Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy. Liquid fule also must take the shape of their container.
It is the fumes of liquid fuels that are flammable instead of the fluid. Most liquid fuels in widespread use are derived from fossil fuels; however, there are several types, such as hydrogen fuel (for automotive uses), ethanol, and biodiesel, which are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation and the economy.
Some common properties of liquid fuels are that they are easy to transport, and can be handled with relative ease. Physical properties of liquid fuels vary by temperature, though not as greatly as for gaseous fuels.
Some of these properties are: flash point, the lowest temperature at which a flammable concentraion of vapor is produced; fire point, the temperature at which sustained burning of vapor will occur; cloud point for diesel fuels, the temperature at which dissolved waxy compounds begin to colesece, and pour point, the temperature below which the fuel is too thick to pour freely. These properties affect the safety and handling of the fuel.