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Gasoline Base Engine Development for Performance and Fuel Economy
Matthew McAllister – Jaguar Land Rover Gasoline Engines
Introduction
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Contents
? ? ? ? ?
The Development Process Performance Theory Fuel Consumption Theory Development Tools Summary
The Development Process
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The Development Process
“How does base engine design & development fit into the company structure?”
Vehicle
The Development Process
Responsibilities Engine Design ? Design components on CAD ? Manage all aspects of component delivery (suppliers, cost, weight, manufacture, package) Engine Development ? Manage all aspects of verifying design of components & systems ? Focus on function and attributes
Body&Exterior
Chassis
Interior Systems
Powertrain
Electrical
Systems
Transmissions
Base Engines
Calibration
Design Development
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The Development Process
The System Engineering “V” Start Job1
The Development Process
System Engineering – DEFINE ? Set targets at customer level and then cascade down to component level e.g. Customer level target: 0-60mph < 6.2sec
Vehicle Level System Level
Vehicle Aero T/M FDR 0-60mph time Tractive Effort T/M Efficiency Vehicle Mass Engine Torque Displacement Traction
Vehicle Level
System Level
Sub-system Level
Component Level
Component Level
Engine Technology Compression Ratio Int & Exh System
Define
Design
Verify
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The Development Process
System Engineering - DESIGN
Design Guidelines Corporate/Legal Requirements Manufacturing Requirements Recycling Requirements Component Attribute Targets (from cascade) Cost & Weight Targets Packaging Constraints Quality & Durability Targets
The Development Process
System Engineering – VERIFICATION Vehicle Level Durability Hot/Cold Climate Performance/NVH CAE System Level 1-D Engine simulation Engine dynamometer testing NVH CAE Component Level Rig Testing Component CAE (e.g. FEA/CFD)
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New Design
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The Development Process
The System Engineering “V” Start Job1
The Development Process
Build Phases Design Optimise Verify Manufacture
Vehicle Level
1. Mule Demonstrator (often reworked/modified existing
System Level
hardware)
2. Attribute Demonstrators (first dedicated prototypes, non
Component Level
production process)
3. Confirmation Prototype (final prototypes, should be
production process & off production tool)
Define
Design
Verify
4. Production Verification (off production line at production
rate)
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P&E Attributes
Engine P&E Incorporates: ?Engine Performance ?Engine Fuel Consumption (Economy) ?Engine Emissions
Base Engine P&E
P&E typically considered separate to Mechanical or NVH Development and in some companies part of Calibration department
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P&E Attributes
Performance & Fuel Consumption Challenge
Performance Theory
Possible Scenario ? Existing engine with following specification: -2.6L V6 – 180bhp -Fixed intake manifold -Intake variable cam timing -10:1 compression ratio -6000rev/min peak power speed ? What is required to increase power to 200bhp without increasing displacement?
