TJPRC: International Journal of Heat and Mass Transfer (TJPRC: IJHMT) Vol. 1, Issue 1, Jun 2016, 1-8 © TJPRC Pvt. Ltd.
COMPUTATIONAL FLUID DYNAMICS SIMULATION OF EXHAUST VALUES IN AN IC ENGINES GEORGIE S PUTHANPURACKAL1, MOHAMED RAFFI ICHANGI2, GRITHEN PINTO3 & KRIPA M. S4 1, 2, 3 4
BE Mechanical Final Year Students, Shree Devi Institute of Technology, Mangalore, Karnataka, India
Assistant Professor, Department of Mechanical, Shree Devi Institute of Technology, Mangalore, Karnataka, India
ABSTRACT A 4-stroke engine is an internal combustion (IC engine) in which the piston completes four separate stroke (suction, compression, power, exhaust) while turning a crankshaft. A stroke refers to a full travel of piston along the cylinder in either direction. An engine consists of inlet and exhaust valve. The inlet valve let in the air fuel mixture in the cylinder whereas exhaust valve forms the path for combust gases to escape from cylinder. Our research throws light on redesigning of diameter, material and introducing air cavity in exhaust valve stem as properties and design are major parameters causing dilution, knocking and short life span of exhaust valve. In order to fabricate the modified design which are time consuming and in turn affect manufacturing process in the market? An alternate approach is to utilize
valve. This method significantly shortens the design cycle by reducing the number of physical test required. KEYWORDS: CFD, Exhaust Value, IC Engine, FEM, HT
Received: Dec 25, 2015; Accepted: Dec 29, 2015; Published: Jan 06, 2016; Paper Id.: TJPRC:IJHMTJUN20161
INTRODUCTION
Original Article
computational methods such as computational fluid dynamics (CFD) to analyze the characteristics property of the exhaust
Exhaust valves are utilized in 4-stroke internal combustion engine to allow the exhaust gases to escape into the exhaust manifold. Due to the exposure to high temperature gases, exhaust valve design is of crucial interest. Apart from high thermal stresses, these valves are also exposed to cyclic mechanical stresses doing opening and closing, causing them to fail prematurely. High temperature is also responsible for decrease in hardness and yield strength of valve materials, and also causes corrosion of exhaust valve. The use of computational fluid dynamic analysis is rapidly gaining importance with regard to work in this exhaust valves. The accuracy of the results obtained has increased considerably with the advent of computational methods. “CFD analysis of Optimizing IC Engine Exhaust Valve Design” was carried out by Karan Soni et al [1]. This article aimed to identify possible design optimization of the exhaust valve for material and weight reduction without affecting the thermal and structural strength. “Diesel Engine exhaust valve design, analysis and manufacturing process” using CFD analysis was done by Singaiah et al [2]. The purpose of the work was to design the exhaust valve using theoretical calculation. Valve Train is the set of components in a 4-stroke engine, responsible for smooth functioning of the inlet and exhaust valve. It makes the valve to open and close as per the timing required for the precise functioning of the engine. The performance of the engine is severely depends proper functioning of valve train. Any malfunctioning in the valve train system could even lead to severe damage to the engine.
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Georgie S Puthanpurackal, Mohamed Raffi Ichangi, Grithen Pinto & Kripa M. S
Manufacturing process that is 2D drawings is drafted from the calculation and 3D model and transient thermal analysis was done on exhaust valve in its open and close position. “Design and Transient Thermal Analysis of a Diesel Engine outlet Bi Metal Valve for Open and Closed condition” was worked by Venubabu P et al S [3]. From [4] the theory about valve assembly, engine parts material and conventional positions of valve
Figure 1: Typical Valve Train Assembly Engine Valve is one of the main parts which are used in all IC Engines. Each cylinder in the engine has one inlet and one exhaust. Figure 1 shows the pictorial representation of the value train. •
The inlet which allows air and fuel mixture into the cylinder.
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Whereas the exhaust valve allows burnt gases to escape from the cylinder to atmosphere. The exhaust valve is made smaller in size when compared to the inlet .By using small sized exhaust valve the
knocking is reduced but due to small mall opening on the cylinder head the exhaust gases completely won’t escape through the manifold during exhaust stroke. This result in presence of exhaust gases inside the combustion chamber. During intake stroke, when the fresh fuel mixes with the exhaust gas, the charge gets diluted and this results in un-burnt un charges left inside the chamber. These un-burnt burnt charges give out emission and also result in increased fuel consumption, affecting the performance of the engine.
