gas exchange process of modern engines

Gas exchange process of modern IC engines

Dr. S. GUILAIN

Technical Expertin Powertain Aerodynamics & Engine air filling

Contents

• Context of modern IC engines

• Diesel Engines– Turbocharger adaptation– EGR requirements and adaptation– New systems in development

• Gazoline Engines– Turbocharger adaptation– Synergy beetween turbo and VTC– New systems in development

• Conclusion

CONTEXT OF MODERN IC ENGINES

�


Context of automotive IC engine

Engine Power

CO2

CustomerFuel

Consumption

ReliabilityFun to drive

PollutantRegulation

Request of more and more powerfull engines

Puissance Max (kW)

0

50

100

150

200

250

1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014

Année de sortie

Diesel

Weight of vehicleSafety requirementsSpace requestComfort demand

Marketing & customerrequest


Engine Power

CO2

CustomerFuel

Consumption


PollutantRegulation

A new cycle to be closer to real usage (Introduction 2017).

Driving Cycle Profile

Test Conditions

Longer, higher speed, more transients

Freeshift / auxiliaries “On”.Inertia Class Closer to real vehicle weightCOP with reduced margin

Urbain & Extra UrbainSpeed Max : 120 km/h

Gear shift imposedInertia Class on lowerweighted applicationCOP with margin

NEDC WLTCTamb : 20 °C & -7°C

Higher OBD demandTamb : 20 °C

Depolution and New cycle For Eu 6c ?

Real Drive Emissions ? RDE ?

A step forward EU7

Real DrivingEmission regulation

Engine operation

NEDC

NEDC

[WLTP]

Customer cycle

What will do the driver ?Impact of the weather ?Where will it be tested? Altitude ?

0,7HC g/km

NOx g/km

CO g/km

PM g/km

Euro 2

Euro 3

0,70,08

1,0

Euro 4

Eur

o6

Euro5

Euro 11993 1996 2000

Euro 22005

Euro 3 Euro 42010

Euro 52015

Euro 6

Pollutant Regulation

Diesel

LeanRich

1 1.5 20.50

500

1000

1500

2000

2500

Air/fuel ratio local

LocalTemperature

(K)

NoxFormation

Sootoxydation

SootFormation T°burnt

gas

AverageT°

Diesel AverageA/F ratio

Distribution of local A/F Ratio in Diesel

Impact of local Air Fuel ratio on pollutant

Swirl =1 Swirl = 1.7

Effect of Swirl on Vapor phase of Diesel Jet

Thanks to the TDC swirl motion,vapor phase covers a larger area=> lower F/A ratio

Swirl

�

Turbocharger & Diesel depollution

O2

N2

WO

EG

R

CombustionTemperature

O2N2

EGRBurnt Gas

CombustionTemperature

WIT

H E

GR

NOx

Intake Exhaust

Need to increaseBoost pressureto compensateEGR volume

NOx

Importance of turbulence on gasoline Engines

Tumble

Depollution systems

�

A key factor of performance:increase the temp. before Depollution System

Load of Precious MetalFuel consumption impact

Dosing Control

Unit

BOSCH

OxyCat DPF SCR

H5 Euro 6

V2V1

O2O2O2O2

CGPFGPF

GPF3W Cat

DIESEL GASOLINE


Engine Power

CO2

CustomerFuel

Consumption


PollutantRegulation

�

FC regulation

Path to improve current enginesGasoline: downsizing, GDI + turbo + VTC

Diesel : High pressure injection, right sizing with turbo & LP EGR

FC and cycle

�

Important operating point are at low speeds

and loads=> Importance of Friction / PMEP => Downsizing / downspeeding

Important operating points cover a larger

range=> Importance of

Gross IMEP + PMEP + Fiction

=> rightsizing

Surface of bubblesrepresents weight in FC

Max power1750rpm Max Torque

Downsizing

Puissance Spé Max (kW/L)

0

10

20

30

40

50

60

70

80

90

100

1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014

Année de sortie

+ 30 kW/L~ + 100 %

32 kW/L

All ready a reality

How to improve FC of current engines

+

-

+

+

Pressure Pressure

Volume Volume

Pexh

Pint

P int

Pexh

Torque is the result of gas work on piston plus frictio nBMEP = IMEP + FMEP

IMEP: Indicated Mean effective pressure PMI=Gross IMEP + PMEP

Gross IMEP

PMEP < 0 PMEP > 0

Gross IMEP

PMEP

PMEP

�

Gasoline Engine and PMEP

Pexh

Pint

Decrease of pumping losses

Volume

Gross IMEP

+

-

CylinderPressure

Pexh

PintReduction of intake throttling

Volume

Gross IMEP

+

-

DisplacementReduction

-

CyinderPressure

PMEP PMEP

Atmo Engine Turbo Engine

�

Effect on FC

0.9

0.8

Ratio of BSFC of 2L Turbo gasoline engine versus atmo 3L

1.1

1

0

100

200

300

1000 2000 3000 4000 5000 6000 7000

Engine speed (tr/min)

