Hydrogen propulsion

from Wikipedia, the free encyclopedia

As hydrogen drive a Power unit is colloquially known that hydrogen as a fuel used. Except for rocket propulsion and jet turbines, which actually use the power of the outflowing, burnt hydrogen as propulsion energy, the hydrogen is usually only used as an energy carrier for a downstream propulsion system.

Basically, the following concepts can be distinguished:

Energy carrier hydrogen

Fuel and exhaust fumes

The hydrogen used as fuel is not primary energy , but has to be produced from primary energy in the same way as electricity is generated . To his production is energy required. This is partially released again during the chemical reaction in a hydrogen combustion engine or in the fuel cell . Due to its low density, hydrogen gas contains more energy per unit weight in terms of mass than any other chemical fuel. However, the energy density is very low in terms of volume. For this reason, hydrogen as a fuel must either be highly compressed (up to around 700 bar) or liquefied (−253 ° C). Both are associated with additional energy input. In addition, the LOHC technology can bind the hydrogen using separate processes, making the two previously mentioned processes superfluous. However, energy is also required for binding.

The exhaust gases from a fuel cell consist of pure water vapor .

When hydrogen is burned in connection with air (in a gas turbine), the exhaust gases also contain nitrogen oxides , which are created from the nitrogen in the air at the high temperatures in the combustion chamber . If there is a high excess of air (λ≫1), fewer nitrogen oxides are produced, but the efficiency then also decreases. In piston engines , traces of CO and CH continue to get into the exhaust gas. They come from the lubricating oil between the cylinder wall and piston and from the crankcase ventilation .

Hydrogen production

The main processes for generating hydrogen are:

  1. The thermo-chemical conversion of carbon- energy sources (usually Fossil fuels ) at temperatures of 300-1000  ° C . The oldest process of this type is steam reforming with a market share of over 90%. This process used to be used to produce town gas ( synthesis gas ) from coal and water vapor , which contained around 60% hydrogen. Through further process steps, almost the entire energy content of the energy source can be bound to hydrogen. The disadvantage of this is the climate-damaging gas CO 2 . There are also technologies to produce hydrogen from biomass in a climate-neutral way . The first commercial facility, the Blue Tower in Herten , was not completed due to the insolvency of Solar Millennium AG .
  2. Hydrogen is a by-product of a number of chemical processes (e.g. chlor-alkali electrolysis ). The quantities are considerable, but are mostly used further. The hydrogen produced as a by-product in the Cologne region alone would be sufficient to operate 40,000 cars permanently (as of 2010).
  3. Hydrogen is produced comparatively rarely by electrolysis of water . Efficiencies of 70–80% have now been achieved here (see also technical water electrolysis) . There are currently projects in which the electrolyser is supplied directly by wind turbines. Wind turbines are now taken from the grid on windy days with low electricity demand; instead they could then be used for electrolysis to generate hydrogen. In addition to the necessary amount of energy, the provision of the required water is also problematic: “ In order to supply all the aircraft that refuel at Frankfurt Airport with hydrogen from the electrolysis of water, the energy from 25 large power plants would be required. At the same time, Frankfurt's water consumption would double. "
  4. Attempts to produce hydrogen in a hydrogen bioreactor with algae via a variant of photosynthesis are still at the research stage.

Hydrogen storage

Linde tank for liquid hydrogen, Autovision Museum , Altlußheim

The technical problems associated with storing hydrogen are now considered to have been solved. Processes such as pressurized and liquid hydrogen storage and storage in metal hydrides are in commercial use. In addition, there are other processes such as storage in nanotubes or as a chemical compound ( N- ethyl carbazole ), which are still in the development stage or in basic research.

Hydrogen filling station

The establishment of the supply infrastructure is a prerequisite for the widespread use of hydrogen drives. Around 1000 hydrogen filling stations are required to maintain a nationwide network in Germany.

