This thesis presents research on upward pointing oil jets that provide cooling
of downward facing heated surfaces. The specific purpose of this research is
to improve understanding of the oil jet cooling of internal combustion engine
In this research, the cooling of heated blocks with flat and concave surfaces
was investigated. Temperature measurements were obtained using an array
of thermocouples embedded inside the heated blocks. A flash illumination
and high resolution CCD camera system was used to observe the liquid jet
impingement. Observations identified a 'bell-sheet' flow pattern, jet
interference, jet splatter and jet breakup which provided insights into the
liquid jet impingement processes normally encountered on downwardfacing
Bespoke contracting-type nozzles were used to produce the jet flow
structure. The data from these nozzles were used to generate new empirical
correlations for oil jet cooling of downward-facing flat surfaces and for
predicting the size 6f impingement. The results obtained from these tests
were also used for comparison with cooling jets from production automotive
piston cooling nozzles.
The research has demonstrated that the effectiveness of oil jet cooling can be
affected by preheating the oil and varying the injector size to alter the
targeted cooling efficiency, and liquid loss due to jet breakup and splatter.
Local heat transfer coefficients were observed to increase when the jet
Reynolds number increased. Piston undercrown cooling was studied using a range of oil jet
configurations. The cooling rates improved with optimised targeted jets. The
results also indicated that the undercrown geometry designs such as crosshatched
surfaces, undercrown-skirt and gudgeon-pin boss, were significant
for enhancing the local rate of forced convective heat transfer.
New empirical correlations were developed from the experimental results
that enabled prediction of the heat transfer coefficient and jet impingement
size for high Prandtl number liquid jets impinging onto downward-facing
surfaces. The heat transfer correlations were developed for normal (θ = 90°)
and inclined (θ = 75°, 60° and 45°) jet impingements.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.