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Since diesel engine oils are part of the low-emission equation, there has been stepped increases in the quality of crankcase oils with the stepped reduction in diesel exhaust emissions. The new API CG-4 oil category, was developed to address the Engine Manufacturers Association's (EMA's) needs for 1994 emission-controlled diesel engines. It also improves the quality of crankcase oils by using modern four-cycle diesel engine tests which: operate on low-sulfur diesel fuel, as used by all on-highway trucks in the U.S., have statistically defined test limits, are incorporated into the Chemical Manufacturers Association's (CMA's) rigorous code for qualification testing.

Starting in October 1993, the sulfur in diesel fuel will be lowered from 0.27 wt % average to 0.05 wt % maximum in order to reduce particulate sulfate emissions from on-highway vehicles. Given such a major change in diesel fuel, the study reported here focused on determining the most appropriate crankcase oils to choose. Using low-sulfur fuel, the study assessed the effects of crankcase oils on: emissions, wear, deposits, oil consumption, viscosity, and Total Base Number (TBN) depletion rates. The engines used were 1994 engines with low oil consumption and direct injection, such as the Detroit Diesel Company (DDC) Series 60, Caterpillar 3176B, Mack E-7, and the Caterpillar single-cylinder engine, which will be used in establishing the next oil category to be announced in 1995. The oils evaluated were SAE 10W-30 and 15W-40 oils with sulfated-ash levels of 1.0, 0.5, and 0.0 wt %.

Higher soot levels in the crankcase oil may be an unavoidable result of lower exhaust-emissions. This study demonstrates that high soot levels in the oil can be dispersed, viscosity increases minimized, and filter plugging prevented by selecting the proper type of ashless dispersant and V.I. improver.

The authors measured camshaft surface temperatures in two different gasoline engines: a Ford 2.3-liter overhead-camshaft engine with finger-follower and an Oldsmobile V-8 5.7-liter engine with rotating tappets and pushrods. Using unique surface thermocouples in the cam-lobes, we found that maximum cam-lobe temperatures occur at the cam-nose and increase linearly with speed and oil temperature. At high speed, the rotating tappet produced lower temperatures than the finger-follower. In addition, at maximum speed the cam-lobe temperatures in the ASTM Sequence V-D and IIID tests were similar--200°C. The similarity in these surface temperatures explains why both engines require similar zinc dithiophosphates (ZnDTP) for wear control. The surface temperature controls the surface chemistry.

We were able to identify engine blow-by as a primary factor affecting camshaft wear in gasoline engines. Using a 2.3-liter overhead-camshaft engine, we isolated the valve-train oil from the crankcase oil and its blow-by using a separated oil sump. We find that: with engine blow-by, the camshaft wear was high. without blow-by, the camshaft wear was low. with blow-by piped into the isolated camshaft sump, the wear was high again. Later studies identified nitric acid as a primary cause of camshaft wear. It is derived from nitrogen oxides reacting with water in the blow-by. But even in the presence of blow-by, camshaft wear can be controlled by the proper selection of zinc dithiophosphates (ZnDTP) and detergent type.

The way in which exhaust valve failure is caused by the ash in crankcase oils is not well understood. This study provides an in-depth analysis of the failure mechanism. It includes: a field test, dynamometer tests, deposit and metallurgical analysis. The valves fail due to high-temperature oxidation and erosion. This results from a loss of deposit from the valve seat. There was a direct relation between the level of sulfated ash in the oil and the time to valve failure. The paper provides recommendations on the type of oils required to prevent these failures in two-cycle engines.

The performances of 1.0% and 1.45% ash, SAE 15W-40-CE/SF oils were compared in on-highway trucks with Cummins, Caterpillar, and Mack engines. This field test was unique in that all the engines were new and premeasured by the OEMs. It was found that 1.0% ash oils provided: (1) wear control equal to 1.45% ash oils and (2) oil consumption control better or equal to 1.45% ash oils. The 300,000-mile (482, 803-km) field test demonstrated that mixed diesel engine fleets can get maximum engine life to overhaul using a high quaiity, CE/SF, 1.0% ash--SAE 15W-40 oil.

At today's low oil consumption rates, high speed diesel engines with chromium-faced rings have experienced corrosive wear problems. This report defines the alkalinity required to prevent these wear problems; and the appropriate oil drain interval. In addition, the mechanisms of chromium-faced ring wear are identified. The study is based on three different engine types—direct injection two-cycle (DDA 8V-71TA), direct injection fourcycle (Mack ETAZ 673), and precombustton chamber fourcycle (Caterpillar 1Y73).

