# fuel

A fuel (including fuel ) is a fuel whose chemical energy by combustion in internal combustion engines ( internal combustion engine , gas turbine , ...) and rocket engines is converted into mechanical energy.

Fuels are mainly used to drive means of transport ( motor vehicle , aircraft , ship , rocket ). Since they each have to be transported, substances with a high energy density are often used. But stationary combustion engines are also operated with them.

Oxygen from the air is usually used as the oxidizer during combustion , sometimes, especially in rockets, but also a separate oxidizer such as liquefied oxygen , nitrous oxide or nitric acid .

## nomenclature

The delimitation of the term fuel from the term fuel is not consistently regulated:

• As a fuel , a substance is usually referred to, which for direct combustion in an internal combustion engine is used. The term is particularly common in the field of automotive engineering .
• As a fuel , a substance is normally referred to, for the propulsion of a means of locomotion, more rarely, a stationary machine, is used. The term thus includes fuels. The term fuel is particularly common in the shipping and aerospace sectors.

In most other languages ​​there is no such distinction. So z. B. in English the term fuel in general fuel . This includes fuels (sometimes called motor fuel ) and fuels (sometimes called propellant ).

Substances that serve as an energy source for a drive, but which do not release any chemical energy , are usually not referred to as fuel . B. water for a water turbine or uranium for the nuclear reactor of a nuclear drive .

## Comparison of fuels

For the range of a vehicle are in addition to the efficiency of its units u. a. the volume of the tank and the energy stored in it are decisive. The physical comparison of the calorific values ( kWh per m³) shows that liquid fuels are optimal in terms of their energy density. In the case of gases, the energy content depends heavily on the pressure.

Surname Physical state Density in
kg / m³
Calorific value in
kWh / kg
Calorific value per
unit of volume
hydrogen gaseous (normal pressure)   0.09 33.3   3 kWh / m³
hydrogen gaseous (20 MPa) 33.3   530 kWh / m³
hydrogen liquid 70.8 33.3   2351 kWh / m³
Natural gas H-Gas (CNG / GNV) gaseous (normal pressure)   0.81 13.0   10.5 kWh / m³
Natural gas L-gas (CNG / GNV) gaseous (normal pressure)   0.82 11.3   9.3 kWh / m³
natural gas gaseous (20 MPa) 12.0 2580 kWh / m³
LPG (" LPG ") liquid 540   12.8   6966 kWh / m³
Premium gasoline liquid 748 11.4 8527 kWh / m³
Methanol liquid 787 5.53 4352 kWh / m³
Ethanol liquid 789   7.43 5862 kWh / m³
Gasoline-benzene mixture liquid 796   11.6   9300 kWh / m³
diesel liquid 833 11.9 9912 kWh / m³
benzene liquid 879 11.1 9756 kWh / m³
Vegetable oil liquid 918 10.4 9547 kWh / m³
1. a b Average or mean values ​​are given for complex substance mixtures.
2. Calculated from the respective convenient value unless otherwise stated.${\ displaystyle m = V \ cdot \ rho}$

The possibility of using a fuel in an engine depends not only on its calorific value, but also on the design of the engine and its fuel supply, the respective chemical and physical properties of the fuel and the additives added to it . For example, valves and valve seats that have been designed for the combustion of petrol can wear out faster when operated with natural gas or LPG (no additives are added), which is why vehicle manufacturers equip their natural gas vehicles with engines specially designed for natural gas operation.

In addition, fuels are differentiated according to the ignition principle, i.e. whether compression ignition (diesel engine) or external ignition (Otto engine) is used. Another important point of discussion when using alternative fuels is whether it can be incorporated into the existing infrastructure or whether it requires new infrastructure. Alternative fuels that can be mixed with existing conventional fuels made from fossil hydrocarbons are particularly beneficial in this regard. The proportion of admixtures can then be gradually increased "infrastructure-neutral".

A crucial aspect when evaluating fuels (conventional and alternative fuels) is the cost situation for the consumer. The fuel costs are strongly dependent on the national taxation and vary considerably depending on the country (see below "Fuel price development")

## Alternative fuels

As alternative fuels fuels are referred to, the conventional from mineral oil can replace fuels produced. A distinction is made between fuels made from fossil fuels , fuels made from biogenic fuels and fuels produced primarily using renewable energies .

