Caterpillar Air Intake Systems LEBW4969-04

8/9/2019 Caterpillar Air Intake Systems LEBW4969-04

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AIR INTAKE SYSTEMS

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


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Contents

Air Intake Systems

Foreword..............................................................................1

Air Cleaners ..................................................................... 2

Standard Air Cleaners.................................................... 2

Heavy-Duty Air Cleaners................................................ 3

Precleaners .................................................................. 3

Dual Element Air Cleaners.............................................. 3

Exhaust Ejector ............................................................ 3

Oil-Bath Air Cleaners ..................................................... 4

Remote Mounted Air Cleaners ........................................ 4

Customer Furnished Air Cleaners .................................... 5

Air Cleaner Efficiency ................................................ 5

Air Cleaner Design Requirements ..................................... 6

Air Cleaner Dust Calculation........................................... 6

Combustion Air Flow Requirements..................................... 8

Air Intake Ducting............................................................. 9

General........................................................................ 9

Marine Intake Air Piping Examples .................................10

C175 Remote Mount Air Cleaner ...................................10

Air Inlet Adapters.........................................................14

Connections to Inlet Adapters and Turbochargers ........14

Joining Two Turbochargers...........................................16

Turbocharger Loading...................................................17

Flex Connections .........................................................18


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Cleanliness During Installation .......................................18

Inlet Air Duct Insulation ................................................19

Air Intake Restriction....................................................19

Example..................................................................20

Additional Considerations .................................................21

Service Indicators ........................................................21

Trip Lock Device......................................................21

Differential Pressure Gauge .......................................21

Intake Air Silencers ......................................................21

Air Inlet Shut Off .........................................................21

Air Manifold Drain Valve...............................................22

Shielding.....................................................................22

Breakaway Joints ........................................................22

Cold Conditions ...........................................................22

Air Cleaner Icing ......................................................22

Boost Control ..........................................................23

Extreme Cold...........................................................23

Considerations for Low Pressure Gas .........................23

Controlling Air Temperature ......................................24

Gas-to-Air Heat Exchanger ........................................25

Reference Material ...........................................................26


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ForewordThis section of the Application and Installation Guide generally describes

wide-ranging requirements and options for the Air Intake System on Cat®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 ofsources. Refer to the Introduction section of this guide for additionalreferences.

Systems and components described in this guide may not be availableor applicable for every engine. Below is a listing of air intake systemcomponents for various Cat engines. Refer to the Price List forspecific options and compatibility.

= Standard

= Optional

- = NotAvailable

3 1 2 6 B

C 7

C - 9

C 9

C - 1

0 / C - 1

2

C 1 1 / C 1 3

3 4 0 6 E

C - 1

5 / C - 1

6

C 1 5 / C 1 8

3 4 1 2 E

C 2 7 / C 3 2

3 5 0 0

C 1 7 5

3 6 0 0

G 3 3 0 0 / G 3 4 0 0

G 3 5 0 0

G 3 5 2 0 C

G 3 6 0 0

Standard DutyAir Cleaners

Heavy Duty AirCleaners - - - - - -

Precleaners - ‡ - - -

Dual Element Air

Cleaners

†

- - -

-Exhaust Ejectors - - - - - - - - - -

RemoteMounted AirCleaners

- - - - - - - - - - - - -

ServiceIndicator, TripLock Device

ServiceIndicator,DifferentialPressure Gauge

- - - - - - - - - - - ‡ - - - -

Intake AirSilencers - - - - - - - - - - - - - - - - -

Inlet Air Shutoff - - - - - - - - - - - ‡ - - - -

Air ManifoldDrain Valve - - - - - - - - - - - - - - - -

Cold WeatherBoost ControlValve

- - - - - - - - - - - - - - - - -

† Standard on select models, Optional on others.

‡ Optional on select models, Not Available on others.


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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, “Caterpillar Yellow,” the “PowerEdge” trade dress as well as corporate and product identity used herein, aretrademarks of Caterpillar and may not be used without permission.


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Application and Installation Guide Air Intake Systems

©2011 CaterpillarPage 2 All rights reserved.

Air Cleaners

Dirt and debris are the major sourceof engine wear. For this reason, aircleaners are necessary to remove dirt

and debris from the incoming air. Anymoving engine part may be subjectedto accelerated wear when dirt iscontained in the inlet air. Since theair intake is one of the primarylocations where dirt may enter anengine, frequent replacement of aircleaners may be needed.