Cou

ple

(Nm

)

Enrichment area

T3 limitKnock area

�

knock

Knock is a massive auto ignition of unburnt gas

Piston damageDelay

ignition

MAISCO2


Engine Power

CO2

CustomerFuel

Consumption


PollutantRegulation

Fun to drive and acceleration

�

Vehicle Weight

Gear ratio CAR AccelerationEngine

TransientTorque

Engine Inertia (inc CDA)

�

Request of responsiveness

0

20

40

60

80

100

120

140

160

180

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Time [s]

Spe

cific

Tor

que

[Nm

/L]

Limite PcolTarget for 20% Downsized engine

Risk for Downsized engine

Ref 1.9 LZone

1

Zone 2

Boost control(2°order)

3L Alpina D10 180 kW

2.0 HDI 80kW

1.9 TDI 110kW

Exemple @ 1500rpm

Diesel engines

�


�

FC regulation



Diesel engines are turbocharged

P2 / T2

P1 /T1

P4 /T4

P2’,T2’

P0,T0

T2 ’’temperature after intercooler

P3 / T3

Names are not standard

�

Why a turbo – Thermal balance

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250

Ene

rgy

Bal

ance

[%

]

Engine speed [rpm]

ENERGY BALANCE: (100% = Fuel LHV)

25 %

45 %

Thermal lossesin Engine cooling system

Exhaust powerT / mass flow

Indicated PowerP=f(Vcyl )

�

Turbocompressor

Compression

Expansion

COMPRESSORTURBINE

Central housing

�

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

0 0.05 0.1 0.15 0.2 0.25

Rap

port

de

com

pres

sion

[-]

Débit d'air réduit [kg/s]

Iso vitesse de rotation

85 000 tr/min

105 000 tr/min

125 000 tr/min

145 000 tr/min

165 000 tr/min

77%

75%

70%

65%

Iso Rendement

Map of compressor

0

0 P

PT

Tmm

entrée

entrée

airComp ⋅= &&

0

TT

NNentrée

Comp =

entréesortie

PP

Comp =π

A Map of possible Operating Points

Limites of compressor MAP

• Surge line(surge line) is defined when the compressor is unstable leading to noise and engine unstabilities

• Choke lineSound speed is reached. Often set as the line of max flow rate for a given efficieny(Comp Eff. = 65 %)

• Max turbo speedgiven by realibility tests

3

1.5

010 20

Pressure Ratio

Corrected mass flow

Surge line

Max Speed

Iso efficiency

Choke line

P / 33

Surge on vehicle

Oscillations fora certain range of engine speed

Recording during acceleration on severe conditions

�

0%

10%

20%

30%

40%

50%

60%

70%

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.0 1.5 2.0 2.5 3.0 3.5

Re

nde

men

t [%

]

Dé

bit r

édui

t [kg

/s]

Rapport de détente [-]

80 000 tr/min 115 000 tr/min 155 000 tr/min


Blocage sonique

Turbine Map

entréesortieDet P

P =π

0

0 P

PT

Tmm

entrée

entrée

gbTurb ⋅= &&

0

TT

NNentrée

Turb =

Only One line !

�

Turbocharger adaptation

Pb : How to adapt the turbine mas flow rate to the various conditions requested by the driver?

1. By a VARIATION OF THE TURBINE MASS FLOW RATE=> « waste-gate » TURBO

2. by CHANGING the turbine characteristic=> VTG

3. by implementing more than one turbo=> Double stage supercharging.

