Mercedes-Benz Fuel-Cell Workshop

Mercedes-Benz Citaro Fuel Cell Bus

Fuel cell vehicles on the way to sustainable mobility

July 17, 2006 6:09 AM
Filed Under: German, Mercedes-Benz

Press Release

Fuel cell vehicles on the way to sustainable mobility

Mobility provides fundamental value to society and is also a key factor for prosperity in a modern economy. Responsible and forward-looking action must therefore be geared toward achieving sustainable mobility – which is why sustainable mobility is an essential corporate goal at DaimlerChrysler. In view of expected developments in the energy sector, it is clear that the present use of largely fossil-based primary energy sources will not allow for sustainability over the long term. “That also applies to the transport sector, with its nearly complete focus on crude oil resources for fuel production,” says Dr. Thomas Weber, Member of the Board of Management of DaimlerChrysler AG, responsible for Group Research & Mercedes Car Group Development. “DaimlerChrysler is therefore calling for a paradigm shift in energy policy, which will require a high amount of effort.”

Sustainable mobility can be achieved only if three objectives are consistently pursued:

  1. Drive systems with greater efficiency. To the extent that fuels continue to be derived mainly from fossil sources, they must be used more efficiently, which means they must be conserved in order to protect limited resources and reduce CO2 emissions. Although renewable energy sources are theoretically unlimited in their availability, they too must be utilized conservatively – not least due to the relatively high costs associated with their production.

  2. CO2 neutrality. The dangers associated with climate change can only be counteracted by substantially reducing carbon dioxide emissions. The achievement of this objective also requires greater utilization of renew-able energy sources that are largely, or even completely, CO2-neutral.

  3. Greater use of renewable resources. Expanded exploitation of alternative energy sources in regions of the world that today are highly dependent on imported fossil fuels will loosen up the dependency and increase the security of supply. Greater use of renewable resources will also safeguard the long-term availability of primary energy for the private and commercial transport sectors.

Our way to sustainable mobility

Energy structures and mobility concepts cannot be changed overnight, because both represent areas in which alterations made to achieve sustainability will lead only gradually to an effective shift in energy consumption patterns. This also means that development strategies suitable for bringing about such changes must include short, medium and long-term outlooks and will require great patience on the part of everyone involved. “DaimlerChrysler is pursuing such a strategy under the motto of “Our Way to Sustainable Mobility”, says Dr. Herbert Kohler, Vice President Group Research and Advanced Engineering Vehicle and Powertrain and Chief Environmental Officer of DaimlerChrysler. “The strategy represents a road map for all development goals that can be achieved today, tomorrow, and further in the future – and the achievement of each objective marks a step along the way.”

Automakers like DaimlerChrysler cannot embark upon this long road by themselves; their job is to design more efficient powertrain concepts that produce fewer emissions, and to bring to market new concepts that offer the potential for achieving great increases in efficiency. Other parties must become involved, however, if the individual objectives and ultimate goal are to be achieved. For example, fuel producers and energy companies must improve their products and develop new fuels at competitive prices. That’s because optimized and innovative drive systems cannot fully exploit their benefits without the help of suitable energy sources and higher-quality fuels. Energy producers and technology developers must gradually expand capacity for the production of renewable energy, and also improve manufacturing processes in order to make such forms of energy available in sufficient quantities and at affordable prices. Additional infrastructures must also be established that will make the new fuels available on a broad basis. Last but by no means least, governments must create the conditions that will help pave the way for sustainable mobility.

In the area of fuels, DaimlerChrysler is supporting a range of developments that represent milestones on the road to sustainable mobility. Current fuels, such as diesel fuel and gasoline, can be further improved in terms of quality. This, in turn, would make it possible to implement combustion-engine optimization measures that are already technically possible. Mixing first-generation renewable biofuels with conventional fuels already offers the possibility of reducing CO2 emissions and lowering the consumption of primary fossil energy sources. Synthetic fuels that are produced from fossil sources but are also renewable (second-generation biofuels) represent the next step toward large-scale implementation of customized engine-fuel concepts, and thus further efficiency gains and lower CO2 emissions. At the end of this process should be the exclusive or primary use of renewable fuels that bring the goal of CO2 neutrality within reach. For several reasons, DaimlerChrysler believes that hydrogen is the ideal energy source for achieving this long-term objective (see press information Hydrogen).

