Gas Engines Oils TechPaper

8/13/2019 Gas Engines Oils TechPaper

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TECHNICAL PAPER

Gas Engines Need Gas Engine Oils

M. R. Logan, K. D. Carabell, and N. K. SmrckaOronite Additives, Division of Chevron Chemical Company


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Gas Engines Need Gas Engine Oils

M. R. Logan, K. D. Carabell, and N. K. SmrckaOronite Additives, Division of Chevron Chemical Company

.

ABSTRACT

Global demand for inexpensive, reliable power isincreasing every year. In Asia, generators powered bystationary gas engines are becoming increasinglypopular in areas where methane gas is available.Engine populations are expected to grow as gasdistribution infrastructure is built. Although gas enginesmay resemble other engine types in their appearanceand lubricant specifications, they generally benefit fromthe use of lubricants developed specifically for them.This is because gas engines stress crankcase oils in

areas that may not be adequately addressed by oilsdeveloped for other applications. For instance, gasengines can expose the oil to severe nitration andoxidation conditions, and can be very sensitive to ashcontent and composition. Oils not designed properly forthis application can shorten head rebuild cycles,accelerate sludge build-up, and shorten oil and filter life.In this paper, we provide background on gas enginetypes and their applications, discuss the formulationrequirements for gas engine oils (GEOs), and provideexamples of their performance.

INTRODUCTION

The world market for stationary gas engines is growing.Gas engines are now in widespread use around theworld where they are used for gas transmission, powergeneration, and many other applications. Most of themare in North America, where field proven gas engine oils(GEOs) are used to extend engine and oil life (1). Gasengine oils are also used in Europe, where the numberof engines in co-generation has grown dramatically overthe past 10 years. In other parts of the world, whereexperience with stationary gas engines is limited,operators may try to lower costs by using oils designedfor other engine applications. This practice cancompromise performance if the lubricant is not suitablefor a gas engine.

Methane burns hot and can cause severe oxidation andnitration of the engine oil in some gas engines. Gasengines do not produce soot and there is no liquid fuel tohelp lubricate the intake and exhaust valves, so the oilsash is relied on to lubricate the hot valve face/seatinterface. Consequently, ash content and compositioncan have a significant effect on head life. Many gasengine installations also run full-load operationcontinuously, placing the engine under extendedexposure to severe operating conditions. Other enginetypes generally do not impose the same mix of

performance requirements on the lubricant as gasengines do, so lubricants designed for them may not

provide optimum performance. Shortened oil and filterlife, as well as higher piston and engine sludge deposits,can result if the oil has inadequate oxidation andnitration resistance for a gas engine. Increased valvewear and detonation can result from use of an oil with aninappropriate ash content. In this paper, we providesome background on gas engines and their applications,describe the engine oils designed for them, and provideexamples of the excellent performance gas engine oilscan provide if they are formulated well.

STATIONARY GAS ENGINES

AND APPLICATIONS

Stationary gas engines are generally used in industrialapplications and vary in output from about 500 to 8000kW. The corresponding bore sizes run from about 125to 450 mm (5 to 18 inches). Both four- and two-strokecycle engines are used, although the two-stroke cyclemodels are not popular outside of North America.Modern gas engines are generally available instoichiometric and lean-burn configurations. The lean-burn engines can produce very low levels of NOx, butthey require more sophisticated air/fuel ratio controltechnology. Both types are found in the Asia Pacific

Region.

There are many gas engine builders around the globe(Figure 1), with Caterpillar and Waukesha having thelargest engine populations worldwide. On a regionalbasis, Dresser and Cooper Industries are majorsuppliers in North America while Deutz-MWM,Jenbacher Energiesysteme, and MAN DezentraleEnergiesysteme are strong in Europe. In Asia Pacific,major suppliers include Caterpillar and Waukesha, butEuropean, Japanese, and other North American enginesare also used.

Figure 1 Major Stationary Natural Gas EngineBuilders

Caterpillar Cooper Industries (Ajax, Cooper Bessemer, Superior) Dresser Industries (Clark, Dresser-Rand, Waukesha) Deutz-MWM Jenbacher MAN Ruston Wrtsil NSD (Sulzer, SACM, GMT) Waukesha Others


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Figure 2 shows an example of a typical gas-gatheringsite. At these sites, it is common to group 10 or moreengines within a range of 500 meters to draw gas out ofa network of wells in the ground and pump it to a largertransmission station. The figure shows two CaterpillarG399TA engines with rotary compressors mounted onskids for easy installation. The engines are four-stroke,

158 mm (6-1/4 inch) V-16's and produce 694 kW (930hp) of power each. As with most gas engineapplications, they run full load, 24 hours a day, tomaximize the return from the installation.