Dirt and debris is introduced intothe intake air ducting through:

• Residual materials from initialfabrication and assembly ofthe intake air ducts.

• Filter changes.

• Leaks in the ducting system.

• Intake air flow.

Engine wear tests have shown thatdust particles under 1 micron(0.00004 in.) size have little effect

on the engine. 99.5% of this dustwill pass out through the engineexhaust.

Dust particles 1 to 10 microns(0.00004 to 0.0004 inch) in size hasa measurable effect on engine life.Inlet air dust particles larger thanbearing oil film thicknesses willseriously affect bearing and pistonring life.

Well designed air cleaners are themost efficient way of assuring thatonly clean air enters the engine andharmful particles are not distributedthrough the engine systems.

The efficiency of dry-type filtersis not affected by installation

orientation. However, special careshould be used in arranging the filterhousing and piping to ensure that

dirt retained in the filter housing isnot inadvertently dumped into theengine air supply during air cleanerservice. A vertically mounted aircleaner with a bottom-mountedengine supply pipe is particularlyvulnerable to this occurrence. A filterdesign incorporating a secondary or“safety” element which remainsundisturbed during primary filter

change should be used. Its higherinitial cost is offset by itscontribution to longer engine life.

Standard Air CleanersThe standard air cleaner on most

Cat engines uses a high-efficiency,dry paper element packaged in a lowrestriction, weather resistanthousing. They remove 99.5% of ACfine dust and are designed to

minimize dust entrance during filterchanges. Some newer models use aPowerCore air cleaner featuring aspecial nanofiber element design.These cleaners achieve the filtrationgoals with lower restriction to airflow thanthe dry paper element design.

On most engine models, theseair cleaners are engine mounted,

however, on some engines the aircleaners are supplied loose forremote mounting. See RemoteMounted Air Cleaners later in thissection. Refer to the engine pricelists for availability of air cleaneroptions on specific engine models.


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Air Intake Systems Application and Installation Guide

©2011 CaterpillarAll rights reserved. Page 3

Heavy-Duty Air CleanersHeavy-duty air cleaners provide the

same protection as standard filtersbut allow extension of filter change

periods. Depending on the engineair-flow rate and filter type, serviceperiods may be extended six toseven times that of standard aircleaners.

Depending on specific design, dualelement air cleaners may also becategorized as heavy duty aircleaners.

PrecleanersPrecleaners are an available option

on some Cat engines, which, whenadded to the standard air cleaner,can extend filter service periods.

The precleaner imparts a swirlto the air, centrifuging out a majorpercentage of the dirt particles whichmay be collected in a reservoir orexhausted out on either a continuousor an intermittent basis.

A flow restriction of 0.25 to1.5 kPa (1 to 6 in. H2O) is imposedby the precleaner, but it can prolongthe life of the filter by three to seventimes. Any application in anenvironment with heavy dust anddebris is recommended to use aprecleaner.

Dual Element Air Cleaners

Dual element air cleaners can beused to provide additional protectionfor the engine. This arrangementuses two elements mounted inseries. The secondary filter remainsin place while the primary filter isserviced.

A dual element configurationdiffers from a double elementconfiguration it that the twoelements are used in parallel.

Dual element air cleaners are also

available with a precleaning stage.

Exhaust EjectorIn extremely dusty environments

where dust and other particles causeair cleaners to plug up quickly, animproved precleaner has beendesigned. It is an integral part of anexhaust aspirated air cleaner systemand will extend the service life of the

air cleaner elements.Using a louvered body design, the

precleaner has a very high separatorefficiency. It will separate andremove over 90% of the dirt andchaff from the incoming air stream.

Example of Precleaner, Air Cleaner

and Exhaust Ejector

Figure 1


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The air comes into the precleanerwhere the dirt and chaff is removedfrom the air. With a slight vacuum,the dirt is sucked directly throughthe muffler into the exhaust flow

and does no harm to the engine.Refer to Figure 1.

The remaining dust in the air isthen removed by the air cleanerbefore it enters the turbo.

With this system, considerationmust be made regarding the locationof exit of the exhaust and thesurroundings, as there may beparticles in the engine exhaust.

Oil-Bath Air CleanersOil-bath air cleaners, while

sometimes required to meetcustomer specifications, are notrecommended by Caterpillar.At best their efficiency is 95%as compared to 99.5% for dry-typefilters. Their relative ease of serviceand insensitivity to water areadvantages easily outweighedby disadvantages, such as:

• Lower efficiency

• Low ambient temperaturelimits, low oil level, highrestriction at low air flow (suchas at low idle), and installed tiltangle may lessen efficiencyfurther.