In conjunction with the transformation of the fuel mix described above, DaimlerChrysler is pursuing short, medium and long-term objectives in the area of powertrain development. Even after more than one hundred years of continual improvement, there is still great potential for increasing the efficiency of combustion engines and reducing their emissions. In fact, our engine developers prove this is the case with every new engine they turn out. Today, with the range and amount of synthetic fuels expected to increase in the coming years, engine developers have even more options for making improvements. Through the development and use of hybrid concepts in applications that bring their advantages to the fore, DaimlerChrysler will create additional possibilities for reducing CO2 emissions over the next few years.

For the long term, however, no drive concept offers greater potential on the road to sustainable mobility than fuel cells powered by pressurized hydrogen. The company therefore began focusing on this promising concept at a very early stage, and its current practical testing program (see press information: Fuel cell powertrain – progress on the way to series production) has put this innovative drive system well on the way to market launch. Moreover, with the F 600 HYGENIUS, DaimlerChrysler researchers have demonstrated how performance capability, power density and suitability for everyday use can all be consistently increased through the new powertrain concept. This will enable DaimlerChrysler customers in the not too distant future to enjoy not only sustainable mobility, but also unlimited driving pleasure.

Fuel cell powertrain development: Input from the F600 HYGENIUS research vehicle

At the Tokyo Motor Show in October 2005, DaimlerChrysler presented the first-ever research vehicle specifically designed as a fuel cell car: the F 600 HYGENIUS. While developing and constructing the unique four-seater, engineers were able to benefit from the extensive experience they had gained with cars such as the A-Class F-Cell.

The vehicle's entire drive unit, including the pressurized hydrogen storage tanks, is tucked away in the vehicle’s sandwich floor, as is the case with the 60-vehicle F-Cell fleet. This type of architecture makes possible a range of technical improvements and innovations that distinguish the F 600 HYGENIUS from a normal F-Cell vehicle.

The most important innovations in the fuel cell drive for the F 600 HYGENIUS include:

Together with other innovations, the new technology package is responsible for the improved fuel economy of the F 600 HYGENIUS, which consumes the energy equivalent of only 2.9 liters of diesel fuel per 100 kilometers. The research vehicle’s fuel cell system operates extremely efficiently: In the partial load range, it has an efficiency rating of 60 percent.

Test drives with clear objectives

Because the F 600 HYGENIUS is a fully operational research vehicle. Researchers and developers actually drive it every day in an effort to further improve its fuel cell powertrain system. In order to examine the stack's power output and fuel consumption, the engineers take the vehicle on different kinds of test drives that measure every conceivable parameter under everyday conditions. They also put the compact research vehicle on the roller test stand, which runs the car through defined driving cycles.

“After all, we want to improve the robustness and service life of the entire system — and the best way to see if we’re succeeding is to take the vehicle on test drives over long distances,” says Dr. Andreas Docter, who was responsible for the construction of the fuel cell system used in the F 600 HYGENIUS and also heads the Fuel Cell Systems Engineering department at DaimlerChrysler Research.

A further goal of the F 600 HYGENIUS test drives is to develop an optimal operating strategy for future B-Class F-Cell vehicles. The questions posed here include: Would it make sense to operate the vehicle only with the stack or only with the high-voltage battery? Under what conditions and performance demands should the booster function be activated, whereby energy for the electric motor is supplied by both the fuel cell and the battery? What are the best situations and points in time to shift the vehicle from one mode to the other? In which charge stage and driving situation should the motor be used as a generator and the battery be recharged? When searching for the answers to these questions, the engineers must take into account a variety of secondary parameters such as driving dynamics, fuel consumption and functional safety.

From the F 600 HYGENIUS to the B-Class F-Cell

The stack that will be used in the B-Class F-Cell and — as a double pack — in the successor model to the Citaro fuel cell bus will include a series of innovations from the F 600 HYGENIUS. Second-generation fuel cell vehicles will thus benefit not only from the experience already gained from fleet tests with the 60 A-Class F-Cell cars, but also from the new expertise gained from DaimlerChrysler’s most recent research vehicle.

