Turbocharging the I'C' Engine Guest Lecture for ME 444 Internal Combustion Engines

1
Turbocharging the I.C. EngineGuest Lecture for
ME 444 Internal Combustion Engines

• Dr. Philip S. Keller
• BorgWarner Inc.
• Engine Systems Group

2
Outline

• Introduction
• Turbochargers
• Thermodynamic Analysis
• Compressor
• Turbine
• Intercoolers
• Benefits
• Challenges
• New Developments
• Conclusions

3
Introduction

• History
• 1885 and 1896, Gottlieb Daimler and Rudolf Diesel
  experiment with pre-compressing intake air
• 1925 Swiss engineer Albert Buchi develops first
  exhaust gas turbocharger which increases power
  output by 40
• 1938 first commercial Diesel truck application by
  Swiss Machine Works Sauer
• 1962 first production application of
  turbochargers in passenger cars - the Chevrolet
  Monza Corvair and the Oldsmobile Jetfire

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Introduction

• History
• 1970s first oil crisis and increasingly
  stringent air emission regulations lead to
  demands for higher power density as well as
  higher air delivery. Outcome -gt virtually all
  current truck engines are turbocharged.
• 1978 Mercedes-Benz puts the 300 SD into
  production marking the appearance of the first
  turbocharged Diesel passenger car
• 1994 VW introduces the variable geometry turbo in
  their TDI Diesel engine significantly improving
  the transient response of the Diesel engine.

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Introduction

• Why boost?

• Definitions

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Introduction

• Power is basically a function of three things
• Air density -gt boosting
• Swept volume
• Engine speed

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Introduction Types of Boosting Systems

• Mechanical Supercharger

Exhaust Gas - Turbocharger
Main problem with supercharging is the parasitic
loss of having to drive the compressor from the
engine output shaft. This loss can be up to 15
of engine output.
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Turbochargers

• The vast majority of turbochargers consist of a
  centrifugal compressor and centripetal turbine
  mounted on a common shaft

Turbine
Compressor
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TurbochargersThermodynamic Analysis

• 30-40 of the fuel energy is released as exhaust
  gas energy
• Area bounded by points 415 is the theoretical
  energy available. This is sometimes referred to
  as blowdown losses

Ideal cycle pressure-volume diagram for a
naturally aspirated engine (Baines, 2005)
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TurbochargersThermodynamic Analysis
Schematic of engine with large exhaust
volume (left) and minimal volume (right) (Baines,
2005)
Ideal cycle pressure-volume diagram for a
turbocharged engine (Baines, 2005)
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Turbochargers - Thermodynamic AnalysisConstant
Pressure and Pulse Turbochargers

• Constant Pressure Turbocharger
• Lower backpressure at higher speeds
• Primarily marine and industrial engines

• Pulse Turbocharger
• More efficient use of exhaust energy
• Better torque at low engine speeds

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Turbochargers - Thermodynamic AnalysisPulse
turbocharger for multi-cylinder engine

• Pulse turbochargers need to have the exhaust
  piping segregated so that exhaust events dont
  interfere with one another

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TurbochargersCompressor

• Consists of three elements
• Compressor wheel
• Diffuser
• Housing
• Compressor limits
• Surge line
• Choke line
• Maximum Blade Speed

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TurbochargersTurbine

• Turbines consist of turbine wheel and housing

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TurbochargersIntercooler

• Temperatures after the compressor can reach 180
  C. Cooling the air can offer a significant
  performance increase.
• Simultaneous improvement in output, fuel economy,
  and emissions

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Benefits

• Fuel Economy
• Reduces pumping work in spark ignition engines by
  enabling engine downsizing
• Major enabler of modern Diesel engines because of
  increase in power density
• Performance
• Eliminates altitude power loss

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Benefits

• Emissions
• Increasing the air mass flow rate by
  turbocharging has enabled significant reductions
  in particulates for Diesel engines. When combined
  with intercooling, there is no increase in NOx.

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Challenges

• Transient Response Turbo lag
• Demands for higher pressure ratios
• Increases in exhaust gas recirculation
• More air for advanced combustion concepts such as
  HCCI
• Higher exhaust temperatures
• Cost

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Challenges Transient Response
Courtesy FEV Engine Technology
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Challenges Transient Response

• Methods to improve transient response
• Reduce turbine and compressor wheel inertia
• Reduce intake and exhaust system volume
• Technologies to improve transient response
• Wastegate
• Variable geometry turbine
• Electrical assist

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Challenges Transient ResponseWastegate

• Improves low speed performance by enabling the
  use of a smaller turbine. Additionally, the
  turbocharger inertia is also reduced with the
  smaller turbocharger

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Challenges Transient ResponseVariable Geometry
Turbine
BSFC, BMEP Improvement

• Improves Transient Response
• Up to 35 EGR Flow Capability
• Improves Diesel Air/Fuel Ratio at Part Load
  Conditions

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Challenges Transient ResponseElectrical Assist
Expansion of the power curve (Münz, et.al)
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Challenges Transient ResponseElectrical Assist
Schematic showing location of eBooster TM
Electrically assisted compressor eBooster TM
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New Developments

• Regulated 2-stage turbocharging
• BorgWarner R2S system
• Characteristics
• Total pressure ratio around 2,5 3(compare
  conventional 2 stage gt4)
• High pressure stage smaller than with
  conventional 2-stage (HD)gt excellent dynamics
• High pressure stage compressor bypassedat high
  volume flows
• boost pressure regulated by control valve in
  part load areahigh pressure turbine bypassed at
  high speeds
• Waste gate for boost pressure control atrated
  power

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New Developments
Regulated 2-stage turbocharging BorgWarner R2S
system

• Advantages
• Higher total pressure ratios than with
  1-stage(higher power outputs possible)
• LP-stage can operate at better efficiencies
• Better low end torque
• Better dynamic performance (small HP-stage - low
  inertia)

• Disadvantages
• Bigger package
• Heavier
• More actuators necessary
• Boost pressure control more complex

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New Developments

• Regulated 2-stage turbocharging BorgWarner R2S
  system

• Actuators
• HP turbine bypass valve splits up mass flow
  between LP and HP-stage
• compressor bypass valve bypasses
  HP-compressor
• LP-turbine waste gate valve controls mass
  flow through LP-turbine

• Control strategy
• PID control of HP-turbine bypass valve for boost
  pressure control in part load
• PID control of waste gate for boost pressure
  control at high loads/speeds
• Open loop control (0/1) of compressor bypass
  valve
• Switching between both control circuits
• Open loop control of the waste gate while
  controlling the HP-turbine bypass (closed at low
  loads/speeds)

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Conclusions

• Turbochargers are, and will continue to be, an
  integral part of modern IC engines
• They offer benefits in performance, fuel economy,
  and emissions
• New technologies are being applied to
  turbochargers to mitigate or eliminate transient
  performance issues