampling and studying it, and this method has been widely recognized. The dilution process of motor vehicle exhaust gas is essentially to simulate the process of being diluted by the atmosphere when it is emitted into the atmosphere, realizing the cooling of high-temperature gas to normal temperature, so that the commonly used atmospheric particulate matter sampling method and on-line particulate matter measuring instrument can be used for the detection of engine exhaust particles. Since there are unburned gaseous organic compounds in the exhaust gas, they may condense and grow to form new particulate matter during the dilution process, and the generation of this part of the substance will interfere with the measurement results, resulting in poor result repeatability. Therefore, designing a reasonable exhaust gas dilution sampling system is one of the key steps in the measurement of motor vehicle exhaust particulate matter.

[0004] The main test methods for motor vehicle exhaust particulate matter are the constant volume sampling system (CVS) and the partial flow dilution sampling system (PFSS). The CVS system can meet the tests of diesel engine exhaust under both steady-state and transient conditions. It is widely used, has high precision, small error, and meets various emission requirements, but has high manufacturing costs and complex equipment. The PFSS system is based on the CVS system, has a small volume, low cost, is sensitive to ultra-low emissions, can test the particulate matter emissions of various engines, and is widely used. The PFSS method only dilutes and samples a small part of the engine exhaust, so it is not affected by the engine displacement and is applicable to the particulate matter test of any large, medium, and small displacement engines. When the dilution exhaust ratio is less than 1%, a single dilution can sample and test the mixed sample gas, which is the PFSS full sampling method; when the dilution exhaust ratio is greater than 1%, the sample gas after the first dilution needs to be diluted again and then collected and tested, which is the PFSS partial sampling method. Research shows that the position, length of the sampling tube, and the cleanliness of the dilution air all affect the measurement results of PFSS.

[0005] The dilution part is the core of the entire test process. The dilution effect directly determines whether the exhaust can meet the regulatory requirements, as well as the accuracy and repeatability of the particulate matter test. Due to the high cost and complex operation of traditional test systems, portable dilution systems are becoming increasingly popular. They simplify the cumbersome test steps with high-performance dilutors, are easy to operate, have low costs, and protect precision detection instruments.

[0006] In related technologies, although the particulate matter dilutors and supporting dilution test systems have different working principles, their purposes are to simulate as much as possible the real situation of vehicle exhaust discharged into the atmosphere, mix clean air with the exhaust, and cool and dilute the high-temperature exhaust. The dilution ratio is one of the most important factors for evaluating the quality of a dilutor, and the dilutor structure is the key factor affecting the dilution ratio of the dilutor. However, in related technologies, no specific design process of the dilutor structure is given, making it difficult for technicians to dilute the motor vehicle exhaust particulate matter according to their own needs, and thus it is not easy to achieve accurate measurement of the motor vehicle exhaust particulate matter. Summary of the Invention

[0007] The purpose of the present invention is to provide a design method for an injection dilutor for diluting ultra-fine particulate matter in vehicles, which solves the problem that the relevant structures and corresponding parameters in the design of the injection dilutor cannot be determined; so as to help achieve accurate measurement of ultra-fine particulate matter in motor vehicle exhaust.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] The present invention provides a design method for an injection dilutor for diluting ultra-fine particulate matter in vehicles, including the following steps:

[0010] S10. Select relevant factors affecting the dilution ratio of the diluter; the relevant factors include: dilution air parameters, vehicle exhaust parameters, and diluter structure parameters;

[0011] S20. Based on the injection dilution principle, use the continuity equation and Bernoulli's total flow equation to deduce and determine the design factors at the exhaust end and air end of the injection diluter among the relevant factors;

[0012] S30. Build a simulation model of the diluter, and according to the design factors, use CFD simulation software, corresponding simulation conditions, and simulation schemes to simulate the internal flow field of the diluter to obtain simulation conclusions;

[0013] S40. Based on the simulation conclusions, and according to the relationship between some data in the design factors and the dilution ratio, randomly combine some data in the design factors to obtain diluters with any dilution ratio.

[0014] Further, in the step S10: the dilution air parameters include: air quality, air pressure, air velocity, and air temperature;

[0015] The vehicle exhaust parameters include: exhaust pressure, exhaust velocity, and exhaust temperature;

[0016] The diluter structure parameters include: nozzle position, sampling position, exhaust pipe length, exhaust pipe diameter, air pipe length, air pipe diameter, injection chamber angle, and mixing chamber length.