The most important technological innovations that DaimlerChrysler will take from the F 600 HYGENIUS are:

Two other innovations from the F 600 HYGENIUS will be gradually introduced to new fuel cell fleets. First of all, the bipolar plates in the fuel cells will be made of metal foils in the future, allowing for more space-saving installation than today’s graphite plates. Secondly, a light electric compressor — rather than the heavy screw-type compressor — will be used to supply air to the stacks.

Challenges for the future

DaimlerChrysler researchers are already looking far beyond the launch of commercial applications for fuel cells in automobiles. They are examining new procedures and materials that may one day lead to further technical improvements. For example, the scientists are working on a wide range of new catalytic materials for fuel cells that require only small amounts of platinum and allow for a very long lifetime. In addition, they are assessing the advantages and disadvantages of wheel hub motors, which are constantly mentioned in connection with electric drive systems, and are also attempting to develop optimization strategies for such motors.

Technology transfer from research vehicles to series production

Mercedes-Benz has presented 11 research vehicles since 1981. The technologies and interior and exterior design concepts in these unique automobiles have often served as clear indicators of the direction automotive development is taking. Many of the systems first used in research vehicles and viewed as revolutionary just a few years ago are now used in production vehicles.

Such systems include Distronic — a proximity cruise control feature that was implemented for the first time in the F 100 research car in 1991 and was launched in a production vehicle in 1998 (S-Class). The F 100 was also equipped with gas-discharge lamps, which as xenon lights are now standard equipment in many vehicle models. Other examples of the successful transfer of systems from research vehicles to series production are Active Body Control (which is today found in the CL, S and SL-Class), window bags, cornering lights and voice-operated vehicle systems. The F 600 HYGENIUS and the fuel cell powertrains based on its fuel cell system will continue in this tradition and pave the way for the series production of environmentally friendly zero-emission technology.

Fuel cell powertrains - progress on the way to series production

A total of 60 A Class vehicles with fuel cell powertrains are currently in use worldwide. These F Cell test vehicles are being driven by various customers at six locations in Europe, Asia and the United States. In the largest fuel cell fleet test to date, all relevant measured values are sent on a daily basis via radio and the Internet to the DaimlerChrysler researchers and developers in Nabern and Ulm, where the evaluation of the data provides valuable insights for the next generations of fuel cell vehicles.

The experts are busy working on concepts for these pioneering vehicles so that DaimlerChrysler will be able to launch additional fuel cell automobiles on the basis of the B Class in the coming years. It is estimated that the marketing of fuel cell drive systems will commence sometime between 2012 and 2015. About 100 operational vehicles were built with the alternative drive concept in the decade following the presentation of the first fuel cell automobile Necar1 in 1994. Besides the 60 A Classes F Cell used by customers, these vehicles include various concept cars and research vehicles, as well as three Sprinter vans and 36 Citaro urban buses that have been successfully used in regular service by public transit authorities - in some cases since 2003.

Complexity demands a gradual approach

“Fuel cell technology is very complex,” says Dr. Christian Mohrdieck, who is Director of Fuel Cell Dive System Development. “It is an entirely new drive concept, which is not based on thermodynamics as is the case with internal combustion engines, but on electrochemistry.” Twelve years ago, the researchers and developers at DaimlerChrysler entered uncharted territory with the Necar 1. There were plenty of surprises and it was a learning experience for even the most accomplished engineers. The approximately 100 fuel cell vehicles that DaimlerChrysler has built to date demonstrate that the engineers have gained sufficient expertise with the alternative drive system to know where to make future adjustments in order to gradually prepare the technology for the market. As soon as the current field tests with the A Class F Cells are completed, DaimlerChrysler will commence testing the second generation fuel cell powertrain systems in B Class vehicles. The fleet tests will focus on mastering further technical and economic challenges and realizing various improvements. Besides making further enhancements, DaimlerChrysler will be striving in particular to substantially reduce costs in its third generation of fuel cell vehicles.

Simplifying components and cutting costs

On the way to achieving this goal, DaimlerChrysler has set clear objectives for its engineers: First, the entire fuel cell system will have to be made simpler and more robust by reducing the number of components. Fewer components also mean fewer opportunities for faults, which in turn results in lower costs. Another goal is to make existing components smaller in order to save space and reduce weight. Finally, the engineers will also be working to further increase the lifetime and power density of the fuel cell stacks by the time the system is ready for series production. To achieve this goal, the company has developed various programs and technical concepts, with one of the main challenges being a substantial reduction in costs. This is not only a difficult task for automakers, but also for suppliers of important components, who for the most part are also entering uncharted terrain when it comes to mobile fuel cell applications.

