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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.

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.

Investigations into fuel compositional effects on emissions using model and full range fuels suggest aromatic components promote NOx conversion over the catalyst Steady state results derived from a single engine (Ricardo Gasoline Fuels Consortium data) show that at a typical part load condition, the catalyst removes NOx less effectively with lower aromatic fuels. Neither CO nor H2 contribute significantly to catalyst performance. Two vehicles were tested over a European cycle. Toluene formed more combustion chamber NOx, offset by increased catalyst conversion efficiency giving lower tailpipe NOx than isooctane in the vehicle with the better catalyst light-off and AFR control.

The transport of fuel droplets into the combustion chamber of an SI engine and their subsequent evaporation has been studied, using a new optical diagnostic technique, Interferometric Laser Imaging for Droplet Sizing (ILIDS), which allows temporally and spatially resolved measurements of droplet size distributions. The measurement technique and its application to in-cylinder engine measurements are described. Measurements were made under warmed-up conditions, with open valve injection timing, in a Ricardo Hydra single cylinder engine. The results showed differences in the evolution of the droplet size distribution in cylinder with variations in load and speed. At 1200 rpm under full load, droplets arrived quickly into the cylinder, and were small, the Sauter Mean Diameter (SMD) being in the region 10-12 μm on arrival, so that mixture preparation was good.

The formation of combustion chamber deposits in modern SI engines is predominantly derived from hydrocarbon fuels and occurs as a consequence of the quenching action of the combustion chamber walls on the flame. A laboratory experiment has been designed which enables rapid generation of deposit material in the form of viscous brown liquids. Heating these deposits produces material that is consistent in composition and physical appearance with mature engine deposits. The deposit-forming tendency of a number of individual hydrocarbon species has been determined. The amount of deposit increases with i) the amount of unsaturation present in the molecular structure and ii) the boiling point of the hydrocarbon fuel being burned. A structurally derived parameter for each hydrocarbon molecule is found to correlate well with deposition rate, allowing a unified treatment of the different generic forms of hydrocarbons in which deposit-forming tendency is linked to molecular structure.

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.

A unique time-resolved Fourier Transform InfraRed (FTIR) spectrometry technique has been developed to obtain full mid-IR lubricant spectra directly from the ring-pack region of a firing, single cylinder, diesel engine. Initial studies of the detailed spectra show a growth of oxidation products, as indicated by a strong carbonyl absorption peak, observed to increase with load close to the top ring location, for both power and exhaust strokes. Similarly, the formation of alcohol, ketone, aldehyde and carboxylate oxidation products is accessible. Thus it is possible to gauge gross changes to lubricant composition as a function of spatial location through the ring-pack, engine stroke and the severity of engine operation.

An experimental programme has been carried out to quantify the influence of Combustion Chamber Deposit (CCD) removal on vehicle acceleration performance, fuel consumption and tailpipe emissions in several modern European car models. Vehicles were performance and emissions tested dirty', following accumulation of 16,000 kilometres (10,000 miles) with a light duty cycle, then ‘clean’, following removal of CCDs. This scheme was repeated for one model using a heavy duty driving cycle. Additional tests were carried out on three vehicle models equipped with knock-sensors for which ignition timing was monitored. CCDs reduced fuel consumption relative to the clean engine, in amounts dependent on vehicle model. CCDs had only small, detrimental effects on acceleration performance and power. They generally (but not always) increased NOx emissions and had variable and usually small effects on HC and CO emissions.

Departures from optimum stoichiometry during transients (acceleration and deceleration) and cold start can lead to significant degradation in driveability and emissions control. Such departures occur as a result of a complex interplay between fuel transport mechanisms and the fuelling strategy. The relative contributions of several of these mechanisms are affected by fuel composition. To help understand these effects an open-path differential infra-red absorption technique has been used to monitor the transient evolution of the fuel vapour phase directly within the combustion chamber. The sensor projected a narrow infra-red beam which traversed the cylinder of an optical access engine along an open path under the head, and measured the path-integrated attenuation caused by absorption of the infra-red radiation by the fuel vapour. It operated in the near infrared (NIR) spectral region around 2.3 μm, an absorption band in hydrocarbon species containing methyl groups.

Methods of identifying cars responsive to TML, and the connection between a car’s response to TML and its severity are examined. Fuel segregation in the inlet manifold is studied with the object of improving laboratory bench procedures. Laboratory results are supported by customer reaction trials, the techniques of which are fully described. The optimum scavenger combination for use with TML is shown to be 1.0 T ethylene dibromide plus 0.2 T tritolyl phosphate.

This paper discusses in detail a new technique for air-fuel mixture entering individual cylinders of a multicylinder engine. The method described provides estimates of the weights of both air and fuel entering individual cylinders and the proportions of the fuel that are present as liquid at points just upstream of the inlet valves. The technique has been developed for steady-speed conditions and is not applicable to transient operating conditions.

Vehicle driveability is a function of gasoline volatility, ambient conditions and engine design. The ability to predict driveability performance from a knowledge of fuel/air mixture temperatures and gasoline properties would greatly assist both fuel and engine development. Accordingly, a model to predict engine hesitation under full-throttle accelerations (a major driveabilty malfunction) has been developed. Hesitation occurs when the fuel/air mixture reaching the combustion chambers is too lean to burn. Thus the model is based on the calculation of heat flow and air/fuel vapour ratios in the engine inlet manifold. Chassis dynamometer tests for two different cars using a range of fuels and a range of test temperatures have shown that the model gives an accurate prediction of mixture temperatures and engine hesitation under full-throttle conditions.

A 1.8 litre four-cylinder engine with a slice between the head and the block carrying instrumented plugs has been used to study the growth of combustion chamber deposits and some of their effects on engine operation. Different techniques for measuring deposit thickness, knock onset and deposit effects on the thermal characteristics of the cylinder have been developed. Deposit growth as measured by deposit weight on the plugs is reasonably repeatable from run to run and cylinder to cylinder. The presence of deposits already in the cylinder does not affect deposit growth on clean plugs introduced into the combustion chamber. Deposit thickness and morphology vary substantially at different locations, the thickness being greatest at the coolest surfaces. Deposits increase the flame speed and reduce the metal temperatures just below the surface. They also reduce the mean heat flux away from the cylinder.