PETROLEUM DIESEL ENG RATINGS & CONFIGURATIONS - APPLICATION & INSTALLATION GUIDE - LEBW4996-00.pdf

8/17/2019 PETROLEUM DIESEL ENG RATINGS & CONFIGURATIONS - APPLICATION & INSTALLATION GUIDE - LEBW4996-00.pdf

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PETROLEUM DIESEL ENGINE

SELECTION, RATINGS &CONFIGURATIONS

P P L I C T I O N N D I N S T L L T I O N G U I D E

3600 • C175 • 3500C32 • 3400

C18 • C12 • C9 • C7


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Contents

Petroleum Diesel Engine Selection, Ratings & Configurations...... 3 Engine Configuration......................................................... 4

Load Analysis .............................................................. 4

Power Demand Based on Practical Experience .............. 4

Calculated Horsepower Demand ................................. 4

Engine Measured Power Demand ................................ 4

Horsepower, Torque & Machine Productivity ................ 4 Torque Rise Effect on Performance ............................. 5

Transient Response Performance ................................ 6

Adequate Machine Performance.................................. 6

Tolerances............................................................... 6

Auxiliary Loads......................................................... 7

Engine Ratings ................................................................. 8 Engine Capability Determines Ratings.............................. 8

Power Setting Determines Maximum Fuel Rate................. 8

Caterpillar Petroleum Engine Rating Classifications ............ 8

Industrial A — Continuous Ratings .............................. 8

Industrial B — Ratings (Mud Pump Service) .................. 8

Industrial C — Intermittent Ratings (Hoisting Service) .... 8 Industrial D — Ratings............................................... 9

Industrial E — Ratings ............................................... 9

Establishing a Rating..................................................... 9


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Rating Validity.......................................................... 9

Engine Design .......................................................... 9

Rating Curves ........................................................ 10

Special Ratings .......................................................... 10

Actual Power Output Derives from Load Demand............ 10

Diesel Engine Considerations........................................ 10

Turbocharging........................................................ 11

Diesel Fuel Heating Value ........................................ 11

Diesel Engine Rating Conditions................................ 11

Altitude Derating .................................................... 12

Life Related to Load Factor ...................................... 12

Diesel Engine Fuel Conservation ....................................... 13

General Information ................................................ 13

General Conservation Practices .................................... 13

Minimizing Diesel Prime Mover Fuel Consumption ........... 14

Modifying Drilling Practices & Machinery ....................... 16

Engine Sizing versus Generator Sizing........................ 18

DC Motor Characteristics......................................... 19

DC Motor Effects On Generator Selection .................. 19

Drawworks Capability ............................................. 23

Power Outage Concerns .......................................... 28

Other Considerations............................................... 29

Diesel Engine Fuel Conservation Summary ..................... 30


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©2006 Caterpillar®All rights reserved.

Information contained in this publication may be considered confidential.Discretion is recommended when distributing. Materials and specificationsare subject to change without notice.

CAT, CATERPILLAR, their respective logos and “Caterpillar Yellow”, as wellas corporate and product identity used herein, are trademarks of Caterpillarand may not be used without permission.

ForewordThis section of the Application and Installation Guide generally describes

Petroleum Diesel Engine Selection, Ratings and Configurations for Caterpillar®engines listed on the cover of this section. Additional engine systems,

components and dynamics are addressed in other sections of this Applicationand Installation Guide.Engine-specific information and data are available from a variety of

sources. Refer to the Introduction section of this guide for additionalreferences.

Systems and components described in this guide may not be available orapplicable for every engine.


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Application and Installation Guide Petroleum Diesel Engine Selection

©2006 Caterpillar®All rights reserved. Page 3

Petroleum Diesel Engine Selection, Ratings &Configurations

The various petroleum applications of Caterpillar engines require specificconsiderations for engine selection to ensure dependable performance and a

long, trouble-free life. This guide may be used as a checklist of these specificconsiderations for engine selection. Referring to this guide during preliminaryplanning will reduce the possibility of after-installation changes.

SECTION CONTENTS

Engine Configuration ............ 3• Load Analysis• Fuel ConsiderationEngine Ratings..................... 8• Engine Capability Determines

Ratings• Power Setting Determines

Maximum Fuel Rate• Caterpillar Petroleum Engine

Rating Classifications• Establishing a Rating• Special Ratings• Actual Power Output

Derives from Load Demand• Diesel Engine Considerations

Diesel Engine FuelConservation......................1 3• General Conservation

Practices• Minimizing Diesel Prime

Mover Fuel Consumption• Modifying Drilling

Practices/Machinery toReduce Prime

• Summary


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Petroleum Diesel Engine Selection Application and Installation Guide

©2006 Caterpillar®Page 4 All rights reserved.

Engine Configuration

Load AnalysisA major concern in applying

petroleum engines is properapplication of engine horsepower toobtain desired performance,economic operation, and satisfactoryengine life. Successful application ofpetroleum engines requiresunderstanding of powerrequirements, how engines arerated, applicable emissionsrequirements, and knowledge of theproper selection and use of theseratings.Power Demand Based on PracticalExperience

If the power demand of theproposed equipment is not alreadyknown, it must be analyzed. Thisprocess can be simplified ifexperience is available with similarequipment that is powered by anengine of known rating and fuel rate

performance. This informationshows whether the existingequipment is underpowered,correctly powered or overpowered.This assessment can serve as astarting point for the newinstallation; however, it is not asubstitute for calculated horsepowerdemand.

Calculated Horsepower Demand

Using basic engineering principleson work, energy and data on thetype of task to be accomplished, it ispossible to convert all functions ofan application to torque demand andthen to power demand. Calculationmay be the only way available toestimate power requirements at the

start of a new machine design. Ofcourse, this approach is accurateonly if all factors are considered and

assumptions are correct. Forapplications such as pumps or othercontinuous loads, where demand isknown quite well, calculated valuesare quite accurate. In otherapplications, actual demand candiffer significantly.