There were around 274 hydrogen filling stations worldwide (as of May 2017). In Germany there were around 30, of which only 7 were publicly operated. In cooperation with Linde AG, the Daimler Group will build a further 20 hydrogen filling stations to initially ensure continuous connections on the north-south and east-west axes. → See also: Hydrogen highway

In February 2020 there were 87 hydrogen filling stations in Germany; According to the Federal Ministry of Transport, the number should rise to 130 by 2021. There were 177 ready-to-use hydrogen filling stations across Europe in February 2020.

A hydrogen filling station costs around EUR 1 to 1.5 million.


Rocket engines

Rocket propulsion with a hydrogen / oxygen mixture

Hydrogen / oxygen mixtures are used as rocket fuel , e.g. B. for the main engines of the Space Shuttle or the Delta IV Heavy .

Marine propulsion

Surface vessels

From 2007 to 2013, a passenger ship for 100 passengers operated on the Hamburg Alster , powered by electricity (approx. 100 kW) from fuel cells. The cost of the fuel cells was 3 million euros, the entire ship cost 5 million euros. It was developed as part of the Zemships project. The shutdown was due to the shutdown of the H 2 filling station due to inefficiency.

The Norwegian Viking Lady is used as a hydrogen-powered ocean-going ship. It is a supply ship for drilling platforms , which in 2009 was equipped with a fuel cell in addition to the diesel-electric drive . Like the conventional drive, this is operated with LNG (liquefied natural gas).


Class 212 A submarine with hydrogen propulsion

In the Type 212 submarine and the newer boats of Dolphin-class fuel cell drives are used. The nine water-cooled polymer electrolyte membrane fuel cell modules have a total output of 306 kW. They are supplied with oxygen from pressure tanks and hydrogen from metal hydride storage tanks. The resulting water is used as service water. The cooling water coming from the fuel cells heats the metal hydride reservoir in order to drive out the hydrogen.

The DeepC (in English: deep sea) is a hydrogen-powered, unmanned underwater vehicle. It was put into operation in 2004. The project has now ended.

Aircraft engines

Vehicle drives

Nowadays, hydrogen is still produced from fossil fuels and therefore has no environmental advantages compared to the direct combustion of fossil fuels. As part of the global transformation towards sustainable energy systems using renewable energies , the so-called energy transition , it is planned to produce hydrogen either directly through artificial photosynthesis or indirectly through electrolysis from renewable energies, in particular wind energy , solar energy and hydropower . This hydrogen can then be used emission-free in hydrogen drives.

Hydrogen drives will compete with other forms of drive, in future mainly with electric cars in motorized individual transport . It should be noted, however, that cars powered by regeneratively generated hydrogen are on the one hand more efficient and cleaner than fossil-fueled vehicles, but on the other hand electric vehicles are significantly more efficient than hydrogen vehicles. From the point of view of energy efficiency , battery-operated electric vehicles are therefore more useful than hydrogen vehicles, as they require significantly less electricity than when using hydrogen. However, hydrogen is necessary for applications in which battery-powered vehicles cannot be used sensibly, for example in heavy goods traffic, air traffic or shipping. Since both the production of hydrogen and the reconversion into electricity in the fuel cells of the hydrogen vehicle are loss-intensive, hydrogen vehicles need around 2.2 times as much electrical energy as battery-operated electric cars for the same distance.

Internal combustion engine

12-cylinder hydrogen combustion
engine in the BMW Hydrogen 7

Mazda has been leasing the hydrogen RX-8 since March 2006, making it the first automaker to offer a vehicle with a hydrogen combustion engine.

