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Ten Reasons |
August 22, 2006
Fifteen years of Mazda research into hydrogen vehicles
Source: Full
Boost
Mazda’s interest in hydrogen vehicles covers a span of 15 years:
the first prototype, the HR-X, was presented at the 1991 Tokyo Motor Show.
Even back then, the concept car had a hydrogen-powered rotary engine as
its powerplant.
Mazda is strongly involved in the issue of sustainable development, and is highly committed to researching new energies to meet the mobility needs of future generations while at the same time looking after the environment. However, Mazda’s goal is to solve such problems without sacrificing its ‘zoom-zoom’ values of dynamism and driving pleasure; hence the decision to choose the route of a hydrogen-powered rotary engine. The Renesis engine based on Wankel’s patent is ingrained in Mazda’s DNA, and was for good reason chosen as a partner for the company’s new environmentally-friendly requirements.
Although the hydrogen rotary engine remains a key area of development for Mazda, this has not prevented the Hiroshima-based company from continuing development of fuel-cell vehicles at the same time.
The hydrogen-powered Mazda prototypes resulting from this intense research work have succeeded one another at a steady pace since the early 1990s, up to the latest Mazda RX-8 Hydrogen RE concept car presented at the Tokyo Motor Show in 2003.
The 2004 road homologated prototype formed the basis of the Mazda RX-8 Hydrogen RE which is now actually driven on public roads in Japan. Equipped with a ‘dual-fuel’ power system, it is capable of operating just as well on hydrogen as on petrol, making it easier to use in everyday life.
In 2006 the Mazda RX-8 Hydrogen RE vehicles are supplied on a lease arrangement to Japanese companies and local governments – a world first for a passenger car with a hydrogen internal combustion engine. This unique ‘commercial’ endeavour is providing Mazda with valuable experience for the future development of its hydrogen-powered vehicles.
Akihiro Kashiwagi, Program Management Div., Hydrogen RE Program Manager
“A hydrogen rotary engine only emits water. It is not as efficient as a fuel cell, but structurally it is closer to the petrol engine, hence its manufacturing cost is lower and it has fewer durability issues.
Compared to fuel cells, hydrogen engines with dual-fuel system are more likely to play a significant role in the initial phase of the hydrogen energy society in the future. That is why Mazda is currently focused on developing dual-fuel system hydrogen engine.
Furthermore, under normal circumstances, a hydrogen vehicle is fueled by hydrogen gas for clean driving. But what if a hydrogen vehicle is also powered by petrol? It would mean greater convenience, because the driver does not have to worry about running out of hydrogen gas or about driving to a place where there are no hydrogen filling stations. Mazda has achieved such a system and calls it “dual-fuel system”, a highly innovative function not achieved with fuel cell vehicles.”
What is the difference between fuel-cell technology and a hydrogen internal combustion engine?
A fuel cell generates electricity by causing a chemical reaction between hydrogen and the oxygen contained in the air, with water as a by-product. A fuel-cell vehicle is powered by electricity generated by fuel cells.
A hydrogen internal combustion engine vehicle is powered by combusting hydrogen in a combustion chamber similar to today’s petrol engines, which also produces water as emissions. The expansion of the gases caused by this combustion then turns the rotor (in the case of the RX-8 Hydrogen RE) to drive the vehicle.
Hydrogen combustion: how does it work?
Hydrogen: a clean, recyclable and abundant fuel source
Hydrogen is one of the most widely available fuels: it accounts for 75%
of the matter in the universe on its own. It is found in abundance in
the stars and gassy giant planets.
On Earth, however, it is very rare in its natural state (its very low mass means that it escapes gravity’s pull). It is, however, found in river and ocean water. Water electrolysis is needed to extract it, a process which splits the H20 water molecule in two: this produces dioxygen 02 on the one hand, and dihydrogen H2 on the other. This electrolysis uses electricity, which can be produced in a variety of ways (wind, solar, hydro-power, etc.).
Hydrogen can also be extracted from organic fossil matter (coal, petrol, natural gas), and is a by-product of a number of industrial processes (chemical, welding, etc.). Hydrogen combustion follows the simplest of chemical formula: two H2 molecules combine with an 02 molecule to form two H20 molecules in vapour form, while at the same time releasing a very large quantity of energy. This reaction produces extremely few NOx nitrogen oxides and gives off no C02 (a greenhouse gas) whatsoever.
Hydrogen is considerably more combustible than conventional petrol. It can cope with very low concentrations (a mere 4% in air is sufficient for combustion to occur), and the flame front spreads much more quickly (approximately 265 cm/sec in stoechiometric conditions as opposed to 40 cm/sec for petrol). However, hydrogen does possess less energy at an equivalent volume. It is a fuel which is used widely in rockets, including the Space Shuttle. And it can be used as a fuel for an internal combustion engine as on the RX-8 Hydrogen RE.
Unlike fossil fuels, hydrogen forms part of a perfectly-balanced cycle: the hydrogen extracted from water by electrolysis is liberated after use in the form of vapour, which returns to the natural water cycle, while the C02 given off by the combustion of fossil fuels is in excess of the quantity usually absorbed by plants.
