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General information
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Description
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The hydrogen engine is a spark ignition engine running on hydrogen fuel.
Conventional gasoline engines used in cars can be converted into hydrogen
engines by some modifications.
Main exhaust emission is water. As far as energy efficiency and applicability
in ground transportation are concerned, the main challenges lie in hydrogen
generation and on-board storage.
Hydrogen storage
The following table shows the heat value of hydrogen compared to gasoline.
|
Heat value per
weight |
Heat value per
volume |
Hydrogen |
33
kWh/kg |
3
Wh/l |
Gasoline |
10 kWh/kg |
9000
Wh/l |
Source: Buchner 2000
Due to the low volume-specific heat value of H2 (about 3000 times smaller
than that of gasoline), on-board storage in both cars and railways is a
challenge.
The following methods exist:
- as compressed gas
- in liquid form
- in a hydrogen-absorbing metal alloy (metal hydride).
The benefits of metal hydride storage include the fact that a relatively
large volume of hydrogen can be stored per tank, and the fact that it is almost
impossible for large volumes of hydrogen to be released into the air, which
gives a safety advantage. The disadvantage of this method are tank weights. In
order to combat this, R&D (e.g. at Mazda) is putting effort into the
development of metal alloys with higher absorption capacity.
Hydrogen generation
The most common way of obtaining hydrogen is water electrolysis according to
the reaction:
2 H2O -> 2 H2 O2
Another promising approach lies in direct conversion from fossil sources.
Options discussed are:
- Reforming from carbon gas
- Partial oxidation of heavy hydrocarbons
- Steam reforming from natural gas
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General criteria
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Status of development: research & experiments |
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Time horizon for broad application: in > 10 years |
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Expected technological development: highly dynamic |
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Benefits (other than environmental): none |
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Barriers: high |
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Applicability for railway segments: medium |
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Type of traction: diesel
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Type of transportation: passenger - main lines, passenger - regional lines, passenger - suburban lines, freight
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Grade of diffusion into railway markets:
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Diffusion into relevant segment of fleet: 0 % |
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Share of newly purchased stock: 0 % |
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Market potential (railways): highly uncertain |
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Environmental criteria
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Impacts on energy efficiency:
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Energy efficiency potential for single vehicle: not applicable |
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Energy efficiency potential throughout fleet: not applicable |
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Efficiency of conversion chain and choice of hydrogen generation
The efficiency of the hydrogen motor is only about 25 %.
The efficiency of hydrogen storage and transport is 95%.
The efficiency of the total conversion chain including fuel generation and
transport strongly depends on the efficiency of the hydrogen generation
process.
The following table gives the efficiencies for different ways of hydrogen
generation and the corresponding total efficiency:
|
Efficiency |
|
of hydrogen
generation |
of total
conversion chain (incl. fuel
transport and motor) |
Electrolysis |
32 %</p>
<p>(power generation 40 %, electrolysis
80 %) |
~ 7,6 % |
Reforming from carbon
gas |
~ 55 % |
~ 13 % |
Partial oxidation of heavy hydrocarbons |
~ 70 % |
~ 17 % |
Steam reforming from natural
gas |
~ 81 % |
~ 19
% |
Source: data from: Althammer, Hattensperger 1998.
These values show that direct conversion from fossil sources is much more
efficient than conversion via power generation and electrolysis.
CO2 emissions
As far as Greenhouse gases are concerned, the best option is electrolysis
using power from renewable sources (water, wind, nuclear) which produces only
minor quantities of CO2 during transport etc. |
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Other environmental impacts: positive |
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Hydrogen combustion
As far as emissions are concerned, H2 is the ideal fuel. Even without
after-treatment, there are only some minor emissions from lubricant combustion
(HC 0,04 g/kWh; PM<0,05g/kWh), and NOx (0,4 g/kWh).
Resource saving
Apart from environmental impact, the long-term availability of the resources
used has to be taken into account. Since hydrogen is a means for storing energy
rather than an energy source, its advantage does not lie in unlimited
availability but in offering a technology, which is compatible with any energy
source (fossil or renewable). |
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Economic criteria
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Vehicle - fix costs: (no data) |
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(no details available) |
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Vehicle - running costs: (no data) |
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(no details available) |
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Infrastructure - fix costs: high |
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A supply infrastructure for hydrogen fuel has to be built up. A railway independent distribution infrastructure as in the diesel case is not in place. |
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Infrastructure - running costs: (no data) |
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(no details available) |
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Scale effects: high |
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In case hydrogen combustion technology wins over fuel cells as clean vehicle technology in automotive sector, scale effects from engine and storage technology and especially supply infrastructure would be considerable. |
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Amortisation: (no data) |
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(no details available) |
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Application outside railway sector
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Status of development outside railway sector: test series |
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The first prototypes of hydrogen fuelled automobiles go back to the seventies. The US Post Office experimented with the liquid hydrogen fueled jeeps for mail distribution.
DaimlerChrysler tested a small car series in Berlin in the 1980s (> 750.000 km driven). Currently, DaimlerChrysler is focussing on the fuel cell.
BMW tested hydrogen cars in 2000 at Munich Airport. |
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Time horizon for broad application outside railway sector: in > 10 years |
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It is highly uncertain if cars propelled by a hydrogen engine will ever become widespread. This will mainly depend on the progress made in fuel cell technology and society's future environmental priorities. |
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Expected technological development outside railway sector: highly dynamic |
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Further advances are to be expected, especially in storage technology and energy efficient hydrogen generation. |
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Market potential outside railway sector: highly uncertain |
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Future market potential for hydrogen combustion engines is highly uncertain. At present, more R&D and PR emphasis is put on fuel cells. |
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Overall rating
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