Engine Measured Power DemandUsually, the most practical way to

assess power demand and engine

capability is to make a selectionbased on calculation or comparisonwith an existing installation and testit. There is no substitute for arigorous evaluation of an engine inservice and operating equipmentsimilar to the proposed application.This provides final proof of machineperformance acceptability, or it willidentify shortcomings in need ofcorrection.

Horsepower, Torque & MachineProductivity

Torque, speed and time are thecomponents of horsepower.Understanding the relationship ofthese components allows them to beleveraged toward an advantage for aparticular application.

Horsepower is the time rate of

doing work; restated, horsepower isproportional to the product of torqueand rpm. Some basic relationshipsare:


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English unitsT x rpmbhp = 5252

5252 x bhpT = rpm

33,000 ft-lb1 hp = min

Where:T = Torque, ft-lb

Metric units T x rpmbKw = 9537

9537 x bKwT = rpm

33,000 ft-lb1 hp = min

Where:T = Torque, N•m

Torque Rise Effect on PerformanceFor equipment capable of lugging

the engine (i.e., applying sufficientload to pull the engine speed downbelow rated speed at full throttle), itis important to consider two other

characteristics of engineperformance. These are torque riseand response to sudden loadchange.

Torque Rise % =

(Peak Torque) – (Rated Torque)Rated Torque x 100

A torque curve is the graphicalrepresentation of torque versusspeed.

Caterpillar diesel engines used inmechanical drives typically providehigh torque rise to perform well in awide variety of applications.

If torque rise capability is higherthan necessary, the machinedriveline may be subjected to torquelevels which may shorten the life ofgearing and bearings. For thisreason, it is sometimes desirable tolet the machine operator shift to alower gear to increase engine speedinstead of always lugging the enginewithout a gear change. So, thedecision to use an extra high torquerise engine must also considerdriveline capability. By contrast, anengine with insufficient torque risewill seem weak and may even stoprunning before the operator has timeto make a gear change. This is not

acceptable either. The bestcompromise is to use enough torquerise to satisfy machine performancerequirements, but not so much thatdriveline life becomes unacceptable.

Devices such as blowers andcentrifugal pumps cannot lug anengine because power demand dropsoff faster than engine capability asspeed is reduced. The amount of

torque rise available in theseapplications is generally meaninglessbecause torque rise is not required,except as it may contribute to theability to accelerate the load.

Generator sets are constant speedapplications and the engines do notneed torque rise capability.


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Transient Response PerformanceThe load response characteristics

of the engine need to meet the loaddemands of the driven equipment.This is not only true for steady state

loads but also for transient loadchanges. For applications where theload changes rapidly, proper engineselection is important to ensure theengine’s ability to pick up the loadwhile maintaining the desired speed.

An important factor in transientresponse is the engine air intakesystem. Naturally aspirated enginesuse air at atmospheric pressure; the

air is not pressurized or forced intothe combustion cylinder. The intakeair on turbocharged engines ispressurized before entering thecombustion cylinder.

A naturally aspirated engine hasthe fastest response to sudden loadincrease because the requiredcombustion air is readily available.There is no additional process of

compressing the air prior to delivery.However, naturally aspirated enginesmay not meet the applicableemissions requirements and havelower power density (power toweight ratio) than a turbocharged

There is a momentary lag in theresponse of a turbocharged orturbocharged and aftercooled enginebecause it takes a moment for theturbo to accelerate upon loadincrease.

Progress in turbochargerdevelopment has produced smaller,faster responding turbochargers and,therefore, turbocharged engineswhich respond quickly to suddenload increase. With steady load and

speed, turbocharger response is ofno consequence. Air/fuel ratiocontrollers, also called smokelimiters, momentarily limit fueldelivery until sufficient air is

available for combustion. Theyrespond to inlet manifold boostpressure. The proper air/fuel ratiosetting provides optimum machineresponsiveness and acceptable levelof transient smoke for a particularapplication.

For applications with widelyvarying cyclic loads (e.g. petroleum

jack pumps or sucker rod pumps),

care must be taken to match theengine’s capability with the loaddemand. On some applications, thelag due to the turbocharger may notallow the engine to keep pace withthe load changes.

Adequate Machine PerformanceManufacturers and customers

develop their own ideas of whatconstitutes adequate machine

performance. Insufficient powercauses low productivity and userdissatisfaction. Excessive powercosts more to purchase, requiresheavier drive system components,and may reduce equipment life if theoperator is careless. The idealmachine is responsive, productive,and durable, satisfying the owner’sneed for performance and overallvalue.

TolerancesActual engine power output may

vary by up to ±3% from nameplatevalue on a new engine. Similarly,where load demand of some work-producing device is published, themanufacturer’s tolerance should be


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added to the demand power, ifpower needs are to be met in allcases.

Auxiliary LoadsIn addition to the engine’s main

load, allowance must be made forengine-driven auxiliary loads. Extraloads imposed by a cooling fan,alternator, steering pump, aircompressor and hydraulic pump mayrepresent a significant proportion oftotal engine power available.

After establishing main load powerdemand and adding all auxiliarypower demands, some additionalpower should be allowed for peakloads (such as grades and roughterrain) and reserve for acceleration,where applicable.


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Engine RatingsPublished engine ratings are

representative statementsexpressing engine power and speedcapability under specific loadingconditions. It is important tounderstand the ratings and themethods in which they aredetermined. Proper use of theratings will assist in the selection ofan engine that meets desiredperformance, economic operation,and satisfactory engine life.

There are several ratings for eachconfiguration of petroleum enginemodel.

