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Pneumatic Hybrid An alternative to electric
hybrid (?)
Bengt Johansson Sasa Trajkovic, Div. of
Combustion Engines Lund University
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Outline

• Pneumatic Hybrid
• Experimental Setup
• Results Evaluation of the Free Valve Technology
  system
• Results Pneumatic hybrid
• Conclusions

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Outline

• Pneumatic Hybrid
• Experimental Setup
• Results Evaluation of the Free Valve Technology
  system
• Results Pneumatic hybrid
• Conclusions

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Pneumatic Hybrid- Background -

• Electric hybrids have proven to have significant
  potential to improve fuel economy and reduce
  exhaust emissions ? high customer attractiveness

Cumulative reported US sales of hybrid vehicles
during the period 1999-2007
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Pneumatic Hybrid- Background -

• The electric hybrids suffer from a high
  end-product price due to the additional
  propulsion source and batteries
• Also, the limited life-cycle of the batteries
  contributes to a higher life-cycle cost
• One way of reducing the extra cost due to vehicle
  hybridization is the introduction of the
  pneumatic hybrid

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Pneumatic Hybrid- Background -

• The pneumatic hybrid is a quite simple solution
  utilizing only an internal combustion engine as
  propulsion source
• Instead of batteries, the pneumatic hybrid uses a
  relatively cheap pressure tank to store energy

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Pneumatic Hybrid- Operating principal -

• Compressor mode, CM
• During deceleration, the engine is used as a
  compressor that converts the kinetic energy of
  the vehicle into potential energy in the form of
  compressed air which is stored in a pressure tank
• Air-motor mode, AM
• During acceleration, the engine is used as a
  air-motor that utilizes the pressurized air from
  the tank
• Air-power assist mode, APAM
• The stored pressurized air is used for
  supercharging the engine when there is a demand
  for higher torque
• Stop-start functionality
• During idling the combustion engine can be
  completely shut off with no fuel consumption
  during this period as a result

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Pneumatic Hybrid- Compressor Mode -

• 1-2 Induction of fresh air
• 2-3 Compression stroke
• 3-4 Charging of pressure tank
• 4-1 Expansion stroke

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Pneumatic Hybrid- Air-motor Mode -

• 1-2 Charging of the cylinder
• 2-3 Expansion stroke
• 3-4 Intake stroke
• 4-1 Compression stroke

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Outline

• Pneumatic Hybrid
• Experimental Setup
• Results Evaluation of the Free Valve Technology
  system
• Results Pneumatic hybrid
• Conclusions

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Experimental setup
The Scania D12 Diesel Engine
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Outline

• Pneumatic Hybrid
• Experimental Setup
• Results Evaluation of the Free Valve Technology
  system
• Results Pneumatic hybrid
• Conclusions

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Free Valve Technology System
The Pneumatic Valve Actuators mounted on a Scania
cylinder head
Illustration of Cargines Pneumatic Valve Actuator
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Free Valve Technology System
Pneumatic Valve Actuation valve lift profile

• The valve lift event consists of three sections
• Open period
• Dwell period
• Closing period
• Solenoid 1 (S1)
• Starts the flow of pressurized air into the
  actuator ? starts the opening of the valve
• A hydraulic latch prevents the valve from
  returning as long as S1 is active
• The valve duration is set by the deactivation of
  S1
• Solenoid 2 (S2)
• Stops the air charging of the actuator ?
  determines the valve lift
• May not be deactivated before S1 since it would
  lead to an additional valve event

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Results Evaluating the EPVA system- Evaluation
objectives -

• The objective of the evaluation of the EPVA
  system can be divided into two parts
• Testing EPVA system performance
• Valve timing and lift
• Energy consumption
• Testing of three different valve strategies
  enabled by EPVA
• HCCI with Negative Valve Overlap
• HCCI with Reberathe Strategy
• HCCI with Atkinson/ Miller Strategy

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Results Evaluating the EPVA system - Testing
valve stability -
The valve lift duration remains constant when the
valve lift height is varied
Variation of valve lift at constant valve lift
duration of 200 CAD and an engine speed of 1000
rpm
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Results Evaluating the EPVA system - Testing
valve stability -
The valve lift height remains constant when the
valve lift duration is varied
Variation of valve lift duration at constant
valve lift height of 7 mm and an engine speed of
1000 rpm
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Results Evaluating the EPVA system - Testing
valve stability -
Cycle-to-cycle variations of valve lift and
duration
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Results Evaluating the EPVA system - EPVA
energy consumption -
EPVA energy consumption
The air consumption per engine cycle increase
with increasing valve lift due to longer actuator
piston stroke
The air consumption per engine cycle is not
engine speed dependant
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Outline

• Pneumatic Hybrid
• Experimental Setup
• Results Evaluation of the Free Valve Technology
  system
• Results Pneumatic hybrid
• Conclusions

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Results Pneumatic Hybrid- Engine modifications-

• The Scania engine was converted to work as a
  pneumatic hybrid engine
• A 50 liter pressure tank was connected to one of
  the inlet ports
• The corresponding inlet valve was converted to a
  tank valve with a valve head diameter of 16 mm
  (originally 45 mm)

