From the September print issue
Ben Whitworth
Don’t be fooled by the colour. Mazda’s
advanced RX-8 Hydrogen RE may be a glossy white but it’s arguably
the greenest car on the planet.
It’s the first production-ready dual-fuel hydrogen and petrol
hybrid, and although the RX-8’s arresting shape is now a common
sight on our roads, what sits beneath the swoopy sheetmetal of this
Mazda is a glimpse of real 21st century motoring.
Akihiro Kashiwagi, Mazda’s Hydrogen RE programme manager believes
that hydrogen cars – cars that use hydrogen-fuelled combustion
engines – are the crucial step between today’s fossil-fuelled
cars and cars powered by ultra-efficient fuel cells.
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Reporter Ben Whitworth models
the latest in service station fashion, an H2 pump |
“Compared to fuel cells, hydrogen engines are likely to play a
significant role in the initial phase of the hydrogen energy society
of the future,” says Kashiwagi, who spent the last two and half
years developing the RX-8 Hydrogen RE.
“A hydrogen rotary engine 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,” adds Kashiwagi.
Mazda’s transformation of the RX-8 from petrol to a petrol-hydrogen
hybrid is a relatively straightforward one. The award-winning Renesis
twin-rotor engine is fitted with a second set of injectors for the hydrogen;
these are situated above the intake chamber. The hydrogen is stored
in liquid form in a second fuel tank – a high-pressure carbon
and aluminium cylinder that’s housed in the boot.
To further boost combustion efficiency and performance, Mazda’s
engineers installed an exhaust gas recirculating system as well as a
second powerful engine management system to look after the engine when
it’s running on hydrogen.
Mazda’s perseverance with the rotary engine – an oddly stubborn
persistence when other manufacturers left it by the wayside a long time
ago – suddenly makes a great deal of sense when viewed in the
context of hydrogen propulsion. A rotary engine is far better suited
to burning hydrogen than a traditional piston engine, because it’s
construction neatly sidesteps the problems of pre-combustion that has
plagued hydrogen-fuelled engines to date.
Hydrogen as you know, is more than a touch volatile– it’s
“flame front” – the speed at which its combustion
flame travels – is almost seven times that of unleaded petrol.
Which means keeping it away from any form of heat until actual combustion
is crucial.
Unlike a piston engine where intake and combustion occur in the same
chamber, a rotary engine has separate intake and combustion chambers,
so the temperature in the intake chamber is always going to be much
lower than in a piston engine. It’s a neat and elegant solution
that the piston engine cannot match without major structural modification
to its inlet manifold.
If you peeled off the Mazda’s garish decals, there would be little
to alert your passengers to the RX-8’s advanced propulsion system.
It may burn the same fuel as the space shuttle, but Mazda has understandably
kept the hydrogen technology in the RX-8 very low key.
Flip open the bonnet and apart from two visible hydrogen sensors that
sit on either side of the engine firewall (there’s a third hidden
in the bowels of the engine) the engine bay looks entirely normal. Only
a small outlet vent in the rear of the roof, used to expel the hydrogen
in the event of crash or burst tank, separates this from a standard
petrol RX-8.
In the cabin, the giveaways are two fuel gauges – one for hydrogen
and one for unleaded, as well as a rather neatly integrated rotary shaped
button for switching between hydrogen and petrol. Hold down the blue
button for a two seconds and the engine will switch from one fuel to
the other. And the engine will start on either fuel, so it really is
a twist-and-go car.
Unfortunately, when the RX-8 is running on hydrogen, there’s not
a great deal of go. Despite its volatility, hydrogen releases less energy
at equivalent volumes than petrol because it has a lower density than
petrol. This impacts on performance – power drops from 192bhp
(in the low-power petrol version) to a very modest 107bhp, while torque
drops from 162lb ft to 103lb ft.
You can feel it on the go – if you switch from hydrogen to petrol
at a steady speed, the car leaps forward and bristles with acceleration
as all that extra petrol-derived muscle arrives. There’s talk
of a turbocharged hydrogen engine to boost output. “It’s
well within the realms of possibility – we aren’t looking
at turbo technology at the moment, but we do have a long history of
turbo rotary engines,” says Kashiwagi.
Hydrogen’s density also impacts on the RX-8’s range. Despite
being stored in liquid form at a very high 350bar pressure in that large
24-gallon tank, the RX-8’s hydrogen range is a mere 60 miles.
And that tank takes up the whole of the boot space. Hardly ideal.
|
The down side: Open the
boot to put your bags in and you find Mazda has got there first |
But some perspective here – these are very early days, and don’t
forget, when it’s running on hydrogen, the only gas coming out
the Mazda’s exhaust is water vapour – there’s no CO2
and exceptionally low levels of NOx nitrogen oxides.
So it’s green credentials are impeccable – and it makes
the current crop of green cars such as the Toyota Prius and Honda Civic
IMA look terribly old hat.
Of course, you also have to take into account the environmental impact
of producing the hydrogen in the first place – and that’s
a headache-inducing subject in itself – but even still it’s
a mighty impressive bit of tomorrow’s-motoring-today.
Hold onto your chequebook though – you won’t be able to
buy one for some time. The problem is that although Mazda could start
producing a hydrogen-powered RX-8 tomorrow, finding somewhere to refuel
it might be tricky because there are less than 100 hydrogen stations
in the world.
AE travelled to the Norwegian town of Stavanger for the opening of the
country’s first hydrogen fuel station, which highlighted the main
problem with hydrogen – chickens and eggs. Do car manufacturers
wait until energy suppliers create a comprehensive network of hydrogen
fuel stations, or do the manufacturers start producing hydrogen cars
and wait for suppliers to respond to customer demand?
At least we know Mazda is no chicken. And it’s already leasing
hydrogen RX-8’s in Japan for €2800 a month – half the
cost of fuel cell vehicles. So far three RX-8 Hydrogen RE models have
been leased – one to the local government offices of the Hiroshima
City and Prefecture, and the remaining pair to Japanese industrial giants
Idemitsu Kosan in Tokyo and Iwatani International Corporation in Osaka.
The RX-8 RE is Mazda’s first tentative toe-dip in the hydrogen
pool, but it is a mighty impressive one. And Akihiro Kashiwagi is full
of ideas for future hydrogen applications at Mazda. He reckons a pure
hydrogen-burning rotary-engined Mazda, complemented by a pair of small
but powerful in-hub electric engines running on captured energy lost
during braking, is the way the company will eventually go green.
Mazda’s history of hydrogen-fuelled vehicles goes back to the
HR-X of 1991, the futuristic Ken Arakawa-penned two-seater that featured
a rear-engined hydrogen-powered rotary engine. A year later came Mazda’s
fuel-cell golf cart and in 1993 a second HR-X model as well as an MX-5
roadster prototype with a hydrogen-fuelled rotary engine made their
debut. The Capella Cargo estate, unveiled in 1995, was the first hydrogen
rotary car to undergo tests on Japanese public roads, followed by the
Premacy FC-EV in 2001 and the RX-8 Hydrogen RE prototype which arrived
three years ago.
