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An intake manifold geometry for enhancement of pressure drop in a diesel engine
Fuel 261 (2020) 116193
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
An intake manifold geometry for enhancement of pressure drop in a diesel engine
T
⁎
Kenan Gocmena, , Hakan Serhad Soyhanb,c a
Science and Technology Institute, Sakarya University, Turkey Engineering Faculty, Mechanical Engineering Department, Sakarya University, Turkey c Team-SAN Co., Technopark, Sakarya University, Turkey b
A R T I C LE I N FO
A B S T R A C T
Keywords: Intake manifold design Optimization CFD
Intake manifolds are one of the most important components affecting performance in internal combustion engines. An intake manifold having low pressure drop is very important to maximize the mass of the drawn air into the cylinder. In addition, the intake manifolds ensure that the air is sent in equal amounts to the cylinders in order to obtain stable and compatible piston movements. Therefore, optimizing the geometry of intake manifolds is very important. One of the traditional methods in optimization is to manufacture a prototype having different manifold geometries, to test these manifolds in engine tests and to select the best performance. This method is very expensive both in terms of time and cost. It also does not provide the best possible design with an information about the behavior of the air passing through the manifold. If a designer gets this information, he may know exactly which regions need to be improved. Nowadays, optimization studies supported by computational fluid dynamics (CFD) is used commonly since they cost lower in time and money than conventional methods and give optimum results faster. The influence of the changes in the manifold geometry on the flow and pressure can be investigated in detail by using the CFD method. The best solution can be obtained with a high accuracy by focusing directly on the region where the geometry problem is. Our optimization study has been carried out by using Ansys-Fluent software.
1. Introduction This study has been carried out to improve the intake manifold by the CFD method for a diesel engine having four cylinders developed in a tractor factory. A cylinder has two pieces air ports; one is fill port and the other one is swirl port which significantly affect the engine performance [1]. In order to increase power taken from the engine, number of valves per cylinder increased from 2 to 4. Thus the multivalve engine has four-valves; 2 intake and 2 exhaust valves to have better breathing and achieve better efficiency. In addition, this multivalve design provides faster and better mixing of air in the combustion chamber of the cylinder. The intake manifold is essential for the optimal performance of an internal combustion engine [2]. The aim of the improvement is to reduce the pressure losses of the firstly designed intake manifold and the pressure loss differences between the intake manifold inlet and outlet through each cylinder as much as possible. By these improvements, we also aim to equalize the air mass flow to each cylinder [3]. In the other words, to ensure that the designed geometry equally distributes the
⁎
flow through each runner, we performed CFD [4]. It is required that equal mass of air fuel mixture is delivered to each cylinder of the engine. Unequal distribution of charge reduces the efficiency of the engine [5]. One of the best and reliable way to understand areas where pressure losses are unacceptable is to perform a CFD analysis. The CFD simulations help to improve the pressure drop distribution without making drastic geometric changes. Due to surrounding components, there are strict limitations in changing the design of the intake manifold. Thus we could make only two changes which are investigated in this manuscript as seen in Fig. 1. These suggestions are made to expand the ‘’narrow neck’’ between the first and second manifold cavities. In suggestion-1, the bolt hole causing the narrow neck has been canceled so the bolt hole effect had been examined. In suggestion-2, the manifold surface to which the inlet pipe is connected has been raised by 10 mm. The effect of the two geometric changes to the pressure loss and air behavior has been investigated throughout the manifold. For this, streamlines and total pressure distributions has been evaluated. After these improvement studies, a new intake manifold which is
Corresponding author. E-mail addresses: [email protected] (K. Gocmen), [email protected] (H.S. Soyhan).
https://doi.org/10.1016/j.fuel.2019.116193 Received 20 March 2019; Received in revised form 13 July 2019; Accepted 9 September 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 4. Manifold Design Process.
Fig. 5. Boundary Conditions for Existing Manifold.
Fig. 1. Existing Model and Improvements.
