Hybrid Vehicle

With the increasing number of private cars, more and more gasoline and diesel will be needed as energy for cars. However, the use of this kind of fossil fuel will produce green house gas (GHGs) which will cause global warming. What`s more, the amount of fossil fuel on the earth is limited and it is a kind of unrenewable resources. Based on these reasons, Hybrid vehicle is invented.

Toyota Prius, a hybrid electric car marketed worldwide

A hybrid vehicle uses two or more distinct types of power, such as internal combustion engine+electric motor, e.g. in diesel-electric trains using diesel engines and electricity from overhead lines, and submarines that use diesels when surfaced and batteries when submerged. Other means to store energy include pressurized fluid, inhydraulic hybrids. 
Hybrid fuel(dual mode)
In addition to vehicles that use two or more different devices for propulsion, some also consider vehicles that use distinct energy sources or input types (‘fuels’) using the same engine to be hybrids, although to avoid confusion with hybrids as described above and to use correctly the terms, these are perhaps more correctly described as dual mode vehicles:
1. Some electric trolleybuses can switch between an on-board diesel engine and overhead electrical power depending on conditions.
2. Flexible-fuel vehicles can use a mixture of input fuels mixed in one tank--typically gasoline and ethanol, or methanol, or biobutanol.
3. Bi-fuel vehicle: liquified petroleum gas and natural gas are very difficult from petroleum or diesel and cannot be used in the same tanks, so it would be impossible to build an flexible fuel system. Instead vehicle are built with two, parallel, fuel systems feeding one engine.

hybrid-cars-gasoline electric hybrid system with internal combustion engine

Benefits of hybrid vehicle.

The hybrid vehicle typically achieves greater fuel economy and lower emissions than conventional internal combustion engine vehicles(ICEVs), resulting in fewer emissions being generated. These savings are primarily achieved by three elements of a typical hybrid design:

1. Relying on both the engine and the electric motors for peak power needs, resulting in a smaller engine size more for average usage rather than peak power usage. A smaller engine can have less internal losses and lower weight.
2. Having significant battery storage capacity to store and reuse recaptured energy, especially in stop-and-go traffic typical of the city drive cycle.
3. Recapturing significant amounts of energy during braking that are normally wasted as heat. This regenerative braking reduces vehicle speed by converting some of its kinetic energy into electricity, depending upon the power rating of the motor/generator;

Images from:
https://upload.wikimedia.org/wikipedia/commons/4/41/Toyota_Prius_Life_%28ZVW30%29_front-2_20110116.jpg
http://www.consulente-energia.com/in556.jpg