Ameer Randolph
The world is witnessing a shift towards cleaner and more sustainable energy sources, with automotive technology evolving to include electric cars, hybrid vehicles, and more efficient internal combustion engines. This has sparked a curiosity among car owners about the fuel they pump into their vehicles. Gasoline, also known as petrol, is a transparent, yellowish, and flammable liquid, that is the most common fuel for cars. It is a mixture of hydrocarbons with between four and twelve carbon atoms per molecule, derived from the fractional distillation of petroleum. The combustion of gasoline with oxygen from the air yields carbon dioxide and water as exhaust.
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What You'll Learn
Gasoline/petrol
Gasoline, or petrol in Commonwealth English, is a petrochemical product. It is a transparent, yellowish, and flammable liquid used as a fuel for spark-ignited internal combustion engines. The combustion of gasoline releases about 46.7 megajoules per kilogram (13.0 kWh/kg) or 33.6 megajoules per liter (9.3 kWh/L) of energy.
Gasoline is chemically composed of organic compounds derived from the fractional distillation of petroleum and later enhanced with additives. It is a mixture of hydrocarbons with between four and twelve carbon atoms per molecule (C4-C12). These include paraffins (alkanes), olefins (alkenes), napthenes (cycloalkanes), and aromatics. The specific gravity of gasoline ranges from 0.71 to 0.77, with higher densities having a greater volume fraction of aromatics.
The ability of a gasoline blend to resist premature ignition (knocking) is measured by its octane rating. Tetraethyl lead was historically used to increase the octane rating but is no longer used in automotive gasoline due to health hazards. Leaded gasolines are still used in aviation, off-road motor vehicles, and racing car engines. The demand for gasoline is peaking in many countries and may decline as smaller and more efficient cars are developed.
In Brazil, gasoline for automobile use is required to contain 27.5% ethanol, while in Australia, ethanol use is limited to 10% of gasoline. Pure hydrated ethanol is also available as a fuel. Gasoline blends can vary according to the season and producer, affecting their energy content.
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Crude oil
The composition of crude oil consists primarily of hydrocarbons, which are organic chemical compounds composed of hydrogen and carbon molecules. These hydrocarbons vary in length, with shorter chains containing one to four carbon atoms forming petroleum gases such as methane, ethane, propane, and butane. Longer hydrocarbon chains, with more than twelve carbon atoms, are used for heavier fuel oils like kerosene, diesel fuel, and lubricating oils.
The process of refining crude oil is essential to obtain the portion that can be optimised for motor oil or gasoline. This refining process, known as fractional distillation, separates the different constituents of crude oil based on their boiling points and vaporisation temperatures. The crude oil is heated to high temperatures, typically between 315°C and 370°C, and fed into a fractionating column. Lighter hydrocarbons, including petrol, are collected from the top of the column, while heavier ones, such as diesel, separate out lower down.
The demand for petrol and gasoline has led to the development of cracking processes, such as thermal and catalytic cracking, to convert heavier fractions into lighter ones. Thermal cracking involves heating hydrocarbons to high temperatures under pressure, resulting in a low-grade fuel that undergoes further refinement. Catalytic cracking, on the other hand, utilises a chemical catalyst, typically aluminium-silica powder, to break down heavy fractions into lighter ones, yielding a higher proportion of useful products.
The products derived from crude oil play a significant role in the automotive industry. Gasoline, also known as petrol, is a transparent, yellowish, and flammable liquid used as fuel for spark-ignited internal combustion engines. The combustion of gasoline releases energy through the reaction of its hydrocarbons with oxygen, producing carbon dioxide and water as exhaust. The performance of gasoline-powered engines is influenced by factors such as octane rating, energy content, and vapour pressure.
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Hydrocarbons
The vast majority of hydrocarbons found on Earth occur in crude oil, petroleum, coal, and natural gas. Crude oil is a fossil fuel created from the remains of tiny plants and animals that lived millions of years ago. These remains were covered with layers of sediment that were subjected to high pressures and temperatures, resulting in the formation of hydrocarbons. The ability of a particular gasoline blend to resist premature ignition (knocking) is measured by its octane rating. Tetraethyl lead was once used to increase the octane rating but is no longer used in automotive gasoline due to health hazards.
