Department of Mechanical Engineering

Powertrain & Vehicle Research Centre

Boosting System Challenges for Extreme Downsizing

1

Thanks to contributors to this presentation

UNIVERSITY OF BATH Andrew Lewis Sam Akehurst Chris Brace

IMPERIAL COLLEGE Alessandro Romagnoli MingYang Yang Ricardo Martinez-Botas

JAGUAR LAND ROVER James Turner Nick Luard Rishan Patel

2

The Turbocharged Engine

Turbine Inlet Temperature

Turbine Efficiency, Pulse Conversion

Backpressure PMEP

Combustion efficiency

Δpin-exh Scavenge

EGR

Compressor Efficiency

Temperature and tip speed

Map width (surge & choke)

Transient response

Manifold temperature and volume Pulse Division

Knock, Exhaust

Residuals

3

0

5

10

15

20

25

30

35

0 1000 2000 3000 4000 5000 6000 7000

BM

EP

(bar

)

Engine Speed (rpm) Audi 2.5 TSI 5Cyl VW 1.4 TFSI 4cyl. SC+TC Mahle 1.2 3cyl Single Turbo

AJ133 NA UB100 Target

Torque Curve

Shape of torque curve of downsized engines are often boost system limited Ultraboost aimed for ambitious targets in these areas

Peak power 140 kW/L

Low-End Torque 400Nm@1kRPM

4

Compressor Map Width Radial Compressors:

Surge: determines run-up line and thus, low-end torque Choke, Speed & Temperature: determines rated power point

Extreme downsizing: Maintaining flat torque curve of NA, SI engine very difficult. Very small turbochargers necessary to produce high boost at low RPM Two and three stage turbochargers systems in production High EGR rates adds challenges

Run-up line choke-limited

5

Compressor level solutions

Problems: Flow range reduction at high pressure ratio Shallow run-up line

Source: Chen, 2010 6

Problems: Flow range reduction at high pressure ratio Shallow run-up line

Compressor Level Solutions: Inlet guide vanes

Compressor level solutions

7

Problems: Flow range reduction at high pressure ratio Shallow run-up line

Compressor Level Solutions: Inlet guide vanes Variable diffusers

Compressor level solutions

angle C angle A

Open angle C Open angle A

Honeywell prototype 8

Problems: Flow range reduction at high pressure ratio Shallow run-up line

Compressor Level Solutions: Inlet guide vanes Variable diffusers Passive casing treatments

Compressor level solutions

blade

Without SRCT With SRCT

MingYang, Imperial College 9

System-level solution TWO-STAGE PARALLEL

TURBOCHARGING TWO-STAGE SERIES TURBOCHARGING

SERIES TURBOCHARGING & SUPERCHARGING

10

Turbocharger Turbine Matching Decreasing turbine effective area:

Increases turbocharger boost at given exhaust mass flow Increases expansion ratio and thus exhaust backpressure

Increasing turbine expansion ratio: Backpressure increases engine pumping work Cylinder scavenging on overlap Trapped in-cylinder residuals can increase knock propensity

Very small turbine build necessary for 400Nm@1000rpm (2.5 bar boost)

Wastegate: Limits operable region VGT: tailor turbine effective area – but temperature limited (~800°C)

11

HP Turbocharger versus Supercharger

VS

Supercharger a parasitic engine load but greater scavenging and better PMEP BSFC favours turbo build at high load, but smaller difference over NEDC drive cycle (with supercharger clutch)

12

Turbine inlet temperature Not unusual to run rich at high load to protect exhaust components including turbine Most downsized engines must aim to run λ=1 for fuel economy Increasing use of integrated/water-cooled exhaust manifold

Water exit

Water inlets

13

Cooled EGR and using a WCEM

Intake manifold pressure 2.5 bar abs

600

650

700

750

800

850

900

950

1000

1050

-15 -10 -5 0 5 10

Spark Advance [°CA]

Exha

ust M

anifo

ld T

empe

ratu

re [°

C]

EGR rate = 0%

EGR rate = 5%

EGR rate = 10%

EGR rate = 15%

EGR rate = 0%

EGR rate = 5%

EGR rate = 10%

EGR rate = 15%

EGR rate = 10% WCEM

2000 rpm at 29 bar BMEP / 460 Nm

Approximately 16 kW is rejected to the coolant in the WCEM

160

°C

~ 24

%

170

°C,

~ 15

%

Cooled EGR reduces exhaust temperature (heat capacity) Improves combustion phasing further reducing temperature With WCEM, temperatures within standard VGT operation