[0017] Further, in the step S20, the design factors include:

[0018] The flow rate at the exhaust end is respectively related to the pressure difference between the inlet and outlet of the exhaust pipe, the exhaust pipe diameter, and the exhaust pipe length; the pressure difference between the inlet and outlet of the exhaust pipe is the difference between the exhaust pipe inlet pressure and the exhaust pipe inlet pressure;

[0019] The flow rate at the air end is respectively related to the pressure difference between the inlet and outlet of the air pipe, the air pipe diameter, and the air pipe length; the pressure difference between the inlet and outlet of the air pipe is the difference between the air pipe inlet pressure and the air pipe inlet pressure.

[0020] Further, in the step S30, the CFD simulation software and the corresponding simulation conditions include:

[0021] (1) The internal fluid flow state of the injection diluter is laminar, the calculation model is selected as Laminar, and the parameters are default;

[0022] (2) The exhaust density and air density are similar, and the materials at the exhaust end and air end are both set as air, and the parameters are default;

[0023] (3) According to the physical process of the operation of the lean injection type diluter, the boundary conditions of both the exhaust gas inlet and the air inlet are set as pressure inlets, and the mixture gas outlet is set as a pressure outlet and at atmospheric pressure;

[0024] (4) Set the convergence error to 10 -3 , and keep the others default.

[0025] Furthermore, in the step S30, the simulation scheme includes multiple sets of data; each set of data includes: air inlet pressure, exhaust gas inlet pressure, air pipe diameter, exhaust pipe diameter, air pipe length, exhaust pipe length, and the corresponding number of simulation times;

[0026] Among them, during the simulation process, a preset value needs to be applied to the exhaust gas inlet pressure to ensure it as an inlet.

[0027] Furthermore, in the step S30, the internal flow field of the diluter is simulated to obtain simulation conclusions, including:

[0028] 1) The air inlet pressure and the dilution ratio are in a logarithmic relationship;

[0029] 2) The smaller the exhaust gas inlet pressure, the faster the dilution ratio increases, the larger the stabilized dilution ratio value, and the smaller the air inlet pressure corresponding to the stable dilution ratio; however, when the exhaust gas inlet pressure is too small, the air inlet pressure range for the dilution ratio to be stable is very small;

[0030] 3) The air pipe diameter and the dilution ratio are in an exponential relationship;

[0031] 4) The exhaust pipe diameter and the dilution ratio are in an inverse proportion relationship;

[0032] 5) The relationship between the air pipe length and the dilution ratio satisfies a cubic polynomial;

[0033] 6) The exhaust pipe length and the dilution ratio are in a linear relationship.

[0034] Furthermore, the step S40 includes:

[0035] Based on the simulation conclusions, according to the relationships between the air inlet pressure, air pipe length, air pipe diameter, exhaust pipe length, exhaust pipe diameter and the dilution ratio, first determine two of the parameters, and then change the other three parameters to obtain a diluter with any dilution ratio.

[0036] Furthermore, based on the simulation conclusions, and according to the relationships between the air inlet pressure, air pipe length, air pipe diameter, exhaust pipe length, exhaust pipe diameter and the dilution ratio, first determine two of the parameters, and then change the other three parameters to obtain a diluter with any dilution ratio; specifically including:

[0037] S401. Given the optimal exhaust pipe diameter, air inlet pressure, and the set exhaust gas inlet pressure;

[0038] S402. Determine the required dilution ratio of the diluter;

[0039] S403. Initially set the exhaust pipe length, air pipe length, and air pipe diameter according to the required dilution ratio;

[0040] S404. Obtain the stable dilution ratio through simulation;

[0041] S405. Calculate the difference between the stable dilution ratio and the required dilution ratio;

[0042] S406. When the difference meets the error requirement, output the corresponding exhaust pipe diameter, air inlet pressure, exhaust inlet pressure, exhaust pipe length, air pipe length, and air pipe diameter to complete the design of the diluter.