Figure 2 - Two Caterpillar G399TA Engines at a GasGathering Site

Figure 3 - A Clark TCVC Two-Cycle Integral Engine/Compressor at a Gas Transmission Site

Figure 3 shows where the gas may go next on its way toits customers. It shows a large two-stroke cycle enginehoused in a transmission line pumping station. Thesestations are typically fully enclosed, and house fromabout three to twenty similar engines mounted next toeach other. The figure shows a Clark TCVC engine.This is a two-stroke cycle, 450 mm (17-3/4 inch) V-20engine producing 7437 kW (10,000 hp). The engines

integral compressors can be seen on the right side ofthe engine. They are referred to as integral because

their connecting rods share one of the enginescrankshaft journals with those driving the powercylinders. These are permanent installations designedto operate for many years. It is not uncommon for someof the engines in these pumping stations to be 30-50years old. They generally operate from 70% to 100%load around the clock. These types of engines are

found mostly in North America where they support anationwide network of gas transmission lines. Outsideof North America, where transmission installations aregenerally newer, it is more common to find gas turbinesat installations where this amount of pumping power isrequired.

Figure 4 shows an example of a gas engine operatingon the downstream side of the gas distribution system.Rather than pumping gas, it is generating power. Inareas where gas is available, gas engines are generallya more cost-effective way to produce power than dieselengines. Such installations can be found around the

globe in many applications where local power is needed.They can provide the primary source of power,supplement other sources, or provide emergencybackup. The figure shows a Caterpillar 3516, 170 mm(6.7-inch bore) V-16 engine producing 750 kW (1006 hp)of power. These engines are typically skid-mountedunits purchased as a combined engine-generator set.Depending on the installation, the engines may run onlya few hours a year, but normally they run at full loadcontinuously.

Figure 4 - Caterpillar G3516 Gas Engine GeneratorSet Producing 750 kW (1000 hp)

Figure 5 shows a schematic of an energy efficientadaptation of the gas engine to power generation that ispopular in Europe. Often referred to as combined heatand power (CHP) or co-generation, heat from the enginecoolant and exhaust gases are used to provide hot wateror steam. Co-generation boosts the overall thermal

efficiency of the gas engine from less than 50% to morethan 80%, giving a clean source of power and heat forsmall housing complexes, hospitals, greenhouses, and


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other applications. CHP installations can stress theoxidation inhibition of the engine oil because they maymaintain elevated engine jacket water temperatures tomaximize heat transfer. This can increase local oiltemperatures in various parts of the engine and increaseoxidation rates. Some engine builders maintain aspecial list of products approved for this tough

application.

Figure 5 - Schematic of Co-Generation Installation

Aside from burning natural gas comprisedpredominately of methane, gas engines are run on othertypes of gas as well. One of the most challenging gasesto operate on from both an engine and lubricant designstandpoint is landfill gas. It is produced fromdecomposing organic refuse that has been deposited ata collection site, capped off when filled, and thenplumbed with a network of gas collection pipes (Figure

6). Landfill gas typically contains about 50% methane, issaturated with water, and contains dirt particles. Landfillgas can be made into good quality fuel by drying andfiltering it adequately. However, there may still remain asignificant challenge for the engine oil if the landfill sitehad solvents and/or refrigeration systems dumped in it.

As they decay, these may release chloro- or fluoro-hydrocarbon vapors. Once these vapors are drawn intothe combustion chamber and burned, they can producestrong acids that attack the engine parts. Speciallyformulated oils can be required to minimize corrosion insuch installations. In addition, corrosion resistanthardware may be required. Natural gas engines are

also used to generate power from sewage gas, coal gas,and other types of gas. These gases are often high inhydrogen sulfide and can also be corrosive, but they areusually less corrosive than landfill gas. Short oil drainintervals may be required for these applications. Oilswith higher Total Base Number (TBN) may also beneeded, but this not recommended for all enginesbecause it increases oil ash levels and may affectengine component life.

Figure 6 - Schematic of Landfill Site Gas CollectionSystem

In the Asia Pacific Region, most gas engines are used toproduce local power, but the applications are diverse(Figure 7). They include power generation for airports,hospitals, casinos, and factories. While most of theseengines use pipeline gas, they are also used inapplications where other gas types are used includingcoalfield gas to provide power to local mines and landfillgas. Gas engines may also be found in a number of

mechanical operations including gas compression andbuilding chillers.

