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Our basic understanding of the chemical and physical nature of soot, its interaction with lubricant components and its role in promoting wear and oil thickening in heavy duty diesel engines continues to grow. Our current study in the GM 6.5L engine focuses on examining the effects of variations in base stock type (Group I vs. Group II), viscosity index improver or viscosity modifier (VM) chemistry (OCP vs. dispersant OCP), zinc dithiophosphate (ZDP) type and dispersant type (low MW vs. high MW) on roller follower wear, viscosity growth and other measured responses. In this study, more robust fluids were tested producing very low wear results and minimal viscosity increase of the lubricant. Fluids containing dispersant OCP (DOCP) and high MW dispersant produced a lower degree of wear, whereas varying the ZDP type (1° vs. 2°) showed no effect on wear. The use of Group II base stocks was associated with significantly lower viscosity increases.

Statistically designed experiments were developed to investigate the nature of soot, to understand its role in oil viscosity growth, and to study the interactions involved with additives that inhibit viscosity growth. The matrix was designed to examine effects of engine type, mode of operation, and the oil formulations. Mack EM6-285 and GM 6.2L engines operating under both high speed and high torque conditions were used in this study. An API CE\SG quality lubricant was used as the baseline. The detergent sulfonate substrate was varied from standard to three-fold levels; the dispersant TBN contribution ranged from 1.1 to over 3.0. The surface and bulk exhaust soot properties were determined. Colloidal suspension stability and rheology were measured to evaluate the design factor effects on the formation of soot and subsequent effects on oil thickening. The Mack EM6-285 engine produced less soot, less oil viscosity growth, and less oxidation than the GM 6.2L engine.

This work presents a follow-up to previous efforts by the authors to investigate the susceptibility of gasoline direct injection (g-di) engines to deposit formation and the effect of those deposits on vehicle performance. A series of injector keep clean and clean up tests in base and additized fuels utilizing the ASTM D 5598 cycle provided a range of injector fouling levels. It is found that the g-di engine employed here is more susceptible to injector deposits than even the sensitive port fuel injected (PFI) engine used as industry reference in the D 5598 procedure. Injector keep clean and clean up performance of several representative deposit control chemistries are evaluated. In order to determine the effect of injector fouling on performance, emissions and driveability tests are performed on the vehicles at varying levels of injector fouling. Regulated emissions, particulates, fuel consumption and driveability are all shown statistically to be linked to injector fouling.

The International Lubricant Standardization and Approval Committee (ILSAC) GF-2 specification requires Passenger Car Motor oils to provide enhanced fuel economy in a modern low friction engine (ASTM Sequence VIA). The durability of this fuel economy improvement is becoming increasingly important and will be address in the successor to the Sequence VIA, the Sequence VIB, which is currently under development for ILSAC GF-3. Previous investigations have indicated that the choice of detergent system and friction modifier has a large impact on the fuel economy of a lubricant. As a result of a study undertaken to further investigate these effects in a 1994 Ford Crown Victoria running the EPA Federal Test Procedure, a significant impact on tailpipe emissions was discovered. Detergent system affected both regulated emissions (hydrocarbon (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) emissions), and non-regulated emissions (carbon dioxide emissions).

Low temperature flow improvers help refiners meet diesel fuel cold flow specifications and optimize profits. However, some additives, cloud point depressants in particular, are under scrutiny since there have been cases where they interacted with other cold flow improvers and became less effective at depressing the cloud point of the diesel fuel[1]. This second paper in a series of studies[2] examines what effect mixing cloud point depressed diesel fuel with other cloud point depressed diesel fuel or with diesel fuel diluted with kerosene will have on the resultant fuel mixture's cloud point. The data show that cloud point depressants can be used safely and effectively with kerosene blended fuels and in conjunction with other cloud point depressants.

Water-emulsified diesel fuel technology has been proven to reduce nitrogen oxides (NOx) and particulate matter (PM) simultaneously at relatively low cost compared to other pollution-reducing strategies. The value of this technology is that it requires absolutely no engine adjustments or modifications to reduce harmful emissions. Technologies that break the NOx -particulate trade-off are virtually non-existent, therefore understanding how the water contained in an emulsified fuel can reduce both NOx and PM simultaneously is critical. To understand this phenomenon, emulsified fuels with varying water levels (0 to 20%) were evaluated in a multi-cylinder marine engine using three different injection timings. This testing in an actual engine confirms that as the water level is increased the amount of NOx and PM are reduced without compromising engine performance.