• Oil carry-over, which is the oil

becoming airborne in the airintake system whether resultingfrom overfilling or increased airflow, can seriously affectturbocharger and engine life,and may actually become anengine fuel.

Remote Mounted Air CleanersDue to air flow requirements and

size considerations, it is impracticalto mount G3520C and 3600/G3600air cleaners on the engine. They are

furnished as shipped loose items,and must be remote mounted andplumbed by the customer. Aircleaner systems, and their supportstructures, should never be mountedon the engine block, or any enginecomponent. The engines are notdesigned to support this extraweight and engine vibrations will betransmitted to the structure and

piping. The air cleaner housings maybe wall, floor, or roof mounted withthe inlet facing downward, or theycan be oriented for horizontal entry,but modifications are required tosupport the elements.

Two element (double) and threeelement (triple) air cleaner housingsare available. Unlike the dualelement arrangement, air flowthrough these elements is in parallel.

The double and triple air cleanerhousings have optional precleanersand soot filters, to extend elementlife in severe applications. Examplesof remote air cleaner housings areshown in Figure 2 and Figure 3.


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Double Element Housing

Figure 2

Double Element Housing with

3 Precleaners

Figure 3

For marine and offshoreapplications, where remote mountedair cleaners may be located in a saltwater environment, epoxy coatedhousings are available. Refer toFigure 4 and Figure 5 in the nextsection for typical marine arrange-ments for remote mounted aircleaners.

Dirty or improper filters can restrictintake air flow. Differential pressurereadings should be used to signalneeded filter changes.

Caution: Under no circumstances

should the engine be operatedwithout air cleaners.

If the air cleaner enclosure(s) areoutside in the weather, a protectiveshield is recommended to preventrain from being pulled into thecleaners/precleaners.

Customer Furnished Air

Cleaners

Air Cleaner Efficiency

Customer furnished air cleanerselection should be based upon thefollowing air cleaner efficiency test:

A satisfactory air cleaner mustmeet the International Organizationof Standardization’s requirement ofthe ISO 5011 dust test.

The filter should have 99.5%minimum efficiency as calculatedfollowing test code with additionsand exceptions as follows:

• Air flow corrected to m3/min at99.9 kPa pressure and32.2°C (ft3/min at 29.6 in. Hgpressure and 90°F).

• Use sonic dust feeder.

• Dust quantity determined bylight-duty class.

• Filter to be dried and weighed inan oven at 93°C to 107°C(200°F to 225°F) before andafter test.

• Use AC fine dust.


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AC fine dust is defined as follows:

Particle Size

(microns)% Total Weight

0 – 5 39 ± 2

6 –10 18 ± 311 – 20 16 ± 3

21 – 40 18 ± 3

41 – 80 9 ± 3

99.5% filtration of the AC finedust has been determined to be apractical combination of the kind ofdirt likely encountered in service,and will result in an air cleaner

efficiency expected to giveoptimum engine wear life.

Air Cleaner Design RequirementsFollowing the above procedure will

establish sufficient control on thefilter media filtering ability of thetested air cleaner, but there are otherdesign variables needing furthercontrol.

•

Choose filters supplied bymanufacturers that can bestprovide quality control.

• Design filters to be resistantto damage at initial assemblyor during cleaning. If end sealand filter media are subjectto damage, dust leakage intothe engine can result.

Air Cleaner Dust Calculation

3600/G3600 engines must notingest more than 34.5 mg/hr/cylinderof dust at rated power to achieveacceptable engine life. Air cleanersoffered by Caterpillar are designed tothis requirement. Customer providedair cleaners must also meet this

requirement or reduced engine lifewill result. Specific dust consumptionfor various engines, air cleaners, andenvironments can be calculated usingthe following formula.

V x d x (1 - e) x 60 D =

n

Where:

D = Specific dust consumptionin mg/hr/cylinder

V = Intake air flow in cu ft/min(cfm).

d = Dust concentration in mg/cu ft(Estimated dust concentrationfor residential and offshoreapplications is 0.001 to0.002 in mg/cu ft. Estimateindustrial and inland waterwayapplications at 0.002 to0.05 in mg/cu ft.)

e = Average air cleaner efficiency(always < 1.0) (estimatedefficiency of paper elements =

0.99, & estimated efficiency ofnon-paper elements = 0.95)

n = Number of engine cylinders(6, 8, 12 or 16)

Example A

A 3606 Engine operating at900 rpm in an EPG applicationwith non-paper elements.