Figure 7 - Gas Engine Application Examples in theAsia Pacific Region

Power Generation Airports Hotels Hospitals Casinos Factories Mines Glass Factories Paper Mills Other Industrial Facilities

Mechanical Gas Pumping Building Chillers

GAS ENGINE OIL DESCRIPTION

Our introductory remarks may have left you asking whatis so special about gas engine oils. First, let's discussthe primary fuel used in gas engine applications,

methane (Figure 8). Its four C-H bonds give it a higherspecific heat content than liquid fuels like gasoline ordiesel that contain some lower energy C-C bonds.Consequently, it burns hotter than other fuels undertypical conditions. In addition, since it is already a gas,methane does not cool the intake air by evaporation asliquid fuel droplets do. Furthermore, many gas enginemodels are run either at or near stoichiometricconditions, where less excess air is available to diluteand cool combustion gases. As a result, gas enginescan generate higher combustion gas temperatures thanengines burning liquid hydrocarbon fuels. Since the rateof formation of NOx increases exponentially withtemperature, gas engines can generate NOxconcentrations high enough to cause severe nitration ofthe engine oil. If the engine oil is not formulated to


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handle this environment, it will deteriorate in a mannersimilar to severe oxidative degradation, causing enginesludge, piston deposits, oil filter plugging, and in severecases, accelerated ring and liner wear.

The degree of nitration of the oil can vary significantlydepending on the engine design and operating

conditions. Lean burn engines produce less NOx thantheir stoichiometric counterparts, so they tend to nitratethe oils less. Indeed, they may produce less NOxthan acomparative diesel. Some operators may richen theair/fuel mixture on these engines to increase poweroutput and consequently increase oil nitration levels. Atsome sites, a single oil may be required to lubricate anumber of engines including stoichiometric and lean-burn models, so a product with good nitration resistanceis required in most gas engine installations.

Figure 8 - Whats So Special About Gas Engines? They Burn Natural Gas

They Burn Natural Gas Gas Burns HOT! Severe Oil Nitration and

Oxidation Leads to Sludge Formation andViscosity Increase

Gas Has No Heavy Ends No Soot in Oil Gas is Dry Oil Ash Controls Valve Wear -

Optimum Ash Level is Required But Ash Deposits Can Cause Preignition Ash

Level Must Be Optimized No Sulfur (Usually) Less Base Number

Required

Gas Engines Are Used in Industrial Applications

High Load Factor Severe Oil Stress Remote Operations Reliability Essential Wide Variation in Types Flexible Products

Required

There Are No Industry Oil Specifications

Oils Must Demonstrate Performance in FieldTesting

Oils Must Be Compatible With Engine Catalyst Oil and Additive Company Expertise is Required

We mentioned earlier that gas engines burn fuel that is

introduced to the combustion chamber in the gaseousphase. This has a significant affect on the intake andexhaust valves because there is no fuel-derivedlubricant for the valves like liquid droplets or soot.Consequently, gas engines are solely dependent on thelubricant ash to provide a lubricant between the hotvalve face and its mating seat. Too little ash or thewrong type can accelerate valve and seat wear, whiletoo much ash may lead to valve guttering andsubsequent valve torching. Too much ash can also leadto detonation from combustion chamber deposits.Consequently, gas engine builders frequently specify anarrow ash range that they have learned provides theoptimum performance. Since most gas is low in sulfur,

excess ash is generally not needed to address alkalinityrequirements, and ash levels are largely optimized

around the needs of the valves. There may beexceptions to this in cases where sour gas or landfill gasis used.

The applications in which gas engines are used mustalso be taken into consideration. In most cases, theyare used continuously at 70 to 100% load with oil drain

intervals typically ranging from about 750 to 1500 hours.In comparison, an engine operating in vehicular servicemay only spend 50% of its time at full load. Drainintervals can vary in vehicular service, but may convertto fewer hours of service in many cases. Gas enginesmay also be installed in remote areas where servicemay not be readily available, and may be expensive.Reliability is essential to minimize downtime andmaintenance costs.