BMW is the second manufacturer to have brought a hydrogen combustion engine for passenger cars to series production. The engine can run on both hydrogen and gasoline. At the 2006 Auto Show in Los Angeles, BMW presented the 760h " Hydrogen 7 " model, which will be available from November 2007 . It is based on the 760i of the BMW 7 series and can be leased from BMW (no sale is planned). The conventional 12-cylinder combustion engine of the 7 series was modified for the combustion of hydrogen and gasoline. It is stored as liquid hydrogen. However, a lot of energy is required to liquefy hydrogen (−253 ° C). In addition, some of the hydrogen will volatilize due to unavoidable insulation losses during storage if continuous consumption is not ensured. With the BMW Hydrogen 7, for example, outgassing begins after 17 hours of idle time; after 9 days, the contents of a half-full tank have evaporated.

Two buses with hydrogen combustion engines were in continuous use in Berlin for the 2006 soccer World Cup . They laid there 8,500 kilometers back and had in the course of 2006 in Berlin-Spandau the regular service included. In 2009, the manufacturer announced to MAN that it would give up the project due to increased defects.

At the end of 2009, the Austrian Hydrogen Center Austria presented a concept vehicle (Mercedes W211) with a combustion engine under the name HyCar1, which can be operated multivalent with petrol, hydrogen, natural gas or gas mixtures.

BMW announced at the end of 2009 that the further development of hydrogen combustion engines will be discontinued. The field test with luxury limousines that run on hydrogen will not be continued. "There will be no new hydrogen test fleet for the time being," said the BMW Development Board Member in December 2009. In 2010, BMW presented the 1 Series with fuel cell drive.

The Welsh company Riversimple has developed a vehicle with a hydrogen combustion engine ( Rasa model ) that will go into series production from 2021.

HCNG (or H2CNG) is a mixture of compressed natural gas (CNG) and hydrogen . The hydrogen content is up to 50 percent by volume. In principle, this fuel can be burned with any natural gas engine and reduces the cost of design changes to conventional internal combustion engines.

Fuel cell vehicles

Fuel cell cars

As early as 1995, car manufacturers were intensively involved in fuel cell cars. With the Necar II (New Electric Car), Daimler-Benz presented a research vehicle and praised it as “by far the most environmentally friendly car in the world”. In contrast, the production of hydrogen as a pre-chain up to the refueling ( well-to-tank ) in the Including consideration ( well-to-wheel consideration ), if its ecological balance deteriorates drastically, it is even referred to as “one of the most climate-hostile cars of all”. A more recent eco-balance from 2015 now shows the framework conditions under which fuel cell vehicles become ecologically competitive compared to battery-powered electric vehicles and conventional gasoline cars.

In 2008, the Swiss-based company ESORO presented a concept vehicle called “HyCar”.

Mercedes-Benz F-Cell
Mercedes-Benz GLC F-Cell
Hyundai Nexo

The vehicle manufacturers Toyota, Nissan and Honda have stated that they have significantly reduced production costs for hydrogen-powered vehicles. It is intended to start manufacturing large series in Japan from 2015 and to set up numerous hydrogen filling stations in the Japanese metropolitan regions.

In 2013, Hyundai in Korea was the first manufacturer to start series production of the Hyundai ix35 FCEV fuel cell car in small series; The main target market is Europe. Since 2015, the car has been part of the official Hyundai Germany sales program under the name ix35 fuel cell.

In 2015 Toyota launches the mass-produced fuel cell car under the name Mirai on the international market.

Daimler wanted to start large-scale production of hydrogen vehicles in 2014. In order to prove the suitability of the hydrogen drive for everyday use, Daimler started a circumnavigation of the world with several fuel cell vehicles of the Mercedes-Benz B-Class . In 2010, 200 series vehicles of this type were delivered to customers on a leasing basis. At the end of 2012 it became known that the series production of affordable BSZ cars at Daimler would be postponed by several years.

In April 2011, Opel announced that it would be producing the first series models with fuel cell drives in series from 2015 and pushing ahead with the development of a comprehensive infrastructure for hydrogen filling stations parallel to the market launch. In connection with the nuclear phase-out, consideration would be given to using excess energy from wind and solar power plants for ecological hydrogen production. A first pilot project is planned with the wind power generator Enertrag . At the end of 2012 it became known that fuel cell development at Opel had been abandoned.