14

Pressure Charging and EGR Testing

WCEM

Coolant

Intake Plenum

Catalyst

Coolant

Variable speed Pump

Heat Exchanger Heat Exchanger

Charge Air Handling Unit (CAHU)

~100

°C

Up to 850°C ~150°C ~200°C

2.4 L Diesel ‘2 stroked’ as hot gas

compressor

Variable Speed Motor

Bowman Heat Exchanger ~850°C ~150°C

~200°C ~100°C

Bespoke Heat Exchanger

AIR HANDLING UNIT

BACK-PRESSURE VALVE

BESPOKE EGR PUMP

15

Knock-limited Spark

Advance

Exhaust gas temp. limit on retard

Typical Performance envelope investigation- No EGR

Advance Retard

16

410

420

430

440

450

460

470

480

490

500

-8 -6 -4 -2 0 2 4 6

Torq

ue (N

m)

Spark (°BTDC)

2000rpm - 0, 5, 10 and 15% EGR

0%EGR, Pin=2.5barA, Pex=1.6barA 5%EGR, Pin=2.5barA, Pex=1.65barA 10%EGR, Pin=2.5barA, Pex=1.65barA 15%EGR, Pin=2.5barA, Pex=1.65barA

Spark Retard Limited on EGT or CoV IMEP

Knock Limited Spark Advance KLSA

Target Torque = 467.7Nm (Post S/C req'ment)

Engine response to cooled EGR at target torque

17

Engine response to cooled EGR at target torque

18

Engine response to cooled EGR at target torque

19

EGR and the Boost System

Short Route EGR Removes turbine energy Relies on pressure gradient from exhaust to intake manifolds

Medium Route EGR HP compressor must process higher mass flow Potential for higher HP temperatures

Long Route EGR Full exhaust flow through turbine Higher temperature pre-compressor LP compressor must process higher mass flow

20

EGR and the Boost System

Exhaust pulses most effectively drive short route EGR at higher speeds Long-route, low pressure EGR at low engine speed Medium or short route EGR at high engine speed

21

EGR and the Boost System – 10% EGR

AIR FLOW +10%

22

EGR and the Boost System

10%

23

Transient Response Targets

Assessed in GT-Power model: 10-90% of rated torque at constant rpm Naturally aspirated response ~300ms for all speeds (stretch target) Minimum acceptable response: twin turbocharged 3.0L V6 diesel

24

Transient Response - modelling

E-Booster

25

Initial Transient test results at 1500 rpm

DEMAND

TURBO BOOST

TORQUE

TOTAL BOOST

10-90% ~ 1.7 sec

NOT FULLY OPTIMIZED !! INVESTIGATIONS ARE ON-GOING 26

Conclusions The standard ‘fixed geometry’ turbocharger is being stretched in a number of different areas due to the extreme downsizing trend Boost system and engine/combustion chamber interactions increasingly important to understand for high BMEP engines. Over 20bar BMEP at ~1000rpm and 140KW/L is particularly challenging for turbocharger systems applied to SI engines

Very small turbochargers could lead to increase exhaust back pressure issues Superchargers helpful but parasitic unless declutched Small VGT turbines could be helpful if temperature limit addressed

Transient response increasingly reliant on the high boost for most of the torque delivery.

Superchargers potential is high especially with variable ratio E-boosters hold a lot of promise 27

Conclusions EGR highly beneficial from the SI engine perspective for improved combustion phasing, fuel economy and NOx. EGR and WCEM synergistic to broaden λ=1 operation, improve warm-up and protect turbine components High EGR rates can have a significant influence on the boost system matching and operation. There is a potential benefit to narrow compressor operating region by using a hybrid high-pressure and low-pressure (long and short) route EGR. The University of Bath engine Air Handling Unit (boost system emulator) and EGR pump is a powerful tool in the understanding of the pressure charging and combustion interactions.

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THANK YOU

29

Time to Torque Test, 3000rpm NA V8

Start of Pedal Input

10% of Torque

90% of Torque

T10 T90

Start of Torque Response 30