Fig. 6. Boundary Conditions for New Manifold. Fig. 2. New Model Geometry.
completely different has been designed to achieve the best ideal situation by CFD analysis as seen in Fig. 2. One of these ideal conditions is to deliver the air to the engine cylinder through the intake port with least flow losses, other one is to enhance the flow swirl in the intake manifold to improve the combustion in the engine cylinder [6]. Intake manifold has a major effect on a vehicle’s engine performance and emission noise and pollutants [7,8]. Another ideal condition is to distribute the air flow equally to all cylinders [9,10]. In the new manifold, the passage of the injector pipes and cables through the opening in the manifold has minimized area loss as seen in Figs. 3 and 4. 2. Manifold design process The first model (existing model) was made under restrictions due to the componenets (fuel pipes, egr, etc.) around the manifold. Problems in the manifold have been identified by CFD analysis and so on it has been understood that a new manifold should be designed. For this purpose, a new manifold has been designed roughly as below. (This rough design is not a carelessly made design, but rather a design made considering the location of the fuel pipes and the compressor of the turbocharger.) CFD analysis showed that the pressure and flowrate distributions in the rough manifold have been very stable. Afterwards,
Fig. 3. Manifold Assembly on the Engine.
2
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 9. Mesh Densities in the Manifold Section.
Fig. 7. Mesh for Existing Manifold.
Fig. 8. Mesh for New Manifold.
zones that do not affect the air flow and sharp corners has been determined and geometry of the manifold has been rounded and reduced. CFD analysis has been repeated and it has been observed that rounding and reduction of the manifold had no negative effect to flowrate and pressure distribution. In this way, the final design of the manifold geometry has been obtained. 3. Boundary conditions
Fig. 10. Mesh Size Evaluation Charts.
Solid flow volumes of the intake manifolds are shown as above (Figs. 5, 6). In the model, the manifold inlet and outlets are extended to obtain more accurate results. The combustion in the cylinders beings at very short time intervals and the air fills each cylinder at different time periods, not
simultaneously. Therefore, the amount of air entering each cylinder has been calculated theoretically, and this value has been defined as the manifold inlet flow boundary condition. As a manifold outlet boundary conditions, while an outlet has been defined as the atmosphere 3
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 12. Suggestion-1 (Velocity and Pressure Distributions).
Fig. 11. Original Geometry (Velocity and Pressure Distributions).
Model; Realizable, k-epsilon Fluid; Incompressible ideal gas Pressure; Effective pressure Physical Properties of Air; Density; 1,128 kg/m3 Dynamic Viscosity 1,91E−05 kg.m/s Specific Heat; 1005 J/kg.K Thermal Conductivity; 0,0271 W/m.K Molecular Weight; 28,97 kg/kmol
pressure, the other outlets have been defined as the wall boundary condition. Thus, the pressure loss between the manifold inlet and each cylinder outlet has been easily calculated by CFD analysis. In order to be able to examine a model, steady state analysis has been performed as many as the number of cylinders. Another approach in the manifold analysis is to define manifold inlet as flowrate boundary condition and to define all manifold outlets as atmospheric pressure. In other words, the entering air to the manifold leaves from all manifold outlets simultaneously. Although this approach does not represent actual flow conditions exactly, it is important to obtain the flow distribution for each cylinder. If the flowrate distribution is balanced, manifold geometry is successful. Because of these reason, evaluation of this parameter is useful and important.
K-epsilon turbulence model is frequently used in manifold studies in the literature [3,5,7,10]. In addition, in our previous CFD studies, kepsilon turbulence models showed satisfactory results compared to the experimental results.
4. Physical properties of CFD model Time; Steady 4
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 14. Original Geometry (Velocity and Pressure Distributions).
independence of the analysis results from the mesh. This evaluation is very important for the reliability of the analysis results. Small mesh size causes to deformation of the model geometry, in addition the eddies formed in the real flow are not obtained. Hence, accurate analysis results can not be reached by using low mesh. On the contrary, very dense mesh causes to long solution time and data storage problem. At this point, an optimal mesh size should be decided. As shown in Fig. 9, the mesh size has been increased gradually in order to evaluate mesh size effect. As shown in Fig. 10, analysis results obtained in the low mesh sizes are quite different from high mesh sizes. As the mesh size increases, the analysis results converge to each other. Especially, the analysis results of the reference mesh size are very close to the analysis results of the high dense mesh size. This result shows that the reference mesh size (4 million) is proper for mesh independency.
Fig. 13. Suggestion-2 (Velocity and Pressure Distributions).
