A method for calculating exhaust pipe resistance loss of opposed two-stroke engine

Abstract

The invention discloses a method for calculating the resistance loss of an exhaust pipe of an opposed two-stroke engine, which belongs to the technical field of engines and comprises the following steps: step 1, determining the size parameters of a bend, including a curvature radius, a bending angle and a pipe diameter; step 2, determining the cross-sectional area at an outlet of the bend; step 3, determining the flow velocity at the outlet of the bend; step 4, determining the Reynolds number of the bend; step 5, determining the Darcy friction factor; step 6, determining the friction loss coefficient; step 7, determining the bending loss coefficient; step 8, determining the total loss coefficient; step 9, adding a correction factor of the Reynolds number to correct the total loss coefficient; step 10, determining the corrected total loss coefficient; step 11, determining the resistance loss of the bend; the method for calculating the resistance loss of an exhaust pipe of an opposed two-stroke engine provided by the invention solves the problem that the resistance loss of a bend part of the exhaust pipe cannot be directly calculated during the design process of the opposed two-stroke engine.

Description

Technical Field

[0001] The invention belongs to the technical field of engines, and in particular relates to a method for calculating the exhaust pipe resistance loss of an opposed two-stroke engine. Background Art

[0002] The opposed two-stroke engine uses two pistons that move relative to each other and share a cylinder space. This layout eliminates the cylinder head and valve mechanism, and its intake and exhaust ports are directly arranged at both ends of the cylinder liner, which greatly reduces the height and total volume of the engine, greatly reduces the weight of the whole machine, and has a simple structure and is easy to flatten. Compared with traditional engines, the opposed two-stroke engine has a more compact structure and achieves higher space utilization.

[0003] For opposed two-stroke engines, in order to adapt to the opposed layout of the cylinders and the movement of the pistons, the exhaust pipe cannot simply use a straight pipe and may require more bends. When the fluid flows through the bend, the uniform flow is disrupted, and the increase in air flow resistance will cause more energy loss, which in turn affects the flow capacity and ventilation quality of the ventilation system. Therefore, a method is needed to calculate the resistance loss of the exhaust pipe bend of an opposed two-stroke engine, but a method for calculating the resistance loss of the exhaust pipe bend of an opposed two-stroke engine has not yet been made public. Summary of the invention

[0004] The purpose of the present invention is to provide a method for calculating the exhaust pipe resistance loss of an opposed two-stroke engine, so as to solve the problem that the resistance loss of the exhaust pipe bend part cannot be directly calculated during the design process of the opposed two-stroke engine in the prior art.

[0005] To achieve the above object, the present invention provides a method for calculating the exhaust pipe resistance loss of an opposed two-stroke engine, and the specific steps are as follows:

[0006] Step 1: Determine the size parameters of the elbow, including the radius of curvature R , bending angle i , Pipe diameter d ;

[0007] Step 2: Determine the cross-sectional area at the elbow outlet S ; According to the pipe diameter of the elbow d Calculate the cross-sectional area at the elbow outlet S ;

[0008] Step 3: Determine the flow rate at the elbow outlet ; According to the flow rate flowing through the elbow outlet and the cross-sectional area at the elbow outlet S Calculate the flow velocity at the outlet of the elbow ;

[0009] Step 4: Determine the Reynolds number of the elbow Re ;

[0010] Step 5: Determine the Darcy friction factor l ; Obtain the equivalent roughness of the pipeline according to the material table , according to the equivalent roughness , Reynolds number Re and pipe diameter d , find the Moody diagram to determine the Darcy friction factor l ;

[0011] Step 6: Determine the friction loss coefficient ;

[0012] Step 7: Determine the bending loss coefficient ;

[0013] Step 8: Determine the total loss coefficient ; According to the friction loss coefficient and bending loss coefficient , calculate the total loss coefficient ;

[0014] Step 9: Add the Reynolds number correction factor Correction of total loss coefficient;

[0015] Step 10: Determine the corrected total loss coefficient ;

[0016] Step 11: Determine the resistance loss of the bend ; Based on the corrected total loss coefficient and the flow velocity at the elbow outlet Calculate the resistance loss of the bend.

[0017] Preferably, the cross-sectional area at the outlet of the elbow in step 2 is S The calculation expression is as follows:

[0018] ;

[0019] In the formula, is the pipe diameter of the elbow.

[0020] Preferably, the flow rate at the elbow outlet in step 3 is The calculation expression is as follows:

[0021] ;

[0022] In the formula, is the flow rate through the elbow outlet.

[0023] Preferably, the Reynolds number of the elbow in step 4 is ReThe calculation expression is as follows:

[0024] ;

[0025] In the formula, Indicates kinematic viscosity.

[0026] Preferably, the friction loss coefficient in step 6 is The calculation expression is as follows:

[0027] ;

[0028] In the formula, l is the Darcy friction factor, i is the bending angle, R is the radius of curvature.