[0043] Furthermore, it also includes:

[0044] S407. When the difference does not meet the error requirement, re - execute step S403.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The design method of the jet diluter for vehicle ultrafine particle dilution provided by the embodiment of the present invention can realize the optimal design of the internal structure parameters of the jet diluter, which helps to directly build a PFSS dilution system on the laboratory engine bench to test the dilution ratio under different working conditions, and helps to accurately measure the ultrafine particles in vehicle exhaust. In addition, the accuracy of the design method of the present invention can be verified through experiments, and it has strong practical application value. Description of the Drawings

[0047] Figure 1 It is a flowchart of the design method of the jet diluter for vehicle ultrafine particle dilution provided by the embodiment of the present invention;

[0048] Figure 2 It is a schematic diagram of the jet diluter principle;

[0049] Figure 3 It is a schematic diagram of the key factors affecting the dilution ratio of the diluter;

[0050] Figure 4 It is a schematic diagram of the exhaust end;

[0051] Figure 5 It is a schematic diagram of the air end;

[0052] Figure 6 It is a schematic diagram of the three - dimensional model and the fluid domain;

[0053] Figure 7aSchematic diagram of the fluid simulation model;

[0054] Figure 7b Mesh schematic diagram of the fluid simulation model;

[0055] Figure 8a Dilution ratio change diagram at P5;

[0056] Figure 8b Dilution ratio change diagram at P10;

[0057] Figure 8c Dilution ratio change diagram at P1;

[0058] Figure 9a Dilution ratio change diagram with the change of the air pipe diameter;

[0059] Figure 9b Dilution ratio change diagram with the change of the exhaust pipe diameter;

[0060] Figure 9c Dilution ratio change diagram with the change of the air pipe length;

[0061] Figure 9d Dilution ratio change diagram with the change of the exhaust pipe length;

[0062] Figure 10 Specific flowchart of step S40. Detailed implementation mode

[0063] To make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific implementation modes.

[0064] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "front end", "rear end", "both ends", "one end", "the other end", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0065] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, terms such as "installation", "equipped with", "connection", etc. shall be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0066] On the basis of referring to the dilution sampling principle stipulated in the National V Standard for Light-Duty Vehicles, with reference to Figure 1 As shown, the present invention provides a design method for an injection-type diluter for vehicle ultrafine particle dilution, including the following steps:

[0067] S10. Select relevant factors affecting the dilution ratio of the diluter; the relevant factors include: dilution air parameters, vehicle exhaust parameters, and diluter structure parameters;

[0068] S20. According to the injection dilution principle, by derivation using the continuity equation and the Bernoulli total flow equation, determine the design factors of the exhaust end and the air end of the injection-type diluter among the relevant factors;

[0069] S30. Build a simulation model of the diluter, and according to the design factors, use CFD simulation software, corresponding simulation conditions, and simulation schemes to simulate the internal flow field of the diluter to obtain simulation conclusions;

[0070] S40. Based on the simulation conclusions, and according to the relationship between some data in the design factors and the dilution ratio, randomly combine some data in the design factors to obtain a diluter with any dilution ratio.

[0071] Among them, in the above step S10, the dilution air parameters include: air quality, air pressure, air flow rate, air temperature, etc.; the vehicle exhaust parameters include: exhaust pressure, exhaust flow rate, exhaust temperature, etc.; the diluter structure parameters include: nozzle position, sampling position, exhaust pipe length, exhaust pipe diameter, air pipe length, air pipe diameter, injection chamber angle, and mixing chamber length, etc.

[0072] In the above step S20, among the relevant factors, the determined design factors include: the flow rate at the exhaust end is respectively related to the pressure difference between the inlet and outlet of the exhaust pipe, the exhaust pipe diameter, and the exhaust pipe length; the pressure difference between the inlet and outlet of the exhaust pipe is the difference between the inlet pressure and the outlet pressure of the exhaust pipe;

[0073] The flow rate at the air end is respectively related to the pressure difference between the inlet and outlet of the air pipe, the air pipe diameter, and the air pipe length; the pressure difference between the inlet and outlet of the air pipe is the difference between the inlet pressure and the outlet pressure of the air pipe.

[0074] This method can achieve the optimal design of the internal structure parameters of the jet diluter, which helps to directly build a PFSS dilution system on the laboratory engine bench to test the dilution ratio under different working conditions, and helps to accurately measure the ultrafine particles in vehicle exhaust. In addition, the accuracy of the design method of the present invention can be verified through experiments, which has strong practical application value.

[0075] The technical solution of the present invention will be described in detail in the following four parts:

[0076] I. Theoretical basis

[0077] 1.1. Jet dilution principle:

[0078] The jet diluter is based on the jet dilution principle, as Figure 2 shown. Compressed air enters from the inlet A of the venturi tube, and a small part is discharged through the nozzle B with a very small cross-section. The cross-sectional area decreases from A1 to A2, the pressure increases from P1 to P2, and the flow velocity increases from V1 to V2. A vacuum is generated at the exhaust gas inlet C. Due to the negative pressure, the exhaust gas is sucked into the venturi tube and mixed with the dilution air and then enters the dilution mixing chamber together. By changing the ratio of the inner diameters of the cross-sections A and B, the dilution ratio of the diluter can be adjusted.