This background helps identify the formulatingrequirements for gas engine oils (Figure 9). A highresistance to oxidation and nitration is required. Good

valve wear control is critical for keeping engine operatingcosts down and is achieved by providing the properamount and composition of ash. Minimizing combustionchamber deposits and spark plug fouling are alsoconsiderations in setting the ash content andcomposition in these oils. Since the ash levels arelimited, extreme care must be taken in the detergentselection to minimize piston deposits and ring sticking.Good wear protection is also required to prevent scuffingand corrosion. Again, the antiwear components used inthe formulation must be selected carefully for gas engineapplications to ensure that nitration-resistant additivesare used.

Figure 9 - Formulating Requirements of Gas EngineOils Four Stroke

High Resistance to Oxidation and Nitration Good Valve Wear Performance Low Combustion Chamber Deposits No Spark Plug Fouling Good Piston Deposit Control Good Antiwear and Antiscuff Properties Optimized Ash Content

While gas engine oils have specific needs, there are no

industry specifications for them. Extra care must betaken in selecting a lubricant for this application. Mostbuilders only specify the physical and chemicalproperties of lubricants for their engines, and emphasizethe use of field service to demonstrate performance.Figure 10 lists the ash and performance specificationsfor most of the major engine builders. (See Appendix fora complete listing of specifications.) The ash levelsrecommended for gas engines are generally specified innarrow concentration bands to maximize the valve lifefor particular engine models. The optimum levelspecified varies somewhat by builder, and may also varyfor particular engine models from the same builder.Products with about 0.5% ash meet many of thebuilders specifications, and are referred to as low-ashproducts. However, some builders recommend higher


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ash levels for lean burn engines or applications wheremore alkalinity is required. A second product, with about0.9 wt % ash, should serve most other applications.These are referred to as mid-ash formulations. Most ofthe builders recommended ash levels are lower thanthose currently in use for vehicular applications. Thesetypically range from a low of about 0.8% ash to 1.8%

ash.

To ensure that at least minimum quality oil is applied,some gas engine builders also specify that API CC orCD engines oils should be used. These are obsolete

specifications developed around diesel engines, and areno guarantee that satisfactory performance will beattained in a gas engine. As a result, even oils marketedas GEOs can have a wide range of performancedepending on whether they were formulated properly forthis application or not. To illustrate this, we provide acomparison of crankcase sludge between two gas

engine oils run in a laboratory engine in Figure 11.Although Product B met the specifications for API CC, itwas not formulated to resist nitration. As a result itformed a heavy sludge in the crankcase of the engine.

Figure 10 - Natural Gas Engine Oil Ash and Performance Requirements(Sweet Gas, Spark Ignited Four-Cycle)

Builder Ash, Wt % API Category Field TestCaterpillar 0.4 - 0.6 YesDresser Rand Yes

Jenbacher StoichLeanox


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Additive systems that meet the widest range of gasengine builders specifications and provide cascadingoptions offer the most flexibility to oil suppliers. Finally,because field experience is so important in thisapplication, the engine builder or major oil supplier isoften involved in selecting the right lubricant for a

particular gas engine installation.

EXAMPLES OF GAS ENGINEOIL PERFORMANCE

Natural gas-fueled engines typically run continuouslynear full load at a constant speed. This type of serviceplaces extreme demands on the crankcase oil.Nevertheless, oils can provide exceptional performancein this application if they are formulated properly for it.The proof of a products performance is in its ability tolubricate these engines in the field. In this section, weprovide examples of the field performance of gas engineoils designed specifically for this application. All arebased on oils formulated with an additive systemproviding a 0.45 wt % ash, 5.1 TBN, 1200 ppm calcium,280 ppm phosphorous, and 300 ppm zinc, and will bereferred to here as GEO-1.

Piston deposit control is critical in any engine to preventring and liner wear. If deposits become excessive in thegrooves, they will push the ring against the liner andcause adhesive wear. If they become excessive on thelands they can polish and abrade the liner surface. Thefollowing provide field test examples of piston depositcontrol and liner wear with GEO-1.

Caterpillar G3516TA

Figure 12 shows a piston from a Caterpillar G3516TAengine. This is a 16-cylinder, turbocharged andaftercooled gas engine. During the test, it was operatedat 90 to 100% load and 1125 rpm, and produced 783 kW(1050 hp). It ran for 8354 hours with 1300-hour oil drainintervals, 30% longer than Caterpillars recommended1000-hour interval for this engine. As the photo reveals,the piston was clean with no carbon deposits in thegrooves or lower lands. The rings were checked prior toremoval, and all of them were free so they couldoperate as designed. Figure 13 shows that the

undercrown was also clean, ensuring that the pistoncould continue to be cooled by the oil.

