2009

University at Buffalo UB By Sumit Tripathi, Prabhdeep Singh Parmar

[FINAL PROJECT 577] Final Report

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Contents OBJECTIVE ....................................................................................................................................................................... 3

The Compressor Assembly: .............................................................................................................................................. 4

Connecting Rod:............................................................................................................................................................... 5

Liner ................................................................................................................................................................................ 8

Crank Shaft .....................................................................................................................................................................10

Suction Valve ..................................................................................................................................................................15

Piston .............................................................................................................................................................................17

Piston rings .....................................................................................................................................................................22

Relief Valve .....................................................................................................................................................................24

Air Inlet/Outlet Housing: .................................................................................................................................................25

Water and Air connection box:........................................................................................................................................27

Cooler .............................................................................................................................................................................28

Cylinder Head .................................................................................................................................................................30

Water Separator: ............................................................................................................................................................32

Exploded View ................................................................................................................................................................36

Mechanism Analysis of Crank and Piston:........................................................................................................................37

Conclusions .....................................................................................................................................................................39

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OBJECTIVE Prime objective of this project is to model a single stage air compressor using Pro/E. The modeling is

accomplished based on the functioning of air compressor.

Some of the design challenges like buckling of connection rod, stress analysis of liner, piston, crank

shaft etc. are addressed using Pro/Mechanica.

Finally we have shown the animation of rotating and translating components of compressor using

Pro/Mechanism

Design Specifications:

Bore: 130mm

Stroke length: 100mm

Working Pressure: 10 Bar

Speed: 900 Rpm

Through put : 860

MATERIAL : Steel, high strength alloy ASTM A514 , Yield strength690 (MPa)

hrm /3

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The Compressor Assembly:

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System Components

Connecting Rod:

Bearing Shells

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Connecting rod is subjected to varying axial /lateral loading. The maximum loading is achieved when piston is

at top position while in upward stroke. At this point of time all of the load passes through axis of the

connecting rod.

The connecting rod is considered as long column for buckling analysis.

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Load Applied= piston area* maximum applied pressure

=𝜋 × 𝑟2𝑃 = 𝜋652 × 1 = 13273 𝑁, 𝑤𝑕𝑒𝑟𝑒 max 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 10 𝑏𝑎𝑟 = 1𝑀 𝑃𝑎𝑠𝑐𝑎𝑙

Buckling load is calculated based on Euler equation

Where, C depends on the loading condition. In our case we have taken pinned-pinned column.

Hence, C=1;

E= young’s modulus= 199948 MPa.

I= Area Moment of inertial of the cross section of the beam. = 20 ∗ 83 ∗ 106 𝑚2 = 10240 × 106 𝑚2

𝐵𝑢𝑐𝑘𝑙𝑖𝑛𝑔 𝐿𝑜𝑎𝑑 = 1 ×𝜋2199948 × 106 × 10240 × 106

12 × 0.2402= 29235.6𝑁

𝐵𝐿𝐹 =𝐵𝑢𝑐𝑘𝑙𝑖𝑛𝑔 𝑙𝑜𝑎𝑑

𝐴𝑝𝑝𝑙𝑖𝑒𝑑 𝑙𝑜𝑎𝑑=

29235.6

13273= 2.2

Clearly our hand calculation matches with PRO/Mechanica results

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2

L

EICPcr

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Liner FEM Stress Calculations:

Liner has backup from the jacket of the compressor, which in turn is strengthened by stiffener. The actual

modeling for FEM will take very high computation cost. However, we can simplify with the understanding of

the loading conditions. We have modeled liner as a thick plate with a hole for FEM computation. The

symmetry in the loading allows us to take only quarter section of the model.

Loading Description:

Pressure load of 1 N/mm^2 applied through cylindrical coordinates, in radial direction. Top and left most surfaces are constrained in all degree of freedoms.

H1

H2

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H3

Mesh Refinement: FEM solutions might be less reliable, if the elements involved in FEM computations are too stiff, i.e. the angle between the edges of the element. This happens because of difficulty in fitting the polynomial over sharp corners of elements. My Approach in Mechanica: Increase the minimum allowable angle between edges so that better polynomial curve fitting is achieved. This process in effect increases the number of elements to mesh volume. We did this in conjunction with reduction in aspect ratio and increment of manual nodes

H1

H2

H3

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Liner Von Mises Stress Convergence

Mesh

Refinements

Max Stress in axial

direction(yy) N/mm^2

%Convergence

h1 11.81 11.73

h2 12.89 3.65

h3 13.23 1.13

Exact Solution 13.38

Maximum stress is well within the safe working stress, i.e. Yield strength /safety factor (690/2 = 345Mpa)

Crank Shaft

Crank shaft is modeled to support connecting rod and provide rotation torque to the bottom end of

the connecting rod.

For lubrication of the bottom end bearing and leading lubrication of gudgeon bearing and liner hole is

drilled through the crankshaft axis and the crank pin.

Collar is given at one end to support flywheel.

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

h1 h2 h3

%C

on

verg

ence

Liner Von Mises Stress Convergence

Series1

100

Sex

SfeSex

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Drilled Holes for lubrication oil

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FEM Analysis of Crank Pin:

As discussed previously crank is also subjected to maximum loading, when piston is at top position while in

upward stroke.