5. Mesh A mesh structure growing from the surface to the interior has been formed. Tetrahedral mesh has been applied to the manifold body (Figs. 7, 8). Sweep mesh has been applied to the extended inlet and outlets. There is a large change in velocity in the wall normal direction and it is important to CFD simulation to capture this gradient correctly [2]. To do this, boundary layer mesh has been applied to the surfaces. In the Fluent analysis program, the tetrahedral mesh type has been converted to polyhedral mesh type, so mesh size has been reduced to approximately 1,8 million cells from 4,7 million cells for existing model (for new model; to approximately 4 million from 10 million). Thus, analysis time has been shortened, and the storage size of the file on the computer has been reduced.
7. Analysis results (Outlet to each one cylinder) for the existing manifold The original geometry of the manifold and the analysis results are shown below. According to the analysis results, when the pressure losses between manifold inlet and outlet to the each cylinder are examined in the Fig. 11, the pressure losses increase towards the fourth cylinder from the first cylinder. This means that the air pressure absorbed into the cylinder decreases from the first cylinder to the fourth cylinder, in other words, the combustion performance gets bad.
6. Mesh independence study One way to check the accuracy of the analysis is to show the 5
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 15. Suggestion-1 (Velocity and Pressure Distributions). Fig. 16. Suggestion-2 (Velocity and Pressure Distributions).
Especially, due to narrow neck zone, the pressure loss between the first cylinder and the second cylinder is very high (about two times). On the other hand, the pressure losses between the second, third and fourth cylinders are close to each other. This situation is also evident in the distribution of total pressure contours on the manifold surface in Fig. 11. Therefore, the following improvement trials have been made to reduce pressure loss in the narrow neck (throat) zone. In the first suggestion (Fig. 12), the bolt cavity under the narrow throat has been canceled, so the narrow throat has been enlarged. The effect of this bolt cavity has been evaluated. It appears that the pressure loss differences between the manifold inlet and manifold outlet for each cylinder is considerably reduced. Thus, a more stable / homogeneous pressure distribution has been obtained. In the second suggestion (Fig. 13), the manifold surface to which the inlet pipe is connected has been raised 10 mm to enlarge the narrow throat section. Even in this suggestion, the pressure loss differences between the manifold inlet and manifold outlet for each cylinder has been considerably reduced and a more balanced pressure distribution has been obtained according to the original geometry.
cavities of the manifold. The imbalance in pressure distribution confirms this situation as well. The flowrate and pressure drop distributions in the second, third and fourth outlets are close to each other, indicating that there are not negative geometric effect between these cavities. In the Fig. 15, flowrate distribution in the first suggestion manifold is better than original manifold. Pressure losses of the first suggestion manifold is lower and pressure drop balance is better than original manifold. In the first suggestion manifold, the flowrate and pressure drop distributions in the second, third and fourth outlets are close to each other which is similar to original manifold. There are similar flowrate and pressure drop distribution characteristics between first and second suggestion manifolds (Fig. 16), except outlet-1b. In the outlet-1b of the second manifold, flowrate is the highest value and pressure drop is the lowest value. The geometry improvement study shows that the narrow throat zone between the first and second cavities of the manifold needs to be expanded. The expanded throat geometry significantly reduces the pressure loss differences between the manifold inlet and manifold outlet for each cylinder and provides a much more balanced pressure distribution. Although the suggested geometries significantly provide more balanced pressure drop and flowrate distributions between the manifold inlet and outlet for each cylinder, as seen from analysis results these improvements are not satisfactory. Unbalanced pressure drop distribution in the manifold adversely affects swirl values in the cylinder
8. Analysis results (Outlet to all cylinders simultaneously) for the existing manifold When the simultaneously air flow situation from the all manifold outlets is examined for original geometry (Fig. 14), flowrate of the outlet-1ab is two times higher than other outlets. This result shows that there is an important geometric problem between first and second 6
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 18. New Geometry (Velocity and Pressure Distributions).
9. Analysis results (Outlet to each one cylinder) for the new manifold The new geometry of the manifold and the analysis results are shown according to flow from one inlet to one outlet for each cylinder in Fig. 17. A significant decrement in the pressure losses between the new manifold inlet and outlets are observed. Pressure drop disribution in the new manifold also appeared to be quite balanced. Due to the geometric constaint in the outlet-1a zone, the pressure drop at this zone increased slightly.