Fig Figure 2: Design of Value Dimension
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Computational Fluid Dynamics Simulation of Exhaust Values in an IC Engines
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EXPERIMENTAL SET UP Purpose of Redesigning Exhaust Valve •
From Figure 2 the basic design of the exhaust valve is designed in such a way to alter the diameter and material to get better efficiency than the existing one.
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The design of the exhaust valve is poppet valve.
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To reduce the mixing of burnt gas and fresh charge inside the combustion chamber.
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To reducing the emission and utilize fuel completely.
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To reduce the rapid pressure rise inside the combustion chamber (knocking).
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To increase the turbine efficiency in turbo chargers.
Finite Elemental Analysis (FEM) and Heat Transfer (HT) Studies The finite element method is a numerical procedure that can be used to obtain solutions to a large class of engineering systems, including stress analysis, heat transfer, fluid flow and electromagnetism. Experimental analysis may help the researcher understand where these stresses arise in a component, hence lead to the prevention of such outcomes. Finite element analysis may support experimental findings and predict results for more complex situations. There are many finite element method software programs available to yield various engineering solutions. The rate of heat transfer mainly depends on the cross sectional area on which the heat transfer is taking place and the thermal conductivity of the material. For two different diameters with two different materials were applied with boundary conditions, Analysis shows that with increase in diameter, rate of heat transfer increase and heat flux drops. Therefore with increase in diameter there is possibility of knocking also increase due to high surface high temperature region on the seat of the exhaust valve. Hence the possibility of knocking is reducing by changing the material used in the exhaust valve. The exhaust valves are usually made of high resistance material like Aluminum alloy whose thermal conductivity is 177w/mk. Titanium alloy is used as an alternative material which has a thermal conductivity of 22 w/mk. Exhaust Seat diameter is 23.40mm and the length of the valve stem is 81.18mm.The diameter is modified to 26.00mm (inlet valve diameter remains the same) with no change in diameter. Due to the increase in cross sectional area and change in material the rate of heat transfer is increased which in turn reduced the hot spot- high temperature region on the valve seat there by reducing knocking possibilities. Thermal analyses are made for the modified valves with same assumptions.
CFD ANALYSIS DATA ANSYS multi physics from ANSYS 15.0 is used for analyzing the design. The basic boundary conditions are as follows Table 1: List of Boundary Condition for the Analysis Study Material Mesh Specific heat: Density Thermal Conductivity www.tjprc.org
Aluminium Tetrahedral 904 J/Kg K 2404kg/m3 177w/mk
Titanium Tetrahedral 504 J/Kg K 4620 kg/m3 22 w/mk
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Georgie S Puthanpurackal, Mohamed Raffi Ichangi, Grithen Pinto & Kripa M. S
Diameter Length Air cavity
Table 1: Contd., 23.40mm & 26mm 81.18mm Present Absent
23.40mm & 26mm 81.18mm Present Absent
The analyses of redesigned exhaust valve data are given in table 1. By varying the parameters the results were found and the conclusions were drawn.
Figure 3: Nodal Temperature Distribution in Aluminium
Figure 5: Meshing of the Exhaust Valve Ф 23.40mm
Figure 7: Nodal Temperature Distribution in Titanium www.tjprc.org
Figure 4: Nodal Temperature Distribution in Aluminium
Figure 6: Meshing of the Exhaust Valve Ф 26mm
Figure 8: Nodal Temperature Distribution in Titanium
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Computational Fluid Dynamics Simulation of Exhaust Values in an IC Engines
Figure 9: Heat Flux Variation of Modified Exhaust Valve
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Figure 10: Heat Flux Variation of Modified Exhaust Valve
Stem Modification The stem is introduced with an air cavity and stress and deformation is compared with the completely solid stem.