Waukesha 7042 GSI

Figure 14 shows a piston from a Waukesha 7042GSI.This is a 12-cylinder, turbocharged and aftercooled gasengine. During the test, it operated at 1000 rpm, 90%load, and produced 865 kW (1160 hp). This engine ran5904 hours with 2000 to 2500-hour oil drain intervalsversus Waukeshas recommended 1500 hours. Again,the pistons ring grooves and lower lands were clean.

All of the rings were free (not trapped in the grooves by

deposits).

Figure 12 - Caterpillar G3516TA Piston

8354 Hours on GEO-1 With 1300-Hour Oil Drain Intervals

Figure 13 - Caterpillar G3516TA Piston Undercrown5904 Hours on GEO-1 With 2000-2500 Hour

Oil Drain Intervals

Figure 14 - Waukesha 7042GSI Piston5904 Hours on GEO-1 With 2000-2500 HourOil Drain Intervals

Control of valve recession is also important tosuccessfully lubricate stationary gas engines. In fact,overhaul intervals are often driven by the need torefurbish the heads and valves because the wear limithas been reached. To help extend valve life andminimize valve recession, gas engine builders may


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lower their seat angles to increase the valve to seatcontact area and improve heat transfer. Seat angleshave been as high as 45 but now are usually about 30.Since the valves depend on the oils ash to lubricate thiscontact area, the ash throughput and composition arecritical to achieving maximum head life.

Figure 15 shows the test engines exhaust valves on theleft and the intake valves on the right. For this engine,the average exhaust valve recession rate was 0.0381mm/1000 hours (0.0015 in./1000 hours). Waukeshaslimit on average valve recession rate for exhaust valvesis 0.0508 mm/1000 hours (0.0020 in./1000 hours). Thishead should make it to or beyond its normal serviceinterval of 20,000 hours before an overhaul is required.

Figure 15 - Waukesha 7042GSI Valves5904 Hours on GEO-1 With 2000-2500 HourOil Drain Intervals

If the engine oil contains too much ash, it can causevalve guttering and torching. The guttering is initiated bya section of the ash film on the valve seat flaking off andcreating a leak path for hot exhaust gases (2,3). Overrepeated cycles, the leak path widens and eventuallyallows enough hot gas through to melt the valve.Torching can also be caused by detonation of the air/fuelmixture during the compression cycle caused byexcessive ash deposits in the combustion chamber.Figure 16 shows an example of a torched valve from agas engine burning landfill gas and using an oilcontaining 1% ash.

Figure 16 - Torched Valve From a Landfill GasEngine

Waukesha 9390GL

Lean burn engines produce lower levels of NOxbut canincrease valve recession rates. This may be related togreater valve face and seat corrosion rates because ofhigher oxygen concentrations in the exhaust gases. Asa result, lean burn engines can be very sensitive to ashthroughput (as determined by the oils ash content andconsumption rate) and composition. Figure 17 showsthe valve recession rates for a Waukesha 9390GLoperating on the GEO-1 oil described above. This is a16-cylinder, turbocharged and intercooled gas engine. Ithas the same power assembly (VHP) as the Waukesha7042 discussed above, but is a lean burn type run with

about 9.8% oxygen in the exhaust. This engine ran15,388 hours at 85 to 90% load, producing 1193 kW(1600 hp) at 1000 rpm. The oil was changed per theOEM recommended 1500-hour drain interval. As thefigure shows, the valve recession rate was well belowthe limit for this OEM, indicating that the operator maybe able to extend the normal overhaul interval for thisengine.

Figure 17 - Valve Recession Rates in Lean BurnWaukesha 9390 GL Engine With GEO-115,388 Hours on GEO-1 With 1500-Hour Oil Drain Intervals

0

0.01

0.02

0.03

0.04

0.05

0.06

Intake Exhaust

ValveRecessionRate,

mm/1000Hours

Waukeshas Limit 0.0508


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Sludge control is also important in gas engines. Asmentioned earlier, gas engines can produce high levelsof NOx. These oxides of nitrogen attack engine oil andnitrate it, leading to an increase in the oils viscosity andthe formation of sludge. While lean burn engines tend tohave lower levels of nitration than their stoichiometric

counterparts, the long duration of this test (of roughly 2years) makes it an interesting one to look at sludgedeposits on. The picture in Figure 18 shows that GEO-1kept the rocker box in this engine extremely clean for theextended period that this test was run for. This kind ofperformance is evidence that the nitration of the oil hasbeen kept under control.

