Finite Element Investigation of a Piston Assembly of a Diesel Engine
Authors: Rahman Mosfequr , Mitra Aniruddha , Salekeen Sirajus , Buentello Jeremy , Harden Tyler , Masocol Timothy 
Published: February 2017

Ensure a safe, long life and efficient combustion within a diesel engine is an important challenge in the applications of engine technology. Much research has been done on thermal stress within engine cylinders and on engine piston heads, and how to reduce some of this stress in order to prevent failure or increase the life of the engine. The failure of a piston head tends to occur from it enduring the gas effect of the high pressures and temperatures. By performing static and dynamic Finite Element Analysis (FEA) on a piston mechanism of a diesel engine proper dimensions for different parts of an engine can be determined and failure of an engine in service can be avoided. In this research finite element analysis has been performed to determine the total deformation, stresses, and other parameters that are essential from design point of views. Real world input data for simulation obtained from running an existing diesel engine have been effectively used. Static structural and dynamic reaction of a piston assembly under the applied load of internal combustion in a diesel engine were closely observed. ANSYS workbench was utilized to perform these simulations. Using SolidWorks a piston assembly model consisting of the piston, connecting pin, connecting rod, cylinder head, crankshaft, and cranks was designed and used for simulation. Simulation results were being collected from the static structural and rigid body dynamics modules.

The static structural simulation was conducted in order to obtain the structural response of the piston assembly under the combustion phase. This simulation was intended to replicate the pressure forces applied to the piston assembly at the moment of combustion. A pressure force of 7 MPa was applied to the top of the piston. From the simulation results, the maximum total deformation 1.9 mm occurred at the top edge of the piston head on the same side as the combustion chamber. Maximum equivalent Von Mises stress 323.9 MPa occurred at the joint of the connecting rod and crankshaft and the minimum equivalent stress 27 kPa occurred at the bottom of the connecting rod. Principal stresses were also examined, where the maximum principal stress 335.1 MPa occurred at the joint of the connecting rod and crankshaft and the minimum principal stress 63.5 MPa occurred inside of the connecting rod joint. The maximum shear stress 177.7 MPa occurred at the joint of the connecting rod and crankshaft and the minimum shear stress 14.26 kPa occurred at the bottom of the connecting rod.

Two types of forces were considered acting upon the geometry in the rigid body dynamic simulation, one is standard earth gravity and the other is a linear dynamic load of 55,000 N applied to the top of the piston head which is used to simulate the act of combustion within the combustion chamber of a cylinder. From the rigid dynamic simulation, it was found that after the first combustion cycle, the linear velocity of the entire system, acceleration of the entire system, and the crank angular velocity reach to the maximum of 24.77 m/s, 17684 m/s2 and 5487 rpm respectively at 0.0187 seconds. Then after the second combustion cycle, the linear velocity of the entire system and the crank angular velocity reach to 27.56 m/s and 6043 rpm respectively at 0.0481 seconds; however the acceleration of the entire system took 0.0551 seconds to reach to 30115 m/s2.