 |
Motors & Pumps |
PRBC Concept |     Back to the main menu |
| 1. Some facts | 2. Sources of usable energies on a vehicle | 3. Hybrid architectures | 4. Specifications overview |
2. Usable sources of energy on a vehicle
One will be able to download here (in french) a more precise document on this topic as well as some elements of presizing.
2.a) The chemical energies
- the chemical energies to basis of hydrocarbons (coal excluded)
They are numerous and, for most, used nowadays extensively. One can mention :
o gasolines : 'supercarburant",
"without plomb" used for controled ignition motors.
o oil and heavy oils destined to the
motors with spontaneous ignition (Diesel)
o the
gas
of liquefied oil
(GPL) used as alternative fuel for gasoline engines. Their introduction
in France at the end of nineties proved to be a failure since the rate
of equipment of the vehicles gas is lower to 5%, although their
emissions of pollutants are reduced and that the State, in his big
goodness, limits the taxes on this type of fuel, not really ecological since the
GPL is an essentially fossil origin hydrocarbon.
o The
"green" fuels: methanol, esters. that put
well a long time to pass the stage of the experimentation, but which
are not THE solution, but contribute to improve the balance carbon of
the road transportation. Biofuels
are not ecological to the strict sense because they
require energy and chemical fertilizers to be produced and
raise a lot of agricultural problems (Do farmers make fuel for rich
countries or food for poor people?...)
As one signalled it higher, they are extremely energizing (heat released by combustion of the order of 30 000 kJ / kg of fuel), but polluting.
- Pci is the calorific power of the fuel in kJ / kg of fuel
- Pco is the air consumtion power of the fuel in normal temperature and pressure conditions
Pco = [mas of air required to burn the mass of gaseous fuel] / [mass of gaseous fuel]
The conversion of this chemical
energy is irreversible: it means that one
only can "déstocker" this shape of energy inside a
terrestrial vehicle. One exploits the chemical energy of the
hydrocarbons schematically as indicated below :
chemical energy irreversible combustion pressurized hot gases: expansion mechanical energy with air (4N2O2) in a deformable volume thermal and pneumatic energies with thermal losses
Moreover, one can mention the projects of dihydrogen used as fuel (essentially led by BMW on the serie type 7) that faces very big problems of production, storage and transportation, as difficult to overcome that the idea to reject only water is attractive...
Hydrogen has a Pci of 120 000 kJ/kg and a Pco of 34,47, but a gaseous density of only 0,0831 kg/m3 at 20°C under 1 Bar.Thus it as a volumic PCi of 9972 kJ / m3, and only 9,972 kJ/ Liter. Whereas hydrocarbons fuels are liquid at 20°C under 1 Bar and contain 40 000 kJ/ Liter. This very weak volumic density of energy for hydrogen prevent it to develop itself on current engines which are not enough compact and lead to a very high pressure storage of liquid hydrogen, particulary difficult when one know that it is the most diffusive among all the gases : it can cross any material because of the very little size of H2 molecules..
- the
chemical energies stocked as electrolytes or gases (non hydrocarbons)
They are used under the shape of electric accumulators, of which most widespread is the accumulator to plomb used in the batteries of cars (electrolytic accumulators). They are based on reactions of oxydoreduction to create an electric current. Their big interest resides in the reversibility of these reactions, that is to say that one can, while applying it a tension, reload the accumulator. However, the number of load / discharge cycles is limited, but important (of the order of 2000 according to the used technologies). The increase of the number of load / discharge cycles of the accumulators is the subject of active researches, the applications are indeed numerous (batteries of portable, of cars, of aerospace shuttles).
chemical energy regenerating the reagents