Figure 18 - Waukesha 9390GL Top Deck15,388 Hours on GEO-1 With 1500-Hour Oil Drain Intervals

Caterpillar G398TA

An older, but very common engine in gas service is theCaterpillar 6-1/4 inch (158 mm) bore G300 seriesengines. These are run near stoichiometric conditions,so they stress the oils nitration resistance. The engineused was a G398TA model. This is a 12-cylinderturbocharged and aftercooled gas engine producing448 kW (600 hp) at 1000 rpm. The photos shown weretaken after 7860 hours of operation with 1500-hour drainintervals at 85 to 95% load. This is double Caterpillarsrecommended 750-hour drain interval for this engine.Figures 19 and 20 show the piston and undercrowndeposits. The piston grooves and lower lands had

minimal deposits, giving a total weighted demerit of 39.9,and the undercrowns were clean. These low depositlevels helped control liner wear, as shown in Figure 21

where the cross-hatching is still visible throughout mostof the bore. The sludge deposits were also negligible asshown by the condition of the rocker cover in Figure 22.

Figure 19 - Caterpillar G398TA Piston7860 Hours on GEO-1 With 1500-Hour Oil Drain Intervals

Figure 20 - Caterpillar G398TA Piston Undercrown7860 Hours on GEO-1 With 1500-Hour Oil Drain Intervals

Figure 21 - Caterpillar G398TA Liner7860 Hours on GEO-1 With 1500-Hour Oil Drain Intervals


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experiment, three oils with similar ash content (0.54-0.56wt %) and metallic source (1190-1260 ppm calcium and790-800 ppm zinc) were compared. The results areshown in Figure 26. In spite of the similarity in these oilsby ash and metal content, Oils C1 and C2 gave lessthan one-third the valve recession rate of the high

reference oil. This helps illustrate the impact that theoils formulation can have on head life. Both ash leveland ash type can have an influence on head life. As aresult, the best performance is likely to be achieved froma product optimized for gas engine applications.

Figure 26 - Illustration of How Oils That AppearSimilar May Not Perform the Same in ValveRecession Control

0

50

100

150

200

250

300

350

400

High Ref. Cand. C1 Cand. C2

ExhaustValveRecession,mm

Estimated From EOT

Valve Seat Measurements

Oil High Ref. Cand. C1 Cand. C2

Ash, Wt % 0.56 0.54 0.54

Ca, ppm 1260 1200 1200

Zn, ppm 790 800 800

Vis. Grade 15W-40 15W-40 15W-40

*Reprinted With Permission From SAE Paper No. 981370 1998Society of Automotive Engineers

COSTS ASSOCIATED WITHPREMATURE HEAD REBUILD

As shown above, the use of an optimized GEO in gasengine applications will help maximize engine life butusers may be discouraged from purchasing them

because of higher oil costs. Instead, users may use alow cost, low quality oil. One must look at the entirepicture to understand the relative cost involved in the oilselection. To illustrate the overall cost impact of usinggas engine oils, lets consider the combined oil and headrebuilt costs associated with a 20,000-hour period in ahypothetical gas engine. Lets assume that the cost torebuild the heads on a gas engine is around $30,000 forparts and $2,500 for labor and the engine uses about5500 liters of oil per year. If a gas engine oil is $0.20 perliter more expensive compared to a low cost engine oilat $1 per liter, the savings is $1100 in oil per year. Onthe other hand, gas engine oils control valve recession

better than low cost oils and could give about 50%longer head life, as the data in the above section shows.

An engine that runs 20,000 hours on a gas engine oil

may only run 13,000 hours on a low cost engine oil. Theextra cost of the additional head rebuilds for the low costoil far outweighs the savings in oil expense as Figure 27shows. In 20,000 hours of operation, the use of a lowcost oil can actually cost an additional $13,500 becauseof the additional maintenance costs. The true cost of

using the wrong oil in a gas engine can be substantiallyhigher than expected if one adds in the extramaintenance, downtime, and lost production.