Source: COMMISSION OF THE EUROPEAN COMMUNITIES - SEC(2007) 1723
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Performance Theory
Performance Theory
Air Mass Trapped
Volumetric Efficiency (manifold & port ?P, tuning) Intake System Losses
Fuel-Air Ratio
Power =
η fuelconversion ×ηvolumetric × N × Vd × QHV × ρ air × ( F / A)
2
Power =
η fuelconversion ×ηvolumetric × N × Vd × QHV × ρ air × ( F / A)
2
Thermal efficiency
Heat losses Mechanical losses Pumping losses Mixing Ignition efficiency
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Engine Speed
Displacement
Fuel Energy
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Performance Theory
Displacement
Power [hp] 700 600 500
Performance Theory
Intake losses
208 206 Power [bhp] 204 202 200 198 196 194 10 20 High performance Performance vs Intake Loss typical family car 30 40 Intake Loss [mbar] 50
? Power ~ proportional to displacement ? Often easiest way of achieving power increase but increases fuel economy, engine mass and package requirements ? Can limit maximum engine speeds Engine Speed ? Power is “rate of doing work”, therefore proportional to engine speed ? Requires changes to engine design to ensure volumetric efficiency does not drop ? Can involve significant costs to achieve durability
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400 300 200 100 0 0 1 2 3 4 5 6 Displacement [litres] 7 8
European Gasoline Engines 2007
AIS CFD
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Specific Power [hp/L]
120 100 80 60 40 20 0 4000 5000 6000 7000 8000 Max Power Speed [rev/min]
? Minimize losses – rule of thumb: 1.2% power / 10mbar intake ?P increase ? Minimize detrimental tuning effects as a result of layout
European Gasoline Engines 2007
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Performance Theory
Volumetric Efficiency - ?P ? Minimize pressure losses (throttle sizing, manifold runner R/D, manifold detail design, managing interfaces, surface finish, port design, valve design, valve seat design) Throttle ?P (CFD)
Flow Coefficient 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 Valve Lift/Diameter
Performance Theory
Volumetric Efficiency – Intake Tuning
R D
R/D
Port flow
? Objective: maximise mass of air trapped at specific speeds or across speed range by harnessing wave and inertial tuning effects ? WAVE tuning – dependent on intake cam period & runner length
Depression Wave Runner PLENUM Cylinder Reflected Pressure Wave Runner PLENUM Cylinder
? Inertia tuning – inertia of air column in runner/port continues charging process past piston BDC - dependent on runner diameter, volume and intake valve closing time
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Performance Theory
Typical production I4 performance curve…
150% 250
Performance Theory
Volumetric Efficiency – Optimum Runner Lengths ? Theoretical optimum runner length vs engine speed:
2500 Intake Length Optimum Runner Length [mm] 2000 Exhaust Length
130% Volumetric Efficiency [%]
200
110%
150
Torque [Nm]
Closed Valve Tuning Secondary Tuning
1500
90%
Primary tuning
100
1000
70%
50
500
50% 0 1000 2000 3000 4000 5000 6000 Engine Speed [rev/min]
0 7000
0 2000
3000
4000
5000
6000
7000
Engine Speed [rev/min]
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Performance Theory
Volumetric Efficiency – Exhaust Tuning ? Objective: maximise extraction of residuals by harnessing wave tuning effects in exhaust / minimise negative tuning effects between cylinders ? Limited opportunity in modern passenger vehicles as design is dominated by emissions requirements (catalyst) Log Manifold and under-bonnet package
Blow-down pulse
Performance Theory
Fuel Air Ratio (1/AFR) ? Maximum performance at ~12:1-13:1 AFR (Power Enrichment) ? AFR settings at higher engine speeds generally dictated by component (e.g. exhaust valves, turbine, catalyst) protection requirements
PE - AFR~13:1
% Performance degradation 0% -1% -2% -3% -4% 10 11 12 AFR 13 14 15
Collector Cylinder
4:2:1 Manifold
Reflected extraction wave
Load
λ=1 (AFR~14.6:1) (for max. catalyst eff.)
Collector Cylinder
Engine speed
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Performance Theory
Thermal Efficiency Friction: ? At max power speed friction is approximately 15% of brake power ? 10% reduction in friction 1.5% increase in power ? Not only contact friction – need to consider windage / inter-bay breathing Heat losses: ? At max power ~22% of fuel energy lost in heat transfer to air/oil/coolant ? 10% reduction in heat loss 8% increase in power (!)