In November 2014, Toyota announced the series production of the fuel cell car (“ Mirai ”), which has been available in Japan since December. This car has also been sold in Germany since 2015.

A pre-production model of the Mercedes-Benz GLC F-Cell was presented at the IAA 2017 . The vehicle has been available for leasing as a production model since 2018.

At the CES in January 2018, Hyundai presented the successor to the ix35 fuel cell with the Nexo .

Fuel cell buses

Fuel cell buses generate electrical energy using a fuel cell that drives electric motors. They mostly have a traction battery as intermediate storage and for the recovery of the recuperated braking energy, which makes them part of the serial hybrid buses .

EvoBus from Daimler

A small series of hydrogen-powered city ​​buses was built by the Daimler subsidiary EvoBus and made available for worldwide testing in large cities . Since these are city buses, the problem of the missing petrol station network is eliminated . In the city, only a gas station on the is depot of bus operator needed. In 2004, hydrogen-powered buses were tested in a joint project between DaimlerChrysler, Shell and the Icelandic Ministry of the Environment in Reykjavík . Newer models are manufactured as Mercedes-Benz FuelCell hybrid buses .

Fuel cell buses in Hamburg

In Hamburg , three city buses powered by fuel cells and electric motors from Daimler-Benz were in practical testing from 2004, and six more since April 2006. The project of Hamburger Hochbahn AG and Vattenfall Europe was called HH2 . The overall efficiency ( well-to-wheel ) of the vehicles operated with hydrogen from green electricity is, however, controversial, since enormous amounts of electricity are required for hydrogen production and storage. The energy consumption of the hydrogen buses corresponded to a diesel consumption of 100 liters per 100 kilometers. This second advanced generation was in use until 2010. The third, significantly improved version was in use from 2011 to the end of 2018. These were serial hybrid buses, the fuel cell of which worked with up to 60% efficiency and which stored the electricity in lithium-ion batteries . This made purely electric driving and recuperation possible. The two wheel hub motors each had a continuous output of 60 kW and could produce up to 240 kW for a short time. The hydrogen consumption could be reduced by up to 50%, whereby the overall efficiency was improved. 4 of the buses have been in use on the premises of the Frankfurt-Höchst industrial park since 2019.

Fuel cell buses in NRW

The first hydrogen buses by the Belgian bus manufacturer Van Hool were delivered in Wuppertal and Cologne in 2019 . By mid-2020, 10 buses are to go into operation in Wuppertal and 30 in the Cologne region.

Fuel cell buses in the Rhine-Main area

In Frankfurt, Wiesbaden and Mainz, the use of hydrogen buses initially failed because the Polish manufacturer Autosan cannot deliver. In January 2020, the joint order for 11 vehicles was canceled. They should be used from summer 2019. The tank facility in Wiesbaden for 2.3 million euros stands around unused. Frankfurt now wants to order 22 buses from another manufacturer. A fuel cell bus has been running between Darmstadt and Groß-Umstadt since May 2019 in the regular service of the bus operator Winzenhöler.

Ursus City Smile

A new electric bus model with fuel cells from the Polish manufacturer Ursus was presented at the Hannover Messe 2017 . The Ursus City Smile city bus has a range of 450 km with the range extender and can be fully refueled in around eight minutes. The bus is 12 m long, has space for 76 passengers, drives a maximum of 85 km / h and, according to the manufacturer, has a hydrogen consumption of approx. 7 kg H 2 per 100 km. The electric ZAwheel wheel hub drives from Ziehl-Abegg achieve an efficiency of 90% and a maximum output of 364 kW. The fuel cell with a maximum output of 60 kW was supplied by the Dutch company HyMove. The battery came from the German manufacturer BMZ .

