DIRECTFUELINJECTION

1

Michigan State University College of
Engineering ME 444 Fall 2007

• DIRECT-FUEL-INJECTION
• GASOLINE ENGINES
• Arun Solomon
• General Motors R D and Planning
• Powertrain Systems Research Laboratory

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OUTLINE

• Historic evolution of fuel delivery systems for
  gasoline engines
• Direct-fuel-injection - benefits
• Past direct-injection stratified-charge (DISC)
  engine programs
• Why revisit the DISC engine?
• The modern gasoline direct-injection engine
• Summary and conclusions
• 
  

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Gasoline-Engine Fuel Delivery Systems
Direct (In-Cylinder) Fuel-Injection
????
1996
Advanced Multi-Port-Fuel-Injection
1995
????
Multi-Port-Fuel-Injection
1980
????
Single-Point, Throttle-Body Fuel
Injection
1980
1995
Carburetor

• 1900

1985
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Port-Fuel-Injection
Carburetor
Direct-Injection
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A Typical Reverse-Tumble Wall-Controlled
Direct-Injection Gasoline Engine
Vertical Intake Ports that Generate
Reverse-Tumble AirFlow
Spark Plug
Direct-Fuel Injector
Piston with Bowl to Aid in Creation of Suitable
Fuel-Air Mixture
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Historic Evolution of Gasoline-Engine Fuel
Delivery Systems

• The evolution of gasoline-engine fuel delivery
  systems has been dictated by the need to improve
  transient and cold engine performance and
  emissions.
• With each evolutionary change in the fuel
  delivery system, air-fuel mixture preparedness,
  within the cylinder, had to be engineered and
  restored to the traditionally acceptable
  homogeneous state.

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Gasoline-Engine Fuel Delivery Systems

• Fuel System
• Carburetor
• Single-Point,
• Throttle-Body
• Fuel Injection
• Multi-Port-
• Fuel-Injection
• Advanced
• Multi-Port-
• Fuel-Injection
• Direct-Fuel-
• Injection

Transient Emissions Control

Cold Emissions Control

Mixture Preparation Quality

Cost Complexity

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Will direct-fuel-injection replace electronic
port-fuel-injection at a similar rate?
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Direct-Fuel-Injection - Preliminary Goal

• Preliminary goal for a Direct-Fuel-Injection
  system is therefore to be able to achieve the
  traditionally acceptable homogeneous air-fuel
  mixture state at the time of ignition, by
• Promoting maximum air-fuel mixing
• Using a finely atomized spray
• Prevent wall wetting
• Injecting early during intake stroke
• Intake-port design
• Injector location

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Direct-Fuel-Injection - Benefits

• However, because of the big increase in cost and
  complexity of a DFI system, would like to get
  more benefits to offset system costs than just
  improved cold and transient engine performance
  and emissions.
• Are there any additional benefits of a DFI
  system?
• Yes. Increased Fuel Economy !!
• But, this increase in thermal efficiency is
  currently possible only if the mixture-preparation
  state, within the cylinder, is stratified and
  not the traditionally acceptable homogeneous
  state.

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DI Gasoline Fuel Economy Emissions(First Order
Benefits and Risks)
Needs Lean NOx Catalyst
Emissions Risk
Needs In-Cylinder NOx and HC Control
Fuel Economy
Expect Reduced Cold and Transient Emissions
Likely Operating
Range
Mixed Mode
Homogeneous Charge (Throttled)
Stratified Charge (Unthrottled)
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Thermodynamic Levers to Increase Thermal
Efficiency

• Increased volumetric efficiency
• increased compression ratio
• Decreased throttling losses
• Lean combustion
• Decreased heat losses

In trying to work the above levers, DFI is an
enabler with high potential. Note that advanced
MPFI systems are also enablers, but with lesser
potential than DFI.
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Direct-Fuel-Injection Benefits Increased
Volumetric Efficiency
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Direct-Fuel-Injection Benefits Increased
Volumetric Efficiency
Direct-Fuel-Injection can result in an increase
(up to 8 has been reported) in airflow due to
spray-cooling of the intake air, when injection
occurs during the intake stroke. The resulting
increased performance can be converted to 1-2
increase in fuel economy.
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Direct-Fuel-Injection BenefitsIncreased
Compression Ratio

Note Otto-Cycle efficiency is used as a gross
approximation for illustrative purposes
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Direct-Fuel-Injection BenefitsIncreased
Compression Ratio
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Direct-Fuel-Injection BenefitsIncreased
Compression Ratio

