MBD Simulation on a Piston Assembly
Aim: To perform an MBD Simulation on a Piston Assembly and plot the results for the given conditions.
Theory:
Internal combustion engines are seen every day in automobiles, trucks, and buses. The name internal combustion refers also to gas turbines except that the name is usually applied to reciprocating internal combustion (I.C.)
engines like the ones found in everyday automobiles. Spark ignition engines take a mixture of fuel and air, compress it, and ignite it using a spark plug. The name `reciprocating' is given because of the motion that the crank mechanism goes through. The piston-cylinder engine is basically a crank slider mechanism, where the slider is the piston in this case. The piston is moved up and down by the rotary motion of the two arms or links. The crankshaft rotates which makes the two links rotate. The piston is encapsulated within a combustion chamber. The bore is the diameter of the chamber. The valves on top represent induction and exhaust valves necessary for the intake of an air-fuel mixture and exhaust of chamber residuals. In a spark-ignition engine a spark plug is required to transfer an electrical discharge to ignite the mixture.
Problem Statement:
Model all the parts and then assemble them in SolidWorks. The motion analysis is going to be carried out in three different conditions,
| Sl.No |
Wrist Pin Offset ` |
Crank Speed (Rpm) |
| 1 | "0" mm | 2000 |
| 2 | 10 mm Positive | 2000 |
| 3 | 10 mm Negative | 2000 |
Wrist Pin Offset - The position of the wrist pin is going to be varied as followed. But the center of the axis of the piston head and the crank are coincident to each other (i.e) They are on the same plane in all the three cases.
"0" mm Offset - Run a simulation as seen in the video.
10 mm Positive Offset - If the crank rotation is in the Clockwise direction.
10 mm Negative Offset - If the crank rotation is in the Clockwise direction.
Obtain the Linear displacement of the Piston Head in all the three cases. Then export the graphs into Excel. Then Superimpose all the three graphs into a single graph.
Components:
Piston Head: Also known as the piston crown or dome, the head of a piston is its top surface. It is the part that comes into contact with the combustion gases. As a result, it gets heated to extremely high temperatures. To prevent melting, piston head parts are made using special alloys, among them steel alloy.
Wrist Pin: Also known as wrist pin or Gudgeon pin, the piston pin is the hollow or solid shaft in the skirt section. The piston rod pivots on this pin, held in the piston ring bushing. For tensile strength, piston pins are usually built from alloy steel and machined to fit the piston bearing. Holes in the connecting rod deliver oil to the wrist pin, helping to reduce friction.
Connecting Rod & End Cap: Often shortened to conrod or rod, the connecting rod is one of the most important piston parts. It links the piston to the engine’s crankshaft and moves the piston in and out of the combustion chamber. Connecting rods have to bear a lot of mechanical strain and should be sturdy enough. For this reason, the parts are mostly forged, although casting is also frequently used.
Crank: A crank is an arm attached at a right angle to a rotating shaft by which circular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convert circular motion into reciprocating motion, or vice versa. The arm may be a bent portion of the shaft or a separate arm or disk attached to it.
Geometry modeling:
These are the following drawings which were referred to while creating the parts for the Assembly and Simulation process.
Motion Study Setup:
This image shows the body contact being given to the different parts and the rotor is provided with 2000 rpm for all the three cases along with gravity in the y-direction.
We select the fps to be 7200 and use precise contact so that the result we get is an accurate one.
Results:
For 0 mm Offset
We can observe from the graph that the linear displacement of the piston head remains constant throughout the simulation without any undue changes or variations.
For 10 mm positive Offset
We can observe from the graph that the linear displacement of the piston head remains constant throughout the simulation without any undue changes or variations.
For 10 mm negative Offset
We can observe from the graph that the linear displacement of the piston head remains constant throughout the simulation without any undue changes or variations.
After Superposition, we get this graph.
Here we can observe that the no offset and 10 mm negative offset are converged and they differ in their values when compared with the positive offset.
Conclusion:
When the piston and the crank don't have an offset a lot of power has to be spent in order to move the piston up to the TDC from the BDC. So there is an offset pin provided in the wrist pinb which all the piston have a postitive or a negative offset and this in turn gives it an angle which is not exactly straight and hence the power and rpm required to bring it original position reduces and the final speed also increases.
The Simulation on a Piston Assembly is successfully run and the necessary plots and results are achieved.
Animation:
For 0 mm Offset
https://www.youtube.com/watch?v=7pDkToE75jY
For 10 mm positive Offset
https://www.youtube.com/watch?v=HVVtPp-JrSA
For 10 mm negative Offset
https://www.youtube.com/watch?v=frLYN524RBM
CAD Files:
https://drive.google.com/drive/folders/1QA0EQxjlumAvV1CMOYKnZ_tSK8ud-Mlf?usp=sharing
References:
https://www.ijsr.net/archive/v4i6/SUB155788.pdf
https://mzwmotor.com/piston-parts-and-functions/
Project Link: https://skill-lync.com/projects/mbd-simulation-on-a-piston-assembly-144