0%

10%

20%

30%

40%

50%

60%

70%

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.0 1.5 2.0 2.5 3.0 3.5

Re

ndem

ent

[%]

Déb

it ré

duit

[kg/

s]

Rapport de détente [-]



Blocage sonique

1 MAP 1 line

�

Turbine with Wastegate

– Only One characteristic line,– Trade off between low end torque and max power,– Turbine flow capacity must de adapted with regards to low engine flow rate

and high ones– Need to « by pass » a part of gas => direct loss of efficiency

Gas from the cylinders

Gas throughthe

wastegate

Turbine Outlet

Interests :

- simple- cost

Drawbacks :

-Limited turbine performance turbine at low or high engine speed=> 55 kW/L- Sealing of the wastegate

�

Variable Geometry Turbine

• Several lines for Expansion ratio / mass flow rate => A MAP• All gas from the cylinders are used to get turbine power• All Engine operating points must be covered by the turbine MAP

Diffusor vanes=> Change flow velocityangle towards vane

Open VanesClosed Vanes

Interests :

- Efficiency

Drawbacks :

- Cost- Limitation up to 65 kW/L- Control issues due to non linear behavior of vanes

P / 38

Turbine MAP of VTG

Max efficiency

Discrepancy between two turbo is done by Efficiency MAP

1 1,5 2 2,5 3 3,5

0,5

0,55

0,6

0,65

0,7

0,45Closed position

entréesortieDet P

P =π

0

0 P

PT

Tmm

entrée

entrée

gbTurb ⋅= &&

Open Position

P / 39

« Big » Turbo Low Pressure

« small » Turbo High Pressure

Turbine By-pass ValveTBV

CompressorBy-pass Valve

CBV

Outlet of compressedair

Actuateur TBV

Actuator CBV

Actuatorwastegate turbo

BP

Bi turbo « serial – sequential »

Air Inlet

Exhaust

2 turbo :A“big” one named LP

A”small” called HP

3 actuators

Must be very compact

P / 40

Simplified description of functioning at low engine speed

Waste-Gate Turbine BP

TBVCBV

3000

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

Débit corrigé (kg/s)

Rap

port

de C

ompr

essi

on (t

/t)

Zone HP ZONE HPZONE

BPZONE

LP

Régime

Couple

ZONE HP

Turbo LP

Turbo HP

Global

Both LP and HP turbo are running

All vanes are closed

Both turbo give their max potential

Turbo LP

Turbo HP

P / 41

Simplified description of functioning at mid engine speed


TBVCBV

3000

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18


Rap

port

de C

ompr

essi

on (t

/t)

Turbo LP

Turbo HP

Global

Zone HP ZONE HPZONE

BPZONE

LP

Régime

Couple

ZONE HP

Both turbo are running

Boost pressure is regulated by openingthe TBV – HP turbine does not give

its full potential

The HP turbine gives the max power it can produce

Turbo LP

Turbo HP

P / 42

Simplified description of functioning at High engine speed


TBVCBV

3000

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18


Rap

port

de C

ompr

essi

on (t

/t)

Zone HP ZONE HPZONE

BPZONE

LP

Régime

Couple

ZONE HP

Turbo LP

Turbo HP

Global

Only the LP turbo is runningthe HP turbo is stopped

The two HP by pass (TBV & CBV) are fully opened

LP turbo can be regulated through its Wastegate

Turbo LP

Turbo HP

P / 43

Classical Architecture : HP EGR

EGR HP

• From turbine upstream to upstream of intake manifold

– Huge coupling EGR / turbo– EGR rate done by

• Vane / wastegate turbine • Valve EGR• Intake throttle

∆P EGR = P3 – P2’

P / 44

New Architecture : LP EGR

EGR LP

DPF

• From downstream DPF to compressor upstream

– No coupling EGR / Turbo– EGR rate obtained by

• Exhaust Flap• EGR Valve

∆P EGR = Bck P – P1

EGR HPHigh temperature

P / 45

LP EGR on 1.6L DCI Renault engine

EGR Inlet

EGR coolerEGR ValveEGR Diffusor

P / 46

Impact of architecture choice in compressor MAP

90000110000

130000

150000

170000

190000

210000

230000

0,6

0,65

0,68

0,70,72

0,74

1,00

1,20

1,40

1,60

1,80

2,00

2,20

2,40

2,60

2,80

3,00

3,20

3,40

3,60

0,0 2,0 4,0 6,0 8,0 10,0 12,0 14,0 16,0 18,0 20,0 22,0 24,0 26,0 28,0 30,0 32,0

W* [Lb/min]

PR

tot/t

ot

EGR HPEGR BP

TITLE:

90000110000

1,00

1,20

1,40

1,60

1,80

2,00

2,20

0,0 2,0 4,0 6,0 8,0 10,0 12,0 14,0

PR

tot/t

ot

TITLE:

Points with the surge area with EGR HP⇒CGV ?, ⇒Bi turbo ?

