In this work, an effort has been designed to raise the reliability of engine using Al-Sic composites with other alternatively materials for the engine valve guides. Aluminum matrix composites have found the most suitable inside automotive, aerospace and aircraft industries and contain the greatest promise for future year’s growth. The finite element analysis of the Al-Sic composite with Titanium alloy (Ti-834), Copper Nickel Silicon alloys (CuNi3Si), and aluminum bronze alloy as an alternative material for engine valve guide was done using Ansys 13.0 software. The stress analysis of engine valve guide under the different pressure and temperature is considered, the pressure is taken as from 10 MPa to 100 MPa with different temperatures varying from 600 ℃ to 650 ℃. The temperature, principal stress and principal strain distribution on the entire surface area of the engine valve guide were obtained. The stresses were observed to be well below the permitted stress for all the materials but the Al-Sic composites found the most suitable one. Valve guide is modeled in pro-engineer software and analysis is carried out in Ansys 13.0. The deformations and stresses induced due to structural and thermal loading is illustrated and discussed.
In reaction to increasing worldwide competition and developing concern for environment, the auto manufacturers have already been encouraged to meet up the conflicting demands of increased power and performance, lower fuel consumption, lower pollution emission and reduced vibration and noise. To be able to fulfill these newer and emerging needs, the automobile industry has acknowledged the necessity for materials substitution. Metal matrix composites are providing outstanding properties in a true number of automotive components such as for example piston, cylinder liner, engine valves, brake discs, brake drums, clutch discs, linking rods etc. Several function has been documented on the substitution of presently utilized materials by the aluminum matrix composites for various automotive parts viz. piston, cylinder liner, engine valves, valve seat inserts etc. Al-Sic composite engine valve guides have already been fabricated through powder metallurgy and casting processes. The radial crushing strength, hardness, and wear resistance of the Al-SiC cast and composite iron engine valve guides were measured and compared. Al-SiC composites with 5 to 30 wt.% of SiC were discovered to have increased Rockwell hardness and radial crushing strength compared to the cast iron engine valve guides. Al-SiC composite engine valve guides with 20 and 30 wt.% of SiC were discovered to possess higher wear level of resistance compared to the cast iron engine valve guides. Existing work incorporates the finite element strategy to include the prospects of Al-SiC composites just as one alternative material for the engine valve guides. The finite element Analysis of the engine valve guides was done making use of Ansys 13.0 software program. Temperature, displacement and pressure boundary conditions were used and the temperature, stress and stress distribution on the entire surface area of the engine valve guides was obtained. Aluminum alloys have discovered greater adoption while potential matrix materials in comparison to some other alloys.
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Issue of sustainbility, stability, durability and reliebility of prsent material for engine guide valve at high tempreture about 600˚C to 1000˚C under very high pressure about 10 mpa - 100 mpa.
At the moment the engine valve guides are made of iron-based materials, which result in a true amount of problems within an automotive engine
· During cold start condition the viscosity of oil is high and also sufficient lubricant is not available therefore high wear of the valve stem/valve guide takes place. In the adverse conditions the valve may jam in the guide.
· During running condition of the engine the temperature of the valve stem and valve guide increases to about 500˚C. Therefore at high temperature the clearance between valves stem and valve guide decreases due to thermal expansion, which results in high wear of the valve stem and the guide.
· The superimposed rocking motion in addition to the sliding of the engine valve causes high wear at the ends of the valve guide called “bell-mouthing”, generally more pronounced in the rocker arm actuation mechanism.
These problems call for a high wear resistant material with low coefficient of thermal expansion and engine valve guides based on the Al-SiC composites are expected to provide a better solution.
Al SIC composites
Mechanical properties
Thermal properties
Properties
Properties
Modulus of elasticity X-Direction (Pa)
1.3e+011
Thermal expansion coefficient X-Direction
1.6e−006
Major Poisson’s ratio Z-Plane
0.32
Minor Poisson’s ratio Z-Plane
0.32
Density (kg/m3)
8870
Thermal conductivity X-Direction (w/m.k)
230
To understand the problem of wear and decreasing the clearance the clearance due to temperature change at various load condition, firstly have to analyze the temperature distribution in the valve and valve guide.
Typically we take example of exhaust valve temperature distribution in spark ignition engine of V-8 car with full throttle (3500 r/min). During expansion stoke the temperature of the burnt gases is about 600˚C - 800˚C. These hot burnt gases get impact with head of poppet valve and head of poppet valve conduct the heat through various portion of poppet valve.
· Small part about 30% of the heat is conducted through valve seat and remaining 70% heat conduct through valve stem.