Fig. 17. New Geometry (Velocity and Pressure Distributions).
so performance of the engine and exhaust emission values affected negatively. Due to this reasons and difficulties in the application of the suggested geometric changes, a new intake manifold designed which is completely different from original manifold.
7
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
more stable results would be obtained. 11. Conclusions The following charts are prepared in order to show the analysis results more clearly and collectively. If two different approach types of manifold outlet boundary conditions are evaluated, pressure characteristics of the approaches are similar to each other. Second approach includes flowrate distribution which is an important evaluation criteria. As seen that the pressure losses in the new manifold are the lowest level, in addition the balance in the pressure drop and flowrate distributions in the new manifold reflects the best condition. At the same time, the results show that the ideal balance state is almost captured by the new manifold geometry. As a result, the new manifold provides an important contribution to improving the swirl values in the cylinder and reducing exhaust emissions Figs. 19–21.
Fig. 19. Pressure Drop Chart (first approach; one inlet and one outlet).
12. Inferences of the study This study showed us that an intake manifold of the engine is an important part which should be designed carefully. CFD analysis is the best way to detect areas where air flow is adversely affected in the manifold design. Therefore, the intake manifold should be designed beastly by CFD analysis before the motor manufacturing phase is started. Because the intake manifold has a significant impact on engine performance and exhaust gas emissions. To obtain accurate results with CFD analysis, the independence of the mesh should be checked. In addition, the boundary layer mesh should be applied to the walls. If these issues are not taken into consideration, obtaining wrong analysis results are inevitable.
Fig. 20. Pressure Drop Chart (second approach; one inlet and four outlets).
References [1] Sharma Vinod Kumar, Mohan Man, Mouli Chandra. Effect of intake swirl on the performance of single cylinder direct injection diesel engine. IOP Conf. Series Materials Science and Engineering. 2017. 062077. [2] Indira Priyadarsini Ch. Flow analysis of intake manifold using computational fluid dynamics. Int J Eng Adv Res Technol (IJEART) 2016;2(1). ISSN: 2454-9290. [3] Chaubey Abhishek, Prof AC, Tiwari.. Design and CFD analysis of the intake manifold for the Suzuki G13bb engine. Int J Res Appl Sci Eng Technol (IJRASET) 2017;5(VI). ISSN: 2321-9653. [4] Singhal Arpit. Designing & validating a new intake manifold for a formula SAE car. Int J Eng Res& Technol (IJERT) 2016;5(07). ISSN:2278-0181. [5] Gangacharyulu D, Sharma Sumeet, Singla Sachin. Study of design improvement of intake manifold of internal combustion engine. Int J Eng Technol, Manage Appl Sci 2015;3(Special Issue). ISSN 2349-4476. [6] First A. Jason D’Mello, Second B. Omkar S. Siras. Performance Analysis for 4Cylinder Intake Manifold: An Experimental and Numerical Approach. International Engineering Research Journal 917-922. [7] Sulaiman S, Murad S, Ibrahim I, Abdul Karim Z. Study of flow in air-intake system for a single-cylinder go-kart engine. Int J Automotive Mech Eng (IJAME) 2010;1:91–104. [8] Arvindkumar K, Adhithiyan N, Darsak VS, Dinesh C. Optimisation of intake manifold design using fibre reinforced plastic. Int J Sci Eng Res 2014;5(4). [9] Gupta Amit Kumar, Mishra Abhishek. Design and development of inlet manifold for six cylinder engine for truck application. India J Res 2014;3(7). [10] Suresh Aadepu ISNVR, Prasanth Jarapala Murali, Naik. Design of intake manifold of IC engines with improved volumetric efficiency. Int J Mag Eng, Technol, Manage Res 2014.
Fig. 21. Flowrate Chart (second approach; one inlet and four outlets).
