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The benefits of diesel fuel additives have been demonstrated in a broad range of performance and operational areas, from the refinery, through storage and distribution, to fuel dispensing and vehicle operation. The customer is certainly aware of their effects on fuel performance in many of these respects, such as cold-weather operation, ease of starting, foaming, odour, etc. An area of particular interest in customer perception, however, is fuel economy. Excluding the use of after-market fuel-treatment devices, it is claimed that additives of different types can improve fuel economy, for example by improving combustion, by maintaining injection equipment in optimum condition, or by reducing engine frictional losses.

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.

Following a small scouting programme to examine the scale of emissions benefits achievable by different degrees of gasoline base fuel redesign (SAE 930372), a larger programme has been initiated to investigate more systematically the influence of individual fuel parameters on tailpipe emissions. This coordinated study has been spread across five participating Shell Group laboratories, using a set of common fuels specifically designed and centrally blended for this purpose. Additionally, subsets of these fuels have been used for detailed systematic examination of selected topics within the overall programme scope. This paper summarises the plan for the integrated study. It describes the composition and properties of the fuels and their blending. The results covered here are those of chassis dynamometer-based regulated emissions studies conducted on a composite fleet designed to represent a range of vehicle technologies, using a variety of regulatory driving cycles.

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 study of the characteristics of combustion knock in a 1 cyl prechamber diesel engine is reported here. The intensity of the knock showed pronounced cyclic dispersion and an electronic counting technique was developed to measure the intensity distribution. The knock had a major frequency of 2370 Hz and was most apparent at low speeds. Advancing fuel injection timing and also increasing rate of fuel injection increased intensity. Tests with a wide range of fuels showed that cetane number was the only fuel property important to knock. A study of the relationship between knock intensity and the pattern of combustion pressure development showed that the time origin of knock was at or near the position of maximum rate of pressure rise, and that knock intensity could be related to a time function of pressure rise.

Significant differences have been observed in the behaviour of elastomeric seals exposed to various automotive diesel fuels. This behaviour is governed not only by the chemistry of the elastomer but also by the aromatic content of the fuel and is typical of elastomer/fluid interactions occurring under diffusion control. Although no significant differences were observed in the response of nitrile elastomers exposed to peroxides, the use of antioxidant additives in “low” aromatic diesel fuel needs to be considered. The normal seal housing design criterion is such that seal integrity should not be compromised by the use of “low” aromatic fuels in normal operating circumstances. Some three years' experience in the Swedish market supports this view.

As a first attempt to assess the scope for reducing the emissions from gasoline fuelled vehicles in the European market via fuel changes, an experimental scouting programme has been conducted to examine the effects of fuel composition and properties on both regulated emissions and detailed exhaust gas composition. This 4 fuels/4 vehicles programme involved exhaust emission tests on a chassis dynamometer, and was carried out mainly on non-catalyst vehicles, using two commercial gasolines and two (“reformulated”) test gasolines representing “intermediate” and “extreme” changes of the base gasoline design. The fuel characterization includes analysis by hydrocarbon type and carbon number; the exhaust analysis comprises both regulated emissions and hydrocarbon speciation measurements. In the case of regulated emissions, the fuel effects are, as expected, relatively small in comparison with the effect of installing exhaust catalysts.

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.

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.

As a result of increasing concerns over air quality, environmental legislation has led to more stringent emissions limits for diesel engines and vehicles. This has affected both engine manufactures and fuel suppliers. Whereas in the US, only the fuel requirements for heavy-duty diesel engines are of key interest, in Europe light-duty diesel applications are also important since diesel-powered passenger vehicles are accepted by customers and their market penetration has increased rapidly. This paper gives an update of Shell's ongoing research on correlations between diesel fuel quality and particulate emissions in both heavy- and light-duty applications. In heavy-duty testing (both steady-state and transient), sulphur is the dominant fuel property affecting particulate emissions. After sulphur correction, fuel effects are small and can best be described by a combination of cetane number and density.

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.

Net heat release rates and knock characteristics were derived from in-cylinder pressures for different fuels in a single-cylinder engine; the effect of an ashless antiknock, N-methyl aniline (NMA) was also studied. The maximum net heat release rate (MHRR) resulting from the final high-temperature chemistry determines the knock intensity. Paraffinic fuels have similar knock intensities at comparable knock occurrence frequencies. Aromatic fuels have significantly lower MHRRs and give much lower mean knock intensities for a given knock occurrence frequency compared to paraffinic fuels. Adding NMA to a paraffinic fuel increases the spark advance required to get a chosen frequency of knock occurrence as it increases the octane number of the fuel but has little effect on MHRR and hence knock intensity.

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.

Principal formulation effects on oil-fluoroelastomer compatibility in European specification tests are reviewed, and detailed surface analysis of elastomer samples after exposure to oil reported. The mechanism of fluoroelastomer degradation has been investigated and found to be based on fluorine depletion of a thin surface layer by dispersant additives. Compatibility is determined by both the oil and the detailed composition of the elastomer. Correlations with field performance have not been published for current European elastomer tests. Failing oils have demonstrated satisfactory performance in field trials. Oil preageing affects seal compatibility, but probably differently for gasoline and diesel engine lubricants.

A series of engine dynamometer tests was carried out with 100% ethyl ester of soya oil as fuel and six different diesel engine lubricants. In each case the lubricant became contaminated by unburnt fuel during the tests with measured dilution rates of up to 0.2% of the fuel throughput. The lubricant/fuel mixture eventually underwent degradation to such an extent that phase separation occurred. The tests were terminated when the lubricant lost all dispersancy, as evaluated by a blotter-spot teat. Used oil analysis revealed that rapid oxidation of some of the fatty acid ester components of the fuel diluent had occurred in the later stages of the tests. At the high levels of fuel dilution recorded in these tests there was little difference between the performances of the six lubricants, despite their differing performance categories.

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.

A “CARS” System using a modeless dye laser has been extensively calibrated and shown to give average temperatures of acceptably good accuracy. It has been used to measure temperatures in the end-gas of a single-cylinder E6 engine under knocking conditions using propane, commercial butane, iso-octane and a primary reference fuel made up of 90% iso-octane and 10% n-heptane by volume. These measurements show that there is significant heating of the end-gas because of pre-flame chemical reactions for all the fuels except propane. Propane has to be compressed to a much higher pressure compared to the other fuels studied in order to make it knock. At a given engine operating condition, there is significant cycle-by-cycle variation in both combustion and knock.

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.

Six full range gasolines were tested in two engines (one with a catalyst) operated at 4 steady states. Engine-out regulated emissions responded to equivalence ratio, Φ, in the accepted manner. For both CO and NOx, there was a characteristic, single emissions response to changes in Φ. Changing fuel composition will primarily alter the production of these emissions by modifying the stoichiometric air/fuel ratio, projecting engine operation onto another part of the Φ response curve. These Φ effects, which are independent of engine design, also determine how operating conditions affect engine-out CO and NOx. Speciated hydrocarbon measurements at engine-out and tail-pipe confirm results seen in previous test-cycle based programmes.