• Direct-Fuel-Injection permits an increase in
  compression ratio from 10.5 to about 12.0,
  resulting in about 2 increased efficiency. The
  increase in compression ratio results from a
  higher knock-tolerance (I.e., higher
  knock-limited spark advance) due to
• 1. Spray cooling of the intake air when
  injection occurs during the intake stroke
• 2. Reduced end-gas temperature when injection
  occurs during compression stroke

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Direct-Fuel-Injection BenefitsDecreased
Throttling Losses

• Throttling losses are reduced by diluting the
  mixture with EGR or with excess air. But in a
  conventional homogeneous-charge system, the
  extent of dilution is limited due to flame
  initiation and propagation limits.
• By stratifying the fuel-air mixture within the
  combustion chamber, the engine can be operated
  with extended dilution, at air-fuel ratios of
  501 or greater.

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Ideal Throttling Loss Effects on Net Thermal
Efficiency ()
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Diluting the Air-Fuel Mixture Reduces Pumping (or
Throttling) Losses
Partially Diluted Combustion (Partially
Unthrottled)
Fully Diluted Combustion (Fully Unthrottled)
Undiluted Combustion
IMEP
IMEP
IMEP
Ln Pressure
PMEP
PMEP
Ln Volume
Reduced Pumping Loss Due to Dilution
Net MEP IMEP - PMEP
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Direct-Fuel-Injection Benefits Lean Combustion
Note Otto-Cycle efficiency is used as a gross
approximation for illustrative purposes
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Direct-Fuel-Injection Benefits Lean Combustion

• When the working fluid has a higher
  specific-heat ratio like that of lean air-fuel
  mixtures, less fuel energy is wasted in raising
  the internal energy of the charge, so more is
  available for useful work.
• By stratifying the fuel-air mixture within the
  combustion chamber, the engine can be operated at
  very lean (up to 501) air fuel ratios.

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Direct-Fuel-Injection BenefitsDecreased Heat
Losses

• By stratifying the fuel-air mixture in the center
  of the combustion chamber and keeping the hot
  burnt products away from the walls, heat losses
  can be decreased.

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Idealized Unthrottled Stratified-Charge Operation
(FuelAir) or (FuelAirEGR) AF 18-20
Mid-Load
Air or (Air EGR)
Idle
High-Load
Ln Pressure
Ln Volume
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Idealized Unthrottled
Stratified-Charge Operation

• Fuel Economy (Relatively Easier to Demonstrate)
• Little or no throttling losses (no pumping loop)
• Reduced heat losses (burning occurs with less
  contact with walls overall temperature lower)
• Lean combustion (less heat used up in raising
  internal energy of charge so more available for
  useful work)
• Higher compression ratio (more knock tolerant
  because end-gas properties are favorably
  modified reduced thermal dissociation)

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Idealized Unthrottled
Stratified-Charge Operation

• Emissions (High Risk)
• Ideal properties of fuel-air cloud are difficult
  to attain, especially over entire load range
• Excessive lean fringes of cloud extinguish to
  cause a HC emissions problem
• Excessive stoichiometric regions of cloud cause
  NOx emissions problem
• Lean nature of combustion prevents use of a
  conventional 3-way catalyst (and lean-NOx
  catalysts still under development))

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Some Major DISC-Engine Programs of the Past

• U.S. Army/Texaco - Texaco controlled combustion
  system (TCCS)
• Fords programmed combustion (PROCO) engine
  (1970s)
• GMs direct-injection stratified-charge (DISC)
  engine (1980s)
• UPS-Texaco controlled combustion system (TCCS)
• Volkswagen gasoline direct injection (GDI)
• M.A.N. FM combustion engine
• 
  
• 
  
  
  

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Some Other DISC-Engine Programs and
Activities of the Past

• Engine Manufacturers
• White, Porsche (SKS-engine), Deutz (AD combustion
  process), Honda, International Harvester,
  Curtiss-Wright
• U.S. Government
• U.S. Army/TACOM, EPA, DOE
• U.S. National Labs
• Sandia, Los Alamos, Lawrence Livermore, NASA
  Lewis
• Universities
• Princeton, MIT, Wisconsin, Michigan State,
  Imperial College, Aachen-Germany
• Consulting Houses
• SwRI, Ricardo

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Past DISC-Engine Programs - General Results

• Late Injection
• Fuel is injected relatively late in the
  compression stroke, ignition occurs during the
  injection process, and mixing of fuel and air
  occurs during and after ignition permits
  relatively high compression ratio.
• High thermal efficiency (30 gain), good
  multi-fuel capability and excellent cold-start
  performance was demonstrated.
• Problems were encountered with high light-load
  hydrocarbon emissions, high mid-load nitric-oxide
  emissions, high-load particulates, combustion
  variability and specific power.