Figure 27 - Illustration of the Impact an OptimizedGEO Can Have on Head Rebuild Costs

$0

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

$70,000

Low Cost Oil Example Optimized GEO

Head Rebui ld Cos t , $ /Y r

O i l Cos t , $/Y r

COMPRESSED GAS-FUELED VEHICLES

The focus of this paper has been on stationary gasengine oils. However, compressed methane is enjoyinga new popularity as a fuel for vehicles, so a fewcomments about the applicability of these oils to thisemerging mobile application are appropriate. In general,we find that the mobile engines running on this fuel havesome of the same requirements as the large stationarygas engines, but there is an important distinctionbetween the two applications. Both use a gaseous fuelso their oils need good oxidation and nitration controland an optimum ash level for the valves. And of course,soot dispersancy is not an issue. One importantdistinction between the mobile and stationaryapplications is in the valve train design. If the engineshave slider followers, then they may have additionalwear protection requirements beyond what stationaryengines need (4). Since most GEOs are designed tocomply with a 300-ppm phosphorous limit to be

compatible with emission catalysts, they may not providesufficient wear control in slider-follower engines unlessthey are boosted with additional wear inhibitors. Anotherdifference is the duty cycle. Vehicular applications willhave lower duty cycles, but more cyclic loading. As withstationary engines, the mobile engines are likely tobenefit from the use of engine oil designed specificallyfor that application.


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SUMMARY

Gas engines may appear on the outside to resemble thesize and specifications of a diesel engine, but theirengine oil requirements are considerably different.Since the methane in gas engines burns hot, the

crankcase oils must be able to handle high levels ofoxidation and nitration. The lack of liquid fuel or soot tolubricate the exhaust valve-seat interface leaves theengine designer to rely solely on the oils ash to controlrecession. Ash concentration and composition play akey role in determining valve recession rates and headoverhaul maintenance intervals.

A well formulated gas engine oil can provide excellentwear and deposit control, but misapplication of an oil notdesigned for gas engines can degrade performance andnegatively impact operating costs. Oils specificallyformulated for gas engines are available worldwide.Gas engine oils are engineered to perform best in gasengines.

REFERENCES

1. N. K. Smrcka, Development of a New-GenerationLow-Ash Oil Additive Package for Natural GasEngines, ASTM Paper 91-ICE-A (1991).

2. J. A. Mc Geehan, J. T. Gilmore, and R. M.Thompson, How Sulfated Ash in Oils CausesCatastrophic Diesel Exhaust Valve Failures, SAEPaper 881584 (1988).

3. W. R. Pyle and N. K. Smrcka, The Effect of

Lubricating Oil Additives on Valve Recession inStationary Gaseous-Fueled Four-Cycle Engines,SAE Paper 932780 (1993).

4. W. V. Dam, J. P. Graham, R. T. Stockwell, and A. M.Montez, A New CNG Engine Test for the Evaluationof Natural Gas Engine Oils, SAE Paper 981370(1998).


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Appendix

GasEn

gineOilSpecifications-Four-StrokeCycle

OEM

SO4Ash,

Wt%

Phosphorus,

Wt%

Zinc,

Wt%

TBN(D2896),

mgKOH/g

SAEGrade

Other

Bergen

LowAsh

None

~5,~7-8SourGas

SAE40

Caterpillar(1)

0.4to0.6

-

-

-

15W-40,30,

40

APICCorCD

CooperBessemer

bmep175

psi

"

"

Min.MIL-L-45199B/2104B/A

PICD

DresserRand

-

-

-

-

SAE30

FieldTestingRequired

-

SAE15W-4

0

Jenbacher

l=13.0,Prefer>4

SAE40

APICCorMIL-L-2104B

(CRCL-38Pass)

Leanox

0.6-1.0

-

-

~8.0

SAE40

MIL-L-2104CPref./

MIL-L-2104BAccept./(CRCL-

38Pass)

MANB&WDualFuel

1.0Max.

4to6

SAE40

MIL-L-2104D/APICD,Mineral

BaseOil

MANDezentrale

Energiesysteme(MDE)

0.4

-0.7,Lower

Preferred

None

-

>3.0

SAE30/40/20W-40

15W-40/5W-30

FieldTest/ApprovedList/

SealSwellTest/MANCondemnsOil

MANBrons

0.35-0.65Sweet

0.6-0.9Sour

0.5Max.Catalyst

-

-

3-6Sweet

5-8Sour

SAE40

MirrleesBlackstone

1.0Max.

-

-

Min.5

SAE40

APICD/GoodPerformanceList

(DualFuel

Only)

MWMDeutz(KHD)

New:0.50Max.

Old:0.75Max.

Synth:1.0Max.

-

-

Min.3

SAE40

SAE30/SAE

40

MIL-L-2104B/APICC/MWM-B/FieldTest

Niigata

DualFuel

0.9Max.

