MBD Simulation on a Piston Assembly

Objective
To model piston assembly and to do the motion analysis to obtain the linear displacement of the piston head in three different cases

Introduction

Piston assembly consists of the piston head, connecting rod, gudgeon pin, crank and crankpin
The piston is the part of an engine that reciprocates to produce power to rotate the crankshaft. The way the piston moves, the amount of swept volume and the wrist pin offset plays an important role in the power produced inside an engine. In this Project, our concern will be limited to only the wrist pin offset.
Wrist pin offset refers to the piston wrist pin being a bit offset to one side of the piston i.e. not exactly in the centre of the piston. Offsetting the cylinder axis from the crankshaft axis minimizes rod angularity when cylinder pressure is at its highest.
Reduced angularity leads to lower piston thrust forces, hence lower frictional losses during the period of maximum cylinder pressure and hence more power
It also improves the noise characteristics of the engine due to piston slap at the top dead center (TDC)

Piston Assembly

Motion Analysis

S.No Wrist Pin Offset(mm) Crank Speed(rpm)

1 0 2000

2 10(Positive) 2000

3 10(Negative) 2000

10 mm Positive Offset

10 mm Negative offset

Case1:

Case 2:

Case 3:

Result

Linear displacement produced in different cases are :

1. 0 mm offset - 302.708 mm

2. 10 mm positive offset - 302.522 mm

3. 10 mm negative offset - 302.521 mm