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Past DISC-Engine Programs - General Results

• Early Injection
• Fuel injection occurs relatively early in the
  compression stroke major mixing between fuel and
  air takes place before ignition compression
  ratio is more knock-limited like conventional
  homogeneous-charge SI engines.
• Expected gains in thermal efficiency were mostly
  realized. However, problems with high light-load
  hydrocarbon emissions, high mid-load nitric-oxide
  emissions and maximum power were encountered.
• 
  
  
  

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A Simple Summary of the HC/NOx Problem

• Hydrocarbons Major source of engine-out
  hydrocarbon emissions is due to quenching of the
  flame in the overly lean fringes of the fuel-air
  cloud.
• Nitric-oxide Major source of engine-out
  nitric-oxide emissions is stoichiometric
  combustion at local regions, within the
  combustion chamber.

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A Simple Summary of the HC/NOx Problem
Spark Plug
Injector
Too Lean AF 40 Source of HC Emissions
Air or (Air EGR)
Stoichiometric AF 14.6 Source of NOx Emissions
Rich AF
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Lessons from the Past

• Yes,
• unthrottled, direct-injected, stratified-charge
  operation of a gasoline spark-ignited engine
  yields significant gains in thermal efficiency.
  This gain comes from a reduction or elimination
  of throttling losses, increased compression ratio
  and lean combustion.
• But,
• the challenge for the stratified-charge engine is
  meeting future Federal and California hydrocarbon
  and nitric oxide emissions standards. This is due
  to high hydrocarbon emissions at light-loads and
  high nitric-oxide emissions at mid-load.
  

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Why Revisit the DISC Engine?

• Fuel Economy
• Eliminating Throttling Losses - Throttling losses
  still represent the largest single recoverable
  loss for the SI gasoline engine.
• Direct-Injection Gasoline Fuel Systems - Better
  DI fuel systems and large number of fuel-system
  suppliers are available due to efforts on DI
  two-stroke engine programs.
• Lean NOx Catalyst - Required for DISC
  efficiency of these catalysts are constantly
  increasing.

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Why Revisit the DISC Engine?, continued

• Engine Control Systems - Complex control systems
  needed for control of complex DISC combustion
  process are already here.
• Improved Understanding of Combustion Process -
  This is attributable to ongoing work and progress
  in understanding port-injected lean-burn, and
  direct-injected two-stroke and four-stroke
  combustion processes.
• 
  
  
  

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The Modern DFI Gasoline Engine
PROGRESSION OF OEM INTRODUCTIONS
JAPAN 1996
EUROPE 1998
US 200X ??
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The Modern DFI Gasoline Engine
Direct-Injection Combustion System Alternatives
Homogeneous (Throttled)
Mixed-Mode
Stratified (Unthrottled)
Spray-Jet Controlled
Charge-Motion Controlled (VW)
Wall-Controlled
Spray-Jet Controlled
Tumble Wall-Controlled (Mitsubishi)
Swirl Wall-Controlled (Toyota)
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• ADVANTAGES
• Combustion rate scales better with engine speed
• Combustion control over load-range is easier

• DISADVANTAGES
• Optimization over speed and load range is
  challenging, since spray is real-time event
• Potential for highly stratified operation may be
  limited

CHARGE-MOTION CONTROLLED Dominated by interaction
of bulk airflow with spray
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• ADVANTAGES
• Light-load stratification easier to achieve
• Combustion is less sensitive to spray
  characteristics

• DISADVANTAGES
• Wall-wetting during cold and heavy-load operation
  causes HC emissions and smoke
• Combustion modes are different in light-load and
  heavy-load regimes

• WALL CONTROLLED
• Dominated by interaction of spray with wall

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• ADVANTAGES
• Potential for highly stratified operation

• DISADVANTAGES
• Current sprays are not ideal (therefore usually
  requires deep bowl in piston for containment)
• Requires spraying directly onto spark-plug
  electrodes (therefore reduced plug durability)

• SPRAY-JET (or PUFF) CONTROLLED
• Dominated by spray characteristics

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The Modern DFI Gasoline Engine

• SAE 940483 (Ricardo/Isuzu)
• Siemens fuel injector (droplet size 5 to 10
  microns)
• Operated direct-injected engine, with injection
  timings during intake stroke (homogeneous-charge),
  and obtained NOx, CO, HC emissions and fuel
  consumption competitive, with port-fuel-injected
  version of the same engine.
• Cold transient tests demonstrated that a
  direct-injected combustion system has the
  potential to operate without fuel enrichment
  during cold starts.
• 
  
  
  

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The Modern DFI Gasoline Engine

• Advances in direct-injection gasoline
  fuel systems and injectors enables the
  DI gasoline (homogeneous-charge) engine to
  have the potential of having lower emissions
  during cold and transient operation.