Generation 1: Top marks for the F Cell and Citaro

For the current F Cell project, DaimlerChrysler has signed usage contracts with various companies and agencies. The contracts regulate the use of 60 A Classes F Cell over a one to two year period, during which the customers’ employees test the vehicles under demanding everyday conditions in California, Michigan, Berlin, Tokyo and Singapore. Altogether, these vehicles had been driven a total of approximately 800,000 kilometers by the end of June 2006, and had been in operation for more than 24,000 hours. The F Cell vehicles are equipped with a recording device that registers all relevant parameters, from driving speed and the voltage shape in the fuel cells to the pressure in the hydrogen tanks. So far, the engineers have been satisfied with the global field test results: The evaluation of tremendous volumes of collected data clearly shows that the fuel cell system is far less prone to faults than was originally anticipated at the start of the project.

Similar results have been delivered since May 2003 by the 36 fuel cell buses, which DaimlerChrysler has delivered to ten major European cities as well as to Beijing, China and Perth, Australia. The buses had been driven a total of about 1.4 million kilometers by the end of June 2006. During this time, some of the fuel cell stacks had been in operation for more than 3,000 hours — another result that far surpassed all expectations. The two projects funded by the European Union (EU) — Clean Urban Transport for Europe (CUTE) and Ecological City Transport System (ECTOS) — showed that the fuel cell drive systems in the Citaro worked reliably even under the rigorous conditions of everyday use. As a result of this success, the EU decided to hold a follow-up project called HyFLEET:CUTE, which was launched in January 2006. Although the test results for lifetime and operational reliability were extremely encouraging, the fuel cell bus still poses several technical hurdles that will have to be overcome. These include the need to achieve a higher rate of efficiency, improvements in noise, vibration and harshness (NVH) values, and, in particular, significant cost reductions.

Generation 2: B Class with freeze-start capability and high range

For its next generation of F Cell vehicles, DaimlerChrysler will equip B Class automobiles with fuel cell powertrains. Compared to the current A Class F Cell, the B Class vehicles feature a number of improvements that are essential in order to bring the technology further toward the series-production stage and which have been installed as prototypes in the F 600 HYGENIUS research vehicle (see press information: Input from the F600 HYGENIUS research vehicle).

The car’s primary improvements are its cold-start capability, which guarantees problem-free operation even at freezing temperatures, and the increased range of more than 400 kilometers, which was made possible through the use of 700-bar pressurized tanks. In another improvement, the all-new fuel cell stack generates 40 percent more output and has a higher power/weight ratio.

During fleet tests of the B Classes F Cell, the engineers plan to evaluate these components and use the results to improve the stacks’ lifetime, for example. In addition, they want to simplify the overall system to make it even more reliable and robust.

In addition to being installed in the B Class, the new, freezable fuel cell stack also will be used in a twin prototype arrangement to propel the prototype of a next generation fuel cell bus. As is the case with a building block system, the bus program will involve various development steps, making it possible to represent several output levels.

Future generations: Drastically lower costs will be a prerequisite for larger fleets

Not until costs have been substantially reduced will it become economical to produce more vehicles than are required for the technical development process. Appropriate production technologies will also have to be employed during this phase. In order to pave the way for further developments, the specialists in Nabern and Ulm are now cooperating closely with colleagues at the Production and Material Technology department of the Sindelfingen plant. This is because all new technical concepts need to be compatible to production processes from the very start. Improvements need to be made in particular to the fuel cell stack, so that painstaking manufacture by hand, which will also characterize the next generation, can progress to the series production stage.

“Over the long-term it will be possible to create fuel cell powertrains at an acceptable cost,” says Mohrdieck about DaimlerChrysler’s assessment of the technology. “However, attaining this goal will require us to take certain steps and pursue a long-term plan that we have defined in a roadmap for future implementation.” The successful marketing of fuel cell drives will require that the unit costs of each new technology generation never increase or at least remain unchanged.

