Gasoline

Gasoline is a transparent, yellowish, and highly flammable liquid.

It is a petrochemical product used primarily as fuel for spark-ignited internal combustion engines. These engines use a spark to ignite the fuel, which creates the energy needed for movement. Gasoline is a complex mixture of organic compounds known as hydrocarbons. These molecules are derived from petroleum through a process called fractional distillation. Because it is a high-volume and profitable product, it is produced in massive quantities at crude oil refineries.

To understand how gasoline is made, we must look at the refining process. Refineries take crude oil and separate it into different parts based on boiling points. This initial separation produces straight-run gasoline, also known as naphtha. However, naphtha often has a low octane rating, which is a measure of how well fuel resists premature ignition. If fuel ignites too early, it causes a knocking sound and reduces engine efficiency. To improve this, refineries use several chemical processes. They might use a catalytic reformer to create reformate, which has a high octane rating. They may also use an alkylation unit to produce alkylate, a high-quality fuel component. Other methods include isomerization, which changes the shape of molecules into iso-paraffins to improve performance.

Refineries manage several distinct chemical streams to create the final blend. Straight-run naphtha is distilled directly from the crude oil. Catalytic cracked gasoline is produced using a catalytic cracker and has a moderate octane rating. Hydrocrackate is another stream produced by a hydrocracker, offering medium to low octane ratings. Alkylate is a specialty product that contains no aromatics or olefins. It was famously used in aviation fuel during World War II. Finally, oxygenates like ethanol are often blended into the gasoline pool. In the United States, ethanol is common, while other countries might use MTBE or ETBE.

The history of gasoline is tied to the rise of the internal combustion engine. In the last quarter of the 19th century, Otto engines were developed in Germany. These early engines used a volatile hydrocarbon obtained from coal gas. As technology improved, the development of the spray nozzle carburetor allowed for the use of less volatile fuels. A major breakthrough occurred in 1891 with the Shukhov cracking process. This was the first commercial method to break down heavy hydrocarbons in crude oil. This process increased the amount of lighter, more useful products available for fuel. This discovery helped meet the growing demand for transportation energy.

Gasoline production involves very specific quantities and measurements. From a single barrel of crude oil, refineries produce approximately 19 to 20 gallons of gasoline. They also produce about 11 to 13 gallons of diesel fuel and 3 to 4 gallons of jet fuel. The chemical makeup of the gasoline consists of hydrocarbons with four to twelve carbon atoms per molecule. This is often referred to as C4–C12. The density of gasoline is quite low, with a specific gravity between 0.71 and 0.77. Because it is less dense than water, gasoline will always float on the surface of water.

There are several surprising facts regarding the stability and safety of gasoline. If gasoline is not stored correctly, it can become "stale fuel." This happens when the liquid degrades over time, creating gums and solids. These substances can corrode engine components and make it difficult to start a machine. To prevent this, users often use fuel stabilizers, which are mixtures containing mineral spirits or isopropyl alcohol. Another important safety fact involves fire. Because gasoline floats on water, you cannot use regular water to extinguish a gasoline fire. Instead, a fine mist must be applied.

Gasoline is deeply connected to broader chemical and environmental systems. The combustion of gasoline involves reacting hydrocarbons with oxygen from the air. This chemical reaction yields carbon dioxide and water as exhaust. Modern regulations often limit the amount of certain chemicals in gasoline. For example, the European Union sets a limit of one percent benzene by volume. This is done to manage the chemical composition of the fuel. These rules have led refineries to prefer alkane isomers, such as isomerate, over other types. This ensures that the fuel is both efficient for engines and meets safety standards.