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MOTIVATION

Standard for passenger cars in Europe is 175 CO2 g/km which equals 6.6l diesel resp. 7.5 l gasoline per 100 km. It is not feasible to base transportation in the long run on such high energy consumption without provoking heavy access conflicts to oil reserves and/or environmental damages when trying to produce fuel from natural or other fossile sources.
Today's best medium sized cars are consuming 4 l diesel/100 km (59 mpg) which equals 105 g/km.
Some newer examples of efficient commercially available ICE -propelled vehicles:
  • Citroen C3 Stop & Start 5 l Diesel/100 km

  • Honda Civic Hybrid 4.6 l/100 km

  • Honda Insight Hybrid 4.3 l/100 km

  • Toyota Prius (Hybrid) 4.2 l/100 km

    • As targets for the development of vehicles propelled by fossil fuels two classes of Low-energy vehicles are proposed:

  • Low-energy vehicles LEnV having 18.1-105 g CO2/km

  • Ultra-low-energy vehicles ULEnV below 18 g CO2/km (approx. 10% of the usual 175 g CO2/km )

    • That is a relative standard, of course, and will certainly change in the future.

ULEnV will not be feasible with internal combustion engines only working with fossil fuels.


PRECONDITIONS

The high fuel economy is caused by
  • lower parasitic masses (compared to the average load) causing low energy demand in transitional operation (stop and go operation in the cities) {P_{accel}= m_{vehicle} \cdot a \cdot v } where P stands for power, m_{vehicle} for the total vehicle mass, a for the vehicles acceleration and v for the vehicles velocity. Extreme masses will go down to 300 kg from todays 1100 kg to 1600 kg. 5 seaters of the sixties had 625 kg {Link without Title} . Given the high safety standards required nowadays 700 kg will be a minimum.


  • low crossectional area and mirrors replaced by cameras causing very low drag losses especially when driven at higher speed {F_{drag}= A_{cross} \cdot cw_{vehicle} \cdot rac {v_{air}^2 ho_{air}} {2} } where F stands for the force, {A_{cross}} for the crossectional area of the vehicle, { ho_{air}} for the density of the air and {v_{air}} for the relative velocity of the air (incl. wind). Two places in a back to back or in line arrangement drastically reduce the crossectional area down to 1 m2. The drag factor may be as low as 1.16.

  • low rolling resistance due to smaller and high pressure tires with optimised tread and low vehicle mass driving the rolling resistance {F_{roll}= \mu_{roll} \cdot m_{vehicle} } where {\mu_{roll}} stands for the rolling resistance factor and {m_{vehicle}} for the vehicle mass. Advanced driver assistance and ABS prevent safety problems caused by the small tires.


It must be added that also the driving style is to be adapted to achieve those low energy consumptions. Energy management becomes possible with Hybrid Vehicle s with the possibility to recuperate braking energy and to operate the Internal Combustion Engine (ICE) at higher efficiency on average. Hybrid power trains of parallel type may also reduce the ICE-engine size thus increasing the average load factor and minimising the part load losses.


FACTS

Average data for vehicle types sold in the U.S.A. (source theautochannel.com):

Drag resistance for SUVs is at least (same drag coefficient) 30% higher and the acceleration force has to be 35% bigger compared to family sedans.
This gives of 40% higher fuel consumptions (even when including parallel hybrid electric SUVs).


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