• Natural gas (CNG) has been available in Germany since the 1990s. Millions of automobiles are already driving it in Argentina, Brazil and Italy. As with LPG , the advantage of natural gas is that it burns cleaner than petrol and diesel. Like gasoline and diesel, natural gas is also a fuel that is harmful to the climate, since CO 2 is produced when it is burned . The main component of natural gas is methane .
• Methane and fuels containing methane such as B. natural gas , biogas or LNG are problematic as alternative fuels, since methane often escapes unburned as a greenhouse gas into the environment during production, storage, transport and use as a fuel, where it is around 20 to 25 times more harmful to the climate than CO 2 is. So-called methane slip often occurs in engines, up to approx. 2% of the methane is not burned and enters the atmosphere as an environmentally harmful greenhouse gas. Even if methane, which is produced with the help of renewable energies, can actually be converted back into energy in a climate-neutral manner, its use in ship engines is therefore i. d. Usually more harmful to the climate than diesel. This problem should not occur in some 2-stroke engines. Methane slip is also problematic in the production of methane-based fuels and should amount to up to 8%.
• Ethanol fuel ( bio-ethanol ) is obtained from sugar beet, sugar cane or wheat. Since 2005, it has been mixed with normal petrol in small quantities in Germany. Many automobiles drive it in Brazil, see Flexible Fuel Vehicle . Processes for the production of cellulosic ethanol from plant biomass are under development.
• Biodiesel is made from vegetable oils esterified with methanol (mainly rapeseed oil ). Since biodiesel can attack seals and hoses in the fuel system, engines must be suitable for this or have to be converted. Biodiesel can hold a large amount of water, which can lead to corrosion problems on the injection equipment. It also serves as an admixture to normal diesel fuel; the proportion is so limited that diesel engines that have not been converted can also be operated with this mixture. Disadvantages are the high cost of production and the inefficiency or competition for food and feed in terms of land use.
• Biogas can be used for stationary engines and for heating purposes near the generating plants, but natural gas vehicles can also be refueled with it. For the utilization of biogas, the methane content is the most important. For the disadvantages see above under "Metane".
• BtL fuel (Biomass to Liquid) is also marketed under the brand name SunDiesel . It is made from biomass, such as B. won wood or straw. BtL is still in the testing phase and still has a great need for research. With him all components of the plant can be used and he has a high energy density. Conventional diesel vehicles can also drive it. An overall energy balance for the BTL processes is not yet available.
• Pure vegetable oils e.g. B. from rapeseed , sunflower or camelina , also called "Pöl" or natural diesel, can be used as fuel in diesel engines. In particular, the higher viscosity compared to diesel fuel means that an adaptation of the fuel and injection system is necessary for the permanent operation of diesel engines with vegetable oil. Vegetable oils tend to gum up under the influence of air and can solidify in winter. The disadvantage is the low utilization of solar energy and the competition for food and feed in terms of land use. One advantage of vegetable oil is the low risk potential for humans and the environment (not hazardous to water, not hazardous, non-toxic, high flash point).
• Hydrogen can be obtained from water (H 2 O) by means of electrolysis . However, it is cheaper to obtain it by direct chemical conversion of natural gas ( steam reforming ), which is, however, harmful to the climate as CO 2 is then produced. Hydrogen can be used with combustion engines or fuel cells .
• Ammonia can be produced as a carbon-free fuel with electrical energy, u. a. are used in internal combustion engines or in fuel cells ; The advantage is the liquid state of aggregation with little cooling or the low pressure of liquid ammonia at room temperatures. Applications are (as of 2020) still on a laboratory scale. In the USA, however, trams were powered by ammonia as early as the 1870s and buses in Belgium during World War II. If the ammonia is obtained from renewable energies, it is a climate-neutral fuel. The advantage over hydrogen is that it is easier to transport. The disadvantage is the potential toxicity, whereby poisoning should rarely occur due to the unpleasant smell, as well as in the ammonia slip, i.e. of small amounts that degenerate unused in the exhaust gas, whose elimination is currently being researched and which, unlike methane slip, is not harmful to the climate. Manufacturers also already offer ammonia slip catalysts that are said to be able to oxidize the slip to harmless products nitrogen (N2) and water (H 2 O). Since ammonia very often z. B. is used as a fertilizer or environmentally friendly refrigerant , the production of ammonia is widespread, currently around 2 - 3% of the total commercial energy needs are used for this worldwide. If no renewable energies are used, around 1.5 tons of climate-damaging CO 2 are produced per ton of ammonia . see also: Power-to-Ammonia
• Wood gas was a common alternative in the 1940s under the pressure of acute fuel shortages. Vehicles with self-made wood gasifiers can still be found in Finland today. In the process, normal wood, often wood waste, carbonizes in the absence of air in a pressure vessel or decomposes under a lack of air combustion. The resulting flammable gases (mainly methane when there is no air, mainly carbon monoxide , hydrogen and methane when there is insufficient air decomposition) are fed to an engine after cooling and cleaning. Stationary wood gas systems are used for heating purposes and in combined heat and power systems.
• Polyoxymethylene dimethyl ether for short OME (with n between 3 and 5) can be used as diesel fuel components or as a complete alternative to diesel fuel. They bring about a reduction in soot emissions during the combustion process. The production costs for making OME are comparable to making diesel fuel. The primary raw material for the production of OME is methanol, which can be produced from conventional natural gas as well as regeneratively from COx and hydrogen. Other ethers are also being investigated for their suitability in fuels.