Toyota Sora

The fuel cell bus Sora from the Japanese manufacturer Toyota was presented at the Tokyo Motor Show in 2017 . In 2018 the bus received approval for use in Japan. Toyota wants to have 200 vehicles in operation in the Tokyo area by 2020 - on the occasion of the Olympic Games. The same technology is used in the Toyota Mirai car , but with two electric motors.

Fuel cell rail vehicles

Fuel cell two-wheelers

Bicycles and scooters powered by fuel cells are in the development phase. The Suzuki Burgman Fuel Cell Scooter was the first fuel cell two-wheeler ever to receive EU type approval for road approval. Now the scooter is to be tested in England for its suitability for everyday use. The heart of the vehicle is an air-cooled fuel cell and a hydrogen tank integrated into the frame.


In contrast, drives that use fossil fuels were cheaper than hydrogen-powered vehicles in 2011. Hydrogen from renewable energies is only used by the consumer if it is made economical for a transitional period through government measures ( promotion of renewable energies / taxation of fossil energies).

The profitability of hydrogen vehicles depends on several factors (see table). In addition to the costs of hydrogen vehicles compared to conventional drives, the relative price of fossil primary energy carriers to hydrogen is an important factor for economic efficiency.

In a study by DENA , which was carried out on behalf of the Federal Ministry of Transport in 2009, prices between $ 85 / barrel and $ 130 / barrel are mentioned as a breakeven point for the profitability of fuel cell vehicles , provided that the prices for a fuel cell vehicle are in the range of a diesel vehicle. According to the assessment of well-known automobile manufacturers , this should be achieved around 2014. However, the start of series production of fuel cell vehicles is being postponed again and again by leading car manufacturers.

Factors that increase the profitability of hydrogen Factors that reduce the profitability of hydrogen
The scarcity of resources in fossil primary energies leads to price increases. This reduces or compensates for the price difference compared to the hydrogen price. New technologies initially require high investments, e.g. B. for the expansion of the infrastructure.
In 2011, the potential for increasing the efficiency of hydrogen technologies has not yet been exhausted. With the technologies for the production and storage of hydrogen, but especially with the fuel cell technology, cost reductions and efficiency increases are to be expected. The potential for increasing the efficiency of conventional fossil technology has not yet been exhausted in 2011. Increases in efficiency are to be expected above all in the further development of combustion engines and hybrid drives .
The climate protection goal of the German federal government (80 percent reduction in CO 2 emissions by 2050) requires high investments to avoid climate-damaging emissions, which reduces energy efficiency and increases costs. This increases the profitability of climate-neutral hydrogen.

For the same reason, renewable energies are promoted by the German federal government in order to raise them more quickly to the area of ​​economic efficiency.

The ecological and social follow-up costs of using fossil fuels are difficult to quantify and are usually not assigned to economic efficiency in an economic analysis, which apparently reduces the economic efficiency of climate-neutral hydrogen compared to fossil fuels.


Fuel cell vehicle Vehicle with a gasoline engine
In order to be able to drive 100 km with a fuel cell vehicle of the Mercedes B-Class with a consumption of 0.97 kg / 100 km and a price of 8.099 euros / kg (with conventional generation from fossil primary energies), one pays 7.86 euros .

A Toyota Mirai consumed in real operation about 1 kg / 100 km / kg at a price of 9.50 euros (as of 2016) and thus costs to 100 km about 9 , 50 euros .

To be able to drive 100 km in a Mercedes-Benz B-Class vehicle with a gasoline engine with a consumption of 7 l / 100 km and a petrol price of 1.579 euros ( E10 ), you pay 11.05 euros .

A Toyota Prius IV comparable to the Toyota Mirai costs 7.90 euros with a high fuel consumption of 5 liters / 100 km and a price of 1.579 euros / liter per 100 km .

This means that the fuel cell vehicle is more economical in terms of fuel consumption than the vehicle with a gasoline engine. This applies to the fuel prices that the customer has to pay at the petrol station. It should be noted that mineral oil and hydrogen are taxed differently. No energy tax is levied on hydrogen .