Engine Capability DeterminesRatings

Horsepower rating capability isdetermined by engine design.Combined capability and durability ofall engine components determinehow much horsepower can be

produced successfully in a particularapplication.

Power Setting DeterminesMaximum Fuel Rate

Horsepower output of a basicengine model can be varied withinits design range by changing theengine fuel setting or speed setting.Both settings affect the engine’smaximum fuel rate and, therefore,the horsepower output capability.Thermal and mechanical designlimits will not be exceeded if anappropriate engine and rating isselected.

Caterpillar Petroleum EngineRating Classifications

Caterpillar ratings are offered in afive tier format:

Industrial A — Continuous Ratings• For heavy duty service when

engine is operated at ratedload and speed up to 100% ofthe time without interruptionor load cycling.

• Time at full load up to 100%of the duty cycle.

• Typical examples are: pipelinepumping, well service mixingunits.

Industrial B — Ratings (Mud PumpService)

• For service where powerand/or speed are cyclic.

• Time at full load not to exceed80% of the duty cycle.

• Typical examples are: oil fieldmechanical pumping/drilling,independent rotary drive, wellservice blenders, cementers.

Industrial C — Intermittent Ratings(Hoisting Service)

• For service where powerand/or speed are cyclic. Thehorsepower and speedcapability of the engine which

can be utilized for oneuninterrupted hour followedby one hour of operation at orbelow the Industrial A —Continuous power.



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• Typical examples are: off-highway truck, fire pumpapplication power, blast holedrills, oil field hoisting,nitrogen pumping, well service

kill pumps, cementers, electricdrill rig power (also calledPrime power).

Industrial D — Ratings• For service where rated power

is required for periodicoverloads. The maximumhorsepower and speedcapability of the engine can beutilized for a maximum of 30

uninterrupted minutesfollowed by one hour atIndustrial C — Intermittentpower.


• Typical examples are: offshorecranes, fire pump certificationpower, coil tubing units,offshore cementer.

Industrial E — Ratings• For service where rated power

is required for a short time forinitial starting or suddenoverload. For emergencyservice where standard poweris unavailable. The maxi-mumhorsepower and speedcapability of the engine can beutilized for a maximum of 15uninterrupted minutesfollowed by one hour at “INDC” — Intermittent power orduration of emergency.


• Typical examples are: oil fieldwell servicing frac/acidpumping.

Note: Applications examples are forreference only. For exactdetermination or rating tier, refer tothe specific application informationand guidelines in TMI.

Establishing a RatingSome of the application conditions

considered by a manufacturer indetermining a rating for anapplication include the following.

• Load Factor• Duty Cycle• Annual Operating Hours• Historical Experience at a

Particular Rating Level• Expected Engine Life to

Overhaul.

Rating ValidityA properly maintained engine in

actual use will determine whether a

particular rating level is appropriate.Ratings which are validated byacceptable field experience areretained. Continuing enginedevelopment results in ongoingengine improvement and someincrease in ratings may result fromthis process.

Engine DesignEngines are designed and

developed to produce specific powerlevels for particular applications.Subsequent lab and field experienceconfirms the rating validity.Increasing engine horsepowerbeyond approved levels tocompensate for excessive load is not


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acceptable; excessive engine wearor damage can result.

Rating CurvesConsult Technical Marketing

Information (TMI) for availableratings at various speeds for eachmodel and configuration.Specification sheets also providesome of this information forpreliminary sizing purposes.

Special RatingsMost engine applications are well

understood and utilize one of theabove existing published ratings

which have been confirmed bythousands of hours of successfulexperience. However, occasionally, aunique application merits specialrating consideration because ofunusually low load factor orunusually short life requirements. Inthis case, consult your enginesupplier. Factory applicationengineers will require that a specialrating request data sheet besubmitted for review before a specialrating can be considered forapproval. Emissions certificationregulations reduce the feasibility ofsome special rating requests.

Actual Power Output Derivesfrom Load Demand

Regardless of engine rating (powerand speed setting), the actual power

developed by an engine isdetermined by the load imposed bydriven equipment. For example, anengine set to produce 500 hp (373kW) will actually produce only 40 hp(30 kW) if the driven load demandsonly 40 hp (30 kW). For this reason,average fuel consumption indicates

average load demand. Average fuelconsumption also indicates loadseverity on the engine by comparingit with the rated fuel rate associatedwith that rating. When this ratio is

expressed as a percent, it is calledload factor.

Diesel Engine ConsiderationsOn a given engine model, a power

range capability is created byproviding different engineconfigurations such as naturallyaspirated, turbocharged andturbocharged-aftercooled. Someengines may have the aftercoolercooled with engine jacket water(JWAC). Some engines may havethe aftercooler cooled with aseparate lower temperature freshwater circuit (SCAC). Some enginesmay have the aftercooler cooled inan air-to-air cooling device (ATAAC).Emissions requirements many timesdetermine the type of aftercoolingused. Internally, these engines may

differ significantly.Naturally aspirated engines

generally do not meet emissionsregulations.

Increasing power output byinjecting more fuel requiresadditional air for completecombustion and internal cooling.This requires additional mechanicalstrength of internal components and

additional design features such as oil jet cooling for pistons. In any engine,the mass flow of air supplied to eachcylinder determines the amount offuel which can be efficiently burned.The entire engine must be designedfor strength and durability atapproved power levels.


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Turbocharging, using energy fromwaste exhaust gas, provides anefficient means to increase air flow.The power rating of a turbochargedengine is usually limited by internal

temperatures, turbocharger speedand structural limits. Compression ofthe air by the turbocharger increasesair temperature.

An aftercooler between theturbocharger and intake manifoldcools the hot compressed air. Thisincreases air density and allowsmore air to be packed into thecylinder and more fuel to be burned.