V = 5554 CFM

d = 0.02 mg/cu fte = 0.95

n = 6

5554 x 0.02 x (1 – 0.95) x 60D =

6


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Example A equates to a dustconsumption of 55.54 mg/hr/cylinder. Since the engine mustnot ingest more than 34.5 mg/hr/cylinder of dust for acceptable

engine life, this air cleaner systemis unacceptable.

Example B

Using the same engine but withpaper air cleaner elements that offerapproximately 0.99 efficiency(e = 0.99).

5554 x 0.02 x (1 – 0.99) x 60D =

6

Example B equates to a dustconsumption of 11.1 mg/hr/cylinder.This air cleaner system will provideacceptable engine life.


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Combustion Air Flow Requirements

Combustion air flow requirementswill vary, depending on the specificengine model and rating. Specific airflow data for Cat engines is given inboth volumetric [m3/min (cfm)] andmass [kg/hr (lb/hr)] flow terms, atstandard reference conditions.

Reference conditions fortemperature and pressure are usedto provide a basis for consistentmeasure of combustion airquantities. However, different partsof the world subscribe to different

standards, thus it is important tonote that the metric and Englishconditions are not equivalent.Caterpillar practice is to use ISO8528 “normal” conditions of 25°C(77°F) and 101.3 kPaa (14.7 psia)when providing values in metricunits, and ASME SAE J1349“standard” conditions of 25°C(77°F) and 101.3 kPaa (14.7 psia)

when providing values in Englishunits.

To convert from mass airflow tovolumetric airflow at referenceconditions, use the followingformula:

MR

SR = QR

Where:

MR = Mass air flow at referenceconditions (kg/hr), (lb/hr)

QR = Volumetric air flow atreference conditions (m3/min),(cfm)

SR = Density of air at referenceconditions (kg/m3), (lb/ft3).(Density of air = 1.292 kg/Nm3 (0.074 lb/ft3))

To convert both mass airflow andvolumetric air flow from referenceconditions to site conditions, use thefollowing formulas:

TS MR x TR

= MS

TS QR x

TR = QS

Where:

MR = Mass flow at referenceconditions (kg/hr), (lb/hr).

MS = Mass flow at site conditions(kg/hr), (lb/hr).

QR = Air flow at referenceconditions (m3/min), (cfm).

QS = Air flow at site conditions(m3/min), (cfm).

TR = Air temperature at referenceconditions (°K), (°R).

TS = Air temperature at siteconditions (°K), (°R).

°K = °C + 273.

°R = °F + 460.


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Air Intake Ducting

GeneralWhen ducting is necessary to

obtain cooler or cleaner air, thefilters should remain on the engineto prevent harmful dirt from leakinginto the engine through ducting joints. When air cleaners must beremote-mounted it is extremelyimportant that all joints be air tightto prevent ingestion of dirt.

When designing air intake ducting,consideration must be given to

appropriate routing, duct supportand system restriction, especially onthe larger engines, where overheadcranes are used to service theengines. Proper support for ductwork adjacent to the engine iscritical, so that its weight is notborne by the turbocharger or otherengine-mounted components.

Locate the air piping away fromthe vicinity of the exhaust piping sothat the air provided to the engine isas cool as possible. Air temperatureto the air inlet should be no morethan 11°C (20°F) above ambient airtemperature. Inlet air temperatureshould not exceed 45°C (113°F)for standard ratings.

Avoid abrupt transitions in theintake ducting to provide thesmoothest possible air flow path.

When unavoidable, transitionsshould be made as far upstream ofthe turbocharger as possible. Keeptotal duct head loss (restriction)below 0.5 kPa (2 in. H2O) formaximum filter life. Any additionalrestriction will reduce filter life.

To allow for minor misalignmentdue to manufacturing tolerances,engine-to-enclosure relative

movement and isolate vibrations,segments of the piping shouldconsist of flexible rubber fittings.These are designed for use on dieselengine air intake systems and arecommercially available. Thesefittings include hump hoseconnectors and reducers, rubberelbows and a variety of specialshapes.