Performance Theory
Thermal Efficiency Exhaust Back Pressure – 3 effects: 1.Increases pumping work to expel charge 2.Reduces amount of fresh charge induced 3.Increases knock sensitivity (ignition retard from optimum)
family car
Typical SI engine heat balance at peak power
Power [bhp]
Ambient 7% Coolant/oil 15% Brake power 28%
Performance vs Exhaust Back Pressure 208 206 204 202 200 198 196 194 200
Exhaust enthalpy 50%
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High performance
300 400 500 Exhaust Back Pressure [mbar]
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Performance Theory
Thermal Efficiency Ignition Efficiency: ? Objective – operate ignition at MBT (Maximum advance for Best Torque) ? Good resistance to detonation (detail chamber design, head cooling) ? Key parameters: compression ratio & fuel RON (trade-off with fuel economy)
Load
420
Performance Theory
Robustness… ? It is not enough simply to demonstrate performance under ideal homologation conditions (low temperature, high RON fuel, best build condition) ? Also need to consider worst case… ? Need to understand sensitivities to these parameters and ensure adequate performance under all conditions to avoid customer complaints
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Torque [Nm]
400 380 360 340 30 20 10 0
MBT
DBL
Ignition [° btdc]
WOT
Knock limited IGN
MBT IGN
Engine speed
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Performance Theory
Back to performance optimisation scenario … ? 200bhp = 11% increase ? Increasing engine speed to 6600rev/min at constant volumetric efficiency would deliver ~10% = 198bhp
Torque [Nm]
Performance Theory
Back to performance optimisation scenario … ?2.6L, 180BHP
280 240 200 160 120 80 40 0 1000 2000 BASELINE
? Increasing compression ratio to 11:1 would deliver ~2-3% = 4bhp = 202bhp (providing engine is not knock limited) ? To deliver good volumetric efficiency at higher engine speed will require re-optimised runner length ? May need to consider variable geometry manifold to not sacrifice too much low speed performance
3000 4000 5000
6000 7000
Engine Speed [rev/min]
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Performance Theory
Back to performance optimisation scenario … ?2.6L, 198/202BHP – but poor driveability
280 240 Torque [Nm]
Performance Theory
Back to performance optimisation scenario … ?2.6L, 202BHP – Optimised Torque Curve
280 240 Torque [Nm] 200 160 120 80 40 0 1000 2000 INCR ENG SPD INCR CR TWIN STAGE MANIFOLD BASELINE
200 160 120 80 40 0 1000 2000 3000 BASELINE INCR ENG SPD INCR CR
4000 5000 6000 7000
3000 4000 5000
6000 7000
Engine Speed [rev/min]
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Fuel Consumption Theory
Fuel economy break-down
Gross Efficiency Fuel required to generate GIMEP
Fuel Consumption Theory
change in BSFC
Maximize Gross Efficiency (1) ? Maximize compression ratio (trade-off with low speed / low RON / high air temp performance)
Log P
10% 8% 6% 4% 2% 0% -2% -4% 9:1
Theory Reality 10:1 11:1 12:1 13:1 14:1 Compression Ratio
Pumping work Fuel “lost” to pumping work
exhaust
Pumping work PMEP
induction
Friction work Fuel “lost” to friction work
Log V Net IMEP = GIMEP + PMEP (-ve) BMEP = Net IMEP - FMEP
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? Minimize heat transfer (surface to volume ratio, charge motion, coolant temperature)
3% 2% 1% 0% -1% -2% -3% 0.90 0.95 1.00 1.05 1.10
Bore/Stroke Ratio
Brake work
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Change in η thermal
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Fuel Consumption Theory
Maximize Gross Efficiency (2) ? Ensure complete burn (good atomisation, complete mixing) ? Ensure optimum spark efficiency (resistance to knock, fast burn, correct calibration)
Increase in Fuel Consumption
Fuel Consumption Theory
Minimize Pumping Pumping Reduction Routes: 1.Charge dilution (stratified DI / lean homogeneous / EGR) 2.Reduction of trapped volume (very early or very late intake valve closing) 3.“Down-sizing”
40% 30% 20% 10% 0% 0 10 20 30 40
Ignition Timing [° btdc]
MBT (opt eff)
Log P
PMEP
New MAP Old MAP
Log V With all these approaches the volume of trapped air is reduced requiring the manifold pressure (MAP) to be raised, i.e. throttle to be opened further, to recover the lost mass This reduces the pumping work
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Fuel Consumption Theory
Dilution by air (Stratified Direct Injection)
Example: MB 3.5L V6 DI
Fuel Consumption Theory
Reduction of trapped volume
Example – BMW Valvetronic