The rating is typically limited byinternal temperature limits,turbocharger speed and structurallimits.

Because turbochargers andaftercoolers provide more air to theengine, the engine fuel rate canusually be increased to use this extracombustion air. As a result, enginecomponent loading or turbocharger

speed become the limit on rating.Caterpillar diesel engines do notutilize turbochargers or aftercoolersas add-ons; rather, engines aredesigned and developed in allaspects for these higher loadinglevels. Then they are testedthoroughly to assure long life andsatisfactory performance.

The air-fuel mixture that a naturallyaspirated engine can draw into itscylinders is limited by the engine’sbreathing characteristics andatmospheric conditions. Therefore,an NA engine’s load capability willbe directly affected by altitude andambient temperatures.

TurbochargingTurbocharging is an efficient

means of increasing airflow andpower output. It also allows theengine to be more tolerant of

differences in altitude and ambienttemperatures. However, aircompression by the turbochargerincreases air temperature.

Diesel Fuel Heating ValueFuel heating value affects the

ability to achieve rated power outputbecause fuel is delivered to theengine on a volumetric basis.Allowance should be made for lower

heat content fuel (higher API thanstandard) where the power level iscritical.

Fuel rates are based on fuel oil of35° API {60°F (16°C)} gravityhaving an LHV of 18,360 Btu/lb(42,780 kJ/kg) when used at 85°F(29°C) and weighing 7.001 lb/U.S.gal (838.9 g/L).

Diesel Engine Rating ConditionsRatings are based on SAE 1995

standard ambient conditions. Ratingsare subject to ±3% PowerTolerance. Ratings are valid for aircleaner inlet temperatures up to andincluding 122°F (50°C).Note: Horsepower shown on theperformance curve for generator setapplications may be slightly belowthe advertised horsepower to match

a generator nominal output.Engine performance is corrected to

inlet air standard conditions of 99kPa (29.31 in hg) dry barometer and25°C (77°F) temperature. Thesevalues correspond to the standardatmospheric pressure and


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temperature as shown in SAEJ1995.

Performance measured using astandard fuel with fuel gravity of35° API having a lower heatingvalue of 42,780 kJ/kg (18,390Btu/lb) when used at 29°C (84.2°F)where the density is 838.9 G/L(7.001 lb/US gal).

The corrected performance valuesshown for Caterpillar engines willapproximate the values obtainedwhen the observed performancedata is corrected to SAE J1995, ISO3046-2 & 8665 & 2288 & 9249 &1585, EEC 80/1269 and DIN 70020standard reference conditions.

Altitude DeratingEach model and rating has

established maximum altitudecapabilities for lug and non-lugapplications. For higher altitudeoperation, power settings must bereduced approximately 3% per 1000ft. (305 m) above that rating’s

altitude limit. Mechanicallycontrolled diesel engines do not self-derate enough so that the fuelsetting can be left unchanged. Ifthey are not reset to appropriate

power levels, naturally aspiratedengines may smoke badly andturbocharged engines may sufferexcessive thermal and mechanicalloading, resulting in internal damagewithout giving external indication ofdistress. Engine derating curves arecontained in the TMI.

Life Related to Load FactorUsing an oversized engine

contributes to longer engine lifebecause it runs at a lower overallload factor. It also provides quickerresponse to sudden load changes.Load factor is the ratio of averagefuel rate to the maximum fuel ratethe engine can deliver when set at arating appropriate for a particularapplication. This value is expressedas a percent.


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Diesel Engine Fuel ConservationRapidly increasing fuel prices

coupled with decreasing fuelavailability is receiving increasedattention by contractors and oilcompanies.

Methods to reduce fuelconsumption are under threesections:

• General ConservationPractices

• Minimizing Prime Mover FuelConsumption

• Modifying DrillingPractices/Machinery toReduce Prime Mover FuelConsumption

General InformationThe amount of flywheel kilowatts

(horsepower) produced by burning aliter (gallon) of diesel fuel dependson engine type, condition, andloading. If an engine is operated at

more than half load, a liter (gallon)of diesel fuel can produceapproximately 3.3–4 kW•h/l (17–20hp-h/gal). In contrast, the sameengine lightly loaded will onlyproduce approximately 2.7–3.6kW•h/L (14–18 hp-h/gal) or muchless if operating at no load.

Engine fuel consumption data isstated as:

“Fuel quantity consumption perhour at various loads. This isexpressed in L/h or gal/h.”

The engine burns fuel at no loaddue to the internal demands of waterand oil pumps, friction losses, othermechanical devices, etc.

This accounts for a major part ofthe slope in B curve, Figure 1 . Theseinternal losses become a smallerportion of the total as the engine isloaded. Thus, the engine is moreefficient.

Curve A, Figure 1 , adds the powerrequired to operate the radiator fan.It is not normally included in theengine’s fuel curve due to the wideselection of radiators used in the oilfield.

Note that a radiator fan that takes5% of the engine fuel consumptionto drive at full load may take 16% ofthe engine fuel consumption at 20%load. The percentage would be muchhigher at no load.

Figure 1

General Conservation PracticesFuel will be saved by converting

small diesel engine-driven auxiliaries,such as mud mix pumps,superchargers, etc., to electricmotor-driven units. As an engine-driven device, these auxiliaries arethe only load on that particularengine. Thus, when at light load,


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fuel consumption per flywheelkilowatt (horsepower) delivered ishigh.

On rigs that require winterizing,engine exhaust and jacket waterheat can be recovered and reduceboiler fuel consumption.

Take measures to prevent theft offuel. Eliminate spillage and leakagelosses.

Turn off auxiliary loads when notneeded. Operation of unneededauxiliary loads may represent up to5-10% of total rig load.