· 25% heat conducted through valve stem is further conduct through valve guide.
Due to this impact of hot gases, the temperature at the center of head is maximum about 700˚C and further distributed at various element, nodes and section as shown in figure below.
Temperature at the starting section of valve stem is 613˚C and at the open end of valve guide is about 580˚C and further temperature distribute in different nodes and elements as shown in the figure below and at other end of valve guide the temperature is about 390˚C.
At this temperature range, materials which are currently used for guide valve expands due to which the clearance between valve stem and valve guide get reduced which creates a lot of problems in the valve operating system such as:
· Valve stems breakage
· Burnt Valve seat
· Valve Stem to Valve Guide Seizure
· Mechanical Damages
· Excessive Valve Stem & Valve Guide Wear
· Valve Tip Breakage etc.
Finite element method has become one of the most widely used techniques, for analyzing mechanical loading characteristics in modern engineering components. Traditional analysis techniques can only be satisfactorily applied to a range of conventional component shapes and specific loading conditions. Unfortunately, the majority of engineering loading situations are not simple and straight forward therefore the traditional techniques often need to be modified and compromised to suit situations for which they were not intend. The uncertainty thus created, commonly leads to the designer applying excessively high factor of safety to the mechanical loads and so to over design components by specifying either unnecessarily bulky cross section or high quality materials, inevitably the cost of the product is adversely affected.
Before using Valve guide in the I.C. Engine first of all we have to check its deformation, Vonmises stresses- Strain value, Maximum & Minimum principle stress-strain and its failure point at every load conditions. FEA is the best method of determining the deformation, Vonmises stresses-Strain value, Maximum & Minimum principle stress-strain and its failure point at each and every load conditions. Main advantage of FEA is that it converts the problem into a number of elements and nodes and then solve problem and give the result at every element and node. It also State that at which node the material is going to fail at which load condition. Therefore this can make our material safe in all load condition. In this way, FEM is applied (using Ansys software ) on Valve guide for making a comparative study of Aluminium silicon carbide of different compositions with other materials (which are currently in use):
· Titanium alloy (Ti-834) (used in racing Cars).
· Copper Nickel Silicon Alloy (CuNi3Si) (used in locomotive).
At different load conditions such as:
Different temperatures varying from 550˚C to 1000˚C.
Pressure varying from 10 MPa to 100 MPa.
Modeling has been carried in pro-engineering software. The Engine guide valve is drawn in Pro-E (
Analysis of guide valve is carried over in following steps.
Guide valve model has been modeled in the pro-engineer as shown in
Case I: When the pressure is 10 MPa and 1 MPa and temperature is 600˚C and 400˚C.
From the resultant variation (
From the resultant variation (
From
Result/Material | Al 10% composites | Al 20% composites | Al 30% composites | Titanium Alloy (Ti 834) | CuNi3Si Alloy |
---|---|---|---|---|---|
Deformation | 0.0169 mm | 0.01436 mm | 0.0123 mm | 0.0778 mm | 0.124 mm |
there the guide valve will be safe. And when the von mises stress are more than the yield stress than the structure will be failed.
Case II: When the pressure is 50 MPa and 5 MPa and temperature is 600˚C and 400˚C.
The pressure load of 50 Mpa at bottom and 5 MPa, at top and temperature of 600˚C, at bottom and 400˚C at top is applied and deformations and stresses are computed on guide valve.
Case III: When the pressure is 100 MPa and 10 MPa and temperature is 600˚C and 400˚C.
The pressure load of 100 Mpa at bottom and 10 MPa, at top and temperature of 600˚C, at bottom and 400˚C at top is applied and deformations and stresses are computed on guide valve.
Case IV: When the pressure is 10 MPa and 1 MPa and temperature is 650˚C and 450˚C.
The pressure load of 10 Mpa at bottom and 1 MPa, at top and temperature of 650˚C, at bottom and 450˚C at top is applied and deformations and stresses are computed on guide valve.