[0029] Preferably, the bending loss coefficient in step 7 is The calculation expression is as follows:

[0030] ;

[0031] In the formula, =min( , 2.5), indicating The value is The minimum value compared with 2.5; =min( , 1.99), indicating The value is The minimum value compared to 1.99.

[0032] Preferably, the total loss coefficient in step 8 is The calculation expression is as follows:

[0033] . ;

[0034] Preferably, the correction factor for the Reynolds number in step 9 is The value is the curvature ratio R / d and Reynolds number The functions are as follows:

[0035] ;

[0036] ;

[0037] ;

[0038] If R / d is between 1 and 1.5 or between 1.5 and 2, linear interpolation is used.

[0039] Preferably, the total loss coefficient corrected in step 10 is The calculation expression is as follows:

[0040] .

[0041] Preferably, the elbow resistance loss in step 11 is The calculation expression is as follows:

[0042] ;

[0043] In the formula, is the acceleration due to gravity, take 9.8m / s 2 .

[0044] Therefore, the present invention adopts the above-mentioned method for calculating the exhaust pipe resistance loss of an opposed two-stroke engine. When the size parameters of the elbow are known, the friction loss coefficient and the bending loss coefficient are calculated respectively, and the correction factor of the Reynolds number is added to obtain the corrected total loss coefficient, and then the resistance loss of the elbow is calculated; this solves the problem that the resistance loss of the elbow part of the exhaust pipe cannot be directly calculated during the design process of the opposed two-stroke engine.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention is a flowchart of an overall process of a method for calculating exhaust pipe resistance loss of an opposed two-stroke engine. DETAILED DESCRIPTION

[0047] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] See also Figure 1 , a method for calculating the exhaust pipe resistance loss of an opposed two-stroke engine, the specific steps are as follows:

[0049] Step 1: Determine the size parameters of the elbow, including the radius of curvature R , bending angle i , Pipe diameter d ;

[0050] Step 2: Determine the cross-sectional area at the elbow outlet S ; According to the pipe diameter of the elbow d Calculate the cross-sectional area at the elbow outlet S; The specific calculation expression is as follows:

[0051] ;

[0052] In the formula, is the pipe diameter of the elbow.

[0053] Step 3: Determine the flow rate at the elbow outlet ; According to the flow rate flowing through the elbow outlet Q and the cross-sectional area at the elbow outlet S Calculate the flow velocity at the outlet of the elbow ; The specific calculation expression is as follows:

[0054] ;

[0055] In the formula, is the flow rate through the elbow outlet.

[0056] Step 4: Determine the Reynolds number of the elbow Re ; The specific calculation expression is as follows:

[0057] ;

[0058] In the formula, Indicates kinematic viscosity.

[0059] Step 5: Determine the Darcy friction factor l ; Obtain the equivalent roughness of the pipeline according to the material table , according to the equivalent roughness , Reynolds number Re and pipe diameter d , find the Moody diagram to determine the Darcy friction factor l ;

[0060] Step 6: Determine the friction loss coefficient ; The specific calculation expression is as follows:

[0061] ;

[0062] In the formula, l is the Darcy friction factor, i is the bending angle, R is the radius of curvature.

[0063] Step 7: Determine the bending loss coefficient ; The specific calculation expression is as follows:

[0064] ;

[0065] In the formula, =min( , 2.5), indicating The value is The minimum value compared with 2.5; =min( , 1.99), indicating The value is The minimum value compared to 1.99.

[0066] Step 8: Determine the total loss coefficient ; According to the friction loss coefficient and bending loss coefficient , calculate the total loss coefficient ; The specific calculation expression is as follows:

[0067] .

[0068] Step 9: Add the Reynolds number correction factor Correct the total loss coefficient; the loss coefficient is usually not only a function of the bending angle and curvature ratio (R / d), but also affected by the Reynolds number. Therefore, the Reynolds number correction factor is added when determining the total loss coefficient. The Reynolds number correction factor is The value is the curvature ratio R / d and Reynolds number The functions are as follows:

[0069] ;

[0070] ;

[0071] ;

[0072] If R / d is between 1 and 1.5 or between 1.5 and 2, linear interpolation is used.

[0073] Step 10: Determine the corrected total loss coefficient ; The specific calculation expression is as follows:

[0074] .

[0075] Step 11: Determine the resistance loss of the bend ; Based on the corrected total loss coefficient and the flow velocity at the elbow outlet Calculate the resistance loss of the elbow; the specific calculation expression is as follows:

[0076] ;

[0077] In the formula, is the acceleration due to gravity, take 9.8m / s 2 .