? Significant fuel economy potential 5-15% depending on engine size/application ? BUT major emissions compliance challenge involving complex and expensive after-treatment system (maybe not possible beyond EU5 in Europe and ever in US?) ? Benefit diminishes significantly for smaller engines
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? Pumping benefit achieved by virtue of controlling load (mass trapped) through variable valve lift/duration instead of throttle ? Limited fuel economy benefit (2-5%) due to reduced combustion efficiency - particularly at light load (effective compression ratio reduced, poor charge motion) ? Expensive technology and major manufacturing challenge
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Fuel Consumption Theory
Minimize Friction ? Typical friction break-down vs engine speed for SI engine:
100% Friction Break-down 80% 60% 40% 20% 0% 1000 2000 3000 4000 5000 6000 Engine Speed [rev/min]
Fuel Consumption Theory
Based on fuel consumption theory just presented what are the two main reasons for the improved fuel consumption of Diesel vs. Gasoline engines? 1) Higher Compression Ratio (no knock limitation)
Valvetrain Coolant Pump + Unloaded Alternator Oil pump Piston group & con-rod bearings Crankshaft
Diesel
? For drive-cycle fuel economy (below 3000rev/min) focus should be on reduction of valvetrain and piston friction ? A 10% reduction in piston friction could reduce part load fuel consumption by ~1%
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Gasoline
7.5 10.0 12.5 15.0 17.5 20.0 22.5
Compression Ratio
Each symbol represents up to 3 observations.
2) Minimized pumping work (load control through level of dilution with air, qualitative vs. quantitative load control)
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Fuel Consumption – CO2 challenge for manufacturers
How to make vehicles that comply with the EU Legislative framework:
? From 2012 to 2019 a vehicle mass based CO2 limit will be applied to all new
vehicles.
? How to address this in a cost effective manner, whilst maintaining key
vehicle attributes? Options available:
Application of Fuel Consumption Theory
? Vehicle level optimisation for increased efficiency: ? Advances predominantly aimed at reducing weight and aerodynamic
drag.
?Powertrain level: ? Mild or micro hybrid technologies. ? Full hybridisation. ? Technologies aimed at reduced friction, pumping and increased
combustion efficiency. Gasoline engines downsizing and boosting – focus of our paper.
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Fuel Consumption – Downsizing and Boosting
?Presented at IMechE Internal Combustion Engines: Performance, Fuel & Emissions Conference - Dec 09 ?Paper title: Future gasoline engine downsizing technologies – C02 improvements and engine design considerations. Authors: M.J.McAllister & D.J.Buckley.
Fuel Consumption – Challenges of downsizing
? Downsizing - The principle behind this approach is to de-throttle the engine to reduce pumping work by making the displacement and/or number of cylinders smaller. ? Boosting – provides a means of increasing the specific performance of the downsized engine, thus maintaining the power and torque of the engine it replaces, typically with a supercharger, turbocharger or combined boosting systems. Gasoline engine downsizing and boosting offers manufacturers significant CO2 reductions without major vehicle modifications such as those required by full hybrid technologies.
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Robust DI combustion system. An advanced boosting system. Emissions countermeasures. Effective integration of downsized engines with complementary CO2 reduction strategies. Refinement. Customer acceptance of smaller engines.
The above challenges are considerable due to competing attributes. Customer acceptance is a problem that requires more than just an engineering solution!
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Fuel Consumption – CO2 benefits of engine downsizing
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2.4L I4
% CO 2 reduction
20 15 10
4L V8 3L V6 3.5L V6
2L I4
Deviation from the trend line is due to BMEP resolution in the fuel map analysis
5 0 0% 10% 20%
SC TC
30%
40%
50%
60%
70%
P&E Development Tools
Level of Downsizing [%]
? For a >10% CO2 benefit a significant level of downsizing is necessary
(35%) requiring a change in architecture, i.e. V6 vs. V8 or I4 vs. V6.
? A moderate level of downsizing (e.g. 4.5L SC vs. 5L NA) does not yield
a meaningful CO2 benefit (<3%).
? Difference between boosting systems is small compared to overall
downsizing effect so other factors will be decisive (e.g. transient response, emissions etc.).