-

-

4to7

SAE30/SAE

40

ISOT/KHT/L-38/4Ball/1G-2/FieldTest

SparkIgnition

0.6Max.

-

-

3to7

SAE30/SAE

40

ISOT/KHT/L-38/4Ball/1G-2/FieldTest

1Alsorecommendashlessoilswithgoo

dfieldexperienceinGXXXengines.


14/15

13

Appendix

GasEn

gineOilSpecifications-Four-StrokeCycle(Cont'd)

OEM

SO4Ash,

Wt%

Zinc,Wt%

TBN(D2896),

mgKOH/g

SAEGrade

Other

Ruston

(SparkIgnition)

Max.:0.5Sweet,

0.7Sour,1.0LFG

Max.:

0.08Sweet,

0.05Sour,

0.03

LFG/Sour

Min.:N/ASweet,

5Sour,8LFG

SAE40Pref./

S

AE30Accept.

(DualFuel)

Max.:0.7Sweet,

0.9Sour,1.0LFG

Max.:

0.08Sweet,

0.05Sour,

0.03

LFG/Sour

Min.:4Sweet,

6Sour,

9LFG/Sour

SAE40Pref./

S

AE30Accept.

W

rtsil(SACM)

(DualFuel)

1.0Max.

7.5Min.

SAE

40Pref./SAE30

Accept.

W

rtsilNSD

V.I.95Min,Vir

ginBase

(SparkIgnition)

0.6Max.

4.0to7.0

SAE40

SEMTPielstick

0.4to0.6Recommended

Superior

NA

0.5to1.0Preferred.

(Ash

lessandLowAshAcceptable)

2Min.Sweet,

6-12Sour

SA

E40CD-IISF

MIL-L-2104E

NoBrightStock,100%Solvent

RefinedBase

Stocks

TC

0.5to1.0

(AshlessandLowAshNot

Acceptable)

2Min.Sweet,

6-12Sour

SA

E40CD-IISF

MIL-L-2104E

NoBrightStock,100%Solvent

RefinedBase

Stocks

1700and2400Series

0.4to0.6Required

2Min.Sweet,

6-12Sour

SAE30,SAE40

APICDWithMinera

lBaseStocks

Wa

ukesha

VGF(2)

0.5to1.0

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

VSG

0.35to1.0

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

Intermediate

0.35to1.0

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

VHP(RichBurn=

1)

0.35Min.

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

VHP2895,5108,5790GL

(=

1.5-2)

0.35Min.

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

VHP3521,5115,7042,

9390GL(=

1.5-2)(3)

0.9to1.7

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

AT25/27

0.35Min.

0.1

SAE30or40(1)

APICDWithMinera

lBaseStocks

1SA

E30below71Csumpand40above.

*WithMineralOil

2So

memodelsrequireanominal0.5wt%

ash,othersa1.0wt%ash;checklate

stWaukeshaServicebulletin.

3En

gineswithrockerarmmodificationspe

rServiceBulletin7-2754,orproductionenginesshippedafterMarch31,1997,mayuseoilswith0.35wt%ashminimum.


15/15

14

Appendix

GasEn

gineOilSpecifications-Two-Strok

eCycle

AshCategory

AshLevel

Builder

Ashle

ss

LowAsh

Min.

Max.

Zinc

Max.,%

Comments

API4

Service

Viscosity

V.I.

BaseStocks

Cooper-Bessemer2

bmep85psi

X X

X

0.00.0

0.80.1

AshlessPref.

Ashless

CACB

SAE40

SAE40

70Min.

70Min.

NoBrightStock

NoBrightStock

Dresser-Rand(Clark)

X

X

PortPlugging

Minimized

WithAshless

1

1.3-13.8

cS

tat100C

Dresser-Rand

(Worthington)

NoAsh

Recommendations

MIL-L-

2104(CB)

SAE40

HVIorMVI

FairbanksMorse,

MEP

DuelFuel

SparkIgnition

X X

0.40.2

1.10.5

3-10TBN

3-7TBN

MIL-L-

2104B(CC)

S

AE30or

SAE401

55to75

Naphthenic(5)

Ajax(2)

X

X

0.0

0.8

0.04

AshlessPref.

CAorCB

SAE303

70Min.

NoBrightStock

1SAE30foroiltemperature185F.

2ManufacturedbyCooperCamero

n.

3Multigradesacceptableifrequiredforcoldstart.

4MostbuildersweighfieldperformancemoreheavilythanAPIclassification.

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