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   Hydrogen engine  evaluated  
Conventional spark ignition engines can be modified to operate on hydrogen fuel. Hydrogen engines are discussed as an alternative to diesel propulsion.
Technology field: Innovative traction concepts and energy sources
close main section General information
  close sub-section Description
   

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
close main section General criteria
  close sub-section Status of development: research & experiments
    In the 1970s investigations were made by the US and Canadian railroads. No data on results.
  Time horizon for broad application: in > 10 years
    It is completely unclear if hydrogen combustion engines will play a role in future railways at all. They could become a long-term option if efforts to improve efficiency and robustness of fuel cells fail.
  Expected technological development: highly dynamic
    cf. Potential for further development outside railway sector
    Motivation:
   

Diesel substitute

Replace diesel traction in long-term perspective by alternative autonomous propulsion with less toxic emissions.

  Benefits (other than environmental): none
    (no details available)
  Barriers: high
   

Technological

Storage problems are still considerable.

Infrastructure

Transition from diesel to hydrogen supply infrastructure is costly.

Safety

If hydrogen escapes into closed spaces, detonating gas is formed. However with modern technology, safety dangers are not higher than with diesel.

    Success factors:
    (no details available)
  Applicability for railway segments: medium
    Type of traction:  diesel
    Type of transportation:  passenger - main lines, passenger - regional lines, passenger - suburban lines, freight
    (no details available)
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: 0 %
  Share of newly purchased stock: 0 %
    (no details available)
  Market potential (railways): highly uncertain
    Depends on technological strategy of railways. In the (unlikely) case of hydrogen technology winning over fuel cells and natural gas as a substitute for diesel, market potential will be huge.
    Example:
    No transfer to railways realised yet.
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: not applicable
  Energy efficiency potential throughout fleet: not applicable
   

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.

  Other environmental impacts: positive
   

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).

close main section Economic criteria
  close sub-section Vehicle - fix costs: (no data)
    (no details available)
  Vehicle - running costs: (no data)
    (no details available)
  Infrastructure - fix costs: high
    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.
  Infrastructure - running costs: (no data)
    (no details available)
  Scale effects: high
    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.
  Amortisation: (no data)
    (no details available)
close main section Application outside railway sector
  close sub-section Status of development outside railway sector: test series
    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.
  Time horizon for broad application outside railway sector: in > 10 years
    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.
  Expected technological development outside railway sector: highly dynamic
    Further advances are to be expected, especially in storage technology and energy efficient hydrogen generation.
  Market potential outside railway sector: highly uncertain
    Future market potential for hydrogen combustion engines is highly uncertain. At present, more R&D and PR emphasis is put on fuel cells.
close main section Overall rating
  close sub-section Overall potential: interesting
  Time horizon: long-term
    Hydrogen combustion technology is one of many (locally) clean alternatives to diesel traction. At present, fuel cells are given more emphasis, since in principle higher efficiencies can be obtained. Nevertheless, the hydrogen combustion engine could become a promising technological candidate for railways if fuel cell development does not meet expectations.
References / Links:  Althammer, Hattensperger 1998;  Buchner 2000;  www.science.edu
Attachments:
Related projects:  Energy chains of alternative fuels
Contact persons:
 date created: 2002-10-09
 
© UIC - International Union of Railways 2003