[0079] 1.2. Dilution ratio:

[0080] The dilution ratio can be calculated according to the inlet and outlet flow method (as shown in Equation 1-1):

[0081]

[0082] In the formula: DR is the dilution ratio calculated theoretically, Q t is the mixed gas flow rate, Q S is the sample gas flow rate, Q d is the air flow rate.

[0083] The exhaust gas flow rate can be obtained according to the pressure difference before and after dilution at the exhaust gas end, the air flow rate can be obtained according to the dilution pressure difference at the air end, and the mixed gas flow rate is the sum of the exhaust gas flow rate and the air flow rate, so as to obtain the dilution ratio.

[0084] 1.3. Influencing factors:

[0085] In the prior art, although the particulate matter diluters and the supporting dilution test systems have different working principles, their purposes are to simulate as much as possible the real situation of vehicle exhaust discharged into the atmosphere, and use clean air to mix with the exhaust gas to cool and dilute the high-temperature exhaust gas. The dilution ratio is one of the most important factors for evaluating the quality of the diluter, Figure 3 which is the key factor affecting the dilution ratio of the diluter.

[0086] The present invention mainly considers the influence of the diluter structure on the dilution ratio.

[0087] 1.3.1. Exhaust end:

[0088] As shown in the exhaust end, according to the injection dilution principle of the injection diluter, it is found through derivation using the continuity equation and the Bernoulli total flow equation that there is a functional relationship between the sample gas flow rate and the pressure difference between the inlet and outlet. The derivation process is as follows: Figure 4 Shown as, according to the injection dilution principle of the injection diluter, it is found through derivation using the continuity equation and the Bernoulli total flow equation that there is a functional relationship between the sample gas flow rate and the pressure difference between the inlet and outlet. The derivation process is as follows:

[0089] Continuity equation: Q = A1V1 = A2V2 (1-2)

[0090] Where: Q is the flow rate in the pipe; A1 and A2 are the areas of cross-sections 1 and 2 respectively; V1 and V2 are the flow velocities at cross-sections 1 and 2 respectively.

[0091] Bernoulli equation:

[0092] Where: P1 and P2 are the pressures at cross-sections 1 and 2 respectively; V1 and V2 are the flow velocities at cross-sections 1 and 2 respectively; α1 and α2 are the kinetic energy correction coefficients at cross-sections 1 and 2 respectively; ρ is the fluid density; h w is the frictional resistance loss along the way.

[0093] Frictional resistance loss along the way:

[0094] Where: λ is the frictional resistance coefficient, l is the length of the fluid flow, d is the pipe diameter, and V is the pipe flow velocity.

[0095] From the exhaust end structure, A1 = A2, so V1 = V2; (1-5)

[0096] From Q = AV; It is obtained that

[0097] From It is obtained that

[0098] Where μ is the absolute viscosity of the gas.

[0099] Substitute equations 1-4 to 1-7 into equation 1-3 and after arrangement, it is obtained that

[0100]

[0101] Referring to relevant literature, it can be known that: α2-α1 takes 1.16. Let ΔP = P1 - P2 and substitute it into equation 1-8. The specific calculation formula is as follows:

[0102]

[0103] Where: ρ is the gas density, d is the sampling tube diameter, l is the sampling tube length, μ is the absolute gas viscosity, and Q is the calculated flow rate.

[0104] Solve the quadratic equation of one variable After simplification, it is

[0105] 8(1.16)ρQ 2 +128μlπQ - ΔPπ 2 d 4 =0

[0106] Δ=(128μlπ) 2 +32(1.16)ρΔPπ 2 d 4 >0 always holds, so the equation has two roots, as follows:

[0107]

[0108] Since Q is always greater than zero, the negative root is discarded, and the expression of Q is obtained as follows:

[0109]

[0110] It is known that ρ is the gas density, and the exhaust density is generally taken as 1.28 kg / m3; μ is the absolute (dynamic) viscosity of the gas, which increases with the increase of the exhaust temperature.

[0111] Therefore: Q∝d 2 , Q∝l, to obtain the relationship between the exhaust end flow rate Q and the pressure difference, the sampling tube diameter and the sampling tube length.