The term electric fuels covers a number of alternative fuels that are produced with the help of electrical energy (e.g. hydrogen, ammonia, methane). In order to make the concept economical, it makes sense to use this energy in a regenerative way, e.g. B. in solar, wind or hydroelectric power plants generated. By means of electrolysis of water, hydrogen is recovered, the (z. B. for either directly as a fuel cell vehicles can be) used or with CO 2 gas at different ( " Power-to-gas ") or liquid ( " Power-to-liquid " ) Hydrocarbons can react; In this way, fuels can be produced that can be used in conventional combustion engines. This offers the possibility of driving long-haul traffic largely CO 2 -neutral, for which there are currently no viable electrification concepts.

## environment

The exhaust gases released when fuels are burned cause health and environmental damage such as acid rain and the greenhouse effect and thus global warming . In particular, carbon dioxide , carbon monoxide , nitrogen oxides , dust (soot), sulfur dioxide and hydrocarbons play important roles. The benzene in carburetor fuels is carcinogenic. Many fuels are poisonous and hazardous to water. The type and scope of the pollutants released are essentially dependent on the composition of the fuel, the design and operating mode of the engine and the exhaust gas aftertreatment (exhaust gas catalytic converter, soot filter ).

In Germany, the ordinance on the composition and labeling of the qualities of fuels and fuels regulates the composition and quality of fuels in order to reduce air pollution. The ordinance regulates the quality of petrol and diesel fuels, gas oil, biodiesel, ethanol, liquid gas, natural gas, biogas and vegetable oil fuel.

## Fuel prices

Fuel prices worldwide (selection) in euros (without considering wage level and cost of living):

country 1 l Super (98) in euros 1 liter of diesel in euros 1 kg CNG natural gas in euros year
Argentina 1.44 1.12 0.53 2011
Bolivia 0.50 0.38 0.17 2011
Brazil 0.92 0.61 0.37 2011
Chile 0.54 0.33 0.21 2011
Germany 1.55 1.45 0.99 2011
France 1.21 1.03 0.55 2011
Italy 1.30 1.14 0.80 2011
Canada 0.38 0.29 0.19 2011
Colombia 0.50 0.25 0.21 2011
Mexico 0.46 0.33 0.19 2011
Netherlands 1.42 1.03 k. A. 2011
Austria 1.11 0.94 0.89 2011
Portugal 1.28 1.00 k. A. 2011
Saudi Arabia 0.10 0.05 k. A. 2011
Spain 1.06 0.90 k. A. 2011
United States 0.57 0.58 0.43 2011
Venezuela 0.09 0.05 0.002 2011

1 kg of natural gas corresponds to approx. 1.5 liters of super, approx. 1.3 liters of diesel

## Web links

Wiktionary: fuel  - explanations of meanings, word origins, synonyms, translations

## Individual evidence

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