Intentionally adding water to oil, in the laboratory, provides an indication of the oil's ability to tolerate the presence of water. Various characteristics, such as emulsion, haze or separation, may be observed. Some blends of oil and water have been shown to form structures when left undisturbed. A visual, qualitative, storage test is capable of detecting this phenomenon as the presence or absence of structure. However, the time frame of formation can be on the order of days or weeks and is sensitive to handling and temperature effects. Quantitative methods are required for any evaluation of chemistry, temperature and handling effects on the rate and strength of structure formation. This paper describes rheological and electrical methods which directly and indirectly measure the tendency to form a structure at the molecular level, yielding rate of formation and strength information.

To meet increasingly stringent emissions and fuel economy regulations, many Original Equipment Manufacturers (OEMs) have recently developed and deployed small, high power density engines. Turbocharging, coupled with gasoline direct injection (GDI) has enabled a rapid engine downsizing trend. While these turbocharged GDI (TGDI) engines have indeed allowed for better fuel economy in many light duty vehicles, TGDI technology has also led to some unintended consequences. The most notable of these is an abnormal combustion phenomenon known as low speed pre-ignition (LSPI). LSPI is an uncontrolled combustion event that takes place prior to spark ignition, often resulting in knock, and has been known to cause catastrophic engine damage. LSPI propensity depends on a number of factors including engine design, calibration, fuel properties and engine oil formulation. Several engine tests have been developed within the industry to better understand the phenomenon of LSPI.

For a diesel lubricant to meet the new Mack EO-K/2 specification, it must be effective in preventing excessive viscosity increase during the 150-hour Mack T-7 test. The severity of this test is shown to be highly dependent upon fuel chemistry and injection timing. A comparison of various lubricant formulations in the Mack T-7 engine run with a given fuel suggests that nitrogen-containing succinimide dispersants, dispersant viscosity improvers, and supplemental ash in the form of overbased sulfonate detergents are effective in controlling viscosity increase. Crankcase oil thickening follows a modified form of Brinkman’s equation and can be predicted from measured values of soot particle size and concentration. Basic lubricant additives are shown to prevent particle size growth by adsorption on to the acidic soot surface, thereby interrupting soot aggregation and retarding oil thickening.

In the first paper in this series (1)*, the extent of oil thickening for a given lubricant in the Mack T-7 engine test was found to be influenced by fuel composition. Based upon the knowledge that thickening is due to the accumulation and aggregation of soot in the oil, a set of experiments has been carried out to identify relationships between fuel chemistry and the oil thickening tendency of soot formed by fuel combustion. Three commercial diesel fuels were treated with chemical combustion aids and/or organic sulfur, and both short-duration and full-length tests were run in a Mack T-7 engine fitted with a filter designed to collect soot from the exhaust stream. A model describing the complex effects of fuel chemistry on the oil thickening process is proposed in which fuel sulfur content is shown to influence soot content of the lubricant after ISO hours of engine operation.

Information relative to oil thickening has been developed in road tests. Typical operating temperatures, as well as the length of time required to thicken oils in these tests, are described. A laboratory test procedure has been developed that shows a good degree of correlation with this field service. The effect of test conditions such as jacket temperature and piston ring design on oil thickening in the laboratory are described.

Piston ring land deposit formation is a key performance criterion in the ASTM Sequence IIIE engine test. Because engine testing of lubricant formulation variables is expensive, a ring land deposit bench test was developed replicating the Sequence IIIE bulk oxidation and deposit formation mechanisms. Following an initial bulk oxidation of the candidate oils, deposits similar in chemical composition and morphology to Sequence IIIE ring land deposits are produced in a modified panel coker apparatus. Good correlation with the ASTM Sequence IIIE engine test has been established. Lubricant additive and base oil effects on oxidation control and deposit formation have been investigated. Their influences on lubricant formulation strategy are discussed.

A major drive to develop methanol-fueled vehicles began with the 1973 oil embargo. Early work with dedicated methanol-fueled vehicles demonstrated that lubricant choice influenced engine durability. The qualities desired were not defined by the gasoline engine oil classification system in place at the time. As a result oils were developed which optimized those properties deemed desirable for methanol fuel. The advent of fuel sensors made it possible to design a vehicle which can operate on gasoline or gasoline with varying levels of methanol without intervention by the operator. This created a need for a lubricant that can handle a diversity of methanol/gasoline mixtures as well as conventional gasoline. The paper reviews some of the lubricants that have been used in prototype methanol-capable vehicles and the improvement of these formulations to meet the latest gasoline engine performance criteria while maintaining satisfactory methanol performance.