Static and thermal analysis is carried over guide valve. The guide valve is analyzed for different pressure load cases (as shown in Tables 1-5). At a pressure of 10 MPa and 1 MPa and temperature 600˚C and 400˚C, the maximum deformation is 0.124 mm and maximum stress is found to be 286.31 MPa (CuNi3Si Alloy). Stresses developed for this pressure for all the materials are less than their respective yield strength. In the same way when the guide valve is analyzed for the different set of pressure and temperature parameters (i.e. pressure 50 MPa and 5 MPa and temperature is 600˚C and 400˚C), (pressure 100 MPa and 10 MPa and temperature is 600˚C and 400˚C), (pressure is 10 MPa and 1 MPa and temperature is 650˚C and 450˚C) the max deformation is found to be 0.2268 mm, 0.1816 mm, 0.1244 mm respectively and max stress is found 338.30 MPa, 340.94 Mpa, 367.18 Mpa in CuNi3Si Alloy. However, it has been observed that at high temperature the stresses produced in Al-SiC composites are very less as compared to other materials at different parameters (pressure & temperature
Load (MPa) | Temp ˚C | |||||||
---|---|---|---|---|---|---|---|---|
Max (bottom) | Min (Top) | Max (bottom) | Min (Top) | Material | Max. deformation, mm | Von-mises, MPa | Safety/Failure | Material yield stress MPa |
10 | 01 | 600 | 400 | Al 10% composites | 0.0169 mm | 23.06 MPa | Safe | 257 MPa |
10 | 01 | 600 | 400 | Al 20% composites | 0.01436 mm | 21.79 MPa | Safe | 263 MPa |
10 | 01 | 600 | 400 | Al 30% composites | 0.0123 mm | 20.09 MPa | Safe | 269 MPa |
10 | 01 | 600 | 400 | Titanium Alloy (Ti 834) | 0.0778 mm | 165.39 MPa | Safe | 910 MPa |
10 | 01 | 600 | 400 | CuNi3Si Alloy | 0.124 mm | 286.31 MPa | Safe | 550 MPa |
Load (MPa) | Temp ˚C | |||||||
---|---|---|---|---|---|---|---|---|
Max (bottom) | Min (Top) | Max (bottom) | Min (Top) | Material | Max. deformation, mm | Von-mises, MPa | Safety/Failure | Material yield stress MPa |
50 | 5 | 600 | 400 | Al 10% composites | 0.0564 mm | 60 MPa | Safe | 257 MPa |
50 | 5 | 600 | 400 | Al 20% composites | 0.05034 mm | 59.79 MPa | Safe | 263 MPa |
50 | 5 | 600 | 400 | Al 30% composites | 0.04662 mm | 61.94 MPa | Safe | 269 MPa |
50 | 5 | 600 | 400 | Titanium Alloy (Ti 834) | 0.12907 mm | 200.33 MPa | Safe | 910 MPa |
50 | 5 | 600 | 400 | CuNi3Si Alloy | 0.2268 mm | 338.30 MPa | Safe | 550 MPa |
Load (MPa) | Temp ˚C | |||||||
---|---|---|---|---|---|---|---|---|
Max (bottom) | Min (Top) | Max (bottom) | Min (Top) | Material | Max. deformation, mm | Von-mises, MPa | Safety/Failure | Material yield stress MPa |
100 | 10 | 600 | 400 | Al 10% composites | 0.192 mm | 129.65 MPa | Safe | 257 MPa |
100 | 10 | 600 | 400 | Al 20% composites | 0.16189 mm | 131.94 MPa | Safe | 263 MPa |
100 | 10 | 600 | 400 | Al 30% composites | 0.1268 mm | 132.93 MPa | Safe | 269 MPa |
100 | 10 | 600 | 400 | Titanium Alloy (Ti 834) | 0.00986 mm | 202.87 MPa | Safe | 910 MPa |
100 | 10 | 600 | 400 | CuNi3Si Alloy | 0.1816 mm | 340.94 MPa | Safe | 550 MPa |
Load (MPa) | Temp ˚C | |||||||
---|---|---|---|---|---|---|---|---|
Max (bottom) | Min (Top) | Max (bottom) | Min (Top) | Material | Max. deformation, mm | Von-mises, MPa | Safety/Failure | Material yield stress MPa |
100 | 10 | 600 | 400 | Al 10% composites | 0.020315 mm | 25.968 MPa | Safe | 257 MPa |
100 | 10 | 600 | 400 | Al 20% composites | 0.01734 mm | 26.183 MPa | Safe | 263 MPa |
100 | 10 | 600 | 400 | Al 30% composites | 0.01625 mm | 29.314 MPa | Safe | 269 MPa |
100 | 10 | 600 | 400 | Titanium Alloy (Ti 834) | 0.0778 mm | 216.61 MPa | Safe | 910 MPa |
100 | 10 | 600 | 400 | CuNi3Si Alloy | 0.1244 mm | 367.18 MPa | Safe | 550 MPa |
both) from the results obtained finally, it is figured that Al/sicp is suitable materials for high temperature applications i.e. Turbo charged engines, racing cars, diesel loco engines air craft engines where cost is not a major factor.