Method for determining fan speed of modified air-cooled diesel engine

Abstract

The present invention belongs to the technical field of diesel engines, and specifically relates to a method for determining the speed of a modified fan of an air-cooled diesel engine. First, the reference power coefficient of the original fan is calculated, and then the actual power coefficient of the original fan is calculated; then the fan is geometrically modified, and then the reference power coefficient and the actual power coefficient of the modified fan are calculated in turn; the relationship between the actual power coefficient and the speed is established through the specific enthalpy ratio, and finally the new speed of the modified fan is determined. The method is applied to the modification and upgrading of the cooling fan of an existing air-cooled diesel engine, which can significantly shorten the design cycle and save design costs.

Description

Technical Field

[0001] The invention belongs to the technical field of diesel engines, and in particular relates to a method for determining the speed of a fan of a modified air-cooled diesel engine. Background Art

[0002] Air-cooled diesel engines are widely used in power equipment in extreme natural environments due to their strong environmental adaptability and high reliability. The requirement for high reliability in extreme environments has led to the adoption of a purely mechanical design for most of the air-cooled diesel engines currently in service, which inevitably brings about the problem of insufficient freedom of the control system. For example, the cooling fan is connected to the crankshaft by a speed gear and a hydraulic coupler, which makes the fan speed regulation not flexible enough, which in turn leads to local overheating of the engine under low-speed and high-torque conditions due to insufficient cooling fan speed. In order to alleviate this problem, air-cooled diesel engines usually use a single-stage high-load axial flow fan, which consists of a negative pre-swirl guide vane and a rotor. Due to the negative pre-swirl effect of the guide vane, the rotor can still obtain a higher total pressure at a lower speed, but the negative pre-swirl effect also leads to a decrease in fan efficiency.

[0003] In recent years, the industry's transmission technology has made new progress, which can achieve the decoupling of fan speed and shaft speed, so that the speed matching between each stage of the diesel engine can be more flexible, and the speed of the cooling fan can be further increased, so that the fan pressure ratio is not reduced while the efficiency is improved. A feasible method is to increase the fan speed while canceling the negative pre-swirl intake design to obtain a modified design, and then carry out aerodynamic optimization on this basis, and finally achieve a significant improvement in efficiency while ensuring the fan pressure ratio.

[0004] However, in the process of fan aerodynamic optimization, aerodynamic performance evaluation based on computational fluid dynamics is an indispensable link, which involves the selection of boundary conditions and working conditions. Therefore, the prerequisite for fan aerodynamic optimization is to determine the new speed of the modified fan. The traditional approach generally uses numerical simulation methods to gradually increase the speed, but it consumes a lot of computing resources and time, which is difficult to meet the engineering needs for the rapid design of air-cooled diesel engine fans. Summary of the invention

[0005] The object of the present invention is to provide a method for determining the speed of a fan of a modified air-cooled diesel engine to solve the problems existing in the background technology.

[0006] A method for determining the speed of a fan of an air-cooled diesel engine modification comprises the following steps:

[0007] S1: Determine the original fan geometry constants, the relevant parameters under the original speed design condition, the original fan geometry constraint dimensionless parameters and the medium characteristic dimensionless parameters;

[0008] S2: Calculate the reference power coefficient μ0 of the original fan;

[0009] S3: Calculate the actual power coefficient μ of the original fan;

[0010] S4: geometric modification of the fan;

[0011] S5: Calculate the modified fan specific enthalpy ratio σ′;

[0012] S6: Calculate the reference power coefficient μ′0 and the actual power coefficient μ′ of the modified fan in sequence;

[0013] S7: The relationship between the actual work coefficient and the rotational speed is established through the specific enthalpy ratio, and finally the new rotational speed of the modified fan is determined.

