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1. Some facts 2. Sources of usable energies on a vehicle 3. Hybrid architectures 4. Specifications overview

The goal of this paragraph is to make a census of the sources of energy reasonably usable for a terrestrial vehicle. A discriminating recourse to one of these sources rather than to another can be revealed only profitable. As from now on, one can consider energetical exchanges  between these different shapes of energy.

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.

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] 

fuels characteristics

calorific power of some hydrocarbons

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 : 

energetic cascade of conversion of hydrocarbons into mechanical power

 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).

One has schematically energetic cascade of conversion of chemical reactants into mechanical energy
reagents                            oxydoreductions consuming /            voltage / electric current                electric motor / generator                    mechanical energy
chemical energy                regenerating the reagents

One notices the double arrows: it means that one can load and discharge this chemical energy within the vehicle, and it in 2 ways: either the thermal motor make turn a generator that loads the batteries, either the kinetic energy of the vehicle is converted in electric energy at each deceleration of the vehicle (Fig. 3.). This is how a car is going to be able to brake without manipulating the mechanical brakes: the energizing gain is very important since a big part of the kinetic energy of the vehicule, usually completely lost in heat with the mechanical brakes, is recovered here (fig. 3.). This recovered energy is particulary useful to reaccelerate again the vehicle, etc...

Fig. 3. : strategy of recuperation of energy and aid motor of a hybrid vehicle

Kinetic enercy recovery of the car when it is braking or descending

start / acceleration / stabilized run / deceleration / slow motion

 Finally, one can mention oxydoreductions in gaseous phase like the particular case of the fuelcell with dihydrogen / dioxygen which actually know a renewal of interest after having endured for many years the clutter of the reservoirs and of various devices.However, a big scale industrialization of such devices shouldn't start not before several years.

2.b) The pneumatic / hydraulic energies

           These 2 shapes of energy have a neighboring behavior and reversible features like the oxydoreduction chemical energies :

bidirectionnal conversion of pneumatic/hydraulic energy into mechanical output and inversly
pressurized gas or fluid                        hydraulic/pneumatic motor or pump                        mechanical energy
                                            pneumatic energy

They can therefore them also to be used to brake or to accelerate the vehicle while limiting the losses Joule to the level of the brakes.

2.c) The mechanical energy

           The 2 big types of mechanical storage are :

*       The wheels of inertia thrown previously to big speed that, connected to a transmission, assure the traction of the vehicle. In the phases of acceleration, the wheel slows down, in the phases of deceleration, the wheels accelerate its rotation (kinetic energy recuperation).

*       The springs put under tension in storage and whose relaxation frees the stocked (recuperation of elastic potential energy) energy.

*    Without forgetting the vehicle in itself which the mass in movement constitutes a very big storage of kinetic energy, currently wasted to every slowing down in most of the vehicles.   

2.d) The renewable energies

               These are the solar and wind energies. They cannot be used to propel the vehicle, except if it is ultralight (less than 300kg with embarked passengers), what is not generally the case. On the other hand, the solar energy via photovoltaic cells can provide power for the electric accessories or to reload some batteries, whatever the vehicle do. For example, one can mention a solar car having crossed Australia in the South / North direction. Unfortunately, the solar panels cannot be very big on a car (surfaces limited at the roof, to the motor hood and to the lateral sides), and they are expensive and fragile.

1. Some facts 2. Sources of usable energies on a vehicle 3. Hybrid architectures 4. Specifications overview
SYstems for COnversion of MOtions and REnewable ENergies Motors
& Pumps
PRBC Concept
Back to the main menu