Hydrogen fuel in the context of "Solar furnace"

A motor fuel is a fuel that is used to provide power to the engine (motor) of vehicles — typically a heat engine that produces thermal energy via oxidative combustion of liquid or gaseous fuel and then converts the heat into mechanical energy through reciprocating pistons or gas turbines.

Currently, the majority of motor vehicles, powerboats and light aircraft worldwide are propelled by internal combustion engines powered by petroleum-based hydrocarbon fossil fuels such as gasoline, diesel or autogas, while larger ships and aircraft use marine diesel oil and kerosene to power gas/steam turbine, turboprop and jet engines. Other fuel types include ethanol, biodiesel, biogasoline, propane, compressed natural gas (CNG) and hydrogen (either using fuel cells or hydrogen combustion). There are also cars that use a hybrid drivetrain of different power sources. The use of synthetic alternative fuels (especially renewable biofuels) is increasing, especially in Europe, as well as increasing mass adoption of battery electric vehicles (which are powered by battery-stored electricity instead of fuels).

A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requiring a continuous source of fuel and oxygen (usually from air) to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from substances that are already present in the battery. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.

The first fuel cells were invented by Sir William Grove in 1838. The first commercial use of fuel cells came almost a century later following the invention of the hydrogen–oxygen fuel cell by Francis Thomas Bacon in 1932. The alkaline fuel cell, also known as the Bacon fuel cell after its inventor, has been used in NASA space programs since the mid-1960s to generate power for satellites and space capsules. Since then, fuel cells have been used in many other applications. Fuel cells are used for primary and backup power for commercial, industrial and residential buildings and in remote or inaccessible areas. They are also used to power fuel cell vehicles, including forklifts, automobiles, buses, trains, boats, motorcycles, and submarines.

Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy; they 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.

Liquid fuels are contrasted with solid fuels and gaseous fuels.

Renewable fuels are fuels produced from renewable resources. Examples include: biofuels (e.g. Vegetable oil used as fuel, ethanol, methanol from clean energy and carbon dioxide or biomass, and biodiesel), Hydrogen fuel (when produced with renewable processes), and fully synthetic fuel (also known as electrofuel) produced from ambient carbon dioxide and water. This is in contrast to non-renewable fuels such as natural gas, LPG (propane), petroleum and other fossil fuels and nuclear energy. Renewable fuels can include fuels that are synthesized from renewable energy sources, such as wind and solar. Renewable fuels have gained in popularity due to their sustainability, low contributions to the carbon cycle, and in some cases lower amounts of greenhouse gases. The geo-political ramifications of these fuels are also of interest, particularly to industrialized economies which desire independence from Middle Eastern oil.

A hydrogen internal combustion engine vehicle (HICEV) is a type of hydrogen vehicle using an internal combustion engine that burns hydrogen fuel. Hydrogen internal combustion engine vehicles are different from hydrogen fuel cell vehicles (which utilize hydrogen electrochemically rather than through oxidative combustion). Instead, the hydrogen internal combustion engine is simply a modified version of the traditional gasoline-powered internal combustion engine. The absence of carbon in the fuel means that no CO₂ is produced, which eliminates the main greenhouse gas emission of a conventional petroleum engine.

Pure hydrogen contains no carbon. Therefore, no carbon-based pollutants, such as carbon monoxide (CO), carbon dioxide (CO₂), or hydrocarbons (HC), occur in engine exhaust. However, hydrogen combustion occurs in an atmosphere containing nitrogen and oxygen, which can produce oxides of nitrogen (NO_x). In this respect, the combustion process is much like other high temperature combustion fuels, such as kerosene, gasoline, diesel, and natural gas. Therefore, hydrogen combustion engines are not considered zero emission.

A hydrogen infrastructure is the infrastructure of points of hydrogen production, truck and pipeline transport, and hydrogen stations for the distribution and sale of hydrogen fuel, and thus a crucial prerequisite before a successful commercialization of fuel cell technology.

Hydrogen stations which are not situated near a hydrogen pipeline get supply via compressed hydrogen tube trailers, liquid hydrogen trailers, liquid hydrogen tank trucks or dedicated onsite production. Pipelines are the cheapest way to move hydrogen over long distances but must be designed to withstand the leakage and steel embrittlement caused by the hydrogen molecule. Hydrogen gas piping is routine in large oil-refineries, because hydrogen is used to hydrocrack fuels from crude oil. The IEA recommends existing industrial ports be used for production and natural gas pipelines for transport, international co-operation and shipping.

Electrolysis of water is using electricity to split water into oxygen (O
₂) and hydrogen (H
₂) gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, but must be kept apart from the oxygen as the mixture would be extremely explosive. Separately pressurised into convenient "tanks" or "gas bottles", hydrogen can be used for oxyhydrogen welding and other applications, as the hydrogen / oxygen flame can reach approximately 2,800°C.

Water electrolysis requires a minimum potential difference of 1.23 volts, although at that voltage external heat is also required. Typically 1.5 volts is required. Electrolysis is rare in industrial applications since hydrogen can be produced less expensively from fossil fuels. Most of the time, hydrogen is made by splitting methane (CH₄) into carbon dioxide (CO₂) and hydrogen (H₂) via steam reforming. This is a carbon-intensive process that means for every kilogram of "grey" hydrogen produced, approximately 10 kilograms of CO₂ are emitted into the atmosphere.

Electrofuels, also known as e-fuels, are a class of synthetic fuels which function as drop-in replacement fuels for internal combustion engines. The production process involves the use of captured carbon dioxide or carbon monoxide, together with hydrogen obtained from water splitting. Electrolysis is a viable option with both conventional fossil fuel energy sources and low-carbon electricity sources, including wind, solar, and nuclear power.

The process uses carbon dioxide during manufacturing, and the release of carbon dioxide into the atmosphere is equivalent to the amount released during the combustion of the fuel, resulting in an overall low carbon footprint. Electrofuels emerge as a viable solution for mitigating greenhouse gas emissions from transport sectors, particularly in the context of long-distance freight, marine, and air transport.