[0112] 1.3.2. Air end:

[0113] The air end is as Figure 5 shown, and it is derived using the Bernoulli total flow equation and the continuity equation. The derivation process is as follows:

[0114] Bernoulli equation:

[0115] Where: P1 and P2 are the pressures at sections 1 and 2 respectively; V1 and V2 are the flow velocities at sections 1 and 2 respectively; α1 and α2 are the kinetic energy correction coefficients at sections 1 and 2 respectively; ρ is the fluid density; h w is the frictional resistance loss along the way.

[0116] Frictional resistance loss along the way:

[0117] Where: l is the length that the fluid flows through, d is the pipe diameter, V is Figure 5 the exhaust pipe flow velocity in m (i.e., V in Equation 1-12), and μ is the absolute gas viscosity.

[0118] The diameters of the air end inlet and outlet pipes are relatively large, and the frictional resistance loss along the way is relatively small compared to the exhaust end. Therefore, only the frictional resistance loss of the capillary (exhaust pipe) is considered during the calculation process. Given that P2 is the atmospheric pressure, and substituting Equation 1-11 into Equation 1-10, we get:

[0119]

[0120] From the continuity equation, we can obtain V1, V2, and V m :

[0121] Air end inlet:

[0122] Mixing end outlet:

[0123] Capillary:

[0124] Where: Q1 is the air end inlet flow rate; Q2 is the mixing end outlet flow rate; Q3 is the exhaust end flow rate, which is a fixed value here; d1, d2, and d3 are the air end inlet diameter, mixing end outlet diameter, and capillary diameter, respectively.

[0125] Substituting Equations 1-13 to 1-15 into Equation 1-12, we get:

[0126]

[0127] Where: P1 is the air inlet pressure; α1 and α2 are the kinetic energy correction coefficients at the air inlet and the mixed gas outlet, respectively; ρ is the fluid density; Q1 is the air end inlet flow rate; Q3 is the exhaust end flow rate, which is a fixed value here; d1, d2, and d3 are the air end inlet diameter, mixing end outlet diameter, and capillary diameter, respectively; l is the capillary length, and μ is the absolute viscosity of the gas.

[0128] Replacing P1 with P and Q1 with Q, expanding and rearranging, we get:

[0129]

[0130] Let

[0131] Solve the quadratic equation:

[0132] aQ 2 + bQ + c = 0

[0133] Δ = b 2 - 4ac. When Δ > 0, there are two roots; when Δ = 0, there is one root;

[0134]

[0135] When Δ < 0, there are no roots and the equation has no solution.

[0136] Since it is very complex to directly solve for Δ, a CFD simulation method is adopted for research.

[0137] II. Simulation process:

[0138] Taking the jet diluter as the research object, a simulation model of the diluter is constructed, and the Fluent software is used to simulate the internal flow field of the diluter. The simulation results provide a way to optimize the internal structure parameters of the diluter. The external shape structure size of the diluter has an impact on the internal flow field and dilution ratio of the diluter. By studying the influence brought by the change of key parameters, the best parameters of the diluter are obtained through comparison. The specific key parameters include: inlet pressure P, capillary diameter D, and capillary length L; among them, the inlet pressure P is a dilution parameter, and the capillary diameter D and capillary length L are structure parameters.

[0139] First, the fluid domain is obtained according to the three-dimensional model. As Figure 6 shown, in order to more clearly see the fluid domain area, it is marked with a black line; then the air inlet, exhaust inlet, and mixed gas outlet are marked on the fluid simulation model, and finally, mesh generation is carried out, as Figures 7a - 7b shown.

[0140] The set simulation conditions are as follows:

[0141] (1) The internal fluid flow state of the jet diluter is laminar, so the calculation model is selected as Laminar, and the parameters are default;

[0142] (2) The exhaust density is similar to the air density, so the materials at the exhaust end and the air end are both set as air, and the parameters are default;

[0143] (3) According to the physical process of the diluter operation, the boundary conditions of the exhaust inlet and the air inlet are both set as pressure inlets, and the mixed gas outlet is set as a pressure outlet and is at atmospheric pressure;

[0144] (4) The convergence error is set to 10 -3 , and the others remain default.

[0145] The simulation scheme is shown in Table 1-1, and the value ranges of the key parameters can also be seen from the table. During physical analysis, the exhaust inlet pressure should be 0, but it will be considered as an outlet during simulation, so a very small pressure is applied to ensure it is an inlet. Initially, 5 Pa and 10 Pa are selected, and then 1 Pa is added. For the sake of convenience in expression, it is simplified to P5, P10, and P1, and a total of 136 groups of data are obtained.

