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Combustion chamber deposit (CCD) formation in SI engines is a complex phenomenon which is dependent on a number of fuel and engine parameters. A mathematical model has been developed, based upon a previously proposed mechanism of CCD formation, which describes the physical and chemical processes controlling the growth of deposits in SI combustion chambers. The model allows deposit thickness to be predicted as a function of time, taking into account gasoline composition and factors influenced by engine operating conditions. Piston top deposit thicknesses predicted by the model for 38 unadditivated fuels show a strong correlation with data from three different bench engine tests. The model offers the possibility of predicting the amount of CCD produced by unadditivated gasolines for a range of engine designs, operating conditions and test durations.

Environmentally acceptable hydraulic fluids are increasingly specified for use in hydraulic equipment working in environmentally sensitive areas. This paper describes the research methodology that was used to develop a high performance synthetic, environmentally acceptable hydraulic fluid. Product development consisted of: (1) setting the standards for environmental acceptability, (2) screening base fluids and additives for technical performance and minimal impact on the environment, (3) designing a formulation to meet these targets and (4) field experience. Test results demonstrating the high performance and low environmental impact of the new fluid are discussed. A key challenge when formulating an environmentally acceptable hydraulic fluid is to achieve satisfactory oxidation stability. The absence of a suitable oxidation stability test, which can differentiate between environmentally acceptable fluids and correlate with field performance, has been an issue for several years.

An optical technique using laser-induced fluorescence (LIF) has been developed to measure the oil film thickness between a fixed point on the cylinder-liner and the piston of a single-cylinder diesel engine. Details are presented of an experimental layout for acquiring fluorescence data from the engine and a strategy for their conversion to oil film thickness. Engine tests have shown that the oil film thickness in the liner/piston contact depends critically on the temperature dependence of the oil viscosity and hence is sensitive to the engine's speed and torque output condition. Oil film thickness measurements were made for two fully formulated lubricants, a 15W/40 Universal Diesel Engine Oil (UDEO) and a 10W/30 Super High Performance Diesel Oil (SHPDO). From these oil film thickness measurements the analysis was extended so as to estimate the oil volumes present between the cylinder-liner and different portions of the piston as they pass the measurement point.

Engine Sludge has reappeared in the last decade as a source of operation problems and in manufacturers warranty claims in Europe and the USA, due to engine malfunction and in some cases engine failure through oil starvation. This sludge has become known as ‘Black sludge’ or ‘Hot sludge’ in Europe. As a result of the problem, bench engine tests have been developed in Europe (CEC-L-41-T-88), and the USA (ASTM Sequence VE). Both these tests have been shown to be particularly sensitive to changes in the fuel composition, even between batches of the same gasoline. A field trial has been conducted by Shell Research Ltd at Thornton Research Centre, to study the effect of fuel composition and fuel-lubricant interactions on the propensity to form sludge, using a mileage accumulation cycle designed to be severe with respect to sludge formation.

Environmentally adapted diesel fuels defined by the Swedish Government contain extremely low levels of sulphur and have limited aromatics contents. Road trials and pump durability tests of these fuels revealed unacceptable wear in injection pumps due to low lubricity. Additive solutions were identified using bench tests and then proven in field trials. Market experience has substantiated the findings that fuels using the chosen additive give fully satisfactory performance. This paper illustrates how practical solutions to lubricity questions can be found, and is applicable wherever specifications demand fuels requiring a high degree of hydroprocessing.

Mid-infrared reflection-absorption spectroscopy, has been applied for the first time to the measurement of lubricant degradation products in the ring pack of a firing single-cylinder, IDI diesel. An IR-transmitting window, mounted in the cylinder wall, enables illumination of the moving piston by a broadband IR source located on the engine exterior. Light reflected from the piston is analysed in three wavebands to measure carbonyl oxidation products and oil volumes. Intra-cycle observations reveal differences in the apparent extent of lubricant oxidation between strokes and at different spatial locations in the ring pack. The data are interpreted in terms of a non-homogeneous sample.

In order to estimate the influence of the fuel composition on speciated hydrocarbon emissions from gasoline engines a model has been developed for the processes undergone by the fuel which escapes the main combustion event. One of the most important ways that this occurs is by trapping in crevices followed by mixing and partial oxidation with the hot burnt gas during the power and exhaust strokes. This complex process has been modelled by recognising some important characteristics. It is observed that the fraction of a fuel species emitted is well correlated with its rate constant for reaction with OH radicals and that this is independent of the rest of the fuel composition. This means that (a) the chemistry is significant (not just mixing) and (b) the radicals carrying out the oxidation originate from the burnt gases. The decoupling of radical concentrations from the fuel composition considerably simplifies the modelling.

A piston ring-pack lubrication model has been developed which takes into account both lubricant viscosity/temperature and viscosity/shear rate variations. In addition, lubricant starvation of the upper piston rings, due to restriction of the oil supply by the lower rings, has been included. Inputs to the model include piston ring profiles (measured using Talysurf profilometry) and gas pressure distributions throughout the ring-pack. The latter were calculated using the (known) combustion chamber pressure diagram at the relevant engine operating conditions. The model was validated by comparing predicted oil film thicknesses with those measured using a laser-induced fluorescence technique on a Caterpillar-1Y73 single-cylinder diesel engine. The engine was run at a range of speeds with two different, fully formulated, multigrade lubricants, and the oil film thickness under each of the piston rings was measured.

The development of cross-flow single overhead camshaft designs of engines led to the introduction of pivoted cam followers with pads that were subjected to uni-directional rolling/sliding under heavy contact loads. Such components were prone to wear failure by a mechanism involving severe surface roughening. The initiating wear mechanism was eventually shown to be a form of “mild” wear and the Archard wear equation was used successfully to model the pattern of wear seen on cams and followers. The use of rigs to assess the wear performance of different lubricants has hitherto been a very poor predictor of engine performance, because of the complex interaction of materials, kinematics and forces in real engines. As a result, most automotive lubricant development relies on engine testing, which is expensive and time-consuming. Also, the complexities of the engine environment make it difficult to obtain much scientific insight into the tribological processes involved.