DLC Coated Piston Skirts Behavior at Initial IC Engine Start Up

  • Zahid ur Rehman
  • S. Adnan Qasim
  • M. Afzaal Malik
Conference paper

Abstract

The diamond-like carbon (DLC) based coating protects the lubricant-starved dry surface of the piston skirts against wear in a low-load and speed initial start-up of an internal combustion (IC) engine. Despite a relatively large radial clearance a physical contact between the skirts and the cylinder liner causes an elastic deformation of the DLC coated surface producing elastic stress and strains of noticeable amplitudes. The elastic stress accumulation may facilitate a subsequent de-lamination of the DLC coating. This study develops the numerical piston dynamics model by incorporating the secondary eccentric displacements of the piston skirts and their contact with the engine cylinder liner during the 720-degree crank rotation cycle. The contact zone in the boundary-value problem is discretized using the finite difference method. The elastic surface displacements, stresses and strains are determined by applying the theory of elasticity and solving the Navier’s or Lame’s equation numerically. The nature and extent of the displacements, stresses and strains produced at the interface of a fairly thin DLC coating with the substrate are analyzed. The results highlight the extent of the depth of the elastic surface displacements, the stresses and strains produced in the coating and the substrate materials. The simulation results show that the dry piston skirts establish a physical contact with the liner in the compression stroke that is maintained in the expansion and exhaust strokes. The stresses produced at the low engine start-up speed are significant, increase beneath the surface and accumulate at the interface between the coating and the substrate. The elastic displacements of a fairly thin DLC coating prevents the stress accumulation on the substrate and protects it from adhesive wear.

Keywords

DLC coating Dry contact Elasticity IC engine Initial engine start-up Piston skirt 

Nomenclature

a

Vertical distance from the top of piston skirt to the piston-pin

b

Vertical distance from the top of piston skirt to the piston center of gravity

Cg

Horizontal distance between piston center of mass and piston pin

Cp

Distance of the piston-pin from the axis of piston

ёb,ёt

Acceleration term of piston skirts bottom and top eccentricities

E1, E2

Young’s modulus of coating and piston

F

Normal force acting on piston skirts

Ffc

Friction force due to coulombs’ friction

FG

Combustion gas force acting on the top of piston

FIC

Inertia force due to piston mass

FIP

Inertia force due to piston pin mass

G, μ

Lam’s constants

Ipis

Piston rotary inertia about its center of mass

l

Connecting rod length

L

Piston skirt length

mpin

Mass of piston-pin

mpis

Mass of piston

Mf

Moment about piston-pin due to friction force

ф

Connecting rod angle

r

Crank radius

R

Radius of piston

\( \tau \)

Shear stress

U

Velocity of piston

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Poisson’s ratio of coating and piston

ω

Crankshaft speed

y

Distance to the direction of sliding

x

Normal to the direction of sliding in depth of coating-substrate

z

Normal to the direction of sliding in width of coating-substrate

ψ

Crank angle

Notes

Acknowledgments

This work was sponsored by the National University of Sciences and Technology (NUST), Islamabad, Pakistan. The financial support for this project was provided by the Higher Education Commission of Pakistan.

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Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  • Zahid ur Rehman
    • 1
  • S. Adnan Qasim
    • 1
  • M. Afzaal Malik
    • 2
  1. 1.Department of Mechanical EngineeringNational University of Sciences and Technology (NUST)IslamabadPakistan
  2. 2.Department of Mechanical and Aerospace EngineeringAir UniversityIslamabadPakistan

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