Figure 11: CAD 3D Model without Air Cavity
Figure 13: Total Deformation in Aluminium Valve
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Figure 12: CAD 3D Model with Air Cavity
Figure 14: Total Deformation in Titanium Valve
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Georgie S Puthanpurackal, Mohamed Raffi Ichangi, Grithen Pinto & Kripa M. S
Figure 15: Stresses in Aluminium Valve for Dia of 26mm
Figure 16: Stresses in Titanium Valve for Dia of 26mm
Figure 17: Total Deformation of Aluminium Valve with Air Cavity
Figure 18: Total Deformation of Titanium Valve with Air Cavity
Figure 19: Stress in Aluminium Valve with Air Cavity
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Figure 20: Stress in Titanium Valve with Air Cavity
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Computational Fluid Dynamics Simulation of Exhaust Values in an IC Engines
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RESULTS AND DISCUSSIONS Comparing the output from figure 3 & 4, the increase in diameter increases the rate of heat transfer as area of cross-section increases. The increase in diameter increases the minimum temperature at the stem end. The above analysis shows that rate of heat transfer increase with increase in diameter; hence the diameter of the valve as 26.00mm is selected. The max temperature is 900˚C and min temperature obtained is 35.4373˚C for the diameter of 23.40mm using aluminium material. The max temperature is 900˚C and min temperature obtained is 35.4386˚C for the diameter of 26mm using aluminium. Figure 5 & Figure 6 represent the mesh used for the analysis. Tetrahedral mesh with fine grain was used for analysis. For both the material same meshing were used. Using titanium as material for analysis, the maximum temperature was seen at 900˚C and minimum temperature is 30˚C. The diameter of 23.40mm was used, when comparing these results with diameter of 26mm, the maximum temperature obtained is 900˚C and minimum temperature drops to 0.17e-3˚C. Here we observe that maximum temperature has no change whereas minimum temperature drops drastically low. This is due to high thermal resistance of titanium when compared to aluminium. This is supported in figure 7 & 8. From Figure 9 the max heat flux is 140498 W and min heat flux is 0.229e-05 W for the diameter 23.4.mm using titanium. From figure 10 the max heat flux is 127495 W and min heat flux is 0.510e-6 W for diameter 26mm using material titanium. The stem end temperature of aluminium is 35.4386˚C and the stem end temperature of titanium is below 1˚C.Since the end temperature of Titanium is less than Aluminium hence Titanium is demanded as best material for valve as Titanium has higher thermal resistance. The Figure 11 and 12 shows the 3D representation of exhaust values without and with air cavity. The analysis is done by CFD and the results obtained from Figure (13-18), we observe that deformation increases as diameter increases. Deformation is more in aluminium when compared to titanium. The presence of air cavity proves beneficial when it is compared with the absence of air cavity. As both the materials are ductile there stress are approximately same in both materials. Figure 19 and 20 shows the stress distribution. This stress shows no much difference which significantly affect the exhaust values. Hence materials plays important role. As the diameter of 26mm is excellent the stress and deformation calculations were done only for this diameter. The above results show no much difference is the two models hence exhaust valve with air cavity selected as the results obtained through numerical analysis suggest that the valve design can be optimized to reduce its weight, without affecting permissible stress and deformation values. The weight of the valve is reduced by 10%, which can be further reduced using the same procedure.
CONCLUSIONS The drawings were imported from Solid Edge in IGS format. The work analyzed the fluid dynamic behavior of a multivalve internal combustion engines by varying the diameter and length of exhaust values with and without air cavity. Also aluminium and titanium materials were used for studying its role in exhaust value. It was found that heat flux and temperature distribution at the inlet of the exhaust valves is not uniform, which is resulting in un-burnt fuel. CFD analyses exposed that, using titanium as a material for exhaust values gives good thermal resistance when compared it with aluminium. The presence of air cavity proves significantly important in redesigning exhaust valve. The weight is reduced and strength increases. Considering mass production significant amount of material can be saved, helping in reduction of the manufacturing costs.
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Georgie S Puthanpurackal, Mohamed Raffi Ichangi, Grithen Pinto & Kripa M. S
REFERENCES 1.
Karan Soni, S. M. Bhatt, Ravi Dayatar, Kashyap Vyas, “Optimizing IC Engine Exhaust Valve Design Using Finite Element Analysis”, International Journal of Modern Engineering Research (IJMER), Vol.5, Issue 5, May 2015, and ISSN: 2249-6645.
2.
Singaiah Gali, Charyulu T.N, “Diesel Engine Exhaust Valve Design, Analysis and Manufacturing Processes” ,Indian Stream Research Journal , Vol.2, Issue 7 , Aug. 2012, ISSN 2230-7850.
3.
Venubabu P , Chandrasekhar Reddy S, “Design and Transient Thermal Analysis of a Diesel Engine outlet Bi Metal Valve for Open and Closed condition”, International Journal and Magazine of Engineering, Technology, Management and Research, Vol.1, Issue 9, ISSN:2348-4845.
4.
Giri N.K, “A Textbook on Automobile Mechanics”, 8th edition, 5th reprint 2011 Khanna Publication, pp 113-204.
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