1. Pneumatic Hybrid – An alternative to electric hybrid (?) Bengt Johansson Sasa Trajkovic, Div. of Combustion Engines Lund University 2008-11-19

2. 2 (42) Outline Pneumatic Hybrid Experimental Setup Results: Evaluation of the Free Valve Technology system Results: Pneumatic hybrid Conclusions

3. 3 (42) Outline Pneumatic Hybrid Experimental Setup Results: Evaluation of the Free Valve Technology system Results: Pneumatic hybrid Conclusions

4. 4 (42) Electric hybrids have proven to have significant potential to improve fuel economy and reduce exhaust emissions  high customer attractiveness Pneumatic Hybrid - Background - Cumulative reported US sales of hybrid vehicles during the period 1999-2007

5. 5 (42) 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 Pneumatic Hybrid - Background -

6. 6 (42) 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 Pneumatic Hybrid - Background -

7. 7 (42) 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 Pneumatic Hybrid - Operating principal -

8. 8 (42) Pneumatic Hybrid - Compressor Mode - 1-2: Induction of fresh air 2-3: Compression stroke 3-4: Charging of pressure tank 4-1: Expansion stroke

9. 9 (42) Pneumatic Hybrid - Air-motor Mode - 1-2: Charging of the cylinder 2-3: Expansion stroke 3-4: Intake stroke 4-1: Compression stroke

10. 10 (42) Outline Pneumatic Hybrid Experimental Setup Results: Evaluation of the Free Valve Technology system Results: Pneumatic hybrid Conclusions

11. 11 (42) Experimental setup Displaced Volume 1966 cm3 Bore 127.5 mm Stroke 154 mm Connecting Rod Length 255 mm Number of Valves 4 Compression Ratio 18:1 Piston type Flat Inlet valve diameter 45 mm Exhaust valve diameter 41 mm Valve Timing Variable Piston clearance 7.3 mm Fuel injection PFI Fuel Isooctane The Scania D12 Diesel Engine

12. 12 (42) Outline Pneumatic Hybrid Experimental Setup Results: Evaluation of the Free Valve Technology system Results: Pneumatic hybrid Conclusions

13. 13 (42) Free Valve Technology System Illustration of Cargine’s Pneumatic Valve Actuator The Pneumatic Valve Actuators mounted on a Scania cylinder head

14. 14 (42) 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

15. 15 (42) 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 Results: Evaluating the EPVA system - Evaluation objectives -

16. 16 (42) Results: Evaluating the EPVA system - Testing valve stability - Variation of valve lift at constant valve lift duration of 200 CAD and an engine speed of 1000 rpm The valve lift duration remains constant when the valve lift height is varied

17. 17 (42) Variation of valve lift duration at constant valve lift height of 7 mm and an engine speed of 1000 rpm The valve lift height remains constant when the valve lift duration is varied Results: Evaluating the EPVA system - Testing valve stability -

18. 18 (42) COV (%) Valve Lift Height0.1805 Valve Lift Duration0.3107 Cycle-to-cycle variations of valve lift and duration Results: Evaluating the EPVA system - Testing valve stability -

19. 19 (42) 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 Results: Evaluating the EPVA system - EPVA energy consumption -

20. 20 (42) Outline Pneumatic Hybrid Experimental Setup Results: Evaluation of the Free Valve Technology system Results: Pneumatic hybrid Conclusions

21. 21 (42) 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) Results: Pneumatic Hybrid - Engine modifications-

22. 22 (42) Tank Pressure = 6.5 bar Tank Pressure = 11 bar Results: Pneumatic Hybrid - Initial testing of Compressor Mode -

23. 23 (42) Results: Pneumatic Hybrid - Initial testing of Compressor Mode - The overshoot in pressure increases with increasing engine speed

24. 24 (42) Continuously open‐loop controlled CM operation done at three different engine speeds Results: Pneumatic Hybrid - Initial testing of Compressor Mode - The open-loop controller is based on valve timings calculated with the polytropic compression law

25. 25 (42) 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

26. 26 (42) 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

27. 27 (42) Results: Pneumatic Hybrid - Optimizing the Compressor Mode - Small tank valve  = 16 mm Large tank valve  = 28 mm The flow area has been increase more than three times

28. 28 (42) 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 Results: Pneumatic Hybrid - Optimizing the Compressor Mode -

29. 29 (42) 5 1 3 2 4 6 Pressure compensated tank valve 1.Pneumatic spring cylinder 2.Spring retainer 3.Tank valve 4.Cylinder head 5.Pressurized air passages 6.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 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 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

30. 30 (42) Results: Pneumatic Hybrid - Optimizing the Compressor Mode - Pressure losses over the tank valve Small tank valveLarge 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 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

31. 31 (42) Optimization of the compressor mode Large tank valveSmall tank valve Results: Pneumatic Hybrid - Optimizing the Compressor Mode -

32. 32 (42) Results: Pneumatic Hybrid - Optimizing the Compressor Mode - Continuously open‐loop controlled CM operation based on optimized valve timings done at three different engine speeds

33. 33 (42) Results: Pneumatic Hybrid - Initial testing of Air-motor Mode - Negative loop contributing with negative IMEP. Occurs due to bad inlet valve operation

34. 34 (42) Results: Pneumatic Hybrid - Optimizing the Air-motor Mode - Optimized tank valve closing during AM for the large tank valve setup

35. 35 (42) 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 (>30 %) This is due to a larger tank valve diameter in combination with proper valve timing

36. 36 (42) Results: Pneumatic Hybrid - Optimizing the Air-motor Mode -

37. 37 (42) 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: Results: Pneumatic Hybrid - Regenerative efficiency-

38. 38 (42) η regen Engine speed6009001200 Small tank valve setup, unoptmized323325 Large Tank valve setup, constant IVC during AM444037 Large tank valve setup484440 Results: Pneumatic Hybrid - Regenerative efficiency-

39. 39 (42) Outline Pneumatic Hybrid Experimental Setup Results: Evaluation of the Free Valve Technology system Results: Pneumatic hybrid Conclusions

40. 40 (42) 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 Conclusions - Electro Pneumatic Valve Actuation -

41. 41 (42) Initial Pneuamtic Hybrid testing showed the potential of the concept with a η 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 Conclusions - Pneumatic Hybrid-

42. 42 (42) 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. Conclusions - Pneumatic Hybrid-

43. 43 (42) 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) Conclusions - Pneumatic Hybrid-

44. Any questions? ????? Thanks for your attention