Minimizing Diesel Prime MoverFuel Consumption

The following items should beconsidered in regard to primemovers. The secret is to get all theenergy out of each drop of fuel andavoid fuel waste due to poormaintenance and adjustment.

Engine should be maintained toassure optimum fuel consumption.Exhaust smoke under steady-stateconditions indicates incompletecombustion of fuel, hence, increasedfuel consumption. It could be causedby such things as dirty air cleanerelements, dirty aftercooler cores,

turbocharger malfunctioning,incorrect fuel injection timing, faultyfuel injection nozzle, etc. A qualifiedserviceman should be called upon toprovide a specific diagnosis.

Turbochargers may also not beproperly matched to the engine. Thiscan happen with engines that areoperating at a speed other than thatshown on the manufacturer’snameplate.

In such cases an improperturbocharger match increases fuelconsumption by 1–5%, in additionto creating other possible adverseoperating conditions, i.e., excessiveexhaust temperature, slower engineacceleration, etc.

Reduce radiator fan powerrequirements. Radiators of the sameambient capability can have greatdifferences in fan power due to fanrpm and fan diameter differences. Alarge diameter fan at a lower rpmcan deliver the same cfm, but at

greatly reduced power demand.Radiators are available with fans

which draw 1.5 to 6% of the enginerating. The effect of radiator fanpower is quantified in Table 1 .

Increase in Rig Fuel Consumption Due to Radiator FanControlled

Speed Fan (2:1)Engine Load 5% Fan 2.5% Fan5% 2.5%

20% to 40% 12% to 16% 6% to 8% 1% 0.5%

30% to 50% 10% to 14% 5% to 7% 1% 0.5%

40% to 60% 8% to 10% 3% to 6% 1.5% 0.75%

60% to 100% 5% to 8% 2.5% to 5% 1.5% to 3% 0.75% to 1.5%

Table 1


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Considering that drilling enginesspend much of their time at reducedload levels, a further reduction in fanpower can be achieved by using atwo-speed drive (electrical,

mechanical or hydraulic) to operatefan. This savings is illustrated inTable 1 under the column labeledControlled Speed Fans. This columnalso reflects the fact that the enginedoes not operate all year round atdesign ambient conditions.

Controlled speed fan would runcontinuously at low speed until hotweather/high load conditions cause

engine water temperature to rise,signaling the fan drive to run at highspeed.CAUTION: Controlled speed fansmay be prohibited by some emissionregulations.

A single-speed fan drive that isturned on or off may not bedesirable. The radiator supplierwould have to be consulted to

determine if the radiator core cantolerate the repeated temperaturecycling that occurs. When the fan isoff, the radiator out-let water is atengine water temperature and willbe cooled toward ambient as the fanturns on — particularly at light load.This temperature reduction causesthe radiator core to contract.Repeated temperature fluctuationscould result in premature core failureunless the radiator canaccommodate these fluctuations.

When operating on cool or colddays, the radiator ambient capacity,in the low speed operation, willincrease. A low temperature isalways reached where the engine

can be cooled at full load with thefan in low speed operation.Therefore, during winter operations(and most summer operations) thefan may never operate in the high

speed position. Table 2 shows theseapproximate values.

RadiatorAmbient Capability

EngineLoad

FanSpeed

ApproximateAmbient

Capability

100% 100% 125°F (52°C)

100% 50% 80°F (27°C}

50% 50% 125°F (52°C)

Table 2

For additional assurance ofreliability, the two-speed drive canbe arranged such that fan belts canbe reattached to the enginecrankshaft pulley if necessary.

Radiator louvers are a desirablefeature in cold climates, but they donot reduce the fan power demand.

Use of a heavy distillate or crudefuel can reduce fuel costs. Fuelconsumption will reduce in anapproximate inverse proportion tothe ratio of the heat content of thisfuel to regular fuel. However, such afuel cost reduction frequently resultsin increased engine operating costs.Depending upon contaminants oroperational difficulties encountered,engine life could be severelyreduced.

A fuel analysis is certainlyrecommended. This should becompared to permissible and


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recommended fuel specificationswhich can be provided by the enginesupplier. Fuel treatment equipmentmay be commercially available thatconditions fuel to meet permissible

or recommended fuel specifications.It may be necessary to start andstop the engine on diesel fuel.

Used lube oil can be blended intothe fuel supply when properprecautions are taken. However, thereduction of fuel consumption wouldbe in the range of 0.5% — and, fuelfilters would have to be changedmore frequently. It also discolors the

fuel so that it cannot be returned tothe supplier.

Modifying Drilling Practices &Machinery

The first drilling practice to bediscussed is the number and size ofengines used to power a rig. An SCRrig will be assumed.

The importance of engine sizing is

shown by engine fuel curves, Figure2 .

Figure 2

The curve is not flat. Moreimportantly, this is a curve for agiven prime mover. Such curves arenot the same for all manufacturersand/or models. In a given engine

family, a V8, V12, and V16 will nothave identical fuel curves. Betweenengine manufacturers, a V8, V12,and V16 will also differ. Fuel curvesgive testimony to engineconfiguration differences such asaspiration-type, fuel-type and enginesize.

Figure 2 represents suchvariations. All these engines, for

purpose of dramatizing thecomparison, have the same full loadfuel consumption.

An additional point is illustrated inFigure 3 . The fuel quantity vs.percent load chart shows that twoengines have the same fuel curve.The fuel quantity vs. kW (hp) chartshows that these same two engineshave dramatically different fuel rates

at specific load points; this indicatesthe engines are different sizes.This understanding of fuel curves

leads to the following conclusion:When using fuel consumption as oneof the criterions in selecting enginesizes, types and quantities, fuelconsumption at normal operatingloads is of greatest importance. Anapproximation of engine load versustime at various well depths is alsorequired.