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Results Pneumatic Hybrid- Initial testing of
Compressor Mode -
Tank Pressure 6.5 bar
Tank Pressure 11 bar
Tank Pressure 6.5 bar
Tank Pressure 11 bar
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Results Pneumatic Hybrid- Initial testing of
Compressor Mode -
The overshoot in pressure increases with
increasing engine speed
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Results Pneumatic Hybrid- Initial testing of
Compressor Mode -
Continuously open-loop controlled CM operation
done at three different engine speeds
The open-loop controller is based on valve
timings calculated with the polytropic
compression law
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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -

• Optimization of CM has been done with regards to
  tank valve opening, TankVO
• Tank valve closing, TankVC 10 CAD ATDC
• Inlet valve opening, IVO 35 CAD ATDC
• Inlet valve closing, IVC 180 CAD ATDC

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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -

• There is a difference in IMEP
• However, the difference is quite small
• The reason might be high pressure losses due to a
  small tank valve diameter

The tank valve diameter was changed
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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -
Large tank valve ? 28 mm
Small tank valve ? 16 mm
The flow area has been increase more than three
times
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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -

• However, increasing the valve diameter does not
  come without a problem
• Due to the increased valve area, the force acting
  on the underside of the valve head is larger and
  thus the valve actuator has to open with a larger
  force.
• Due to limited supply pressure, achieving an
  adequate opening force is not possible
• The solution is to make the valve pressure
  compensated. For this purpose a in-house
  developed pneumatic spring has been used

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Pressure compensated tank valve
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• Pneumatic spring cylinder
• Spring retainer
• Tank valve
• Cylinder head
• Pressurized air passages
• Tank valve port
• Blue arrows Pressurized air entering the
  pneumatic spring
• Yellow arrows The pressurized air acting on the
  underside of the spring retainer and on the
  upside of the tank valve head

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4
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One Problem When the tank valve is open the
force acting on the upside of the tank valve head
is canceled and the net force is acting to close
the valve Solution The valve actuator is fed
with compressed air from the pressure tank
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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -
Pressure losses over the tank valve

• Two new problems arise with the pneumatic spring
• The hump-like behavior occurs due to bad
  interactions between the check-valves when
  switching pressure source
• The increase in pressure drop with increasing
  number of engine cycles is due to a insufficient
  pressure in the pressurized air supply line
  feeding the tank valve actuator. To compensate
  for this, TankVO has to occur earlier than
  optimal

Small tank valve
Large tank valve
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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -
Optimization of the compressor mode
Large tank valve
Small tank valve
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Results Pneumatic Hybrid- Optimizing the
Compressor Mode -
Continuously open-loop controlled CM operation
based on optimized valve timings done at three
different engine speeds
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Results Pneumatic Hybrid- Initial testing of
Air-motor Mode -
Negative loop contributing with negative IMEP.
Occurs due to bad inlet valve operation
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Results Pneumatic Hybrid- Optimizing the
Air-motor Mode -
Optimized tank valve closing during AM for the
large tank valve setup
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Results Pneumatic Hybrid- Optimizing the
Air-motor Mode -
Continuously open-loop controlled AM operation
based on optimized valve timings with the large
tank valve setup

• An remarkable increase in positive work can be
  seen (gt30 )
• This is due to a larger tank valve diameter in
  combination with proper valve timing

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Results Pneumatic Hybrid- Optimizing the
Air-motor Mode -
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Results Pneumatic Hybrid- Regenerative
efficiency-

• In order to estimate the potential of the
  pneumatic hybrid a so called regenerative
  efficiency has been defined
• The regenerative efficiency is the ratio between
  the energy recovered during AM and the energy
  consumed during CM
• It also can be defined as the ratio between
  positive and negative IMEP

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Results Pneumatic Hybrid- Regenerative
efficiency-
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Outline

• Pneumatic Hybrid
• Experimental Setup
• Results Evaluation of the Free Valve Technology
  system
• Results Pneumatic hybrid
• Conclusions

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Conclusions- Electro Pneumatic Valve Actuation -

• Various tests have clearly shown the potential
  with EPVA
• Results show the ability to operate in the
  desirable range associated with heavy duty
  engines
• Great flexibility as valve lift and timing can be
  chosen almost without constraints and
  independently of each other
• Successful test runs with various valve
  strategies have shown the great benefits with a
  fully flexible VVA system

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Conclusions- Pneumatic Hybrid-

• Initial Pneuamtic Hybrid testing showed the
  potential of the concept with a ?regen of up to
  33 , increased to 48 with larger valve.
• The optimization of the compression mode shows
  that there are optimal valve timings for every
  tank pressure.
• In order to increase the efficiency the tank
  valve diameter had to be increased from 16 to 28
  mm
• The new tank valve geometry was combined with a
  pneumatic spring in order do ensure proper valve
  timing at higher pressures

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Conclusions- Pneumatic Hybrid-

• A method for optimizing valve timings during both
  compressor mode and motor mode has been developed
  with good results
• The regenerative efficiency has been increased
  from 33, achieved during initial testing of the
  concept, to 48.
• Further improvements of CM can be done with an
  estimated increase in efficiency by up to 5
  units.

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Conclusions- Pneumatic Hybrid-

• Pneumatic hybrid can absorb more power than
  electric hybrid
• Energy storage is much simpler an air tank is
  MUCH less complex than an electric battery.
• Low end torque with small turbocharged engine can
  be handled with air supplied from tank
• Turbocharger lag can be compensated giving
  instant load change (if desired)

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Thanks for your attention

• Any questions?

?????