[0146] Table 1-1 Simulation scheme

[0147]

[0148]

[0149] According to the conditions of Simulation Group 1, it can be found that the dilution ratio first increases rapidly and then decreases slowly as the air inlet pressure increases. Considering practical applications, only the change of the dilution ratio when the air inlet pressure is between 100 and 10,000 Pa is concerned. As Figure 8a shown, it can be found that the dilution ratio first increases rapidly and then tends to be stable. When fitting with a logarithmic function, R is as high as 0.956. It can be considered that there is a logarithmic relationship between the air inlet pressure and the dilution ratio. At the same time, the stable dilution ratio value is about 32.5, and the inflection point pressure is about 2,000 Pa. Therefore, the air inlet pressure of 2,700 Pa is taken as the pressure of the subsequent simulation group.

[0150] According to the above results and considering the simulation time, the air inlet pressure is only taken as 100 - 8,000 Pa, and the exhaust inlet pressure is taken as 10 Pa, that is, the conditions of Simulation Group 2. The Figure 8b change graph of the dilution ratio is obtained. It can be found that the dilution ratio also first increases rapidly and then tends to be stable. When fitting with a logarithmic function, R = 0.988. There is a logarithmic relationship between the air inlet pressure and the dilution ratio. The stable dilution ratio value is about 25, and the inflection point pressure is about 3,000 Pa. Therefore, the air inlet pressure of 4,800 Pa is taken as the pressure of the subsequent simulation group.

[0151] By comparing two groups of data when the exhaust inlet pressures are 5 Pa and 10 Pa respectively and the air inlet pressure ranges from 100 to 8,000 Pa, it can be found that relative to 10 Pa, the dilution ratio increases at a faster rate at 5 Pa, that is, it reaches the inflection point faster, and the stable dilution ratio value is also larger. When the exhaust inlet pressure is 5 Pa, the dilution ratio begins to decrease when the air inlet pressure value is about 8,000 Pa. If necessary, subsequent simulations will continue with an exhaust inlet pressure of 10 Pa and an air inlet pressure greater than 8,000 Pa to find the dilution ratio drop point.

[0152] The simulation with an exhaust inlet of 1 Pa is added, and the air inlet pressure is taken as 100 - 8,000 Pa, that is, Simulation Group 3. The results are as Figure 8c shown. It can be found that the dilution ratio increases rapidly at a rate faster than that of P5, starts to decrease after reaching the peak, and the air inlet pressure range where the dilution ratio is stable is very small.

[0153] According to Simulation Groups 4 and 5, the air pipe diameter is changed (0.4 - 1.0 mm), and the results are as Figure 9a shown. It can be found that whether it is P5 or P10, the dilution ratio increases as the air pipe diameter increases. When fitting with an exponential function, R is 0.986 and 0.982 respectively. It can be considered that there is an exponential relationship between the air pipe diameter and the dilution ratio.

[0154] According to simulation groups 6 and 7, the diameter of the exhaust pipe was changed (0.5 - 1.5 mm), and the results are as Figure 9b shown. It can be found that whether it is P5 or P10, the dilution ratio decreases as the diameter of the exhaust pipe increases. When fitting with an inverse proportional function, the Rs are 0.999 and 0.9998 respectively, and it is considered that there is an inverse proportional relationship between the diameter of the exhaust pipe and the dilution ratio.

[0155] According to simulation groups 8 and 9, the length of the air pipe was changed (4 - 15 mm), and a cubic polynomial was used for fitting. The results are as Figure 9c shown. It can be found that the Rs are 0.955 and 0.628 respectively. The fitting effect is better at P5, and it can be considered that the relationship between the length of the air pipe and the dilution ratio satisfies a cubic polynomial. The reason for this result is that as the length of the air pipe increases, the air end flow rate decreases significantly, and the exhaust end flow rate decreases slightly. According to the dilution ratio calculation formula, when both quantities change, it is difficult to determine the change relationship of the dilution ratio.