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Figure 3

Calculating or estimating fuelconsumption requires the following:• Engine fuel curves —

tabulated in the same format(and down to no loadoperation).

• An actual or typical wellprofile that plots powerrequired versus days ofoperation.

• A format to calculate anddisplay the requiredinformation.

Refer to the IntroductionApplication & Installation Guide forCaterpillar petroleum engine fuelconsumption data.

In drilling applications, the wellprofile data is required to establishthe basis for estimating engine fuelconsumption. Well depth and fuelcost are values you provide.

The well profile itself can be basedon your experience, on-siteevaluation, documented by datarecording systems or a combinationof all of these.

It is suggested that separatedrilling activities should be tabulatedfor each diameter hole being drilled,hoisting time and a grouping fornondrilling times such as logging andwaiting on cement. Refer to Table 3 .

Top Hole days hpDrilling days hpDrilling days hpTripping days hpWait, Misc. days hp

Table 3

Engine operating techniques reflectthe fuel consumption consequencesof the number of engines inoperation. Caterpillar recommendsoperating engines efficiently, but theconsequences of operating moreengines than required should beexplored.


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Engine operating techniques aretabulated under three headings:

• Run all engines — regardlessof need.

• Run one engine more thanrequired — this prevents apower interruption orreduction if a generating unitshould go off the line.

• Run minimum number ofengines — realizing that atemporary power reduction orout-age will occur if agenerating unit should go offthe line.

Generally, tripping hp (tripping out,tripping in and running casing) forthe entire well averages 10 to 20%of the drawworks rated hp. Anyoperating auxiliary load has to beadded.

Wait and miscellaneous time isspent, throughout the entire well,waiting on cement, logging andother operations.

The profile also assumes nogenerator limitations wereencountered which would haverequired more engines running thanindicated.

It is a known fact well profiles varywidely. Specific well profiles shouldbe utilized if more results that areaccurate are required. It may be

necessary to record kW and kVAvalues on some drill rigs to gainreliable representative data. Refer toFigure 4 .

Drill Rig Load Profiles

Figure 4

Engine Sizing versus GeneratorSizing

The engine operating techniquerecommended in this guide mayspark objections and/or demandqualification.

It could be argued that an SRC rig,operating within its power limit, isalready performing efficiently. Thisstatement requires a word of caution— the SCR system’s power limiteror overload control activates foreither kW or kVA overloads. A rigoperating with the power limiter lighton does not mean the engines arebeing efficiently operated. LargerkVA generators (or other remedialaction) may be needed becausegenerators may be at kVA limit and

engines at only 30 to 50% load.A difficulty in efficiently sizing and

operating an SCR or DC rig is thecommon assumption that “x”amperes represents “y” power; thisis not true.


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This fact is represented by systempower factor. If power factor is 1.0,then “x” amperes represents “y”power. At power factors below 1.0,power is less than the amperes

indicate.A power factor from 0.3 to 0.9 on

an SCR rig, under steady-stateconditions, is evidence thatgenerator sizing is important. Duringhoisting, power factor varies from0.0 to 0.95.

Casually speaking, the enginesupplier’s concern regarding powerfactor is that engine powercapability cannot be utilized due togenerator limitations during lowpower factor operation. Thisnecessitates running additionalengines. Running of additionalengines increases rig fuelconsumption and unnecessarilyincreases annual hourly usage ofengines and total operating costs.

There may be cases where the

minimum number of engines cannotbe operated because of a highgenerator kVA requirement.

Before examining these variables,it is first necessary to review somecharacteristics of DC motors.

DC Motor CharacteristicsThe rpm of DC motors is primarily

controlled by the voltage to themotor (recognizing that motor type— series, shunt — and controlsystem — field weakening, etc. —are related factors).

Ampere draw of the motor controlstorque output of the motor.

In other words, torque comes fromthe interaction of magnetic fieldsand the strength of these fields isproportional to amperes, not to DCvoltage. Therefore, kilowatt

(horsepower) load on a DC motor isthe product of volts and amperesand can be expressed as:

V x AkW(DC Output) = 1000

V x Ahp(DC Output) = 0.746 x 1000

Input power would be higher ininverse proportion to motorefficiency.

This leads to the realization that aDC motor can work hard at low rpm(draw high amperage and producehigh torque) and not load the engine(but load the generator) whenoperating at low DC voltage/lowrpm.

DC Motor Effects On GeneratorSelection

DC motors do not have powerfactor identified with them.However, their DC amperes comefrom an AC generator with an SCRsystem providing rectification. ThisAC current does have power factorassociated with it.

The speed/voltage characteristic ofthe DC motor is thus the majordeterminant of the system’s powerfactor.


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Figure 5

Note: System power factor is aweighted average of the DC motorsystem’s effect on the generator’spower factor and that of the ACauxiliary load. The AC auxiliary loadgenerally is only about 20% of theDC load, so its effect on powerfactor is minimal.

Figure 5 shows a method tocalculate AC generator power factordue to current draw of a DC motorpowered through an SCR system.

Figure 6 graphs the effect of motorrpm (or DC voltage) on the powerfactor of the driving AC generators.For a constant rpm (DC voltage),power factor is the same from noload to full load.

System Power Factor ImprovementThe best way to improve system

power factor is to ensure that DCmotors are run at as high an rpm aspossible.

Every DC ampere presents a 0.85kVA load on the generator,

regardless of DC power. Operating aDC motor at high rpm reducesampere load, therefore kVA.

On the rotary table, this meanskeeping the draw-workstransmission in as low a gear aspossible.