2250 tr/min – 7 barTmassique EGR = 34 %

2000 tr/min – 6 barTmassique EGR = 43 %

P / 47

Evolution des points dans le champs TGV (Euro 5)

0,0000

0,2000

0,4000

0,6000

0,8000

1,0000

1,2000

1,4000

1,6000

1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800

rapport de détente

débi

t réd

uit (

kg/s

. sqr

t(K

) . b

ar)

EGR BP

EGR HP

2250 tr/min - 7 barTmassique EGR 32 %

2000 tr/min - 6 barTmassique EGR 43 %

1 1,5 2 2,5 3 3,5

0,5

0,55

0,6

0,65

0,7

0,45

Impact des architectures sur le fonctionnement de la turbine

OP that cannot be reachedwith VGT Bi turbo ?

Closed position

HP EGR Leads to:- vane position more closed (bad efficiency)- P3 levels higher (CO2 impact through PMEP)

Impact of architecture choice in turbine MAP

Gasoline Engines


�

FC regulation



Turbo Gasoline + 4 cyl : without VTC

P / 50

Exhaust.

BDC

TDC

Intake.

Intake

Air + Burnt gas

Without VTC, to get stable idle mode, the overlap must be reduced

� Exhaust phase not favorable to gaz exchange

A reduced exhaust lift event is a counter measure� Increase of low end torque

BUT PMEP �

5500 rpm

Pint < Pcyl< Pexh

1500 rpm

Turbo Gasoline + 4 cyl + VTC : at low engine speed

P / 51

Exhaust.

BDC

TDC

Intake.

Intake

Air + Burnt gas

Pint > Pcyl> Pexh

1500 rpm

VTC at intake

EarIy IVC� reduced Back flow at

intake end

� overlap when Pexh < Pint

= Scavenging


P / 52

Exhaust.

BDC

TDC

Intake.

Intake

Air + Burnt gas

Pint > Pcyl> Pexh

1500 rpm

VTC at exhaust

EVO is later

� Overlap period islonger

� ImprovedScavenging

Benefit of scavenging

�

BDC

TDC Intake

Air + Burnt gas

Pint > Pcyl> Pexh

Gasoline Combustion

Remove IGR� Less knock sensitivity

Turbine

Increase mass flow rate� More turbine power


P / 54

Increase of torque at1000 rpm from 20 %

Take care when VTC is out of order – very cold conditions

Turbo Gasoline + 4 cyl + VTC :for fun to drive

Huge synergy betweenTurbo & VTC

The transient behaviorin Turbo zone is

transformed

One Major difficulty for control and emissions:

Knowing the trapped air mass to be able to

adjust the fuel quantityto the stoechiometric

level

1500 rpm


Exhaust.

BDC

TDC

Intake.

Intake

Air + Burnt gas

Pint > Pcyl> Pexh

Scavenging is natural with 3

cylinder engines

1500 rpm

Turbo Gasoline + 3 cyl + VTC : at high engine speed

Exhaust.

BDC

TDC

Intake.

Intake

Air + Burnt gas

Pint > Pcyl> Pexh

Due to exhaust instantaneous

pressure shape, we are also close

to allow scavenging

5500 rpm

Turbo Gasoline + 3 cyl + VTC : en transitoire

Once again !Huge synergy between

VTC & turbo

Overlap

� Exemple at 1500 rpm.

Single scroll Turbine Twin scroll Turbine

Single or Twinscroll turbine for 4 cylinder engines

-600

-400

-200

0

200

400

600

800

1000

0 90 180 270 360 450 540 630 720

Pre

ssu

re -

mb

ar

Cranck angle - °CA

Twin scroll Turbine Single scroll Turbine

After optimisation of th overlap period to get the same IGR contentwith Twinscoll turbine, the exhaust Event can be increased

� PMEP can be improved

PMI bp

-2,5

-2

-1,5

-1

-0,5

0

0,5

1

1500 2000 2500 3000 3500 4000 4500 5000

Vite s s e - tr/mn

Turbo c lassique Double volute

Pression échappement

0

500

1000

1500

2000

2500

3000

3500

0 180 360 540 720

Degré vilebrequin

mb

ar

Turbo classique Double volute

PMH croisementAOE

Single or Twinscroll turbine for 4 cylinder engines

EVO

PMEP

Turbo Gasoline + 4 cyl + VTC &exhaust manifold

Twinscroll

« separation wall »The twinscoll turbine allows a exhaust pulse separation

BUTCasting issue

A way to improvesmall gasoline turbo

Turbo Gasoline + 4 cyl + VTC &exhaust manifold

5500 rpm1500 rpmw

ithou

tw

ith

An increase of 2 to 4 % of low torquethrough this shape optimization

«se

para

tion

wal

l»

Limitations with scavenging

Take care to promote too muchscavenging

With MPI injection, Fuel goes directly to exhaust.