[0156] According to simulation groups 10 and 11, the length of the exhaust pipe was changed (15 - 35 mm), and the simulation results are as Figure 9d shown. It can be found that whether it is P5 or P10, the dilution ratio increases as the length of the exhaust pipe increases. When fitting with a linear function, the Rs are 0.983 and 0.948 respectively, and it can be considered that there is a linear relationship between the length of the exhaust pipe and the dilution ratio. This is because as the length of the exhaust pipe increases, the air end flow rate remains unchanged, and the exhaust end flow rate decreases slightly. According to the dilution ratio calculation formula, the dilution ratio will increase.

[0157] III. Simulation conclusions:

[0158] 1) There is a logarithmic relationship between the air inlet pressure and the dilution ratio;

[0159] 2) The smaller the exhaust inlet pressure, the faster the dilution ratio increases, the larger the stabilized dilution ratio value, and the smaller the air inlet pressure corresponding to the stabilized dilution ratio; however, when the exhaust inlet pressure is too small, the range of the air inlet pressure at which the dilution ratio stabilizes is very small;

[0160] 3) There is an exponential relationship between the air pipe diameter and the dilution ratio;

[0161] 4) There is an inverse proportional relationship between the exhaust pipe diameter and the dilution ratio;

[0162] 5) The relationship between the air pipe length and the dilution ratio satisfies a cubic polynomial;

[0163] 6) There is a linear relationship between the exhaust pipe length and the dilution ratio.

[0164] According to the relationships between the air inlet pressure, air pipe length, air pipe diameter, exhaust pipe length, exhaust pipe diameter and the dilution ratio, first determine two of the parameters, and then change the other three parameters to obtain a diluter with any dilution ratio.

[0165] Existing research has shown that the optimal exhaust pipe diameter is 0.8 mm. In order to obtain a stable dilution ratio as quickly as possible, a relatively small exhaust inlet pressure (such as 5 - 10 Pa) is taken, and then the air inlet pressure is selected; referring to Figure 10 As shown, first determine the required dilution ratio. Based on the required dilution ratio, preliminarily determine the exhaust pipe length, air pipe length, and air pipe diameter, and a stable dilution ratio can be obtained; compare the gap between the stable dilution ratio and the required dilution ratio at this time. By sequentially adjusting the exhaust pipe length, air pipe length, and air pipe diameter, the error between the stable dilution ratio and the required dilution ratio can be continuously reduced until the error is less than the set error value, and then the dilution parameters and structural parameters of the injection dilution gas can be determined.

[0166] IV. Advantages of the present invention:

[0167] Based on the design method of the injection diluter for vehicle ultrafine particle dilution provided by the present invention, the designed injection diluter can have the following advantages:

[0168] (1) It can measure ultrafine particles with a particle size range ≤ 23 nm;

[0169] (2) Adopting the partial flow dilution principle, it is not affected by the engine displacement during measurement; the injection diluter has a compact structure, is easy to operate, and has a low cost, and can protect precision instruments;

[0170] (3) Air and sample gas can be evenly mixed to ensure the repeatability and accuracy of the particulate matter test results;

[0171] (4) It has a large dilution ratio range, high dilution ratio stability, and a small relative error; short response time, and can complete the sampling work under transient experimental cycles;

[0172] (5) The diluter material is heat-resistant; the heating temperature can be selected to avoid measuring condensed volatile substances.

[0173] (6) According to the conclusion of the exhaust end part in 1.3.1, the flow rate of the sample gas depends on the pressure drop of the injector. The pressure drop at this place can be measured by two pressure sensors, and a control unit is set to control this dilution parameter of the pressure drop. In practical applications, the dilution parameters can be dynamically adjusted to meet the workload range of the particulate matter monitoring instrument at the back end.

[0174] (7) Based on the present invention, the method of combining engine bench tests and CFD numerical simulations can be further adopted to optimize the internal structural parameters of the injection diluter, and a PFSS dilution system can be directly built on the laboratory engine bench to test the dilution ratio under different working conditions. The test verifies the accuracy of the diluter calculation model, and has strong practical application value.

[0175] (8) Most of the studies on the dilution stage adopt numerical simulation methods, greatly simplifying the actual working conditions of particulate emissions. Few people use self-designed diluters for engine bench tests, lacking experimental verification. The diluter obtained based on the design method of the present invention has been verified through actual tests, and the error compared with the simulation results is very small.

