Boosting System Challenges for Extreme Downsizing

Transcription

1 Department of Mechanical Engineering Powertrain & Vehicle Research Centre Boosting System Challenges for Extreme Downsizing 1

2 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

3 The Turbocharged Engine Compressor Efficiency Temperature and tip speed EGR Turbine Efficiency, Pulse Conversion Turbine Inlet Temperature Map width (surge & choke) Transient response Manifold temperature and volume Δp in-exh Scavenge Backpressure PMEP Pulse Division Knock, Exhaust Residuals Combustion efficiency 3

4 Torque Curve Low-End Torque 25 BMEP (bar) Peak power 140 kw/l 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 4 Shape of torque curve of downsized engines are often boost system limited Ultraboost aimed for ambitious targets in these areas

5 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

6 Compressor level solutions Problems: Flow range reduction at high pressure ratio Shallow run-up line 6 Source: Chen, 2010

7 Compressor level solutions Problems: Flow range reduction at high pressure ratio Shallow run-up line Compressor Level Solutions: Inlet guide vanes 7

8 Compressor level solutions Problems: Flow range reduction at high pressure ratio Shallow run-up line Compressor Level Solutions: Inlet guide vanes Variable diffusers Open angle A angle C Open angle C angle A 8 Honeywell prototype

9 Compressor level solutions Problems: Flow range reduction at high pressure ratio Shallow run-up line Compressor Level Solutions: Inlet guide vanes Variable diffusers Passive casing treatments Without SRCT With SRCT blade 9 MingYang, Imperial College

10 System-level solution TWO-STAGE SERIES TURBOCHARGING TWO-STAGE PARALLEL TURBOCHARGING SERIES TURBOCHARGING & SUPERCHARGING 10

11 Turbocharger Turbine Matching 11 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 (2.5 bar boost) Wastegate: Limits operable region VGT: tailor turbine effective area but temperature limited (~800 C)

12 HP Turbocharger versus Supercharger VS 12 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)

13 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

14 Cooled EGR and using a WCEM rpm at 29 bar BMEP / 460 Nm Intake manifold pressure 2.5 bar abs Exhaust Manifold Temperature [ C] EGR EGR rate rate = 0% = 0% EGR rate = 5% EGR rate = 5% EGR rate = 10% EGR rate = 10% EGR rate = 15% EGR EGR rate rate = 10% = 15% WCEM Spark Advance [ CA] 170 C, ~ 15% 160 C ~ 24% Approximately 16 kw is rejected to the coolant in the WCEM 14 Cooled EGR reduces exhaust temperature (heat capacity) Improves combustion phasing further reducing temperature With WCEM, temperatures within standard VGT operation

15 Pressure Charging and EGR Testing ~100 C Bespoke Heat Exchanger ~200 C Charge Air Handling Unit (CAHU) ~850 C 2.4 L Diesel 2 stroked as hot gas compressor Bowman Heat Exchanger Variable Speed Motor ~150 C Intake Plenum BESPOKE EGR PUMP AIR HANDLING UNIT ~100 C WCEM BACK-PRESSURE VALVE Catalyst Heat Exchanger ~200 C Variable speed Pump ~150 C Heat Exchanger Up to 850 C 15 Coolant Coolant

16 Typical Performance envelope investigation- No EGR Knock-limited Spark Advance Exhaust gas temp. limit on retard 16 Retard Advance

17 Engine response to cooled EGR at target torque rpm - 0, 5, 10 and 15% EGR Knock Limited Spark Advance KLSA Target Torque = 467.7Nm (Post S/C req'ment) Torque (Nm) Spark Retard Limited on EGT or CoV IMEP Spark ( BTDC) 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 17

18 Engine response to cooled EGR at target torque 18

19 Engine response to cooled EGR at target torque 19

20 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 precompressor LP compressor must process higher mass flow 20

21 EGR and the Boost System 21 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

22 EGR and the Boost System 10% EGR AIR FLOW +10% 22

23 EGR and the Boost System 10% 23

24 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

25 Transient Response - modelling E-Booster 25

26 Initial Transient test results at 1500 rpm TOTAL BOOST TORQUE TURBO BOOST DEMAND 10-90% ~ 1.7 sec 26 NOT FULLY OPTIMIZED!! INVESTIGATIONS ARE ON-GOING

27 Conclusions 27 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

28 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. 28

29 29 THANK YOU

30 Time to Torque Test, 3000rpm NA V8 T 10 T 90 90% of Torque 10% of Torque Start of Pedal Input 30 Start of Torque Response