10. Analysis results (outlet to all cylinders simultaneously) for the new manifold In the Fig. 18, outlet of the air from the manifold to all cylinders at the same time examined. Thus, the flowrate distribution in the manifold is also evaluated in addition to pressure drop distibution. Even for this case, pressure drop and flowrate distributions in the manifold are quite stable. If there was no geometric constrain in the outlet-1a zone, a much
8
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
An intake manifold geometry for enhancement of pressure drop in a diesel engine
T
⁎
Kenan Gocmena, , Hakan Serhad Soyhanb,c a
Science and Technology Institute, Sakarya University, Turkey Engineering Faculty, Mechanical Engineering Department, Sakarya University, Turkey c Team-SAN Co., Technopark, Sakarya University, Turkey b
A R T I C LE I N FO
A B S T R A C T
Keywords: Intake manifold design Optimization CFD
Intake manifolds are one of the most important components affecting performance in internal combustion engines. An intake manifold having low pressure drop is very important to maximize the mass of the drawn air into the cylinder. In addition, the intake manifolds ensure that the air is sent in equal amounts to the cylinders in order to obtain stable and compatible piston movements. Therefore, optimizing the geometry of intake manifolds is very important. One of the traditional methods in optimization is to manufacture a prototype having different manifold geometries, to test these manifolds in engine tests and to select the best performance. This method is very expensive both in terms of time and cost. It also does not provide the best possible design with an information about the behavior of the air passing through the manifold. If a designer gets this information, he may know exactly which regions need to be improved. Nowadays, optimization studies supported by computational fluid dynamics (CFD) is used commonly since they cost lower in time and money than conventional methods and give optimum results faster. The influence of the changes in the manifold geometry on the flow and pressure can be investigated in detail by using the CFD method. The best solution can be obtained with a high accuracy by focusing directly on the region where the geometry problem is. Our optimization study has been carried out by using Ansys-Fluent software.
1. Introduction This study has been carried out to improve the intake manifold by the CFD method for a diesel engine having four cylinders developed in a tractor factory. A cylinder has two pieces air ports; one is fill port and the other one is swirl port which significantly affect the engine performance [1]. In order to increase power taken from the engine, number of valves per cylinder increased from 2 to 4. Thus the multivalve engine has four-valves; 2 intake and 2 exhaust valves to have better breathing and achieve better efficiency. In addition, this multivalve design provides faster and better mixing of air in the combustion chamber of the cylinder. The intake manifold is essential for the optimal performance of an internal combustion engine [2]. The aim of the improvement is to reduce the pressure losses of the firstly designed intake manifold and the pressure loss differences between the intake manifold inlet and outlet through each cylinder as much as possible. By these improvements, we also aim to equalize the air mass flow to each cylinder [3]. In the other words, to ensure that the designed geometry equally distributes the
⁎
flow through each runner, we performed CFD [4]. It is required that equal mass of air fuel mixture is delivered to each cylinder of the engine. Unequal distribution of charge reduces the efficiency of the engine [5]. One of the best and reliable way to understand areas where pressure losses are unacceptable is to perform a CFD analysis. The CFD simulations help to improve the pressure drop distribution without making drastic geometric changes. Due to surrounding components, there are strict limitations in changing the design of the intake manifold. Thus we could make only two changes which are investigated in this manuscript as seen in Fig. 1. These suggestions are made to expand the ‘’narrow neck’’ between the first and second manifold cavities. In suggestion-1, the bolt hole causing the narrow neck has been canceled so the bolt hole effect had been examined. In suggestion-2, the manifold surface to which the inlet pipe is connected has been raised by 10 mm. The effect of the two geometric changes to the pressure loss and air behavior has been investigated throughout the manifold. For this, streamlines and total pressure distributions has been evaluated. After these improvement studies, a new intake manifold which is
Corresponding author. E-mail addresses: [email protected] (K. Gocmen), [email protected] (H.S. Soyhan).
https://doi.org/10.1016/j.fuel.2019.116193 Received 20 March 2019; Received in revised form 13 July 2019; Accepted 9 September 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved.
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 4. Manifold Design Process.
Fig. 5. Boundary Conditions for Existing Manifold.
Fig. 1. Existing Model and Improvements.
