Most automobiles in use today are propelled by gasoline (also known as petrol) or diesel internal combustion engines, which are known to cause air pollution and are also blamed for contributing to climate change and global warming. Increasing costs of oil-based fuels and tightening environmental laws and restrictions on greenhouse gas emissions are propelling work on alternative power systems for automobiles. Efforts to improve or replace these technologies include hybrid vehicles, electric vehicles and hydrogen vehicles.
Diesel
Diesel engined cars have long been popular in Europe with the first models being introduced in the 1930s by Mercedes Benz and Citroen. The main benefit of Diesels are a 50% fuel burn efficiency compared with 27% in the best gasoline engines. A down side of the diesel is the presence in the exhaust gases of fine soot particulates and manufacturers are now starting to fit filters to remove these. Many diesel powered cars can also run with little or no modifications on 100% biodiesel.
Gasoline
Gasoline engines have the advantage over diesel in being lighter and able to work at higher rotational speeds and they are the usual choice for fitting in high performance sports cars. Continuous development of gasoline engines for over a hundred years has produced improvements in efficiency and reduced pollution. The carburetor was used on nearly all road car engines until the 1980s but it was long realised better control of the fuel/air mixture could be achieved with fuel injection. Indirect fuel injection was first used in aircraft engines from 1909, in racing car engines from the 1930s, and road cars from the late 1950s. Gasoline Direct Injection (GDI) is now starting to appear in production vehicles such as the 2007 BMW MINI. Exhaust gases are also cleaned up by fitting a catalytic converter into the exhaust system. Clean air legislation in many of the car industries most important markets has made both catalysts and fuel injection virtually universal fittings. Most modern gasoline engines are also capable of running with up to 15% ethanol mixed into the gasoline - older vehicles may have seals and hoses that can be harmed by ethanol. With a small amount of redesign, gasoline-powered vehicles can run on ethanol concentrations as high as 85%. 100% ethanol is used in some parts of the world (suc as Brazil), but vehicles must be started on pure gasoline and switched over to ethanol once the engine is running. Most gasoline engined cars can also run on LPG with the addition of an LPG tank for fuel storage and carburetion modifications to add an LPG mixer. LPG produces fewer toxic emissions and is a popular fuel for fork lift trucks that have to operate inside buildings.
Electric
The first electric cars were built in the late 1800s, but the building of battery powered vehicles that could rival internal combustion models had to wait for the introduction of modern semiconductor controls. Because they can deliver a high torque at low revolutions electric cars do not require such a complex drive train and transmission as internal combustion powered cars. Some are able to accelerate from 0-60 mph (96 km/hour) in 4.0 seconds with a top speed around 130 mph (210 km/h). They have a range of 250 miles (400 km) on the EPA highway cycle requiring 3-1/2 hours to completely charge. Equivalent fuel efficiency to internal combustion is not well defined but some press reports give it at around 135 mpg.
Steam
Steam power, usually using an oil or gas heated boiler, was also in use until the 1930s but had the major disadvantage of being unable to power the car until boiler pressure was available. It has the advantage of being able to produce very low emissions as the combustion process can be carefully controlled. Its disadvantages include poor heat efficiency and extensive requirements for electric auxiliaries.
Gas Turbine
In the 1950s there was a brief interest in using gas turbine (jet) engines and several makers including Rover produced prototypes. In spite of the power units being very compact, high fuel consumption, severe delay in throttle response, and lack of engine braking meant no cars reached production.
Rotary (Wankel) engines
Rotary Wankel engines were introduced into road cars by NSU with the Ro 80 and later were seen in several Mazda models. In spite of their impressive smoothness, poor reliability and fuel economy led to them largely disappearing. Mazda, however, has continued research on these engines and overcame most of the earlier problems.
Future developments
Much current research and development is centered on hybrid vehicles that use both electric power and internal combustion. Research into alternative forms of power also focus on developing fuel cells, Homogeneous Charge Compression Ignition (HCCI), stirling engines[24] and even using the stored energy of compressed air or liquid nitrogen.
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