MBD Simulation of IC Engine Piston Assembly

OBJECTIVE :

• To model a Piston Assembly and to simulate its motion.
• To perform its motion analysis at different values of wrist pin offset.
• To analyse the linear displacement of piston head.

INTRODUCTION :

A slider-crank linkage is a four-link mechanism with three revolute joints and one prismatic, or sliding, joint. The rotation of the crank drives the linear movement the slider, or the expansion of gases against a sliding piston in a cylinder can drive the rotation of the crank. This mechanism is widely used in engines to convert the reciprocating motion of piston into rotational motion at the crank. IC engines, piston slides due to expansion of combustion products.

There are two types of slider-crank mechanisms: in-line and offset.

1. In-line : An in-line slider-crank has its slider positioned so the line of travel of the hinged joint of the slider passes through the base joint of the crank. This creates a symmetric slider movement back and forth as the crank rotates.
2. Offset : If the line of travel of the hinged joint of the slider does not pass through the base pivot of the crank, the slider movement is not symmetric. It moves faster in one direction than the other. This is called a quick-return mechanism.

In this project, I will be analyisng the linear displacement characteristics of the piston head for both in-line and offset cases.

	Wrist Pin Offset	RPM
Case 1	0	2000
Case 2	10 mm (+ve)	2000
Case 3	10 mm (-ve)	2000

Setup Explanation :

1. First, the components are modelled as per known dimensions as shown-

Piston :

Wrist Pin :

Connecting Rod :

End Cap :

Crank :

2. Then the model is assembled using appropriate mates as shown.

3. Now, Solidworks Motion Analysis is used for further motion analysis.

4. RPM is set at 2000 rpm at the crank axis to simulate the motion, and proper contacts are set.

4. Now finally, motion is calculated and plots are made for the given three different cases.

MOTION SIMULATION :

Here is the motion simulation for first case at lower rpm :

RESULTS :

CASE 1: Wrist Pin Offset = 0

CASE 2 : Wrist Pin Offset = 10 mm (+ve)

CASE 3 : Wrist Pin Offset = 10 mm (-ve)

SUPERIMPOSED PLOT :

The 3 graphs are superimposed and the following observations are made. Graph is zoomed in for observation purpose.

1. The max displacement of zero offset case is slightly more than that of +- 10 mm offset.
2. The +10 mm offset case lags behind the 0 mm offset case for the same displacement.
3. The -10 mm offset case leads the 0 mm offset case for the same displacement.

CONCLUSIONS :

1. With offset, the stroke of piston is reduced. This can be used to slightly alter the piston kinematics in an engine.
2. The horizontal lag has no significance since the time period is still the same.
3. Offsetting might prevent the mechanism from locking in a toggle position since the force on connecting rod will never be in line with it. This can make the engine self-starting.

REFERENCES :

1. https://en.wikipedia.org/wiki/Internal_combustion_engine

=================Thankyou================