Burning hydrogen is not the only way of releasing the energy required to power a vehicle: hydrogen can also power a fuel cell, inside which it reacts with oxygen to produce an electrical current. However, despite the fact that the fuel cell has advantages (high energy output, zero nitrogen oxide released), it is also complex and expensive to manufacture, and requires a total redesign of the powertrain and its incorporation into the vehicle. This technology is not yet sufficiently mature, therefore, for use in everyday life.
The rotary engine: ideally suited to hydrogen fuel
Mazda’s decision to opt for the rotary engine rather than a piston
engine as the basis for its hydrogen vehicle designs is not attributable
solely to the brand’s unique experience with this technology. The
rotary engine is particularly suited to the specific requirements of hydrogen
fuel.
As we have seen, hydrogen is astonishingly explosive, which can produce problems in the combustion chamber of a piston engine (abnormal combustion). In a traditional engine, the fuel-air mixture is injected directly into a high-temperature combustion chamber which is sealed by very hot exhaust valves. These are hardly favourable conditions, and make hydrogen less attractive as a fuel for a reciprocal engine.
By contrast, the rotary engine has separate intake, combustion and exhaust chambers. The hydrogen is thus injected at a lower temperature, and only comes into contact with the higher temperatures of the combustion chamber at the last moment.
The other key characteristic of hydrogen is that it produces less energy at equivalent volumes when combusted, because it has a lower density than petrol. The low density of hydrogen – injected in its gaseous state – means that at the quantity required for combustion, it would occupy 29.5 % of the volume of the combustion chamber, compared to a mere 1.7 % for petrol. The result would thus be a reduced quantity of injected air, resulting in incomplete combustion and reduced power.
A better approach, therefore, is to opt for direct injection into the combustion chamber to counteract this phenomenon. As it happens, it is easier to place an additional injector in the inlet chamber of a rotary engine than on the side of the narrow cylinder head of a piston engine.
Lastly, the rotary engine is better than a reciprocal engine at combining the air/hydrogen mix because of its longer cycle. The result is a more uniform mixture which consequently delivers better combustion.
Mazda RX-8 Hydrogen RE
From prototype to the road in just two and a half years
It was logical that the RENESIS rotary engine – winner of four “International Engine of the Year” awards in 2003 and 2004, and renowned for providing high levels of driving fun – should be used as the basis for the development of a hydrogen engine. At the Tokyo show in October 2003, Mazda presented the first prototype of the RENESIS hydrogen engine, which even then incorporated a dual-fuel system enabling it to run just as well on hydrogen as on petrol. The petrol injectors were located in the inlet pipes, as in the normal RENESIS engine, while two hydrogen injectors were added per rotor. The stated goal: to bring this brand-new technology to market within three years.
In 2004, a prototype Mazda RX-8 Hydrogen RE received approval from the Japanese Ministry of Land, Infrastructure and Transport to commence public road tests. Having received the appropriate authorisation, the RX-8 Hydrogen RE underwent an entire battery of tests which provided large quantities of information about the car’s performance with the objective of providing a vehicle for leasing to government bodies and companies.
In March 2006 – six months ahead of the originally stated deadline – the first fleet clients received their Mazda RX-8 Hydrogen RE vehicles.
Mazda RX-8 Hydrogen RE: optimised for the best possible environmental
performance
Apart from its individual badging, the RX-8 Hydrogen RE is virtually identical
to a traditional RX-8. This belies the fact that the vehicle has been
modified to reduce pollutant emissions to a minimum at all stages of the
product’s life.
The vehicle’s tyres have been optimised to reduce fuel consumption and the RENESIS hydrogen engine has been fitted with an exhaust gas recirculation (EGR) system, offering a combination of high performance and reduced exhaust NOx when burning hydrogen.
Mazda RX-8 Hydrogen RE: designed for driving enjoyment and improved performance
Public road tests of the first 2004 RX-8 Hydrogen prototype have yielded
a wealth of useful information for the current version. It differs from
its predecessor in a number of respects:
* Automatic gearbox: the prototype was equipped with a 5-speed manual gearbox. For even greater driving pleasure, particularly in urban traffic conditions, the new version of the RX-8 Hydrogen RE is fitted with a 4-speed automatic gearbox with steering wheel shift paddles.
* Larger hydrogen tanks for longer driving range: with their higher capacity (110 litres), the vehicle’s range in hydrogen mode has been increased to approx. 100 km, despite the added fuel consumption introduced by the automatic gearbox.
* Fuel switching ‘on the fly’: a (rotor-shaped) switch on the dashboard enables the driver to switch from hydrogen to petrol while driving. The switch illuminates in blue when the car is running on hydrogen.
* New instrument layout: in the first version of the RX-8 Hydrogen RE, the hydrogen gauge, fuel mode indicator and warning lights were located in the centre of the dashboard. They have now been incorporated into the instrument panel.
Mazda RX-8 Hydrogen RE: already in service with corporate and local governmental
vehicle fleets in Japan
A world first: the Mazda RX-8 Hydrogen RE is the first hydrogen internal
combustion passenger car supplied for lease. Idemitsu Kosan Co. Ltd. in
Tokyo and Iwatani International Corporation in Osaka were the first two
companies to take this pioneering step, following Hiroshima City and Prefecture.
The lease price for these Mazda RX-8 Hydrogen RE vehicles is set at a
mere 420,000 yen per month (around 2,860 euros per month); that is, just
over half the lease price of an equivalent model with a fuel cell system.
This represents a strong basic competitive advantage to ensure the long-term
development of a hydrogen network.