Figure 6


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ROTARY TABLE OPERATION

114 hp (85 kW) at DC Motor ____ rpm at _____ DC Amp = ___ pf at ____ kVa

960 118 .9 922

860 131 .8 104

750 151 .7 12-

640 177 .6 140

530 214 .5 168

425 267 .4 208

325 349 .3 300

210 540 .2 420

150 756 .14

640

Table 4

1600 hp (1194 kW) TRIPLEX MUD PUMP140 Strokes Maximum

120 Strokes Rated

Customer Needs 300 gpm @2500 psi = 515 hhp(18.9 L/s @ 17237 kPa = 384 HkW)

DC Motors Gear for 140 spm DC Motors Geared for 100 spm

Liner SizeRequired

Pump Strokes

Motor

rpmAC pf AC kVa

Motor

rpmAC pf AC kVa

5 (127) 97 690 .66 577 970 .92 419

5 ½(140)

81 579 .56 690 810 .76 502

6 (152) 68 486 .45 822 680 .64 598

6 ½(165)

58 414 .40 966 580 .55 701

6 ¾(171)

54 385 .37 1035 540 .51 753

7 (178) 50 357 .34 1118 500 .47 813

7 ¼(184)

47 336 .32 1189 470 .44 864

7 ½(191)

44 314 .30 1274 440 .35 1079

Table 5


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To illustrate the effect of rpm,assume a rotary table is operatingunder the following conditions:

rpm = 30

Torque = 20,000 lb-ft (27 138 N•m)Power = 114 hp (85 kW)Regardless of the rpm of the

driving DC motor, engine load willstay at 114 hp (neglecting losses).However, motor rpm will change thekVA (pf) and, therefore, the size ofgenerator required. This is illustratedin Table 4 .

In the extreme case of 150 rpm, it

does not take a large engine toproduce 114 hp (85 kW), but it doestake a large generator to produce640 kVA.

This phenomena of increasing ACgenerator kVA as the DC motorslows down may seem unexpected,but it is just another way of sayingthat DC motor amperes areincreasing as the DC motor is

required to provide the same powerat lower rpm (lower DC voltage).If DC motors are operated at half

DC voltage or less, an alternativemethod of raising AC generatorpower factor is to operate bothdrawworks motors in series;assuming this option is availablefrom the SCR system supplier. Thisdoubles the voltage out of the SCRsystem and proportionally raises thepower factor. System speed,however, is limited to half the motorspeed.

The same considerations apply tomud pumps. Operating speed shouldbe as high as possible. If pumpsmust be operated at less than half

speed (rather than putting in smallerliners) the SCR system supplier maybe able to supply equipment to allowthe motors to operate in series.

When mud pumps are purposelyoversized to reduce cost of fluid endmaintenance, the mud pump will runmuch lower than rated strokes. Inthat case, specify a motor drivesystem ratio such that motors run ator near their rated rpm. Both mudpump drive types are shown in Table5 .

In summary, required engine powercan be determined by knowing onlyload demand (based on Table 6 andTable 7 ). However, generator sizingalso requires knowing equipmentspeed. The kVA values in Table 7 are for constant power levels butwith various equipment rpms.

Load While Drilling

kVahp/kW

Minimum Average Maximum114/85

515/38492

577209966

6401274

RtMP1

629 hp(469 kW)

669 1174 1914

+ Auxiliary load

Rt = Rotary TableMP1 = #1 Mud Pumps

Table 6

Accordingly, definitive rules forsizing generators cannot beprovided. Estimates of generatorsizing are shown in Table 7 .


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Generator SizingEngine Sizehp (bkW)

GeneratorkVA

600 (450) 750-1000

800 (670) 1100-13001200 (900) 1500-18001500 (1120) 1600-20002000 (1490) 2000-2500

Table 7

This discussion illustrates thatoperating a rig in power limit does

not ensure efficient engineutilization. The goal is to operate theminimum number of engines withoutencountering generator limitations.

Drawworks CapabilityAnother argument regarding the

engine operating techniquerecommended by this guide relates

to underpowering. An operator mayclaim that using one engine duringdeep drilling causes the drawworksto be underpowered.

Many times rig operating personnelare reluctant to operate a minimumnumber of engines under deep holeconditions. They express theconcern that, should they need tooperate the drawworks in a hurry,one engine would not be able to“come off bottom,” and time wouldbe lost while starting additionalengines.

With proper equipment selection,this issue can be partially overcome.The key to understanding thispossibility is to draw a distinctionbetween drawworks power anddrawworks torque. Static hook loadcapacity is determined by generatorkVA, not engine power.


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Starting Torque Comparison

Figure 7


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This was discussed earlier underDC motor characteristics where itwas pointed out that motor torquecomes from the strength of motormagnetic fields.

To dramatize the stall torquecharacteristics, it is useful tocompare torque characteristics ofseveral drives when coming off slips,such as mechanical, torqueconverter, steam and DC (SCR).Refer to Figure 7 .

The surprising data shown inFigure 7 is that developing ratedtorque on a DC motor at themoment when coming off the slipsdoes not load the engine. The engineis loaded in proportion to the speedto which the motor is accelerating.Thus, the electric drive iscomparable to a steam rig.

Ideally, an electric rig will initiallyaccelerate the traveling block, whencoming off the slips, at a constantrate regardless of power capability

of the engine. This constant rate isdetermined by generator kVAcapacity. Motors will accelerate atthis constant rate to the rpm atwhich developed power equalsengine capability. The SCR systemkW limit will then begin to reducemotor ampere draw. The motor willnow accelerate at a slower rate ormaintain a constant rpm, dependingon load.