Wire-reinforced flexible hoseshould not be used. Most materialavailable is susceptible to damagefrom abrasion and abuse and is verydifficult to seal effectively at theclamping points unless special endsare provided on the hose.

Inlet ducting should be designed towithstand a minimum vacuum of12.5 kPa, (50 in. H2O), which is also

the structural capability of the Catair cleaner filter element.

Piping diameter should be equal toor larger than the air cleanerinlet/outlet and the engine air inlet.A rough guide for pipe size selectionis to keep maximum air velocity inthe piping to 10 m/s (2,000 fpm).Higher velocities will cause highnoise levels and excessive flowrestrictions. Refer to the Air IntakeRestriction section for guidance indetermining required intake ductsizing.

All piping must be designed andsupported to meet any local seismicrequirements that may be in force.


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The ducting should be of seamlessor welded seam piping to minimizethe flow restriction. The ductingshould also be constructed ofmaterials suitable for local

environmental conditions such asoffshore or marine applications.

Beaded pipe ends at hose joints arerecommended. Sealing surfacesshould be round, smooth and free ofburrs or sharp edges that can cutthe hose. The tubing should havesufficient strength to withstand hoseclamping forces. Either T-bolt typeor SAE type F hose clamps that

provide a 360° seal should be used.High quality clamps must be used.Double clamps are recommended onconnections downstream of the aircleaner.

PVC piping has a number ofbenefits. It is light-weight, providesa good seal without the chance ofweld slag coming loose and will notrust. However, it is not well suited

for high or low temperatureenvironments. It can lose much ofits strength when subjected totemperatures of 150C (300F) orabove. It can also become brittle andshatter at low temperatures. If usingPVC pipe, use at least schedule40 pipe and check that it meetslocal regulations for the areaclassification.

If ferrous material is necessary,it must be properly cleaned afterfabrication and treated to preventrust and scale from accumulating.Stainless steel ducting should be

treated in the same manner. Flangedconnections with gaskets arepreferred over threaded connections.Fasteners such as rivets should notbe used.

Unsupported weight on clamp-type joints should not exceed 1.3 kg(3 lb).

Marine Intake Air Piping

ExamplesFigure 4 shows a 3600 marineapplication configured to use aremote mounted air cleaner andoutside air for combustion. An intakeair heater may be required for coldweather operation.

Figure 5 shows a 3600 marineapplication configured to use aremote mounted air cleaner and

engine room air for combustion.C175 Remote Mount Air

CleanerFigure 5A shows a C175

application to use a remote mountedair cleaner and outside air forcombustion. An intake air heatermay be required for cold weatheroperation.


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Remote Mounted Air Cleaner with Outside Air Intake

Figure 4


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Figure 4A


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Figure 5A

Air Inlet AdaptersCaterpillar offers various air inlet

adapters for connecting toturbocharger air inlets. The adaptersare part of the system to provide anefficient transition from the engineroom intake air ducting to the engineturbocharger. Adapters are typicallyshipped loose and include gasketsand mounting hardware.

CAUTION: Turbochargerperformance may be adverselyaffected if appropriate air intakecomponents are not used (they aredesigned to provide the proper airflow pattern ahead of theturbocharger).

Connections to Inlet Adapters and

Turbochargers

The piping connected to theturbocharger inlet should bedesigned to ensure that air is flowingin a straight, uniform direction intothe turbocharger compressor. Thisis typically achieved by installing astraight section of pipe, equal inlength to at least two or three times

pipe diameter, to the inlet. Thisarrangement reduces the possibilityof premature compressor wheelfailure due to pulsations created byair striking the compressor wheel atan angle. Transitional ductingimmediately preceding the straight


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section of pipe should consider thefollowing guidelines:

• The duct between the straightpipe and elbow cannot haveprotruding edges.

• The bend can be designed as acircular arc or with sections ofmitered pipe with rectangular orround flow cross sections, or as

transition from round torectangular cross section.

• An accelerated flow isexpected to occur in the bend.The flow area (F) should be:

F1 > 1.5 x F2, as shown inFigure 6.

Turbocharger Vertical Inlet Design Options

Figure 6


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Inlet Pipe Design Joining Two Turbochargers

Figure 7

Joining Two TurbochargersWhen ductwork feeding two

turbochargers is combined to form

a single duct, a steadying zone mustbe provided after the dividing joint;as shown in Figure 7. The steadyingzone B must be a minimum of5 times the pipe diameter:

B > 5 x Dh1

The flow area is:

F0 = 1.0 ÷ 2.0 x F1

The transitions from Sections 0-0to 1-1 and from 1-1 to 2-2 will havemany circular or rectangularvariations due to turbochargerhardware and installation sitedesign. Regardless of the transition

selected, the steadying zone mustbe provided.