One problem with the economy of the fuel cell drive is the cost of the catalytic converter. If a catalytic converter requires 60 g of platinum, the costs are almost 2,400 euros for the platinum alone (for comparison: the catalytic converter in a gasoline-powered vehicle only requires approx. 20 g of platinum). Fuel cells using less platinum are under development.

Risk of accident with hydrogen vehicles

See also: Safety instructions

Cars powered by hydrogen are no more dangerous than vehicles powered by gasoline or gas. Due to its low density, hydrogen is a very volatile gas. It evaporates very quickly outdoors. Sufficient ventilation must be provided in closed rooms, as it is flammable in a wide range of 4–75% by volume (petrol: 0.6–8% by volume). Oxygen / hydrogen mixtures with a proportion of less than 10.5 volume percent hydrogen are heavier than air and sink to the bottom. The segregation does not take place immediately, so that the ignitability is maintained until the 4 volume percent limit is undershot. When handling hydrogen, safety regulations and ventilation systems must take this behavior into account.

Gasoline is a liquid that evaporates slowly. The flammable gasoline vapors are heavier than air and stay longer on the ground, and the time it takes for it to ignite is longer.

If hydrogen is released in closed rooms, there is an increased risk of explosion, e.g. B. in garages or tunnels. Here, increased ventilation and possibly additional safety measures must be provided.

The detonation limit of hydrogen is at a concentration of 18% or more. Gasoline explodes much earlier, namely at a concentration of 1.1%. For an explosion or fire to occur at all, a fuel-air mixture that has formed must first be ignited in both cases. In the case of hydrogen, this requires less energy of 0.02 mJ than with gasoline (gasoline: 0.24 mJ), but in practice this does not matter, because the energy of an electrical spark is sufficient to also generate gasoline vapors ignite.

Gasoline has a significantly lower ignition temperature (220–280 ° C) than hydrogen (585 ° C), so it can ignite more easily on hot surfaces such as the exhaust manifold or catalytic converter.

When ignited, hydrogen burns at a faster combustion rate than gasoline. The flame moves steeply upwards with a small diameter if the leak is on the top of the tank.

A hydrogen flame has less heat radiation than a gasoline flame. It is therefore less hot next to a hydrogen flame than next to a gasoline flame - the advantage is that neighboring objects such as B. Car seats do not catch fire easily. People who are near the flame are also less likely to suffer burns. However, the hydrogen flame is hardly visible. Therefore, there is a risk of getting into it unintentionally.

The pressure tanks used today (in contrast to petrol tanks) can withstand serious accidents without damage. Hydrogen vehicles with pressure tanks can easily be parked in multi-storey car parks and underground garages. There is no legal provision that restricts this. In contrast, vehicles with liquid hydrogen must not be parked in closed rooms, as the outgassing can cause explosive gas accumulations.

An example of the behavior of hydrogen was shown in several accidents involving tankers loaded with liquid hydrogen. There was an explosion or burning off of the hydrogen: There were no or only slightly injured people, no one has died so far.

The main problem with hydrogen storage is leaks. Hydrogen tanks and pipes must be due to the opposite z. B. natural gas or propane / butane of smaller molecular diameter can be sealed much better. Some materials are unsuitable because they are permeable to hydrogen. Leaks not only lead to high transport losses, but also create a safety risk when gas accumulates and a hydrogen-air mixture forms. This is why hydrogen tanks and lines are made of special plastics that largely prevent diffusion . Such systems must be approved by the TÜV. The advantage is that hydrogen escapes upwards due to its low density and, unlike petrol vapors, propane or butane, does not collect in depressions.

See also


  • Sven Geitmann: Hydrogen Cars - What will move us in the future . Hydrogeit Verlag, Kremmen May 2006. ISBN 3-937863-07-9

Web links

Individual evidence

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