Energy, Energy comsumption, Motors, Sustainability, Thermodynamics

All fuels (Part 2)

Giving continuity to subject about fuels. In this post will be shown alternatives fuels, it’s features and properties.

To see the first part about fuels, click in the button below.

Fuels (Part 1)Click here


Propane can come from oil or natural gas, to vehicles is called liquefied petroleum gas, it is colorless and smelless. This fuel has a small quantity of butane (C_4H_{10}) and stays inside pressurized tanks in liquid form.

When the pressure decreases, the liquid become gas. A vehicle moved by propane can have a ignition system with liquid or gas propane. Has octane number of 105, a propane gallon is equivalent to 73% of energy of a gasoline gallon, therefore has less autonomy. This fuel pollute less and this is your combustion.

C_3H_8 + 5O_2\rightarrow 3CO_2 + 4H_2O

A gallon (gal) is equal to 3.785 liters.

Natural gas

Is colorless and smelless, more than 85% is composed by metane (CH_4), is lighter than air and dissipates easily. There are two forms to use in vehicles: Compressed Natural Gas (CNG) or Liquified Natural Gas (LNG). In CNG, the gas is compressed to 24.82 MPa (Megapascals) and stored in high pressure tanks.

The CNG is easily mixed with air in the combustion chamber. The LNG is cooled at -162,2 ºC, it is less used than CNG, because needs to be stored in more expensive cryogenic tanks. The liquid is denser than gas, therefore, the LNG is used in long distance trucks, because accumulates more energy.

The two forms has octane number of 120, vehicles moved by natural gas are less polluting and more silent. This is the metane’s combustion equation.

CH_4+2O_2\rightarrow CO_2+2H_2O


The methanol (CH_3OH) can be produced mixing water and coal at 1000 ºC or by metane oxidation. It is liquid in room temperature. Has octane number of 112 and when enters in combustion, its flame is transparent. This fuel is very toxic and corrosive, for that, isn’t very used. It is used in race cars, some jet aircraft and engines to aeromodels, because it has a faster combustion.


The ethanol (C_2H_5OH) can be produced from plant materials like corn, sugar cane and cellulose. Can be mixed with gasoline to reduce polluent emition. This is the combustion equation.

C_2H_5OH+3O_2\rightarrow 3H_2O+2CO_2

Emits less carbon monoxide (CO) than gasoline in the incomplete combustion. It is a colorless liquid, soluble in water, has octane number of 110 and it is less dense than gasoline, so has less energetic yield.


Diesel is very polluting, for that exists the need to search an alternative to this fuel. The biodiesel is produced from soy beans, animal fat, plant oil and any organic material which has triglyceride.

This is the triglyceride’s molecule.

This is the biodiesel’s molecule, the blue part is called ester. The long hydrocarbon chain can have between 12 and 22 carbon atoms.

The cetane number is between 46 and 65, has less energetic yield than diesel and more efficient combustion. The biodiesel can have many colors, depending the origin of production.

And the hydrogen fuel? This needs a dedicated post, which I will publish in the future.


About Pedro Ney Stroski

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