The transitions used to combine

multiple ducts must also followtypical design standards describedin this guide. Ducts should havesmooth transitions and not causedisturbance in the air flow. Pipingdesigns that use a Tee, as shownin Figure 8, should not be used toconnect multiple ducts.

Figure 8


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Turbocharger LoadingWhen remote-mounted air cleaners

are used, turbocharger loading fromthe weight of the air inletcomponents becomes a concern.

The turbochargers are not designedto support any additional weightbeyond standard factoryattachments. When possible, makethe flexible connection directly tothe turbocharger air inlet, as shownin Figure 9. All duct work to thatpoint along with the air cleaner andits support structures, should not bedirectly mounted to the engine

Figure 9

The maximum allowableturbocharger load will vary,depending on the engine model,the inlet adapter and the adapterorientation. In the example below,

Figure 10, the 90° inlet adapter canbe rotated in 30° increments.Turbochargers for 3600/G3600engines are designed to withstanda maximum moment of 294 N•m(217 ft-lb). Figure 10 shows howthe moment can be calculated.

Models that provide a mountingbracket for the turbocharger inletadapter, such as the C15, can

support up to 11.3 kg (25 lb) ofduct weight.


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Provisions should be made toinspect the ducting for cleanliness just prior to initial start up. If thepiping is not clean, it must becleaned before the engine is started

at commissioning. This may requireremoval of the piping from itsinstalled position.

Inlet Air Duct InsulationInsulation may be needed on the

intake ducting for remote mountedair cleaners. Insulation reducesturbocharger noise emitted intothe engine room and will minimizepre-heating of intake air.

Air Intake RestrictionExcessive vacuum on the inlet side

of the turbocharger (or the air inleton naturally aspirated engines) canresult in reduced engine powercapability and degrade engineperformance.

Air intake restriction is also anemissions critical parameter declared

to obtain EPA non-road certification.Therefore, the air intake system’stotal restriction (including dirty filters,duct work, vents, silencers, etc.) islimited depending on engine model,rating and air configuration. The airintake restriction limits for Catengines can be found in the TechnicalInformation Appendix or TMI.

In order to maximize air filter life, it

is important to keep total ductrestriction below 0.5 kPa (2 in. H2O).Every additional restriction caused bythe air inlet system subtracts from airfilter life. Maximum filter life ispartially dependent on the absolutepressure differential between the

turbocharger compressor inlet andatmosphere.

Inlet air restriction includes thepressure losses between the aircleaner and the engine air inlet

connection. For remote mounted aircleaners, the following formulas canbe used to calculate duct restriction.

L x S x Q2 x 3.6 x 106P(kPa) =

D5

L x S x Q2 P(in. H20) =

187 x D5

Where:P = Restriction (kPa), (in. H2O)

psi = 0.0361 x in. water column

kPa = 6.3246 x mm water column

L = Total equivalent length ofpipe, measured in (m), (ft)

Q = Inlet air flow, measured in(m3/min), (cfm). - (found inTMI or performance book,

and corrected for siteconditions when necessary)

D = Inside diameter of pipe,measured in (mm), (inches)

If the duct is rectangular, asshown in Figure 11:

Then:

2 x a x b D =

a+b

Figure 11


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S = Density of air kg/m3 (lb/ft3)

352.5 S(kg/m3) =

Air Temperature + 273°C

39.6

S(lb/ft3) = Air Temperature + 460°F

Use the following formulas toobtain equivalent lengths of straightpipe for various elbows.

33DStandard Elbow(radius = diameter)

L =X

20DLong Radius Elbow(radius = 1.5 diameter)

L =X

15D45° Elbow(radius = 1.5 diameter) L =

X

66DSquare Elbow(radius = 1.5 diameter) L =

X

Where:

x = 1000 mm (12 in.)

As shown above, if 90° bends arerequired, long radius elbows, witha radius of 1.5 times the pipediameter, offer lower resistancethan standard elbows.

Example

Below is an example of an airintake duct restriction calculation.

A 3412 packaged genset has aninlet air flow of 36.7 m3/min

(1292 cfm) with duct configurationconsisting of 3 m (10 ft) of straightlength duct along with 2 standardelbows and a long radius elbow. Thepipe has a diameter of 152.4 mm

(6 in) and the temperature of theair is 55°C (131°F).

