Propulsion Systems - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 121

types of PCM can be produced from biomass whose use would mean basically a
change to an environmentally friendly air conditioning technology [ 7 ].
Using headlights in the daylight requires a high energy demand. However, both
lights are necessary for safety. Nowadays, new light emitting diode (LED) tech-
nology is reducing the electrical power requirements for the car lights [ 8 ].
Accessories need energy and contribute to fuel consumption. However, they are
not considered in the measurements of the nominal consumption balance in the
Type approval as determined by the NEDC. Since all these consumers use energy
and lead to increased fuel consumption and exhaust gas emissions, they should be
considered in the estimation of future fuel consumption [ 9 ].
8.2.3 Energy Dissipation
Propulsion in road vehicles converts the power from the engine to the tires.
A chain of sub-systems can be the source of several losses [ 10 ].
A specific problem of vehicle technology is the variety of road and driving
conditions. Driving in high mountains has different characteristics than driving in
flat regions; or driving in arctic regions differs from travelling through a desert.
Moreover, the energy dissipation in urban and in highway traffic is also very
different. On city roads, the biggest energy losses arise through the internal friction
of the engine and the transmission elements. In urban driving, apart from the kind
of engine and fuel, the efficiency of the vehicle particularly depends on its
accelerating and breaking characteristics.
The efficiency of the vehicle on the highway is largely influenced by its
aerodynamics. The fuel consumption increases with the velocity to overcome air
resistance and depends on the construction of the transmission elements, the
aerodynamic resistance of the vehicle, and the rolling resistance of the tires.
In both urban and highway driving, the dissipation of energy in the propulsion
system mainly depends on its thermal efficiency, its internal friction and the energy
demand of its auxiliary equipment. The energy losses are directly characterized by
the fuel consumption, which can be lowered to a minimum through suitable
maintenance for lower resistances and through the use of optimal driving methods.
8.2.4 Thermal Efficiency
All losses occurring while driving, flying, and shipping are converted into heat,
kinetic energy and exhaust gas emissions. Presumably, thermal efficiency can be
significantly improved in the future [ 11 ]. One of the most intensive phases of fuel
consumption is the ignition. In this phase, the heated air in the compression stroke
must ignite the injected fuel during the combustion period. The necessary
minimum ignition temperature for diesel fuel is approximately 250C (482F).