Why are petrol and diesel the only fuels that can be used to power vehicles?

While petrol and diesel are two of the most commonly used fuels to power vehicles, there are actually a wide variety of fuels that have been used in the past and present.
The following is a non-comprehensive list of the most commonly used alternative fuels that power vehicles. Because scientists are always searching for new ways to generate energy, it is impossible to list every possible type of fuel, but hopefully this list helps you in your research. Click on the descriptions to find a corresponding link containing more information about each type of fuel.


Ethanol: A fuel made from plants, often corn


Hydrogen: Produced from various energy sources and requiring a type of technology known as a "fuel cell"


Biodiesel: Made from "vegetable oils, animal fats, and recycled restaurant greases"


Natural Gas: A type of "clean-burning" fossil fuel


Propane: Another type of "clean-burning" fossil fuel


In addition, while not technically fuels, both solar power and electricity can be used to generate energy to run vehicles.
This link can help you learn more about solar-powered cars: https://physics.ucsd.edu/do-the-math/2011/11/a-solar-powered-car/
Here is a resource for learning more about electric cars: http://www.fueleconomy.gov/feg/evtech.shtml
Without modification, many vehicles designed to run on diesel or petroleum gas cannot use alternate fuels or energy sources. The following resource can be used to determine if a vehicle can run on an alternative fuel: http://www.afdc.energy.gov/vehicles/search/
New technology is constantly being innovated in the field of alternative energy, and there are many books and websites that can help you study and research this exciting topic.