Fig. 6. Boundary Conditions for New Manifold. Fig. 2. New Model Geometry.
completely different has been designed to achieve the best ideal situation by CFD analysis as seen in Fig. 2. One of these ideal conditions is to deliver the air to the engine cylinder through the intake port with least flow losses, other one is to enhance the flow swirl in the intake manifold to improve the combustion in the engine cylinder [6]. Intake manifold has a major effect on a vehicle’s engine performance and emission noise and pollutants [7,8]. Another ideal condition is to distribute the air flow equally to all cylinders [9,10]. In the new manifold, the passage of the injector pipes and cables through the opening in the manifold has minimized area loss as seen in Figs. 3 and 4. 2. Manifold design process The first model (existing model) was made under restrictions due to the componenets (fuel pipes, egr, etc.) around the manifold. Problems in the manifold have been identified by CFD analysis and so on it has been understood that a new manifold should be designed. For this purpose, a new manifold has been designed roughly as below. (This rough design is not a carelessly made design, but rather a design made considering the location of the fuel pipes and the compressor of the turbocharger.) CFD analysis showed that the pressure and flowrate distributions in the rough manifold have been very stable. Afterwards,
Fig. 3. Manifold Assembly on the Engine.
2
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 9. Mesh Densities in the Manifold Section.
Fig. 7. Mesh for Existing Manifold.
Fig. 8. Mesh for New Manifold.
zones that do not affect the air flow and sharp corners has been determined and geometry of the manifold has been rounded and reduced. CFD analysis has been repeated and it has been observed that rounding and reduction of the manifold had no negative effect to flowrate and pressure distribution. In this way, the final design of the manifold geometry has been obtained. 3. Boundary conditions
Fig. 10. Mesh Size Evaluation Charts.
Solid flow volumes of the intake manifolds are shown as above (Figs. 5, 6). In the model, the manifold inlet and outlets are extended to obtain more accurate results. The combustion in the cylinders beings at very short time intervals and the air fills each cylinder at different time periods, not
simultaneously. Therefore, the amount of air entering each cylinder has been calculated theoretically, and this value has been defined as the manifold inlet flow boundary condition. As a manifold outlet boundary conditions, while an outlet has been defined as the atmosphere 3
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 12. Suggestion-1 (Velocity and Pressure Distributions).
Fig. 11. Original Geometry (Velocity and Pressure Distributions).
Model; Realizable, k-epsilon Fluid; Incompressible ideal gas Pressure; Effective pressure Physical Properties of Air; Density; 1,128 kg/m3 Dynamic Viscosity 1,91E−05 kg.m/s Specific Heat; 1005 J/kg.K Thermal Conductivity; 0,0271 W/m.K Molecular Weight; 28,97 kg/kmol
pressure, the other outlets have been defined as the wall boundary condition. Thus, the pressure loss between the manifold inlet and each cylinder outlet has been easily calculated by CFD analysis. In order to be able to examine a model, steady state analysis has been performed as many as the number of cylinders. Another approach in the manifold analysis is to define manifold inlet as flowrate boundary condition and to define all manifold outlets as atmospheric pressure. In other words, the entering air to the manifold leaves from all manifold outlets simultaneously. Although this approach does not represent actual flow conditions exactly, it is important to obtain the flow distribution for each cylinder. If the flowrate distribution is balanced, manifold geometry is successful. Because of these reason, evaluation of this parameter is useful and important.
K-epsilon turbulence model is frequently used in manifold studies in the literature [3,5,7,10]. In addition, in our previous CFD studies, kepsilon turbulence models showed satisfactory results compared to the experimental results.
4. Physical properties of CFD model Time; Steady 4
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 14. Original Geometry (Velocity and Pressure Distributions).
independence of the analysis results from the mesh. This evaluation is very important for the reliability of the analysis results. Small mesh size causes to deformation of the model geometry, in addition the eddies formed in the real flow are not obtained. Hence, accurate analysis results can not be reached by using low mesh. On the contrary, very dense mesh causes to long solution time and data storage problem. At this point, an optimal mesh size should be decided. As shown in Fig. 9, the mesh size has been increased gradually in order to evaluate mesh size effect. As shown in Fig. 10, analysis results obtained in the low mesh sizes are quite different from high mesh sizes. As the mesh size increases, the analysis results converge to each other. Especially, the analysis results of the reference mesh size are very close to the analysis results of the high dense mesh size. This result shows that the reference mesh size (4 million) is proper for mesh independency.
Fig. 13. Suggestion-2 (Velocity and Pressure Distributions).