Water-emulsified diesel fuel technology has been proven to reduce nitrogen oxides (NOx) and particulate matter (PM) simultaneously at relatively low cost compared to other pollution-reducing strategies. While the mechanisms which result in these reductions have been postulated, the development of new analytical tools to measure in-cylinder soot formation using optically accessible engines can lead to a deeper understanding of combustion and the chemical and physical mechanisms when water is present during combustion. In this study, an optically accessible single cylinder engine was used to study how water brought into the combustion chamber via an emulsified fuel changes the combustion process and thereby reduces emissions. In-cylinder measurements of relative soot concentrations were used to determine the effect of water-emulsified fuel on soot formation.

Multifunctional additives can compensate for lower quality diesel fuel. Performance and quality have been decreasing worldwide. This has resulted largely from increased use of heavier crude oils and more severe processing to achieve necessary fuel product mix. Fuel additives provide the refiner and marketer with an economic approach to restoring performance and quality. Additives can be formulated to solve many problems related to deposits and wear, which are major factors affecting engine power, economy, emissions and durability. They are of critical importance to the vehicle owner/ operator to maintain dependability and low operating cost. At the same time, the refiner benefits economically through the use of lower cost crudes, greater operational flexibility and ease of adjusting final fuel blends to meet specifications. Typical additive components include: detergent dispersants, inhibitors, stabilizers, cetane improvers, and flow improvers.

In order to assess the field needs of engine oils to be used in methanol-fueled vehicles, six oils were run in a fleet test over a ten-month period under short-trip service conditions. The results from the field test were compared with results with the six oils in the laboratory engine tests which have been used to predict field performance with methanol fuel. A lack of correlation between the field test and the laboratory engine tests suggests that the laboratory tests need revisions to better serve field needs.

Using a seven-step quality improvement process, some of the engine build-up factors adversely influencing the severity and precision of the Sequence VI dynamometer test were examined. Insights from engineering (theory) and database (statistical) analyses enabled a 23 factorial experiment to identify oil ring tension, piston ring side clearance, and piston fit as critical parameters in a 3-oil, 9-engine, 28-test program. High ring tension was shown to emphasize the friction reducing capability of higher performing oils and the deficiency of a lower performing oil. Interactions were noted. A helpful correlation of test severity with the engine calibration indicators was shown.

Inconsistent fuel filter life is a problem that continues to plague most heavy-duty diesel fleets. It has been proven that fuel filter life can be strongly influenced by the thermal and oxidative stability of diesel fuel that is being filtered. Filters consistently exposed to diesel fuels that produce a tar-like substance in abundance upon heating (sometimes termed “asphaltenes”) will plug far more rapidly than filters exposed to diesel fuel that does not easily form these tar-like substances. Fuel additives have long been used to maintain fuel system cleanliness and to improve diesel fuel stability. It follows logically that such additives could have a positive impact on fuel filter life by maintaining the cleanliness of the fuel filtration media. This paper reviews the laboratory evaluations and field tests that were run to compare fuel filter life in both the presence and absence of diesel fuel additives.

The authors provide evidence indicating that oils meeting only the minimum requirements of API GL-5 do not always provide adequate gear protection, especially in severe duty applications. Increases in commercial vehicle power and loading have accentuated the need for oils of greater load carrying ability. A modified version of the standard L-37 test may help identify oils that possess superior durability and thermal characteristics. Future gear lubricants should provide improved fuel economy, increased manual transmission life; and frictional characteristics that allow noise free performance in limited slip differentials.

Additives are an integral part of today's fuels. Together with carefully formulated base fuel composition, they contribute to efficiency, dependability and long life of gasoline and diesel engines. As a primer, this paper describes the range of chemical additives formulated for gasoline and diesel fuel and their effects. Specific functions and benefits of additives, typical use levels, and test methods for evaluation are discussed. Additive usage may be divided into three major categories: a) to satisfy desired levels of performance in engines, b) to insure delivery of uncontaminated, on-specification fuels to the end user and c) achieve necessary chemical/physical properties as manufactured by the refiner.