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The Modern DFI Gasoline Engine

• SAE 940675 (Hokkaido U./Japan Railway Co.)
• Direct-injected stratified-charge operation with
  two-stage fuel injection.
• First stage fuel injection occurs before
  compression stroke to create uniform premixed
  lean mixture second stage occurs at the end of
  the compression stroke to maintain stable
  ignition and faster combustion.
• 30 reduction in fuel consumption and 50 NOx
  emissions reductions were achieved.

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The Modern DFI Gasoline Engine, continued

• Advances in control systems enables
  direct-injection stratified charge engine to
  address the NOx emissions problem in new ways.

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The Modern DFI Gasoline Engine

• Mitsubishi
• Started production in Japan in Sept 1996
• SAE 960600, SAE 970541, SAE 980150,
  SAE 2001-01-0545
• Toyota
• Started production in Japan in Dec 1996
• SAE 970539, SAE 970540, SAE 980157
• SAE 2000-01-0530 and 2000-01-0531,
  SAE 2001-01-0734, 2001-01-0734
• Nissan
• Started production in Japan in Dec 1997
• SAE 980149, SAE 1999-01-0505

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Toyotas Map of Combustion Regimes
(SAE 970540)
Stoichiometric Homogeneous-Charge Combustion
2-Stage Injection
Torque
Lean Homogeneous- Charge Combustion
Late-Injection, Lean Stratified-Charge Combustion
Engine Speed
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First-Order Benefits and Challenges

• BENEFITS
• Fuel economy
• Increased output torque
• Reduced cold-start HC emissions
• Improved transient fuel control
• Reduced HC emissions
• Increased responsiveness
• Deccel. Fuel cut-off
• Close-coupled catalyst protection
• Idle fuel shut-off
• Faster low-temperature starting

• CHALLENGES
• Cost
• HC NOx emissions
• Combustion control over operating range
• Injector durability
• Injector packaging
• Smoke
• Low exhaust temperatures

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SUMMARY

• Direct-Injection Gasoline engines offer the
  potential for significant fuel economy gains.
• Rapid engine-development progress is being made
  due to progress in DI fuel systems, control
  systems and lean-NOx catalysts technology.
• Rate of introduction into world markets will
  primarily depend on rate of solving emissions
  problems and rate of cost reduction.

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CONCLUSION

• Direct-Injection Stratified-Charge Gasoline
  Engines have significantly higher fuel economy
  than conventional throttled engines but they
  also have significantly higher HC and NOx
  emissions.
• However, due to recent significant advances in
  Direct-Fuel-Injection system technology, engine
  control systems, exhaust aftertreatment systems
  and understanding of lean and direct-injection
  combustion processes, revisiting the DISC engine
  is warranted.

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Suggested Reading

• 1. C. D. Wood, Unthrottled Open-Chamber
  Stratified-Charge Engines,
  SAE Paper 780341, 1978.
• 2. A. J. Giovanetti, et al., Analysis of
  Hydrocarbon emissions in a Direct-Injection
  Spark-Ignition Engine, SAE Paper 830587, 1983.
• 3. A. S. P. Solomon, A Photographic Study of
  Fuel Spray Ignition in a Rapid
  Compression Machine, SAE Paper 860065, 1986.
• 4. Fu-Quan Zhao, Ming-Chia Lai and David L.
  Harrington,A Review of Mixture Dynamics and
  Combustion Control Strategies in Spark-Ignited
  Direct Injection Gasoline Engines SAE Paper
  970627.
• 5. Direct-Injection SI Engine Technology, SAE
  Special Publications SP-1416, 1999.
• 6. Direct Fuel Injection for Gasoline Engines,
  SAE Progress in Technology Series, PT-80, Edited
  by Arun Solomon, Richard Anderson, Paul Najt and
  Fuquan Zhao, 2000.
•