Air Induction

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vance n erna om us on ng nesMAE 589V (Spring 2009)

Air Induction

. ,

Mechanical and Aerospace Engineering Department

or aro na a e n vers y

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Under certain FA ratio, more air means more fuel burnt with more

Increasin the air intake flow is im ortant to increase ower

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Volumetric Efficiency (VE) is defined as the volume flow rate of airinto the intake system divided by the rate at which volume isdisplaced by the piston under ambient conditions

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Volumetric Efficiency can be greater than one based on this

o e: ra s e a r ens y eva ua e a a mosp er ccondition outside the engine

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, . .

For naturally aspirated engine, VE is about 60-90%


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Intake manifold is the system to deliver air into the engine through,

n a e va ves are genera y poppe va ves

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Intake manifold should have no sharp bends, and the surfaces shouldbe smooth with no rotrusion

Length of the intake manifold is optimized for higher volumetricefficiency. In order to meet the requirement at different speed, we needvariable intake manifold

n a e va ves s ou prov e ow passages as arge as poss e Put as more as possible intake valves to increase intake passage

Intake valves generally have larger diameter than exhaust valves Intake valves should o en and close at ri ht timin with as much as

air going into the engine cylinder

Variable Valve Timing (VVT) technology provides optimumperformance at different speed and loads

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Intake system design Fuel addition in the intake s stem- Gasoline Direct In ection

Intake system temperature Valve timing- overlap and intake valve late closing

Fluid friction

o e ow a g spee Intake manifold tuning

Exhaust residual Exhaust Gas Recirculation (EGR) cooled EGR

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Volumetric efficiency reaches a maximum at certain speed with

Empirical equation

tt LcN /5.7 0=Nt = engine speedc0 = sound speed = airkRT

Actively varying intake length makes the engine induct more air forall speed

Lt = intake runner length

Lower speed needs longer length and smaller diameter Higher speed requires shorter length and larger diameter

In order to obtain both ample low/mid-end torque andhigh-end output, a rotary valve is used inside the dual-passage intake manifold. During low/mid rpm, the rotaryvalve is closed, while it opens during high rpm's. By

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,ample torque is gained at all rpm levels. Additionally,

the rotary valve design is superior over past butterflyvalve (flap) in that it reduces intake resistance.


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Intake valve design is importantfor engine performance

operation of engines, andsufficient intake charge andem ty exhaust

Intake opens before exhaust TDCand close after BDC

Exhaust opens before BDC andclose after TDC

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For best performance, different engine speeds require the valveopening and closing at different timing

Higher speed needs longer valve overlap and larger valve liftEach intake valve can be actuated by a fast cam (11mm lift) or aslow cam (5.7mm in one intake valve and 2mm in another inorder to create swirl in the air flow for better fuel mixing at lowspeed). The two cams are mounted on a single cam piece.Which cam acts on the roller cam follower depends on the

longitudinal position of cam piece. This is controlled by a pair ofmetal pins incorporated at the cam cover. There is a spiralgroove ro e n o e cams a . en one me a p n s owere ,it engages the spiral groove on the camshaft and pushes thecam piece by 7mm in longitudinal direction. A spring-loadedlocker will lock the cam piece in the new position. In this way, theoperating cams are changed from one set to another set.

To revert to another cam, another metal pin presses against areverse spiral groove and moves the cam piece back to theoriginal position. The cam piece is locked by the spring-loadedlocker again. The change from one cam set to another takes onecombustion cycle, or two engine revolutions. As Audi

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reprogrammed the ignition and electronic throttle to smoothenthe transition between the two cam sets, it can be hardly

detectable.


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In the VVEL system, a rocker arm and two types of linksclose the intake-valves by transferring the rotationalmovement of a drive shaft with an eccentric cam to the

.varied by rotating the control shaft within the DC motor

and changing the fulcrums of the links. This makes acontinuous adjustment of the valve lift amount possible.

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Based on signals from the cam and crank position sensors, the engine ECU calculates the valve timing. The ECU calculates an electricalcurrent amount to manage the oil flow control valve (OCV) to adjust the valve timing. In accordance with the electrical current amount, the

OCV distributes oil, discharged from the engine oil pump, to two oil chambers of each VCT controller, controlling the oil amounts of the oilchambers. Each VCT controller controls the opening/closing timing of the valve in accordance with the oil amounts of the oil chambers.


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(Camless Engine)

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An effective way to increase intake charge and therefore increasepower output for a specific engine displacement volume

uperc argers are compressors rec y r ven y cran s a ,

while turbocharger is driven by the energy from exhaust gasthrough a turbine.

Advantage: fast response with throttle change

Disadvantage: adding parasitic load, higher cost, higher weight,and noise

Compressors are generally positive displacement pumps, but centrifugalcompressors are also used

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Turbocharger:

Advantage: no parasitic load, recover waste energy, higher fuel efficiency

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Compressors are generally centrifugal compressors driven by a turbinepowered by exhaust gas

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Waste gate is a valve that diverts exhaust gases away from the

turbine wheel in a turbocharged engine system

A turbocharger which is adaptedwith a waste-gate, which acts as a

-when the optimum pressure hasbeen achieved, and enables a

turbocharger with a much smallerturbine wheel than usual to beused. This allows the turbochargerto achieve faster acceleration and

engine speed, and enhancesemission control.

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Variable Geometry Turbocharger

Variable geometry turbochargers (VGTs)are a family of turbochargers, usually

designed to allow the effective A/R ratio of theturbo to be altered as conditions change. Thisis done because optimum A/R at low engines eeds is ver different from that at hi hengine speeds. If the A/R ratio is too large,the turbo will fail to create boost at lowspeeds; if the A/R ratio is too small, the turbo

will choke the engine at high speeds, leadingo arge ex aus man o pressures, g

pumping losses and ultimately lower poweroutput. By altering the geometry of the turbinehousing as the engine accelerates, the turbo'sA/R ratio can be maintained at its optimum.

Because of this, VGTs have a minimalamount of lag, have a low boost threshold andare very efficient at higher engine speeds. Inmany configurations, VGTs do not even

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,whether the fully open position is sufficientlyopen to allow boost to be controlled to thedesired level at all times.


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BMW 306 hp straight-six GDI engine

Air Induction

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