[0176] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. Design method of an injection diluter for vehicle ultrafine particle dilution, characterized in that, It includes the following steps: S10. Select the relevant factors affecting the dilution ratio of the diluter; The relevant factors include: dilution air parameters, vehicle exhaust parameters, and diluter structure parameters; S20. According to the injection dilution principle, deduce using the continuity equation and Bernoulli's total flow equation, and determine the design factors of the exhaust end and air end of the jet diluter among the relevant factors; S30. Build a simulation model of the diluter, and according to the design factors, use CFD simulation software, corresponding simulation conditions, and simulation schemes to simulate the internal flow field of the diluter to obtain simulation conclusions; S40. Based on the simulation conclusions, and according to the relationship between some data in the design factors and the dilution ratio, randomly combine some data in the design factors to obtain diluters with any dilution ratio; Among them, in the step S20, the design factors include: The flow rate at the exhaust end is respectively related to the pressure difference between the inlet and outlet of the exhaust pipe, the diameter of the exhaust pipe, and the length of the exhaust pipe; the pressure difference between the inlet and outlet of the exhaust pipe is the difference between the inlet pressure and the inlet pressure of the exhaust pipe; The flow rate at the air end is respectively related to the pressure difference between the inlet and outlet of the air pipe, the diameter of the air pipe, and the length of the air pipe; the pressure difference between the inlet and outlet of the air pipe is the difference between the inlet pressure and the inlet pressure of the air pipe; The step S40 includes: Based on the simulation conclusions, according to the relationship between the air inlet pressure, the length of the air pipe, the diameter of the air pipe, the length of the exhaust pipe, the diameter of the exhaust pipe, and the dilution ratio, first determine two of the parameters, and then change the other three parameters to obtain diluters with any dilution ratio; specifically including: S401. Given the optimal exhaust pipe diameter, air inlet pressure, and set exhaust inlet pressure; S402. Determine the required dilution ratio of the diluter; S403. According to the required dilution ratio, preliminarily set the length of the exhaust pipe, the length of the air pipe, and the diameter of the air pipe; S404. Simulate to obtain the stable dilution ratio; S405. Calculate the gap between the stable dilution ratio and the required dilution ratio; S406. When the gap meets the error requirement, output the corresponding exhaust pipe diameter, air inlet pressure, exhaust inlet pressure, exhaust pipe length, air pipe length, and air pipe diameter to complete the design of the diluter; S407. When the gap does not meet the error requirement, re-execute step S403.

2. The design method according to claim 1, characterized in that, In the step S10: The dilution air parameters include: air quality, air pressure, air flow rate, and air temperature; The vehicle exhaust parameters include: exhaust pressure, exhaust flow rate, and exhaust temperature; The diluter structure parameters include: nozzle position, sampling position, exhaust pipe length, exhaust pipe diameter, air pipe length, air pipe diameter, injection chamber angle, and mixing chamber length.

3. The design method according to claim 2, characterized in that, In the step S30, the CFD simulation software and the corresponding simulation conditions include: (1) The internal fluid flow state of the jet diluter is laminar, select the Laminar calculation model, and the parameters are default; (2) The exhaust density and air density are similar, and the materials of the exhaust end and air end are both set to air, and the parameters are default; (3)According to the physical process of the operation of the lean injection type diluter, the boundary conditions of both the exhaust gas inlet and the air inlet are set as pressure inlets, and the mixture gas outlet is set as a pressure outlet and at atmospheric pressure; (4)Set the convergence error to 10 -3 , and keep the others default.

4. The design method according to claim 3, wherein In the step S30, the simulation scheme includes multiple groups of data; each group of data includes: air inlet pressure, exhaust gas inlet pressure, air pipe diameter, exhaust pipe diameter, air pipe length, exhaust pipe length, and the corresponding number of simulation times; Among them, during the simulation process, a preset value needs to be applied to the exhaust gas inlet pressure to ensure it serves as an inlet.

5. The design method according to claim 4, characterized in that, In the step S30, the internal flow field of the diluter is simulated to obtain simulation conclusions, including: 1) The air inlet pressure and the dilution ratio are in a logarithmic relationship; 2) The smaller the exhaust gas inlet pressure, the faster the dilution ratio increases, the larger the dilution ratio value after stabilization, and the smaller the air inlet pressure corresponding to the stable dilution ratio; however, when the exhaust gas inlet pressure is too small, the range of the air inlet pressure at which the dilution ratio is stable is very small; 3) The air pipe diameter and the dilution ratio are in an exponential relationship; 4) The exhaust pipe diameter and the dilution ratio are in an inverse proportion relationship; 5) The relationship between the air pipe length and the dilution ratio satisfies a cubic polynomial; 6) The exhaust pipe length and the dilution ratio are in a linear relationship.

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