[0014] Preferably, in S1, the original fan geometric constants include: the original fan blade number Z, the original fan inlet hub diameter D 1h , Original fan inlet rim diameter D 1s , original fan outlet diameter D2, original fan blade trailing edge thickness t2, original fan outlet installation angle change rate

[0015] The original speed condition related parameters include: original fan speed n, inlet total temperature T t1 , the original fan outlet circumferential speed u2, the original fan inlet relative axial airflow angle β 1s , the original fan inlet blade tip relative Mach number M w1 The dimensionless parameters of the original fan geometric constraints include: the original fan outlet blade installation angle β 2A , Original fan outlet radial velocity ratio The original fan specific enthalpy ratio σ, the original fan inlet pre-swirl angle α1; the given medium characteristic dimensionless parameters include: gas constant R and adiabatic index γ;

[0016] Preferably, in S2, the original fan reference power coefficient μ0 is calculated according to formula (1), and the formula (1) is:

[0017]

[0018] Where Z is the original number of fan blades, β 2A is the original fan outlet blade installation angle, D2 is the original fan outlet diameter, is the original fan outlet radial velocity ratio, β 2A Original fan outlet blade installation angle,

[0019] is the rate of change of the original fan outlet installation angle, and t2 is the original fan blade trailing edge thickness.

[0020] Preferably, in S3, the original fan actual power coefficient μ is calculated using formula (2), where formula (2) is:

[0021]

[0022] Among them, μ0 is the original fan reference power coefficient, σ is the original fan specific enthalpy ratio, M w1 is the relative Mach number of the original fan inlet blade tip, u2 is the original fan outlet circumferential velocity, γ is the adiabatic index, R is the gas constant, T t1 is the total inlet temperature, D 1h is the original fan inlet hub diameter, D 1s is the original fan inlet rim diameter, β 1s is the relative axial airflow angle at the original fan inlet, and α1 is the pre-swirl angle at the original fan inlet.

[0023] Preferably, in S4, due to the installation position constraint, the wheel rim hub size remains unchanged, and only the fan blade geometry is modified. The specific parameter changes are as follows: The change rate of the installation angle of the modified fan outlet Modified fan inlet pre-swirl angle α′1, modified fan outlet blade installation angle β′ 2A , the thickness of the trailing edge of the modified fan blade is t′2. The efficiency improvement amplitude of the modified design is set to Δη.

[0024] Preferably, in S5, after the fan is modified, the modified fan specific enthalpy ratio σ′ is calculated according to formula (3), wherein formula (3) is:

[0025] σ′=σ(1-Δη) (3)

[0026] Among them, α is the specific enthalpy ratio of the original fan, and Δη is the efficiency improvement amplitude of the modified design.

[0027] Preferably, in S6, the modified fan reference power coefficient μ′0 is calculated according to formula (4), wherein formula (4) is:

[0028]

[0029] Where Z is the original number of fan blades, D2 is the original fan outlet diameter, is the original fan outlet radial velocity ratio, β′ 2A It is the installation angle of the modified fan outlet blade. is the rate of change of the outlet installation angle of the modified fan, t′2 is the thickness of the trailing edge of the modified fan blade;

[0030] The actual power coefficient μ′ of the modified fan is calculated using formula (5), which is:

[0031]

[0032] Among them, μ′0 is the reference power coefficient of the modified fan, σ′ is the specific enthalpy ratio of the modified fan, M w1is the relative Mach number of the original fan inlet blade tip, u2 is the original fan outlet circumferential velocity, γ is the adiabatic index, R is the gas constant, T t1 is the total inlet temperature, D 1h is the original fan inlet hub diameter, D 1s is the original fan inlet rim diameter, β 1s is the relative axial airflow angle at the original fan inlet, and α1′ is the pre-swirl angle at the modified fan inlet.