Chevron Research Company and Detroit Diesel Allison (DDA) conducted a cooperative field test to determine the performance of SAE 15W-40 multigrade oils in two-cycle engines. The field test utilized 42 new 8V-92TA engines in new Kenworth trucks. A unique aspect of this field test was that all the engines had premeasured piston rings and cylinder liners. The latest DDA fire ring designs were also incorporated. There are three significant conclusions: 1. Grooveless fire rings provided 35% lower wear than the current grooved design. 2. Properly balanced SAE 15W-40 multigrade oils provided satisfactory service. 3. Sulfated ash in the range of 1.0% to 1.85% had no significant effect on exhaust valve deposits.

The modern crankcase oil should prevent wear in both gasoline and diesel engines. This paper addresses the effects of zinc dithiophosphates (ZnDTP) and detergents on wear control in both applications. The authors find a need to properly balance detergent and ZnDTP types in order to obtain optimum wear performance for gasoline valve train wear. In addition, high levels of magnesium sulfonate produce higher bore polishing and/or ring wear than calcium detergents in three different diesel engine tests. Finally, a proper balance of sulfur-containing components and ZnDTP is necessary to prevent corrosive attack of the bronze pins in some diesel camshaft roller followers. Film and metallurgical analyses of used engine test parts are presented.

Lubricant field problems due to diesel engine soot have been reported in stop-go vehicles in Europe and the U.S. Soot generated in these vehicles can cause heavy-sludge, high lubricant viscosity increase, or oil gelling. In field and dynamometer testing, the authors demonstrate that certain oil formulations minimize these problems. Oils labeled CD/SF/EO-K produce significantly different soot dispersancy and viscosity control. In addition, formulations which provide adequate soot dispersancy also reduce engine wear.

The purpose of this paper is to define the factors which affect oil consumption and cylinder bore polishing. The investigation focused on top land deposits, fuel sulfur, and lubricant viscosity in a series of direct-injection diesel engine tests in the U.S. and Europe. In these engine tests it was demonstrated that excessive top land deposits cause high oil consumption and cylinder bore polishing. Cylinder bore polishing can also be caused by corrosion when high sulfur fuels are used with oils of low alkalinity values. Maintenance of the Crosshatch honing pattern is critical to oil control, low ring wear, and prevention of ring scuffing. Low oil consumption and low cylinder bore polishing can be achieved with lubricant formulations which minimize the top land deposit and provide sufficient alkalinity to minimize the corrosive aspect of bore polishing.

This paper reports results from a quantitative study on the effects of diesel piston temperature and fuel sulfur on piston deposits. Tests were conducted in a fourcycle, turbocharged single-cylinder engine using uncompounded oils and distillate fuel. This fundamental study demonstrated that at constant exhaust smoke, piston temperature between 200°C to 260°C is the primary factor in controlling piston top groove deposit formation. The activation energy for this process was determined to be 12 kcal/mole, which is within the normal range of chemical reactions. The rate of top groove deposit formation doubled for every 30°C rise in piston temperature. Piston temperature also increased total piston deposits on all grooves and lands. Fuel sulfur in the range of 0 to 1.0 wt % had no effect on top groove deposit formation, although it did increase lower groove and lower land deposits. Crankcase oil oxidation appeared to correlate with piston temperature.

This paper reports the effects of diesel engine soot on piston deposits and the crank-case oil in a Mack Multicylinder engine. Its authors found in their study: (1) that diesel engine soot can be a predominant factor in the formation of piston deposits at high exhaust smoke density, (2) that the exhaust smoke density correlates with the soot content in the deposits and in the crankcase oil, and (3) that the soot content of deposits correlates with carbon deposit rating; and that the oxidized resin content of the oil correlates with lacquer ratings. The authors also report on an infrared spectrometric method they developed for quantifying soot in piston deposits, crankcase oil insolubles, or directly in the oil, where it can be quickly and easily monitored.

This paper reviews the mechanical factors affecting oil consumption in four-cycle diesel and gasoline engines and the practical solutions achieved by design modifications. There is an abundance of information on specific aspects of oil consumption, and this paper attempts to combine them in a single comprehensive review. It is based on a synthesis of technical papers, augmented by discussion with engine manufacturers. The pertinent information is organized into six discrete chapters: (1) Piston Rings, (2) Piston Design, (3) Cylinder Bores, (4) Valve Guide Seals, (5) Crankshaft Seals, and (6) Material Selection for Seals and Gaskets.