To account for the strong dependence on temperature, a viscosity ratio was used in Equation 5, in which [[micro].sub.w] is the dynamic viscosity based on wall temperature and [[micro].sub.aw] is the dynamic viscosity based on adiabatic wall temperature. The adiabatic wall temperature is an estimate of the oil temperature near the impingement area, taking into account viscous dissipation in the high Prandtl oil jet as it approaches the stagnation zone at the piston surface.
where h is convective heat transfer coefficient, [T.sub.w] is the local wall temperature and [T.sub.aw] is the adiabatic wall temperature, which is used in place of the free stream fluid temperature.
The piston surface temperature, [T.sub.w], was an area-weighted undercrown temperature, and the adiabatic wall temperature (jet temperature) was determined using Equation 10.
[T.sub.aw] - adiabatic wall temperature, [degrees]C