[0033] Preferably, in S7, the modified fan speed n′ is calculated using formula (6), and the formula (6) is as follows:

[0034]

[0035] Where n is the original fan speed, μ is the original fan actual work coefficient, μ′ is the modified fan actual work coefficient, σ′ is the original fan specific enthalpy ratio, and σ′ is the modified fan specific enthalpy ratio.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The method for determining the fan speed of a modified air-cooled diesel engine of the present invention can quickly obtain the new fan speed of the diesel engine only by following the above steps. Compared with the method for determining the fan speed of a modified engine based on numerical simulation, it can greatly save calculation time, thereby significantly accelerating the fan optimization design process, shortening the design cycle, and saving design costs. DETAILED DESCRIPTION

[0038] The specific implementation of the present invention is described in detail below in conjunction with preferred embodiments.

[0039] A method for determining the speed of a modified fan of an air-cooled diesel engine, the method comprising the following steps:

[0040] (1) Determine the original fan geometry constants, the original speed design condition related parameters, the original fan geometry constraint dimensionless parameters and the medium characteristic dimensionless parameters. The original fan geometry constants include: the original fan blade number Z, the original fan inlet hub diameter D 1h , Original fan inlet rim diameter D 1s , original fan outlet diameter D2, original fan blade trailing edge thickness t2, original fan outlet installation angle change rate The original speed condition related parameters include: original fan speed n, inlet total temperature T t1 , the original fan outlet circumferential speed u2, the original fan inlet relative axial airflow angle β 1s , the original fan inlet blade tip relative Mach number M w1 The dimensionless parameters of the original fan geometric constraints include: the original fan outlet blade installation angle β2A , Original fan outlet radial velocity ratio The original fan specific enthalpy ratio σ, the original fan inlet pre-swirl angle α1; the given medium characteristic dimensionless parameters include: gas constant R and adiabatic index γ;

[0041] (2) Calculate the original fan reference power coefficient μ0 according to formula (1), which is:

[0042]

[0043] Where Z is the original number of fan blades, β 2A is the original fan outlet blade installation angle, D2 is the original fan outlet diameter, is the original fan outlet radial velocity ratio, β 2A Original fan outlet blade installation angle, is the rate of change of the original fan outlet installation angle, t2 is the original fan blade trailing edge thickness;

[0044] (3) The original fan actual power coefficient μ is calculated using formula (2), which is:

[0045]

[0046] Among them, μ0 is the original fan reference power coefficient, σ is the original fan specific enthalpy ratio, M w1 is the relative Mach number of the original fan inlet blade tip, u2 is the original fan outlet circumferential velocity, γ is the adiabatic index, R is the gas constant, T t1 is the total inlet temperature, D 1h is the original fan inlet hub diameter, D 1s is the original fan inlet rim diameter, β 1s is the relative axial airflow angle of the original fan inlet, α1 is the pre-swirl angle of the original fan inlet;

[0047] (4) The fan modification design of the air-cooled diesel engine is restricted by the installation position. The wheel rim and hub size remain unchanged, and only the fan blade geometry is modified. The specific parameter changes are as follows: The change rate of the installation angle of the modified fan outlet Modified fan inlet pre-swirl angle α′1, modified fan outlet blade installation angle β′ 2A , the thickness of the trailing edge of the modified fan blade is t′2. Set the efficiency improvement amplitude of the modified design Δη;

[0048] (5) After the fan is modified, the modified fan specific enthalpy ratio σ′ is calculated according to formula (3), which is:

[0049] σ′=σ(1-Δη) (3)

[0050] Among them, σ is the specific enthalpy ratio of the original fan, and Δη is the efficiency improvement amplitude of the modified design;

[0051] (6) Calculate the modified fan reference power coefficient μ′0 according to formula (4), which is:

[0052]

[0053] Where Z is the original number of fan blades, D2 is the original fan outlet diameter, is the original fan outlet radial velocity ratio, β′ 2A It is the installation angle of the modified fan outlet blade. is the rate of change of the outlet installation angle of the modified fan, t′2 is the thickness of the trailing edge of the modified fan blade;

[0054] (7) The actual power coefficient μ′ of the modified fan is calculated using formula (5), which is:

[0055]