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Overview
P&E Specific Tools
Level Vehicle Virtual ? Vehicle performance and FE simulation ? 1-Dimensional Gas Exchange Modelling ? Combustion Modelling ? CFD flow modelling ? Friction modelling Real ? Drive cycle FE and emissions testing ? Performance testing ? Single-cylinder engine testing ? Multi-cylinder engine testing ? Flow bench testing
Valve Seats
CAE
Steady State CFD – Port Flow ? Allows detailed “desktop” optimisation of port design for flow / charge motion prior to evaluation on flow bench test
Pressure Inlet Bell Mouth Ports
Engine
Component
Chamber & Tube Pressure Outlet
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CAE
Steady State CFD – Intercooler Flow Distribution
CAE
1-D Simulation ? 1-D Simulation (Ricardo WAVE) used to analyze the dynamics of pressure waves, mass flows, and energy losses in the engine intake and exhaust ? Engine intake & exhaust geometry broken down into 1dimensional components (ducts and junctions) ? Mass, momentum and energy conservation equations solved for each sub-volume to obtain solution ? Used to predict key engine operating characteristics, e.g. volumetric efficiency, torque, mass flows, etc.
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CAE
WAVE 1-D model – SC V8
Catalyst A-bank
CAE
WAVE 1-D vs Test Data Correlation
WAVE model Test Data
SC & IC
B-Bank Exhaust System
Airbox
B-bank
Torque 1000
2000
3000
4000
5000
6000
Exhaust Manifold
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Engine Speed [rev/min]
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CAE
Advantage of 1-D simulation 1. Time – possible to run multiple simulations 24/7 2. Cost – conducting engine testing is expensive (test facility, tester,
engineer, fuel, maintenance), 1-D simulation only requires 1 engineer and 1 PC
Testing
Engine Dynamometer ? Durability & functional testing ? Steady state & transient dynamometers ? High/low temperature capabilities
3. In-depth understanding – with 1-D simulation detailed
information of pressures, temperatures, mass flows, etc. is available throughout the engine and at every point in the cycle
Disadvantages 1. Need for correlation to existing test data 2. Model does not always behave like real engine 3. 1-D approximation of complex 3-D geometries
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Testing
Typical dynamometer instrumentation 1. Thermocouples e.g. coolant, oil, intake air temperature 2. Pressure transducers e.g. oil gallery, boost pressure 3. Fuel flow (mass/volumetric) used to infer air mass flow 4. Emissions analyser O2, CO, CO2, HC, NOx 5. Smoke meter (Diesel, GDI) 6. Fluid flow meters e.g. engine or intercooler coolant flow 7. Combustion analyser used to measure cylinder pressures and calculate IMEP, PMEP, burn data 8. EMS break out equipment to control engine settings 9. Automated testing controller to schedule automated testing and interface with dyno & EMS 10. Knock monitoring equipment audio/visual
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Testing
Key Challenges ? Maximum utilisation of dynamometers – expensive investment ? Efficient processing of (ever) increasing quantities of test data – up to 250 data channels per test point ? Increased use of design of experiments and data modelling ? Increased use of automated testing ? Increased awareness of the statistical nature of test data
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Testing
Rapid Prototype Parts > key technology in enabling reduced development time ? SLA – Stereolithography
– 3D CAD model is converted into a series of 2D slices (~0.1mm thick). Laser cures photosensitive resin in a tank layer by layer
Summary
? Laser Sintering
– Similar principal to SLA but very thin layers of heat fusible powder are repeatedly deposited. Laser sinters the fresh powder to form a new layer.
? Applications: intake manifolds, air induction systems, moulds for casting, etc.
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Summary
Overview ? Methodology used in vehicle/engine development – System Engineering “V” ? Fundamental performance and fuel consumption theory ? Overview of tools used in development Future Challenges ? Dramatic fuel consumption / CO2 reduction required ? More stringent emissions legislation ? Higher performance (?) ? Reduced development time ? Lower cost (?)
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New Jaguar CX-16 Sports Car 2010 Jaguar XK GT2
Thank You
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