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 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 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 ) [product] Ring Pack =  Sump d[product] Sump /dt where  Sump = 156 hours Flow rate for oil returning to the sump given by [Flow Rate] Ring Pack  Sump = Sump Volume /  Sump = 0.27 cm 3 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 cm °C Summary of Lubricant Transport in Ricardo Hydra Ring Pack Experiment Tribological Model Residence Time60 ± 15  10 seconds Volume of Oil0.30 ± 0.08  0.02 cm 3 Flow Rates Into Ring Pack0.32 ± 0.02  0.17 cm 3 min -1 Returning to Sump0.27 ± 0.01  0.12 cm 3 min -1 Loss From Ring Pack0.05  0.05 cm 3 min -1 Sump Residence Time156 ± 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 Measurement of Lubricant Residence Time in the Ring Pack Add marker to sump (n-C 18 H 38 ) 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 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 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 Lubricant Flow and Degradation in the Piston Ring Pack Infrared Spectroscopy of Carbonyl Group Hydrocarbon Base Fluid Hydroperoxides Ketones Carboxylic Acids 1/8” PTFE Tube Christopher Hammond, John Lindsay Smith, Moray Stark, David Waddington Department of Chemistry, University of York, York, YO10 5DD, UK Harold Gillespie, Eiji Nagatomi, Ian Taylor Shell Global Solutions UK, PO Box 1, Chester, CH1 3SH, UK References 1 S Yasutomi, Y Maeda, T Maeda, Ind. Eng. Chem. Prod. Res. Dev. Vol 20 p 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, S Blaine, PhD Thesis, Reaction Pathways in Lubricant Degradation: Liquid Phase Autoxidation of n-Hexadecane, p32-55, Univ. of Michigan R C Reid, J M Prausnitz, T K Sherwood, The Properties of Gases and Liquids (3 rd ed.), McGraw-Hill,London, p439, 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 Richard Gamble, Martin Priest, Christopher Taylor School of Mechanical Engineering, University of Leeds, Leeds, LS2 9JT, UK 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-C 16 H 34 oxidation Sump Ring Pack Small Volume Short Residence Time Flow Rate Large Volume Long Residence Time Integrated Chemical – Rheological Model n-C 16 H 34 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 f a etc.) 5 Rate of oxidation simulated accurately Predicted viscosity reasonable in early stages, very under-estimated by the end of the oxidation Moray Stark :