On the way to sustainable mobility

Necar 1, DaimlerChrysler’s first fuel cell vehicle, was a test unit in which the drive system weighed 800 kilograms and filled the Mercedes-Benz van’s entire cargo area. Ten years later, the first F Cell’s powertrain system has been so well integrated into a series production A Class that the car’s entire interior and luggage compartment are available for use. By the time this new technology is ready for market launch between 2012 and 2015, only 18 years will have elapsed since Necar 1’s introduction.

DaimlerChrysler Research recognized early on that the technology would be introduced in the near future, which is why it began working on fuel cell vehicles back in 1991. The Necar 1 of 1994 was followed by a long series of other concept and research vehicles: Necar 2 (1996), Necar 3 (1997), Nebus bus (1997), Necar 4 (1999), Jeep Commander (1999), Necar 5 (2000), Jeep Commander 2 (2000), Sprinter van (2001), Town & Country Natrium van (2001), and Citaro city bus (2002).

The researchers and developers used these vehicles to evaluate various energy sources for the fuel cells. In addition to liquid and gaseous hydrogen, these fuels included gasoline, methanol and sodium borohydride, which release hydrogen as a result of chemical processes. DaimlerChrysler will be working with the same determination to develop the successors to today’s fuel cell vehicles and make a crucial contribution to achieving sustainable mobility.

Hydrogen (H2) - providing the energy to power

Hydrogen has been produced on a broad scale for decades. It has been used as an energy source and process gas in the food and electronics industries, for example, as well as in a variety of refinery processes. Hydrogen is also a byproduct of chemical processes: It is created in chlorine production, for example, by means of chlorine-alkali electrolysis — and here it is frequently burned off for lack of any economically viable applications. About 45 million tons of hydrogen are produced every year, with 95 percent originating from primary energy sources such as natural gas and crude oil.

Why hydrogen?

Use of hydrogen per se isn’t new. What’s new is its application as a secondary energy source in a consumer market — something automakers such as DaimlerChrysler are pursuing, and with good reason. DaimlerChrysler’s top priority is develop concepts for sustainable mobility.

“Sustainable” in this context means:

Hydrogen has proved to be the ideal secondary energy source for achieving the above-mentioned objectives. That’s because when hydrogen is used as fuel for fuel cell vehicles, it leads to energy efficiency in the resulting drive system that is nearly twice as high as that achieved by the most modern gasoline and diesel engines. Such fuel cell powertrains therefore offer tremendous gains in efficiency that cannot be achieved even with improved concepts for combustion engines, which DaimlerChrysler is also working on.

Even if the primary energy source and the process used to produce the hydrogen are taken into consideration, fuel cell drives are still superior to all combustion engine concepts when it comes to emissions as well. Fuel cell vehicles that run on pressurized hydrogen are by their very nature always zero-emission when in motion. If the hydrogen is obtained from a renewable energy source, the entire utilization chain is also free of emissions.

Petroleum’s nearly complete dominance as the primary energy source for today’s motor-vehicle fuels cannot be maintained over the long term. There are several reasons for this, including the finite nature of this fossil resource, its very high price at present (which is not expected to decrease significantly), and the fact that much of the world’s crude oil reserves are in politically unstable regions. In light of this situation, most oil-consuming countries have made it their goal to break dependence on petroleum, which is why they are increasingly demanding and supporting alternative primary energy sources for use in the production of fuels. Such sources include natural gas, wind power, and biomass.

Hydrogen opens up new possibilities for producing a motor-vehicle fuel from a wide range of primary energy sources. For example, it can be obtained by steam reforming of natural gas. Hydrogen can also be produced in a CO2-neutral manner using biomass. What’s more, it is conceivable that hydrogen could be produced from coal, provided economically sound concepts can be developed to capture the carbon dioxide created through the coal gasification process (CO2 sequestration). Electricity produced by power plants makes it possible to create hydrogen through electrolysis — and the concept of using electrolysis to produce hydrogen from all available renewable energy sources (wind power, solar energy, geo-thermal energy) is particularly forward looking and appealing. This is because renewable energy sources are nearly inexhaustible, and they also open the door to a system of mobility completely free of CO2. Each region of the world will likely implement its own individual concepts based on customer acceptance and the direction energy-policy discussions take.

