Lubricant Flow and Degradation in the Piston Ring Pack

1
Lubricant Flow and Degradation in the Piston Ring
Pack
Christopher Hammond, John Lindsay Smith, Moray
Stark, David Waddington Department of Chemistry,
University of York, York, YO10 5DD, UK
Richard Gamble, Martin Priest, Christopher
Taylor School of Mechanical Engineering,
University of Leeds, Leeds, LS2 9JT, UK
Harold Gillespie, Eiji Nagatomi, Ian Taylor Shell
Global Solutions UK, PO Box 1, Chester, CH1 3SH,
UK
Engine Specification Ricardo Hydra Fuel
injected gasoline engine Single cylinder 0.5
litre Capacity 1500 rpm 50
Throttle External sump (70 ºC) Camshaft
lubricated separately Lubricant
Specification Shell XHVI TM 8.2 Hydrocarbon
base fluid No additive package used
Description of Oil Flow Continuous oil flow
between well-mixed sump and ring pack
1 Ring Pack described by any two of the
parameters Volume, Residence Time or Flow Rate
Overall Aim of Work To Predict Increase in
Piston Friction due to Oil Degradation. This
requires Chemical model for base fluid
oxidation Rheological model for increase in
viscosity due to formation of oxidised
products Tribological model for the increase in
piston friction due to increase in
viscosity Integration of these three
models Work Reported Here Measured lubricant
flow and extent of oxidation in the sump and ring
pack of a gasoline engine Comparison of extent
of lubricant oxidation in the engine with a
chemical model Comparison of measured lubricant
flow in the engine with a tribological
model Integrated chemical rheological model
tested against n-C16H34 oxidation
Ring Pack
Small Volume Short Residence Time Flow
Rate Large Volume Long Residence Time
Sump
Measurement of Lubricant Residence Time in the
Ring Pack Add marker to sump
(n-C18H38) Monitor build up of marker in ring
pack oil samples Expect exponential increase
to sump concentration 2 Exponential
increase observed, except with 40 sec delay,
due to time for oil to travel down sampling
tube Residence Time ?Ring Pack 60 seconds
Extraction of Oil from Top Piston Ring Via
PTFE tube connected to behind top piston ring
2 High pressures during power stroke drives
a rapid gas flow down the tube Oil droplets
carried by gas flow for sampling outside the
engine
1/8 PTFE Tube
Lubricant Degradation Chemistry and Monitoring by
FTIR Hydrocarbons react to form peroxides that
rapidly decompose to ketones Half of the
ketones react to form carboxylic acids in the
engine Detailed chemical model constructed to
simulate formation of ketones and
acids Extent of oxidation found by FTIR
spectroscopy of the carbonyl group (? 1715
cm-1) i.e. carboxylic acids ketones
Lubricant Degradation in the Sump Oxidation of
the sump oil increases approximately linearly
with time All oxidised product in the sump
originate in the ring pack, as the sump is too
cool (70 C) for significant degradation in
situ Measured carboxylic acid concentration
allows a Total Acid Number to be
calculated By 50 hours ?1 of base fluid
molecules in the sump have reacted to form
acids or ketones
Hydrocarbon Base Fluid
Hydroperoxides
Ketones
Infrared Spectroscopy of Carbonyl Group
Carboxylic Acids
Lubricant Degradation in the Ring Pack
Oxidation levels in the ring pack are high
from the start ? 10 of base fluid molecules
have reacted Comparison of the rate of
increase of oxidised products in the sump, with
the level in the ring pack gives a residence
time for oil to pass through the ring pack
and return to the sump (?Sump) productRing
Pack ?Sump dproductSump/dt where ?Sump 156
hours Flow rate for oil returning to the sump
given by Flow RateRing Pack ? Sump Sump
Volume / ?Sump 0.27 cm3 min-1
Two Reactor Chemical Simulation Detailed
chemical model used to simulate lubricant
degradation Consists of two well-mixed
volumes representing the sump and ring
pack with constant flow between Oxidation
under-estimated by a factor of five Due to
uncertainties in the ring pack temperature, or
dissolved metals or nitrogen compounds acting
as catalysts Residence Time
Volume Temperature Sump
156 hours 3 litres 70
C Ring Pack 60 seconds 0.27 cm3
200 C
Summary of Lubricant Transport in Ricardo
Hydra Ring Pack Experiment
Tribological Model Residence Time 60 15 ?
10 seconds Volume of Oil 0.30 0.08 ? 0.02
cm3 Flow Rates Into Ring Pack 0.32
0.02 ? 0.17 cm3 min-1 Returning to
Sump 0.27 0.01 ? 0.12 cm3 min-1 Loss From
Ring Pack 0.05 ? 0.05 cm3 min-1 Sump
Residence Time 156 8 ? 300
hours Residence Time per litre 52
3 Volume 3 litres Measured flow
parameters for the Hydra engine were compared
with a tribological model of the piston
assembly Lubricant flow driven by blow-by
during the combustion stroke is a dominant
mechanism for oil transport in the piston
assembly Oil loss from the ring pack into the
combustion chamber is dominated by reverse blow-by
Integrated Chemical Rheological Model
n-C16H34 oxidation experiments of Blaine 3 at
140 C were simulated using the chemical
mechanism Group additivity method of Orrick
and Erbar 4 used to calculate viscosity of
oxidation products Viscosity (?mix) of
oxidised hexadecane calculated using geometric
mean of the viscosities of the mixture
components weighted by their relative
concentration (?a and fa etc.) 5 Rate of
oxidation simulated accurately Predicted
viscosity reasonable in early stages, very
under-estimated by the end of the oxidation
References 1 S Yasutomi, Y Maeda, T Maeda,
Ind. Eng. Chem. Prod. Res. Dev. Vol 20 p530-540
1981 2 S B Saville, F D Gainey, S D Couples, M
F Fox, D J Picken, SAE Technical Paper,
International Fuels and Lubricants Meeting, Oct
10-13, 1988 3 S Blaine, PhD Thesis, Reaction
Pathways in Lubricant Degradation Liquid Phase
Autoxidation of n-Hexadecane, p32-55, Univ. of
Michigan 1991 4 R C Reid, J M Prausnitz, T K
Sherwood, The Properties of Gases and Liquids
(3rd ed.), McGraw-Hill,London, p439, 1977 5 I
Pirgogine,The Molecular Theory of Solutions,
North Holland, Amsterdam, 1957 Acknowledgements
CH, RG and MS would like to thank Shell Global
Solutions for sponsorship Thanks to Simon
Chung of Infineum for many helpful discussions
and with whom we are now collaborating on this
topic
Moray Stark mss1_at_york.ac.uk