Alternative drive technology
The term green vehicle (synonym "Alternative Drives") includes concepts for drive of vehicles , which in terms of energy or be constructive solution of the spread on the market driving techniques differ.
With such technologies, the hope is connected that emerging problems of conventional drives such as environmental pollution or exhaustion of fossil fuel sources (petroleum) can be solved. A switch to alternative drives is the cornerstone for an energy turnaround in transport .
Electrification of the powertrain
Here, drive concepts are dealt with, which essentially consist of a combination of conventional drives with internal combustion engines and a more or less large proportion of electrical drive components. In the diagram shown, conventional drives without an electrical component are also included. In the case of purely electric vehicles and fuel cell vehicles (or mixed forms), there is in some cases no longer any conventional proportion.
Hybrid vehicles are generally understood to mean mixed forms of conventional and electric drive components. They are listed in the adjacent drive diagram in columns C to H. The components that characterize the respective scheme are also included in the scheme. The (conventional) drives listed in columns A and B are not hybrid drives for obvious reasons . This also applies to the drives under columns I, J and K. With J (mixed form of the stored forms of energy - but not from the type of drive), there is also no hybrid because the power is generated by the same component, the electric motor.
In hybrid vehicles, energy conversion and energy output are temporally separated by energy storage devices and / or two energy conversion machines are used in parallel ( electric motor and internal combustion engine ). Accumulators or double-layer capacitors are used as energy storage for the electrical part of the drive .
In city traffic, characterized by shorter journeys, lower speeds and frequent acceleration and braking, the hybrid drive usually has advantages in terms of energy consumption. In overland traffic, i.e. longer journeys at higher speeds, a hybrid drive has more of a disadvantage in terms of energy consumption, because in this mode usually only the combustion engine is running and the hybrid drive has the disadvantage of greater mass.
Electric vehicles mostly draw their energy from energy storage devices that are sufficiently charged or refueled beforehand. Fuel cells generate electricity directly from fuel. Solar vehicles usually carry smaller energy storage devices and can also use solar cells to absorb electricity from the sun. However, only very low-consumption vehicles and boats can drive with direct sunlight, as the energy required for most vehicles is significantly higher than the yield from solar cells carried on board (see also electric cars , electromobility ).
Electric drives also include those whose energy is not stored in the form of electricity (e.g. in a lithium-ion battery), but in the form of a fuel that has yet to be converted, such as hydrogen. In this case , the conversion would take place in a fuel cell , and the electrical energy obtained in this way would be made available to the drive. In this case, one speaks of a fuel cell vehicle .
Alternative fuels with a conventional internal combustion engine
Alternative fuels can help reduce the dependence on fossil fuels and net emissions of CO 2 to decrease. The efficiency can be improved, especially with new fuels, which could shift the environmental balance sheet.
Alternative fuels are already being used on a large scale for conventional road traffic with conventional internal combustion engines, mostly as an admixture to commercial gasoline or diesel. Throughout the EU, up to 10% ethanol is added to conventional gasoline, and up to 7% interesterified vegetable oil ( biodiesel ) obtained from biomass is mixed with conventional diesel .
Alternative fuels also require an adaptation of automotive technology. This may concern the fuel supply, storage in the car, the internal combustion engine or the safety devices.
- Hydrogen opens up new potential for gasoline engines thanks to its very high ignitability and octane number. Storage in pressure vessels is now considered technically solved. Storage in liquid form would no longer significantly increase the range compared to the 700 bar technology. Liquid tanks are not compatible with longer shutdowns, since heat transfer leads to evaporation and subsequent blow-off of the hydrogen. → See also: hydrogen storage
- Biodiesel is already on the market in large quantities, but is mainly used as an admixture.
Diesel engines can in principle work with pure biodiesel, but most vehicles are only suitable for max. 10 to 20% approved because of technical problems with seals. Engine oil dilution is another problem, but it could be monitored. Particle filters can be used just like in diesel operation.
- Ethanol fuel
- Today, ethanol is mainly used in additives ( ETBE ). Multi-point injection systems in particular can already tolerate up to 20% ethanol in the fuel (E20), so-called flexible fuel vehicles are also necessary, which are designed for the use of E85 fuel (85% ethanol, 15% Super Plus), but can also be operated with pure gasoline. There are engines whose performance increases by 20% when using E85 instead of gasoline. Control units for retrofitting petrol engines to E85 are in development.