[0056] Among them, μ′0 is the reference power coefficient of the modified fan, σ′ is the specific enthalpy ratio of the modified fan, M w1 is the relative Mach number of the original fan inlet blade tip, u2 is the original fan outlet circumferential velocity, γ is the adiabatic index, R is the gas constant, T t1 is the total inlet temperature, D 1h is the original fan inlet hub diameter, D 1s is the original fan inlet rim diameter, β 1s is the relative axial airflow angle at the inlet of the original fan, and α′1 is the pre-swirl angle at the inlet of the modified fan;

[0057] (8) The modified fan speed n′ is calculated using formula (6), which is as follows:

[0058]

[0059] Where n is the original fan speed, μ is the original fan actual power coefficient, μ′ is the modified fan actual power coefficient, σ is the original fan specific enthalpy ratio, and σ′ is the modified fan specific enthalpy ratio.

[0060] Example

[0061] This embodiment demonstrates the calculation method of the rotation speed of the modified fan by combining the experimental data of an industrial axial flow fan. The new rotation speed is calculated by the following steps.

[0062] 1) Determine the original fan parameters, including: original number of blades Z = 11, original fan outlet diameter D2 = 0.3015m, original fan inlet hub diameter D 1h =0.1075m, original fan inlet rim diameter D 1s= 0.194m, original fan blade trailing edge thickness t2 = 0.00655m, original fan outlet installation angle change rate Original fan speed n = 6045rpm, inlet total temperature T t1 =298K, original fan outlet circumferential velocity u2 =99.27m / s, original fan inlet relative axial airflow angle β 1s =72deg, original fan inlet blade tip relative Mach number M w1 =0.5, original fan outlet blade installation angle β 2A =-48deg, original fan outlet radial velocity ratio The original fan specific enthalpy ratio σ=1.05, the original fan inlet pre-swirl angle α1=-38deg, the gas constant R=287J / (kgK) and the adiabatic index γ=1.4.

[0063] 2) Use formula (1) to substitute the parameters and calculate the reference power coefficient μ0 = 1.7774.

[0064] 3) Use formula (2) to substitute the parameters and calculate the actual power coefficient μ = 2.2361.

[0065] 4) Determine the parameters of the modified fan, including: the change rate of the installation angle of the modified fan outlet Modified fan inlet pre-swirl angle α′1=0, modified fan outlet blade installation angle β′ 2A =-48deg, modified blade trailing edge thickness t′2 = 0.00655m. Set the modified design efficiency improvement amplitude Δη = 0.03.

[0066] 5) Using formula (3) and substituting the parameters into the formula, the specific enthalpy ratio of the modified fan is calculated as σ′=1.0185.

[0067] 6) Use formula (4) to substitute the parameters and calculate the reference power coefficient of the modified fan μ′0=1.7774.

[0068] 7) Use formula (5) to substitute the parameters and calculate the actual power coefficient of the modified fan μ′=1.7774.

[0069] 8) Use formula (6) to calculate the modified fan speed n′=6689 rpm.

[0070] At this point, the new speed of the modified fan has been calculated.

[0071] The method for determining the fan speed of a modified air-cooled diesel engine of the present invention can quickly obtain the new fan speed of the diesel engine only by following the above steps. Compared with the method for determining the fan speed of a modified engine based on numerical simulation, it can greatly save calculation time, thereby significantly accelerating the fan optimization design process, shortening the design cycle, and saving design costs.

[0072] It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for determining the fan speed of a modified air-cooled diesel engine, characterized in that : Includes the following steps: S1: Determine the original fan geometry constants, the relevant parameters under the original speed design condition, the original fan geometry constraint dimensionless parameters and the medium characteristic dimensionless parameters; S2: Calculate the reference power coefficient μ0 of the original fan; S3: Calculate the actual power coefficient μ of the original fan; S4: geometric modification of the fan; S5: Calculate the modified fan specific enthalpy ratio σ′; S6: Calculate the reference power coefficient μ0′ and the actual power coefficient μ′ of the modified fan in sequence; S7: The relationship between the actual work coefficient and the rotational speed is established through the specific enthalpy ratio, and finally the new rotational speed of the modified fan is determined.

2. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S1, the original fan geometric constants include: the original fan blade number Z, the original fan inlet hub diameter D 1h , Original fan inlet rim diameter D 1s , original fan outlet diameter D2, original fan blade trailing edge thickness t2, original fan outlet installation angle change rate The relevant parameters under the original speed design condition include: original fan speed n, inlet total temperature T t1 , the original fan outlet circumferential speed u2, the original fan inlet relative axial airflow angle β 1s , the original fan inlet blade tip relative Mach number M w1 The dimensionless parameters of the original fan geometric constraints include: the original fan outlet blade installation angle β 2A , Original fan outlet radial velocity ratio The original fan specific enthalpy ratio σ, the original fan inlet pre-swirl angle α1; the dimensionless parameters of the medium characteristics include: gas constant R and adiabatic index γ.

3. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S2, the original fan reference power coefficient μ0 is calculated according to formula (1), and the formula (1) is: Where Z is the original number of fan blades, β 2A is the original fan outlet blade installation angle, D2 is the original fan outlet diameter, is the original fan outlet radial velocity ratio, β 2A Original fan outlet blade installation angle, is the rate of change of the original fan outlet installation angle, and t2 is the original fan blade trailing edge thickness.

4. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S3, the original fan actual power coefficient μ is calculated using formula (2), where: Among them, μ0 is the original fan reference power coefficient, σ is the original fan specific enthalpy ratio, M w1 is the relative Mach number of the original fan inlet blade tip, u2 is the original fan outlet circumferential velocity, γ is the adiabatic index, R is the gas constant, T t1 is the total inlet temperature, D 1h is the original fan inlet hub diameter, D 1s is the original fan inlet rim diameter, β 1s is the relative axial airflow angle at the original fan inlet, and α1 is the pre-swirl angle at the original fan inlet.

5. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S4, due to the installation position constraint, the wheel rim hub size remains unchanged, and only the fan blade geometry is modified. The specific parameter changes are as follows: The change rate of the installation angle of the modified fan outlet Modified fan inlet pre-swirl angle α1′, modified fan outlet blade installation angle β2′ A , the thickness of the trailing edge of the modified fan blade is t′2, and the efficiency improvement amplitude Δη of the modified design is set.

6. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S5, after the fan is modified, the modified fan specific enthalpy ratio σ′ is calculated according to formula (3), wherein formula (3) is: σ′=σ(1-Δη) (3) Where σ is the specific enthalpy ratio of the original fan and Δη is the efficiency improvement of the modified design.

7. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S6, the modified fan reference power coefficient μ0′ is calculated according to formula (4), where: Where Z is the original number of fan blades, D2 is the original fan outlet diameter, is the original fan outlet radial velocity ratio, β2′ A It is the installation angle of the modified fan outlet blade. is the rate of change of the outlet installation angle of the modified fan, t2′ is the thickness of the trailing edge of the modified fan blade; The actual power coefficient μ′ of the modified fan is calculated using formula (5), which is: Among them, μ0′ is the reference power coefficient of the modified fan, σ′ is the specific enthalpy ratio of the modified fan, M w1 is the relative Mach number of the original fan inlet blade tip, u2 is the original fan outlet circumferential velocity, γ is the adiabatic index, R is the gas constant, T t1 is the total inlet temperature, D 1h is the original fan inlet hub diameter, D 1s is the original fan inlet rim diameter, β 1s is the relative axial airflow angle at the original fan inlet, and α1′ is the pre-swirl angle at the modified fan inlet.

8. The method for determining the fan speed of a modified air-cooled diesel engine according to claim 1, characterized in that: In S7, the modified fan speed n′ is calculated using formula (6), and the formula (6) is as follows: Where n is the original fan speed, μ is the original fan actual power coefficient, μ′ is the modified fan actual power coefficient, σ is the original fan specific enthalpy ratio, and σ′ is the modified fan specific enthalpy ratio.

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