5. Mesh A mesh structure growing from the surface to the interior has been formed. Tetrahedral mesh has been applied to the manifold body (Figs. 7, 8). Sweep mesh has been applied to the extended inlet and outlets. There is a large change in velocity in the wall normal direction and it is important to CFD simulation to capture this gradient correctly [2]. To do this, boundary layer mesh has been applied to the surfaces. In the Fluent analysis program, the tetrahedral mesh type has been converted to polyhedral mesh type, so mesh size has been reduced to approximately 1,8 million cells from 4,7 million cells for existing model (for new model; to approximately 4 million from 10 million). Thus, analysis time has been shortened, and the storage size of the file on the computer has been reduced.
7. Analysis results (Outlet to each one cylinder) for the existing manifold The original geometry of the manifold and the analysis results are shown below. According to the analysis results, when the pressure losses between manifold inlet and outlet to the each cylinder are examined in the Fig. 11, the pressure losses increase towards the fourth cylinder from the first cylinder. This means that the air pressure absorbed into the cylinder decreases from the first cylinder to the fourth cylinder, in other words, the combustion performance gets bad.
6. Mesh independence study One way to check the accuracy of the analysis is to show the 5
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 15. Suggestion-1 (Velocity and Pressure Distributions). Fig. 16. Suggestion-2 (Velocity and Pressure Distributions).
Especially, due to narrow neck zone, the pressure loss between the first cylinder and the second cylinder is very high (about two times). On the other hand, the pressure losses between the second, third and fourth cylinders are close to each other. This situation is also evident in the distribution of total pressure contours on the manifold surface in Fig. 11. Therefore, the following improvement trials have been made to reduce pressure loss in the narrow neck (throat) zone. In the first suggestion (Fig. 12), the bolt cavity under the narrow throat has been canceled, so the narrow throat has been enlarged. The effect of this bolt cavity has been evaluated. It appears that the pressure loss differences between the manifold inlet and manifold outlet for each cylinder is considerably reduced. Thus, a more stable / homogeneous pressure distribution has been obtained. In the second suggestion (Fig. 13), the manifold surface to which the inlet pipe is connected has been raised 10 mm to enlarge the narrow throat section. Even in this suggestion, the pressure loss differences between the manifold inlet and manifold outlet for each cylinder has been considerably reduced and a more balanced pressure distribution has been obtained according to the original geometry.
cavities of the manifold. The imbalance in pressure distribution confirms this situation as well. The flowrate and pressure drop distributions in the second, third and fourth outlets are close to each other, indicating that there are not negative geometric effect between these cavities. In the Fig. 15, flowrate distribution in the first suggestion manifold is better than original manifold. Pressure losses of the first suggestion manifold is lower and pressure drop balance is better than original manifold. In the first suggestion manifold, the flowrate and pressure drop distributions in the second, third and fourth outlets are close to each other which is similar to original manifold. There are similar flowrate and pressure drop distribution characteristics between first and second suggestion manifolds (Fig. 16), except outlet-1b. In the outlet-1b of the second manifold, flowrate is the highest value and pressure drop is the lowest value. The geometry improvement study shows that the narrow throat zone between the first and second cavities of the manifold needs to be expanded. The expanded throat geometry significantly reduces the pressure loss differences between the manifold inlet and manifold outlet for each cylinder and provides a much more balanced pressure distribution. Although the suggested geometries significantly provide more balanced pressure drop and flowrate distributions between the manifold inlet and outlet for each cylinder, as seen from analysis results these improvements are not satisfactory. Unbalanced pressure drop distribution in the manifold adversely affects swirl values in the cylinder
8. Analysis results (Outlet to all cylinders simultaneously) for the existing manifold When the simultaneously air flow situation from the all manifold outlets is examined for original geometry (Fig. 14), flowrate of the outlet-1ab is two times higher than other outlets. This result shows that there is an important geometric problem between first and second 6
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
Fig. 18. New Geometry (Velocity and Pressure Distributions).
9. Analysis results (Outlet to each one cylinder) for the new manifold The new geometry of the manifold and the analysis results are shown according to flow from one inlet to one outlet for each cylinder in Fig. 17. A significant decrement in the pressure losses between the new manifold inlet and outlets are observed. Pressure drop disribution in the new manifold also appeared to be quite balanced. Due to the geometric constaint in the outlet-1a zone, the pressure drop at this zone increased slightly.
