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Fuel and propulsion technologies


Fuel and propulsion technologies

Low battery and motors can improve safety[43]

The transport sector is a major contributor to air pollutionnoise pollution and climate change.[44]

Most cars in use in the early 2020s run on gasoline burnt in an internal combustion engine (ICE). The International Organization of Motor Vehicle Manufacturers says that, in countries that mandate low sulfur gasoline, gasoline-fuelled cars built to late 2010s standards (such as Euro-6) emit very little local air pollution.[45][46] Some cities ban older gasoline-fuelled cars and some countries plan to ban sales in future. However, some environmental groups say this phase-out of fossil fuel vehicles must be brought forwards to limit climate change. Production of gasoline-fuelled cars peaked in 2017.[47][48]

Other hydrocarbon fossil fuels also burnt by deflagration (rather than detonation) in ICE cars include dieselautogas, and CNG. Removal of fossil fuel subsidies,[49][50] concerns about oil dependence, tightening environmental laws and restrictions on greenhouse gas emissions are propelling work on alternative power systems for cars. This includes hybrid vehiclesplug-in electric vehicles and hydrogen vehicles. Out of all cars sold in 2021, nine per cent were electric, and by the end of that year there were more than 16 million electric cars on the world's roads.[51] Despite rapid growth, less than two per cent of cars on the world's roads were fully electric and plug-in hybrid cars by the end of 2021.[51] Cars for racing or speed records have sometimes employed jet or rocket engines, but these are impractical for common use.

Oil consumption has increased rapidly in the 20th and 21st centuries because there are more cars; the 1980s oil glut even fuelled the sales of low-economy vehicles in OECD countries. The BRIC countries are adding to this consumption.

As of 2023 few production cars use wheel hub motors.[52][53]


In almost all hybrid (even mild hybrid) and pure electric cars regenerative braking recovers and returns to a battery some energy which would otherwise be wasted by friction brakes getting hot.[54] Although all cars must have friction brakes (front disc brakes and either disc or drum rear brakes[55]) for emergency stops, regenerative braking improves efficiency, particularly in city driving.[56]


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