The combustion of hydrocarbons in gasoline-powered internal combustion engines releases energy through the reaction of hydrocarbons with oxygen from the ambient air, yielding carbon dioxide and water as exhaust. This process is known as combustion or burning, where a substance such as coal, oil, or gas reacts with oxygen to produce carbon dioxide, water vapour, heat, and energy. The combustion of gasoline releases about 46.7 megajoules per kilogram or 33.6 megajoules per liter.
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Octane
The octane rating of gasoline indicates its resistance to knocking and measures the amount of octane in the fuel. The higher the octane number, the greater the fuel's stability and resistance to knocking. Knocking, also known as pre-ignition, occurs when the fuel ignites on its own before the spark plug ignites it, leading to reduced engine efficiency and potential damage. Modern engine computers can minimise pre-ignition by controlling the timing of valves and fuel injection, although this may come at the cost of fuel efficiency and emissions.
The standard method for determining octane ratings involves the use of an octane testing engine, which compares the performance of a given fuel sample to Primary Reference Fuels (PRF) of known octane values. The octane rating is then calculated by adjusting the engine's compression ratio until the knocking intensity reaches a specific level.
The demand for high-octane fuel has been increasing, with car manufacturers recommending or requiring premium gasoline (high-octane fuel) for their vehicle models. Higher octane fuel is designed for high-performance engines with higher compression ratios, turbochargers, or specific requirements for premium gasoline. While high-octane fuel offers improved performance and engine efficiency, it also comes at a higher cost.
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Alternative fuels
The use of alternative fuels in vehicles helps countries like the US to cut down on oil consumption and reduce emissions. There are over a dozen alternative fuels in production or development, with electricity and ethanol being the most popular.
Electricity
Electricity is used to power electric vehicles (EVs), including all-electric and plug-in hybrid electric vehicles (PHEVs). These vehicles have lower greenhouse gas emissions than internal combustion engines, even in places where electricity is mainly generated from coal, like China.
Ethanol
Ethanol is a widely used renewable fuel made from corn and other plant materials. It is blended with gasoline for use in vehicles. Ethanol was preferred over methanol due to support from the farming community and government incentive programs and corn-based ethanol subsidies. In 1996, Ford produced a new FFV Taurus, which could run on either methanol or ethanol blended with gasoline. The success of this model led to a continued emphasis on FFV E85 production, which is still the case today.
Biodiesel
Biodiesel is a renewable fuel that can be manufactured from vegetable oils, animal fats, or recycled cooking grease for use in diesel vehicles.
Dimethyl Ether (DME)
DME is a promising fuel for diesel engines, petrol engines, and gas turbines. It has a high cetane number of 55, compared to diesel's range of 40-53. Only moderate modifications are needed to convert a diesel engine to burn DME, and its combustion results in very low emissions.
Ammonia
Ammonia has been proposed as an alternative to fossil fuels for internal combustion engines. Its calorific value is about half that of diesel, and it can be used in existing engines with minor modifications. When produced using coal, the emitted CO2 can be sequestered, with nitrogen and water as the combustion products.
The chemistry of traditional car fuels, on the other hand, is based on hydrocarbons. Gasoline, or petrol, is a transparent, yellowish, and flammable liquid derived from the fractional distillation of petroleum. It is composed of organic compounds, primarily hydrocarbon chains with seven to eleven carbon atoms per molecule, known as C7-C11. These hydrocarbons are organic chemical compounds made up of hydrogen and carbon molecules, formed from the remains of tiny plants and animals that lived millions of years ago.
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Frequently asked questions
Car fuel, or gasoline, is made from a mixture of hydrocarbons that are refined from crude oil or petroleum. This is a fossil fuel, made from the remains of plants and animals that were subjected to high temperatures and pressure over millions of years.
The process of making car fuel involves extracting and shipping petroleum, which is a mixture of hydrocarbons and natural gas. This is then refined through distillation, where the crude oil is heated until it vaporizes, leaving impurities behind. The vapour is then condensed back into a liquid and collected.
As the automotive industry shifts towards cleaner and more sustainable options, renewable fuels and electric vehicles are becoming more popular. Biodiesel, for example, is made from non-petroleum oils like vegetable oil or soy. Ethanol is another alternative, produced through alcohol distillation. E-fuel is also a promising future alternative, produced using renewable energy.
Gasoline engines are composed of many substances, including cast iron and aluminium alloys. Gasoline is combined with air and vaporized, creating a combustible combination. The combustion of gasoline with oxygen yields carbon dioxide and water as exhaust.