These factors are illustrated byusing a hypothetical hoisting

scheme. This drawworks has thefollowing characteristics:

1492 kW (2000 hp) CapacityTwo 746 kW (1000 hp) Motors

Each MotorAt Rated

rpmAt Stall

ConditionsDC amp 995 1200AC amp 812 979

KVA 845 1020kW(hp)

746(1000) 0

Table 8

Figure 8 plots drawworks current,power, and hoisting time for a heavyload. Total time to pull a stand ofpipe is 45 seconds. (This is notbased on actual calculations but issufficient to illustrate the desiredphenomena.)

In Part A of Figure 8 , note thatdrawworks DC amperes areindicated as doing three things:

1. Hold weight of pipeagainst gravity under staticor constant rpmconditions.

2. Overcome hole friction.3. Accelerate pipe.

(Note that on a mechanical ortorque converter rig, it would also benecessary to accelerate the engines.)


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Drawworks Under Heavy Load

Figure 8

Drawworks Under Light Load

Figure 9


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In this example, 1000 amps arerequired to hold the weight of thepipe. The remaining 1400 amps areinitially available to accelerate pipe.

In Part B, drawworks power isindicated as being proportionedamong the same three functions.Note that drawworks power startsat zero and reaches rated powerafter 15 seconds. Once thedrawworks motor reaches rated rpm,the kilowatts (horsepower) drop (andmotor amps) to that required for aconstant speed condition.

If we accept 45 seconds as areasonable estimate of heavy loadhoisting time, we can count the DCmotor revolutions as shown in PartC. For this transmission gear andlines strung, it takes 632 turns ofthe motor to pull pipe the required90 ft. (27.4 m). Note that duringacceleration, pipe is being lifted,although at a slower rate.

To perform according to Figure 9 ,

the draw-works has to be fullypowered both with horsepower(kilowatts) and kVA (amps), whichwould be two 3512s with 1250kVA generators.

Figure 9 shows the drawworksunder a lighter load condition but inthe same drawworks gear.

Note that acceleration time hasbeen reduced from 15 seconds to 7

seconds due to the combination ofhaving 1800 amps available foracceleration as compared to the1400 amps in the previous example,and due to the lighter load to

accelerate. Hoisting time has beenreduced only 3 seconds, from 45seconds to 42 seconds. Part Cindicates this by counting motorrevolutions.

Figure 10 shows an underpowereddrawworks with the same heavyload as in Figure 8 . The drawworksis now powered by one 3512 and a1250 kVA generator.

1250 kVA translates into 1470 DCamps. Comparing Figure 8 , Part A,to Figure 10 , Part A, we see thatthis under-torqued drawworks hasonly 470 amps available foracceleration while the fully powereddrawworks has 1400 amps availablefor acceleration. Therefore, thisunder-torqued drawworks willaccelerate much slower than before.

After an estimated 25 seconds,the horsepower will build to therating of the engine. Accelerationwill now continue at a slower rate asthe SCR system power limiter or

overload control phases back theSCR system. This reduces generatoramps sufficiently to hold generatorand engine at full load. Note theengine is not loaded forapproximately 25 seconds.Therefore, the total trip time couldbe about 60 seconds. This time isbroken down as follows:

O – X seconds Acceleration to

engine power limitX – Y Acceleration at slower rateY – Z Constant rpm


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Drawworks Underpowered

Figure 10

Figure 11 overlays Figure 8 , Figure9 and Figure 10 . Part A shows the

important variable is the percentageof available DC amperes available foracceleration. Oversize generatorsprovide increased accelerationtorque; therefore, the faster thedrawworks accelerates, the soonerthe engine can be loaded. Oversizegenerators come close to providingidentical drawworks performance asthat obtained with additional enginesoperating.

For these figures to be totallyrepresentative, available enginepower and generator kVA should bereduced by the online auxiliary loadsleft running.

In summary, oversized generatorsnot only provided for operation of

mud pumps at reduced powerfactors, but they also reduce the

need to fully horsepower thedrawworks, as long as thedrawworks is close to being fullytorqued.

Power Outage ConcernsAn additional concern expressed

by some drilling personnel is thedomino effect. That is, if the load isequal to one and one-half engines,they prefer to run three engines.

Operators may believe that if onlytwo engines were operated, the lossof either of the two generator setswould overload and stall out theremaining generator set.

This does not happen with modernSCR systems due to the powerlimiter or overload control built into


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the SCR system. This controller willphase-back one or more of the SCR-controlled loads sufficiently toprevent engine or generatoroverload.

Other ConsiderationsWith optimum usage, engines

accumulate fewer hours per year butat a somewhat heavier load.

This heavier load may result in asomewhat lower time betweenoverhauls as expressed in engineservice meter hours. However, time

between overhauls as expressed incalendar years will be greater.

Additionally, there will beconditions where engines arepresently so lightly loaded that theincrease in load may still leave theengine moderately loaded andservice life will be only slightlyaffected.

A final benefit of increasing engineload is that the resulting warmer

jacket water temperatures greatlyaid in combating harmful effects ofsome fuel contaminants.

Drawworks with Oversized Generator

Figure 11


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During deep drilling, where theinvestment in the well isaccumulating to a considerableamount and uncertainty regardingthe exact nature of downhole

conditions is also increasing, it is ageneral practice to operate with80% or less engine load.

Diesel Engine FuelConservation Summary

The main means available toimprove fuel conservation are:

• Use electric motor-drivenauxiliaries.

• Use engine heat on winterizedrigs.

• Prevent theft of fuel.• Eliminate spillage and leakage

losses.• Turn off unneeded auxiliaries.• Keep engines properly

maintained.• Reduce radiator fan power

requirements.• Operate the minimum number

of engines.• Size system for operating

kVA.• Operate DC motors in series.• Increase motor rpm.• Utilize oversize generators for

improved hoisting and mudpump performance.


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PETROLEUM DIESEL ENG RATINGS & CONFIGURATIONS - APPLICATION & INSTALLATION GUIDE - LEBW4996-00.pdf

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