Fig. 17. New Geometry (Velocity and Pressure Distributions).
so performance of the engine and exhaust emission values affected negatively. Due to this reasons and difficulties in the application of the suggested geometric changes, a new intake manifold designed which is completely different from original manifold.
7
Fuel 261 (2020) 116193
K. Gocmen and H.S. Soyhan
more stable results would be obtained. 11. Conclusions The following charts are prepared in order to show the analysis results more clearly and collectively. If two different approach types of manifold outlet boundary conditions are evaluated, pressure characteristics of the approaches are similar to each other. Second approach includes flowrate distribution which is an important evaluation criteria. As seen that the pressure losses in the new manifold are the lowest level, in addition the balance in the pressure drop and flowrate distributions in the new manifold reflects the best condition. At the same time, the results show that the ideal balance state is almost captured by the new manifold geometry. As a result, the new manifold provides an important contribution to improving the swirl values in the cylinder and reducing exhaust emissions Figs. 19–21.
Fig. 19. Pressure Drop Chart (first approach; one inlet and one outlet).
12. Inferences of the study This study showed us that an intake manifold of the engine is an important part which should be designed carefully. CFD analysis is the best way to detect areas where air flow is adversely affected in the manifold design. Therefore, the intake manifold should be designed beastly by CFD analysis before the motor manufacturing phase is started. Because the intake manifold has a significant impact on engine performance and exhaust gas emissions. To obtain accurate results with CFD analysis, the independence of the mesh should be checked. In addition, the boundary layer mesh should be applied to the walls. If these issues are not taken into consideration, obtaining wrong analysis results are inevitable.
Fig. 20. Pressure Drop Chart (second approach; one inlet and four outlets).
References [1] Sharma Vinod Kumar, Mohan Man, Mouli Chandra. Effect of intake swirl on the performance of single cylinder direct injection diesel engine. IOP Conf. Series Materials Science and Engineering. 2017. 062077. [2] Indira Priyadarsini Ch. Flow analysis of intake manifold using computational fluid dynamics. Int J Eng Adv Res Technol (IJEART) 2016;2(1). ISSN: 2454-9290. [3] Chaubey Abhishek, Prof AC, Tiwari.. Design and CFD analysis of the intake manifold for the Suzuki G13bb engine. Int J Res Appl Sci Eng Technol (IJRASET) 2017;5(VI). ISSN: 2321-9653. [4] Singhal Arpit. Designing & validating a new intake manifold for a formula SAE car. Int J Eng Res& Technol (IJERT) 2016;5(07). ISSN:2278-0181. [5] Gangacharyulu D, Sharma Sumeet, Singla Sachin. Study of design improvement of intake manifold of internal combustion engine. Int J Eng Technol, Manage Appl Sci 2015;3(Special Issue). ISSN 2349-4476. [6] First A. Jason D’Mello, Second B. Omkar S. Siras. Performance Analysis for 4Cylinder Intake Manifold: An Experimental and Numerical Approach. International Engineering Research Journal 917-922. [7] Sulaiman S, Murad S, Ibrahim I, Abdul Karim Z. Study of flow in air-intake system for a single-cylinder go-kart engine. Int J Automotive Mech Eng (IJAME) 2010;1:91–104. [8] Arvindkumar K, Adhithiyan N, Darsak VS, Dinesh C. Optimisation of intake manifold design using fibre reinforced plastic. Int J Sci Eng Res 2014;5(4). [9] Gupta Amit Kumar, Mishra Abhishek. Design and development of inlet manifold for six cylinder engine for truck application. India J Res 2014;3(7). [10] Suresh Aadepu ISNVR, Prasanth Jarapala Murali, Naik. Design of intake manifold of IC engines with improved volumetric efficiency. Int J Mag Eng, Technol, Manage Res 2014.
Fig. 21. Flowrate Chart (second approach; one inlet and four outlets).
10. Analysis results (outlet to all cylinders simultaneously) for the new manifold In the Fig. 18, outlet of the air from the manifold to all cylinders at the same time examined. Thus, the flowrate distribution in the manifold is also evaluated in addition to pressure drop distibution. Even for this case, pressure drop and flowrate distributions in the manifold are quite stable. If there was no geometric constrain in the outlet-1a zone, a much
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