First calculate the total equivalentlength of the ducting.

3000 mm + 2(33 x 152.4) 20 x 152.4L =1000 mm

+1000 mm

L = 16.1 m

120 in+ 2(33 x 6) 20 x 6L =

12 in+

12 in

L = 53 ft

Next, calculate the density of

the air.

352.5 S =

55 + 273°C

S = 1.075 kg/m3

39.6 S =

131 + 460°F

S = 0.067 lb/ft3

Lastly, insert the previous resultsinto the duct restriction formula andcalculate.

16.1 x 1.075 x 36.72 x 3.6 x 10

6

P =152

5

P = 1.02 kPa or 104 mm H2O

53 x 0.067 x 12922

P =1.87 x 6

5

P = 0.147 psi or 4.07 in H2O

Total duct restriction should bebelow 0.5 kPa (2 in. H2O). The ductrestriction in this example is abovethe desired value, and therefore thisduct configuration is unacceptable.


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process in the event of anemergency shutdown by stoppingthe flow of combustion air. This isnot recommended for gas engines,as they have the ability to positively

stop the combustion process bycontrolling the source of ignition.

The air inlet shut-off feature isstandard on 3600 diesel engines andavailable on many other Cat dieselengines. It is normally used when anengine will be operating in apotentially combustible environment.This feature can be actuatedmanually or electronically, but is for

emergency use in case of engineoverspeed only, not for normalengine shutdown.

Air Manifold Drain ValveAn air manifold drain valve is

available for the 3600 diesel enginefamily, consisting of an automaticfloat valve that drains thecondensate from the engine airmanifold. The C175 offers a manual

ball type air manifold drain valve asan option. Otherwise, draining mustbe facilitated by removing thestandard plugs from the aftercooleroutlet lines.This feature isrecommended for use in applicationswhere high humidity is expected andthe possibility exists for the air inletmanifold temperature to drop belowthe atmospheric dew point. Refer

to Caterpillar Service PublicationSEBD9317 and SEBU8100 for moreinformation on this subject.

ShieldingThe air inlet should be shielded

against direct entrance of rain orsnow. The most common practice is

to provide a cap or inlet hood whichincorporates a course screen to keepout large objects. This cap should bedesigned to keep air flow restrictionto a minimum. Some users have

designed a front air intake whichprovides a direct air inlet and aninternal means of achieving waterseparation.

Precleaners and prescreenersincorporated into the intake capdesign are also available. They canbe used where special conditionsprevail or to increase the air cleanerservice life. These devices can

remove 70% to 80% of airbornedirt.

Breakaway JointsA breakaway joint may be used on

a cab or hood to tilt away from theengine compartment for accessibilityand servicing of the engine. Half ofthe rubber seal flange remains onthe engine air intake and the otherhalf is secured to the enclosure or

hood.

If carefully designed and used onlyupstream of the air cleaner,breakaway joints may be used.

Note: Never use breakaway jointsbetween the air cleaner and engine.

When breakaway joints arerequired, chose a joint designedfor lifetime sealing under the mostsevere conditions and needinglimited or no maintenance.

Cold Conditions

Air Cleaner Icing

Air cleaner icing can occur insaturated air environments when thedew point of the ambient air is near


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freezing. Small disturbances to theair such as velocity and pressurechanges at the air cleaner inletreduce the moisture-holding capacityof the air. This results in moisture

condensation and ice crystalformation. The ice buildup reducesthe airflow area and increases thepressure differential across the aircleaner. Eventually, a plateau isreached where the pressuredifferential remains constant eventhough ice buildup may continue.Power loss and increased fuelconsumption will result during theseperiods.

Several techniques may be usedto overcome air cleaner icing. Onesolution is to heat the intake airslightly. It is not necessary to heatthe air above freezing. The airrequires only enough heat to beabove the dew point. Heat can besupplied to the air cleaner housingby ducting engine room air. Heatedair from the exhaust piping ormuffler, or electrical heating tapemay also be used.

Boost Control

A boost control valve is availablefor the 3600 diesel engine familyfor use in extremely cold ambientconditions, 0°C (32°F). The valve isused to limit the air inlet manifoldpressure during low air temperatureconditions to maintain acceptable

cylinder pressure.