[0078] Example

[0079] In this embodiment, a smooth circular elbow with equal cross-section is used, and the material is thin steel plate. The basic parameters are as follows: Pipe diameter d =50mm, bending angle i =90°, radius of curvature R =100mm, flow rate through the elbow According to step 1, determine the size parameters of the elbow; according to step 2, determine the cross-sectional area S at the outlet of the elbow, which is 0.00196m 2 ; Determine the flow rate at the elbow outlet according to step 3 , the flow velocity is 68.4m / s; determine the elbow Reynolds number according to step 4 Re The kinematic viscosity of air is generally 1.48×10-5m 2 / s, Reynolds number is 2.3×105; Determine the Darcy friction factor λ according to step 5, and obtain the equivalent roughness of the pipeline according to the material table is 0.18, and the Darcy friction factor is determined to be 0.029 by looking up the Moody diagram; the friction loss coefficient is determined according to step 6 , the friction loss coefficient is 0.0911; determine the bending loss coefficient according to step 7 , the bending loss coefficient is 0.105; determine the total loss coefficient according to step 8 , the total loss coefficient is 0.1961; determine the correction factor for the Reynolds number according to step 9 , the correction factor for the Reynolds number is 1.29; determine the corrected total loss coefficient according to step 10 , the corrected total loss coefficient is 0.2529; determine the elbow resistance loss according to step 11 , the bending resistance loss is 60.36m.

[0080] Therefore, the present invention adopts the above-mentioned method for calculating the exhaust pipe resistance loss of an opposed two-stroke engine. When the size parameters of the elbow are known, the friction loss coefficient and the bending loss coefficient are calculated respectively, and the correction factor of the Reynolds number is added to obtain the corrected total loss coefficient, and then the resistance loss of the elbow is calculated; this solves the problem that the resistance loss of the elbow part of the exhaust pipe cannot be directly calculated during the design process of the opposed two-stroke engine.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating exhaust pipe resistance loss of an opposed two-stroke engine, characterized in that: The specific steps are as follows: Step 1: Determine the size parameters of the elbow, including the radius of curvature R , bending angle θ , Pipe diameter d ; Step 2: Determine the cross-sectional area at the elbow outlet S ; According to the pipe diameter of the elbow d Calculate the cross-sectional area at the elbow outlet S ; Step 3: Determine the flow rate at the elbow outlet ; According to the flow rate at the elbow outlet Q and the cross-sectional area at the elbow outlet S Calculate the flow velocity at the outlet of the elbow ; Step 4: Determine the Reynolds number of the elbow Re ; Step 5: Determine the Darcy friction factor λ ; Obtain the equivalent roughness of the pipeline according to the material table , according to the equivalent roughness , Reynolds number Re and pipe diameter d , find the Moody diagram to determine the Darcy friction factor λ ; Step 6: Determine the friction loss coefficient ; Step 7: Determine the bending loss coefficient ; Step 8: Determine the total loss coefficient ; According to the friction loss coefficient and bending loss coefficient , calculate the total loss coefficient ; Step 9: Add the Reynolds number correction factor Correction of total loss coefficient; Step 10: Determine the corrected total loss coefficient ; Step 11: Determine the resistance loss of the bend ; Based on the corrected total loss coefficient and the flow velocity at the elbow outlet Calculate the resistance loss of the bend; Friction loss coefficient in step 6 The calculation expression is as follows: ； In the formula, λ is the Darcy friction factor, θ is the bending angle, R is the radius of curvature; Bending loss coefficient in step 7 The calculation expression is as follows: ； In the formula, =min( , 2.5), indicating The value is The minimum value compared with 2.5; =min( , 1.99), indicating The value is The minimum value compared with 1.99; Total loss coefficient in step 8 The calculation expression is as follows: ； Correction factor for Reynolds number in step 9 The value is the curvature ratio R / d and Reynolds number The functions are as follows: ； ； ； If R / d is between 1 and 1.5 or between 1.5 and 2, linear interpolation is used; The total loss coefficient after correction in step 10 The calculation expression is as follows: ； Bend resistance loss in step 11 The calculation expression is as follows: ； In the formula, is the acceleration due to gravity, take 9.8m / s 2 .

2. The method for calculating exhaust pipe resistance loss of an opposed two-stroke engine according to claim 1, characterized in that: The cross-sectional area at the elbow outlet in step 2 S The calculation expression is as follows: ； In the formula, is the pipe diameter of the elbow.

3. The method for calculating exhaust pipe resistance loss of an opposed two-stroke engine according to claim 2, characterized in that: Flow rate at the elbow outlet in step 3 The calculation expression is as follows: ； In the formula, Q is the flow rate through the elbow outlet.

4. The method for calculating exhaust pipe resistance loss of an opposed two-stroke engine according to claim 3, characterized in that: Reynolds number of the elbow in step 4 Re The calculation expression is as follows: ； In the formula, Indicates kinematic viscosity.

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