Abstract:
The automobile manufacturers aspire to improve the engine design and enhance its
life apart from optimizing the energy usage in the actual engine operation. A major
concern at the time of the initial start up at the low loads and speed conditions is
the wear of an engine. A significant proportion of the engine life gets compromised
due to the adhesive engine start up wear. The start up wear does not exist during
the normal engine operation due to the fully established elastohydrodynamic
lubricating (EHL) film between the interacting surfaces of the piston assembly and
the cylinder liner at the high loads, speeds and the optimum piston-to-bore radial
clearances. Such arrangements do not exist in a few initial engine start up cycles.
Resultantly, the piston skirts and the 1st compression ring establish a physical
contact with the liner and adhesive wear occurs. This PhD research work
numerically models the lubrication of the piston skirts and the 1st compression ring
in the initial engine start up. The 2-D hydrodynamic and EHL models of the piston
skirts are developed in the initial engine start up conditions. The initial engine start
up conditions cover the secondary transverse piston displacements and the
different start up speeds, radial clearances & viscosity-grades of an engine
lubricant. The realistic aspects include the isothermal & adiabatic conditions, the
steady-state and transient conditions, the Newtonian and non-Newtonian engine
lubricant behavior, the surface roughness factors of the piston skirts and the liner.
These aspects are modeled, studied and analyzed separately as part of the
hydrodynamic and EHL models of the skirts. The 1-D and the 2-D steady-state
isothermal Newtonian lubrication models of 1st compression ring are developed as
applicable to the initial engine start up conditions. The simulation analysis are
studied to optimize the different realistic aspects/characteristics in an effort to
reduce the engine start up wear.
