Future efficiency of the internal combustion engine. Nick Collings Cambridge University Engineering Department

Transcription

1 Future efficiency of the internal combustion engine Nick Collings Cambridge University Engineering Department

2 Motivation and scope What are the concerns? CO 2 emissions Fuel economy Oil price/scarcity Noxious emissions Vehicle intrusivity What are the alternatives? Work from home Public transport (what sort?) More efficient conventional vehicles Different vehicle concepts Hybrid ( + plug-in) All electric Fuel cell?

3 In its mid-term review of the 2001 Transport White Paper, the EU Commission commented:. city dwellers directly experience the negative effects of their own mobility, and may be open to innovative solutions for creating sustainable mobility.

4 What s wrong with current vehicles? They are too big and heavy Their are too many of them, with too few people on-board. Their average speed is low (esp. in the urban environment) There is little/no opprobrium attached to usage last and possibly least They are not very efficient.

5 A few preliminary observations As a rule of thumb:- emissions are proportional to (fossil) fuel consumption True statement for CO2 and H2O More complex for noxious emissions depends on driving patterns + regulation level. Sulphur dioxide more complex due to substitution. Reducing noxious emissions increases CO 2 emissions.

6 A modern gasoline engine

7 The classic 4 stroke engine cycle

8 Gasoline Engine Cycle Plotted on Cylinder pressure vs Cylinder volume axes. Full throttle Part throttle Cylinder pressure Cylinder pressure Cylinder volume Cylinder volume The ratio of air: fuel in a gasoline engine has to be close to chemically correct so power change is via changes in the air and fuel (i.e. dropping the inlet mixture pressure). Diesel engines run without throttling because the fuel (which is injected directly into the cylinder) burns spontaneously so power change is possible with only fuel quantity changes.

9 Just after the spark The flame will only propagate reliably if the air fuel mixture is close to stoichiometric

10 Gasoline Engine Performance Characteristics maximum torque wide open throttle torque Top gear torque road load Engine speed

11 Gasoline Engine Performance Characteristics constant power curves maximum torque wide open throttle torque Torque reserve Top gear torque road load Engine speed

12 Gasoline Engine Performance Characteristics constant power curves Most efficient operating point maximum torque wide open throttle Constant specific fuel consumption curves torque 0.35 Torque reserve Top gear torque road load Engine speed

13 Gasoline Engine Performance Characteristics constant power curves Most efficient operating point maximum torque wide open throttle torque Top gear torque road load Torque reserve Constant specific fuel consumption curves (kg/kwhr) High frictional losses Highly throttled Engine speed

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15 To summarise The losses increase at Low torque High revs (and high speed!) So, how to we reduce/prevent operation in these conditions? Smaller engines (+ turbo charging) Downsizing Energy storage and Boost methods (one does not accelerate for ever.) Gearing (CVT)

16 Hydrogen fuelled engines Burn hydrogen No CO2 Negligible noxious emissions But Where does the H 2 come from? Efficiency similar to current gasoline vehicles H 2 storage issues

17 Hydrogen fuel cell vehicles Use hydrogen to generate electricity using a fuel Cell No CO2 Negligible noxious emissions But Where does the H 2 come from? Efficiency little better than current gasoline vehicles H 2 storage issues

18 Hydrogen in action

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20 Typical fuel cell efficiency % of maximum power

21 Hybrid vehicles What is a hybrid? Typically a vehicle with an IC engine and an electrical drive system combined. Why do they have better fuel economy? The flexibility engendered by the additional hardware allows for better matching of the engine to the driving condition.

22 Gasoline Engine Performance Characteristics constant power curves Most efficient operating point maximum torque wide open throttle torque Top gear torque road load Torque reserve Constant specific fuel consumption curves (kg/kwhr) High frictional losses Highly throttled Engine speed

23 Conventional transmission system

24 (The fastest car in the world) The Differential

25 Series Hybrid System (SHS) Main Characteristics Motor delivers all power Engine drives generator Engine Battery Inverter Electrical Path Mechanical Path Wheel Generator Motor/ Generator Wheel 28

26 Parallel Hybrid System (PHS) Main Characteristics Engine supplies main power Motor assists Engine Battery Inverter Electrical Path Mechanical Path Wheel Transmission Motor/ Generator Wheel 29

27 Toyota Hybrid System (THS) Main Characteristics Two Power Paths Controller Balances Engine Load Engine Motor/ Generator Battery Inverter Electrical Path Mechanical Path Wheel Power Split Device Motor/ Generator Wheel 30

28 Planetary ring gear

29 Toyota Hybrid System Powertrain Motor Generator Engine Planetary gear Reduction Gear Drive Shaft 32

30 THS Cutaway 33

31 Battery Comparison Type Voltage (V) Energy (kw-hr) Specific Energy (W-hr/kg) Power (kw) Specific Power (W/kg) Weight (kg) THS 288 (240 cells) RAV4-EV Nickel Metal-Hydride 288 (24 modules of 10 cells)

32 State of Charge Control Overcharging Area SOC Upper Limit Actual SOC Lower Limit Target SOC Overdischarging Area Time

33 Operational modes Full Throttle Acceleration Motor Battery Energy Engine & Motor Moderate Acceleration Road Load Max. Speed Max. Speed at Cruising Vehicle Speed 36

34 Energy Flow at Light Load Battery (EV drive) 37

35 Energy Flow at Medium Load (HEV drive) 38

36 Energy Flow at High Load Battery (HEV drive + battery assist) 39

37 A few comments Strangely, at motorway cruise conditions, the Prius appears to have a negative fuel economy benefit. Extra cost ICE + power electrical system Battery life? Other energy storage methods:- Flywheels Hydraulic accumulators Super capacitors

38 Let s look at batteries Why? In principle they offer more freedom of movement (compared with trains, trams etc) Pollution free (?) CO 2 free (?) Why aren t we all driving battery powered vehicles?

39 Battery Comparisons

40 Energy density of various materials Material Watt-hr/litre Watt-hr/kg Fission of U x x10 10 Diesel Fuel 10,700 12,700 Heating Oil 10,400 12,800 Gasoline 9,700 12,200 LNG (-160 C) 7,216 12,100 Propane 6,600 13,900 Ethanol 6,100 7,850 Liquid H2 2,600 39, Bar H ,000 STP Propane 26 13,900 STP NG 11 12,100 STP H2 3 39,000 Li-Ion Battery NiMH Battery Lead-Acid Battery 40 25

41 Batteries for transport are being looked at for applications such as:- Improved Prius-like vehicles Plug in Hybrids (Biggish battery + IC engine) With a hope that for many journeys, the IC engine will not operate at all. All-electric vehicles

42 Nothing new in all-battery vehicles

43 Not all are still around.

44 Some are appearing in increasing numbers..

45 Plug In Hybrids Use a bigger battery than in the Prius Charge intelligently Cheaply (grid support)? No trip length limit (c.f. battery only)

46 Near future? - GM VOLT DETROIT (Reuters) - General Motors Corp's plug-in Chevy Volt and other electric vehicles have generated widespread consumer fervour for cleaner, less fuel-dependent cars, but the high battery cost means it will be years before those cars are affordable to most Americans.

47 Progress with Li-ion batteries

48 Plug-in Hybrid battery pack characteristics

49 Battery electric vehicle battery pack specs.

50 So what s the future of My guess:- personal transport? Incremental movement towards more nuclear power + renewables. Transport in cities becomes more electrified. Owning/using a personal vehicle becomes more and more expensive in real terms.

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