Energy efficiency of road vehicles - trends and challenges

Improved energy efficiency is one of society's most important instruments for mitigating climate change. This Chapter deals with assessment of the energy efficiency attainable in road vehicles with various powertrains. Current situation, short-term and long-term trends, and the most important challenges are surveyed and analyzed in this chapter. The scope of technologies that are reviewed includes: conventional powertrains based on internal combustion engines (ICE), powertrains of hybrid electric, battery electric and fuel cell vehicles. Moreover, we discuss a potential increase in energy efficiency of ICE by introduction of advanced technologies, such as: engine downsizing, variable valve actuation, cylinder deactivation, variable compression ratio, homogenous charge compression ignition, etc. A comparison of energy efficiency of powertrains using different energy sources is carried out by application of the "well-to-wheel" (primary) energy use approach. We find that an internal combustion engine is far from reaching its maximal potential. Further development of ICE can lead to significant improvement of its energy efficiency and substantial reduction of pollutant emissions to the "zero-impact" level. It is shown that life cycle emissions of electric vehicles (EVs) differ considerably between regions, depending on the carbon intensity of the power generation mix. Compared with EVs, hybrid vehicles have a capability to benefit from the latest advancements both in ICE technology and in electric propulsion technology. This provides a potential for hybrid vehicles to become a widespread measure of energy consumption and GHG emissions reduction.