Availability and costs

Independent experts believe that the globally available amount of “free” hydrogen (i.e. that currently not being used) is sufficient to provide fuel for more than one million fuel cell vehicles. This level of capacity will certainly be enough for the period leading up to mass commercialization of this drive concept. Depending on the production technique used and the capacity of production facilities, it currently costs anywhere between two and five euros to produce one kilogram of hydrogen (whose energy yield corresponds to approximately three liters of diesel fuel). One goal for the period between now and 2015 is to get the cost per kilogram down to a more or less uniform level of two to three euros, which would make hydrogen production costs comparable to the current pre-tax price of gasoline. Another goal involves increasing the worldwide fleet of fuel cell vehicles, which would increase the share of hydrogen produced from renewable sources. This makes it possible to fully exploit the great potential fuel cell powertrain systems offer with regard to reducing primary energy consumption and eliminating CO2 emissions.

It is very difficult to forecast the course fuel prices will take. Only two or three years ago, for example, practically no expert would have predicted that the price of crude oil would be more than $75 per barrel in 2006 — at that time a barrel of crude was selling for just $25. Nevertheless, over the next few years we can expect further increases in the prices of fuels obtained from fossil energy sources; the only thing not certain is how large the increases will be. Supplies of crude oil will also continue to dwindle, and the need to exploit lower-yielding sources of crude oil, such as oil shale and oil sand (considered too costly in the past), will by itself lead to higher prices. Then of course there is the factor of politics in oil-producing regions, which has a major impact on prices. At the same time, there are several factors in favor of techniques for producing fuels from renewable sources. For one thing, solar energy and wind power, at least, are essentially inexhaustible resources, which means scarcity can never play a role in their prices. And the technological advancements that will be achieved in the future with today’s emerging techniques for producing energy from renewable sources will mean greater efficiency, which in turn will reduce production costs. This development can be clearly seen in techniques for generating electricity from wind power. In general, fuels obtained from fossil energy sources will become more expensive in the future, while prices for fuels from renewable sources will tend to fall. And the greater efficiency of fuel cell drives will help to reduce overall vehicle operating costs.

Customer acceptance and political will

The current cost disadvantage for fuels produced from renewable sources will likely remain a problem for many years, which is why governments must create political conditions conducive to the production and use of such fuels. Lawmakers around the world must summon the political will to initiate a paradigm shift with regard to energy supply that will help prevent supply bottlenecks and dependency on supplier countries, while also leading to further reductions of CO2 and other emissions. This paradigm shift must be marked by use of various primary energy sources to replace the current overwhelming dominance of just a few energy sources. The number of distributed power systems must also be increased by means of regionally optimized supply structures.

DaimlerChrysler supports such a paradigm change, and as part of its strategy “Our Way to Sustainable Mobility”, it has developed a concept for the short, medium, and long terms that points the way to a sustainable energy supply for individual mobility. This concept focuses on hydrogen produced from renewable sources as a vehicle fuel, with the ultimate goal of establishing a system of mobility that is sustainable because it is emission-free and optimized to achieve the highest levels of efficiency. DaimlerChrysler believes that when this excellent secondary energy source is used with fuel cell vehicles, it offers the greatest potential for achieving the ultimate goal, particularly in view of its clear benefits with regard to the complete energy chain.

DaimlerChrysler and its partners in worldwide testing programs for fuel cell vehicles are also paying close attention to customer acceptance of the new technology. After all, it’s very important for motorists to be able to fill up with pressurized hydrogen as quickly and conveniently as they can with gasoline or diesel. Experience gained with the best filling stations from the current testing projects shows that this is already possible: Test motorists who have never used a hydrogen pump before have been able to fill their pressurized tanks in less than three minutes without any problems. Filling pump manufacturers have thus proven they can come up with viable solutions in this area.

A filling station infrastructure also has to be put into place on a broad basis, and here automakers will have to work together with energy companies to develop a hydrogen filling station network. Individual filling stations have already been built in the areas where fuel cell vehicles are currently being tested. The goal now is to establish clusters or mini-networks in the testing regions between 2010 and 2015, and then link them along highways in the years that follow. It will be important not only to achieve a sufficient density of filling stations but also to ensure that all of them have the required technical performance capabilities. That means, for example, being able to fill up tanks with hydrogen pressurized to 700 bars rather than the currently common 350 bars, in order to actually double the vehicle range that is already technically possible. In other words, filling station technology must keep pace and be kept in line with the technical improvements made to fuel cell vehicles.