Extreme Cold

Heated engine room air may berequired (for starting purposes only)in applications at very cold ambienttemperatures, -25°C (-13°F). Thisassumes combustion air is being

drawn from outside the enginebuilding, and the engine ispreconditioned with pre-heaters formetal, water and oil temperatures of0°C (32°F). Admitting engine room

air must be done without thepossibility of allowing dirt or debrisinto the air inlet system of theengine.

Considerations for Low Pressure Gas

Take special care when designingthe air intake system for low-pressure gas engines that do nothave air-fuel ratio control.

Carburetors used in Cat gas

engines meter fuel into incoming airon a volume-for-volume basis. If thedensity of either the air or the gaschanges relative to the other, the air-fuel ratio of the engine will change,affecting emission levels and thedetonation margin.

For example, if a G3516 LowEmissions engine with an 11:1compression ratio and 32°C (90°F)

A/C is adjusted to produce 2 g NOx at full load, the percent of O2 in theexhaust must be set to 8%, whichresults in an air-fuel ratio of 14.75on a volume-for-volume basis.

If the engine is adjusted when theincoming air is 10°C (50°F) and theincoming gas is 21°C (70°F), then:

∆T1 = 10°C - 21°C = -11°C(∆T1 = 50°F - 70°F = -20°F)

If the air temperature is laterincreased to 32°C (90°F) and thegas temperature remained constant,then:

∆T2 = 32°C - 21°C = 11°C(∆T2 = 90°F - 70°F = 20°F)


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The Variation in Air Temperature(VAT) would then become:

V∆T = |-11°C - 11°C)| = 22°C(V∆T = |-20°F - 20°F| = 40°F)

The density of the air would thendecrease, resulting in a lower air-fuelratio of 13.67. The lower air-fuelratio would result in reducing thepercent O2 in the exhaust to 6.5%.The graph in Figure 13 shows howNOx changes as a function ofpercent O2 in the exhaust. Theincreased air temperature in ourexample would increase the NOx emissions to 8.8 g NOx /bhp-hr,

which is an increase of 440%.To maintain a 2.0 g NOx /bhp-hr

level, VAT must not exceed 5.5°C(10°F).

Figure 13

High pressure gas engines are notaffected by these changes to the

same extent as low pressure gasengines. This is because the supplygas temperature remains relativelyconstant at most installations andthe thermostatically controlled

aftercooler maintains a fairlyconstant air temperature to thecarburetor. Since these twotemperatures are not subject tolarge changes, the air-fuel ratioremains relatively constant.

There are two primary methods ofcontrolling VAT, controlling the airtemperature and using a gas-to-airheat exchanger.

Controlling Air TemperatureOne method of controlling air

supply temperature is to regulate theengine room temperature. However,this approach is not recommended.It is difficult to regulate an engineroom to a temperature that is bothcomfortable to work in and highenough to provide a constant airtemperature to the engine. For

example, an installation expecting a32°C (90°F) ambient temperature,will need to regulate the engineroom to about 38°C (100°F) at alltimes. Also, engine rooms havinglarge service doors that, at times,must be left open while the enginesare running, will not maintain the air-fuel ratio while the doors are open.

The preferred method is to use

duct work to supply a temperatureregulated air supply to the engine.See Figure 14. This system uses jacket water to heat the air to thetemperature set by the thermostat.


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Ducting with Temperature Regulator

Figure 14

If one intake system is used tosupply temperature controlled air tomultiple engines, provisions must bemade to ensure that heated water issent to the heat exchanger whenengines are running. If engine jacketwater is used, the engine that thewater is taken from must be runningwhen any of the other engines areoperating.

Gas-to-Air Heat Exchanger

If the use of duct work is notpractical for a given installation,another option is to install a gas-to-air heat exchanger, shown inFigure 15. If done correctly, thissystem will prevent temperaturechanges in the gas or the air fromaffecting the air-fuel ratio.

Design the system so the gasflows through the heat exchanger

before entering the gas regulator.The pressure drop across the heatexchanger at full load must be addedto the minimum gas supply pressurerequired by the engine. Design theheat exchanger to minimize both gasand air flow pressure drop while stillproviding enough heat transfer sothat VAT stays within the givenlimits.

Figure 15


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Reference Material

The following information isprovided as an additional referenceto subjects discussed in this guide.

SEBD9317

Engine News 2003/01/01.

SEBU8100

C175 Series Generator Sets


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Documents

Caterpillar Air Intake Systems LEBW4969-04