The pressure load on the crank pin

=𝐶𝑟𝑎𝑛𝑘 𝑝𝑖𝑛 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎

𝑃𝑖𝑠𝑡𝑜𝑛 𝑡𝑜𝑝 𝑎𝑟𝑒𝑎 𝐼𝑛𝑐𝑙𝑢𝑑𝑖𝑛𝑔 𝑃𝑖𝑠𝑡𝑜𝑛 𝑟𝑖𝑛𝑔𝑠 × max 𝑝𝑟𝑒𝑠𝑢𝑟𝑒 𝑙𝑜𝑎𝑑 𝑖𝑛 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟

=2𝜋𝑟𝑕

𝜋𝑟𝑝2× 10 𝑏𝑎𝑟 =

2𝜋20 ∗ 50

𝜋652∗ 10 = 4.7 𝐵𝑎𝑟

Crank pin at any particular moment acts like simply supported beam, i.e. all degrees of freedom at ends are

fixed.

Now we can model our crank pin in Mechanica to study stress distribution.

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Above study states that maximum stress is achieved at outer periphery of the crank pin.

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Modeling concentric shaft of bearing:

This part of the connecting rod can be

modeled as cantilever beam, if we take

half load on the shaft.

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One fixed end has one degree of motion i.e. rotation about shaft axis. The other end is taken as free, while half

of the total load is applied.

Load Applied= piston area* maximum applied pressure

=𝜋 × 𝑟2𝑃 = 𝜋652 × 1 = 13273 𝑁, 𝑤𝑕𝑒𝑟𝑒 max 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 10 𝑏𝑎𝑟 = 1𝑀 𝑃𝑎𝑠𝑐𝑎𝑙

Half load applied=13273

2𝑁 = 6636.5𝑁

Length=180 mm

There was some hit and trial(say sensitivity analysis) to reach to upto this point.

Suction Valve • Modeling challenge:

– Concentric air passage for suction and discharge air.

– Space restriction rendering into limitation in spring design.

• Solution

– Suction and discharge passages are cut in the same plate.

– Plate springs help resolve the limitation of space.

– Carefully designed passage in cylinder head lead to quick functioning of compressor.

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Discharge Spring

Suction Spring

Outer Two Ports act like discharge ports

Inner Three Ports act like sunction ports

Suction Valve Plate

Discharge Valve Plate

Suction Spring

Discharge Spring

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Piston

Curved slots to allow swivel motion of

connecting Rod

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Drawing of piston

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FEM Analysis of Piston:

Piston is constrained at holes for gudgeon pin in all degree of freedom only rotation about axis of the hole is

left unconstrained.

Load is applied on top surface,

Load Applied= piston area* maximum applied pressure

=𝜋 × 𝑟2𝑃 = 𝜋652 × 1 = 13273 𝑁, 𝑤𝑕𝑒𝑟𝑒 max 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 = 10 𝑏𝑎𝑟 = 1𝑀 𝑃𝑎𝑠𝑐𝑎𝑙

After analysis we observe that the maximum stress occurs at the outer part of holes .

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The dip in the stress is seen because we are calculating stress in

piton’s upward movement, at time when it is reaching top. Most

of the load is on upper half of the gudgeon pin hole.

In pistons downward movement we can see the graph will be

reversed, however the magnitude is decreased. Our objective is

study maximum stress conditions, that is why we don’t discuss

downward movement.

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Piston rings

Piston Rings are supported at piston ring grooves. We have applied the pressure axial load of 10bar on top

surface. The thickness of piston ring is appropriate as it does not allow any stress built up more than the 10%

of the yield strength.

Piston Ring BUTT clearance

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Piston ring Butt

clearance

Top Round surface to smear oil on

to the line clearance

Bottom straight surface to scrap off oil from

the liner surface while downward stroke of

piston, so that oil is not carried away with

compressed air discharge when piston is

going upwards

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Relief Valve

Top screw is provided to adjust lifting pressure of relief valve.

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Air Inlet/Outlet Housing: It is designed to facilitate concentric suction and discharge air passages, as discussed in suction valve:

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Discharge air passage

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Water and Air connection box: It facilitative air and water channels to separate out from each other.

Water Side

Air Side

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Cooler

The compressor uses water tube cooling coil to cool the compressed air. The water enters through a water /

air box as shown previously, in which we have separate channel for water and air, sealed by a gasket.

(Water tubes) Cooling

coils

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Cylinder Head Cylinder head facilitate assembly of suction/delivery valve , guide air to air cooler and acts like cover of air

compressor, which seals air inside it.

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Water Separator: Atmospheric air contains moisture in it which will get condensed when large volume of air is compressed into

very small volume. We need to separate out water from it before storing it in Air Bottles.

This purpose is solved by water separator as shown in the figure

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Compressor Jacket:

Functions:

For supporting liner. (Acting like stiffener for liner)

Allowing compressed hot air to circulate through cooling coils.

Some other Components:

Liner Support

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Exploded View --------_______________________________________________________________________________

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Mechanism Analysis of Crank and Piston: Crank shaft is rotating at constant velocity of 360degree/sec

Small end connection(piston and connecting rod) pin velocity and position

Animation is sent to digital drop box

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Crank shaft velocity and position

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Conclusions 1) Mesh refinement bases on maximum turn angle for FEM analysis work well to get good convergence

2) Specifying Manual nodes also helps to get good convergence.

3) Beam analysis of PRO/Mechanica are very accurate as they almost exactly match with hand calculations.

4) Mechanism helps to study animation of rotating components very well.