� Customer FC impact

With MPI/GDI engine, Exhaust equivalenceratio is decreasing (λ>1) – TWC does not do

the conversionIf tuning done with λ exhaust=1,

λ combustion <1HC/CO and particules for GDI

� TWC Temp. & RDE emission concern

Integrated exhaust manifold in cylinder head

This technology significantly reduces manufacturing costs, emissions and weight on

most gasoline engines.

For an average 1.6 litre gasoline engine with this technology results in:

� Reduces powertrain weight by up to 5 kg

� Reduces exhaust gas heat loss upstream catalyst

�cutting the catalyst light-off time by 20 %� Reduction in emissions � Reduced CO2 emissions

� Reduced catalyst loading requirementReduced package space requirements

� Improved NVH� Improved under hood thermal management

� Reduced thermal distortion� Improved overall engine durability

� Cuts up to 5% of the total build cost

Toyota Etios and Civic 1.8 litiVTECH

P / 65

Same trend for turbocharged engines

Audi 1,8L TSI 125 kW

Claims

Improve catalyst light-off

Increase of boost pressure at lowengine speed through pulsation

effect

P / 66

Compressor + turbo : an example VW TSI

CompressorTurbo

P / 67

Functioning scheme of compressor + turbo

CompressorROOTS

Recirculationvalve

Turbo Compressor

Waste gate

Electromagneticclutch

CompressorBelt

Accessorybelt

Vanne de controle

P / 68

0

1

2

3

4

5

6

5 7 9 11 13 15

Temps [s]

Sig

nal d

u by

-pas

s co

mpr

esse

ur [-

]

0

20

40

60

80

100

120

140

160

180

200

Cou

ple

brut

[N.m

]

Utilisation du compresseur Roots

Couple brut

OFF

ON

0

1

2

3

4

5

6

5 6 7 8 9 10 11 12 13 14 15

Temps [s]

Sig

nal d

u by

-pas

s co

mpr

esse

ur [-

]

0

50

100

150

200

250

300

Cou

ple

brut

[N.m

]

Utilisation du compresseur Roots

Couple brut

OFF

ON

Transient performance of VW TSI 1.4 125 kW

Load step for 2 constant engine speed

1000 tr/min

2000 tr/min

The mechanicalcompressor is used for a short time period to

reduce turbo lag

Air / Water cooling- WCAC

• Interests :• Packaging Standardization (WCAC with the engine)• Thermal inertia on transient with long duration (80 => 120 km/h)• Reduced heat transfer between intercooler and valves•Smaller volume for HP parts

•Drawbacks• Cost• Responsiveness of air system (Wave effect decreased)• Risk of temperature dispersion between cylinders• For diesel HP EGR circuit?

Audi 1.2TSI

RadiatorLow temp.

Water pump

What’s Next?

Conclusions


Conclusions

• Gas exchanges processes have a major contribution in the performance of modern IC engines

• They involves •Many physical phenomena• A lot of trade-off to evaluate whenrules are changing

•Many parts & suppliers• A lot of new ideas are emerging…

�

P / 72

LP EGR for Gasoline

Goals: FC improvementNEDC : -4-5 % targetted

Real drive FC : -8-10 % targetted

Increase of cylinder compression ratioLP EGR to avoid knock issue at

low engine speed - full load

LP EGR to limit T3 and added fuel athigh engine speed high load

Opportunity : Atkinson cyclehigher IVC (> 45°V) => PMEP decease at

part loadand additional potential of increase of

compression ratioDifficulties

Combustion stability => IgnitionImproved supercharging system => VGT ou twin

compression systemEGR circuit & CAC have more requests

Control of EGR rate

Boosting assisted by electic compressor

Advantages :- the turbo matching is less constrained by low end torque

Drawbacks:- Request Advanced Electrical network - limitation of additional boost to

~1.4-1.6 bar- Limitation by the electrical network

capacity for high power engine

Electricalmotor

Secondarythrottle

Eboost (BWTS) e-charger (HTT/Valeo)

VTES (Visteon)ESC (Bosch)

E turbo (As F1)

Under braking, the MGU-K operates as a generator, recovering some of the kinetic energy dissipated du ring braking

The MGU-H is connected to the turbocharger. Acting as a generator, it absorbs power from the tu rbine

shaft to convert heat energy from exhaust gasesActing as a motor, it accelerates the turbocharger to

compensate the turbo lag

Thanks for your attention

gas exchange process of modern engines

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