- BtL fuel
- Synthetic fuels promise fewer technical problems than biodiesel in the engine and allow a hybrid of the diesel and Otto principle. In contrast to biodiesel, BtL fuel is obtained from the whole plant and not just from the oil-containing parts of the plant. It therefore has a broader raw material base than biodiesel and is therefore more sustainable. The production of such fuels is still carried out in pilot plants, so they are not yet inexpensive and not available in large quantities.
- Natural gas vehicles
- Natural gas is less expensive to implement than hydrogen and is currently very popular because of its low costs, not least in cities because of its comparatively low emissions . The adaptation of the engines still has potential: direct injection, highly charged gasoline engines come close to diesel engines in terms of efficiency . Bivalent engines (gas or petrol) in particular are less efficient. Natural gas is extracted through drilling and is, like gasoline and diesel, a finite fossil raw material. Since it theoretically releases up to 25% less CO 2 and significantly fewer pollutants during combustion, it is considered a temporary solution to more sustainable alternatives (e.g. hydrogen, biogas).
- Liquefied petroleum gas as fuel, LPG
- Liquid gas is a gas that is liquid at low pressure. These are longer-chain hydrocarbons such as propane , propene , butane , butene or ether compounds such as dimethyl ether (DME). Liquefied petroleum gas can be used in vehicles with a gasoline engine , and retrofitting is easy. Due to the low storage pressure, the tanks in cars can be toroidal and can be installed in place of the spare wheel , which significantly increases the overall range of the vehicle without changing the trunk, as the original petrol tank is retained. In contrast to methane or fuels derived from it, such as DME, the CO 2 saving with LPG is 10–15%, the pollutant emissions are drastically reduced compared to petrol operation. Methane can also be obtained directly from biogas or wood gas , while the components of LPG (propane and butane) are by-products of the distillation of crude oil , for example in gasoline production. They are therefore finite sources of energy, but no additional oil has to be extracted to extract them. In a sense, one can speak of waste products from gasoline and diesel production.
- Vegetable oil fuel
- Vegetable oil can be used in the diesel engine instead of diesel oil. However, it has a tendency to resinify and no longer flow when it is cold. Addressing these issues led to the development of biodiesel.
- Today, alternative drives are also used for inefficient vehicle concepts such as sports off-road vehicles. Although this results in relative improvements, it does not have any environmental or sustainability effects compared to sensible vehicle concepts. In particular, increasing motorization is destroying achievable sustainability through efficiency improvements and alternative drive concepts.
A number of other concepts are listed here because they also represent alternative drives in the sense of this lemma. However, it must be assumed that this is not associated with any economic relevance in the automotive sector, be it for technical or economic reasons. In other sectors, however, niche applications can certainly be covered with such concepts, for example in stationary energy generation or in areas that are critical with regard to exhaust gas generation.
- Gas expansion engine
- Heat engines with external combustion (Ericsson engine , Stirling engine , vacuum engine)
- Compressed air car
- Multi-fuel engine
- Wood gas engine
- Electric push trailer
Requirements for the use of alternative drives
In order to avoid costly bad investments, the technologies have to be adapted to the application, especially in the case of commercial fleets, as they rarely combine all the advantages of the combustion engine at the same time. The most important criteria are:
- maximum performance (acceleration, inclines)
- Stability or constancy of the energy stored or kept on board
- Acceptable refueling procedure in terms of safety, duration and efficiency of the entire energy chain from the source to the wheel
- Safety for occupants and the environment
- Helmut Tschöke (Ed.): The electrification of the drive train , Springer Vieweg, Wiesbaden 2015, ISBN 978-3-658-04643-9
- Anton Karle: Electromobility: Basics and Practice , Hanser, 2nd updated edition, Munich 2017, ISBN 978-3-446-45099-8
- Information from the UBA ( Memento from October 15, 2012 in the Internet Archive )
- EU strategy for the diffusion of alternative fuels
- Overview of alternative drive technologies
- Current information on the topic of sustainable individual mobility
- Information portal about alternative drives and biofuels
- Alternative drives - information from the Federal Office for Energy
- Braess, Seiffert: Vieweg Handbook Motor Vehicle Technology , Edition 3 from 2003; P. 138