How does a hydrogen-powered RX-8 work – and no technobabble please...
It's simple. The RX-8's rotary engine can run on either petrol or hydrogen, which is stored in liquid form in a second fuel tank. The engine is fitted with a second set of hydrogen injectors that are situated above the intake chamber, and the driver has a switch in the cabin for selecting the fuel of choice. A rotary engine is far better suited to burning hydrogen than a conventional piston engine – which goes some way to explaining Mazda's persistence with the rotary engine when all other manufacturers left it behind.
Why is a rotary engine better suited to hydrogen?
Hydrogen, as you know, is more than a touch volatile – its 'flame front' – the point at which it bursts into flame – is almost seven times that of unleaded petrol. Which means keeping it away from 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. Indeed, in converting it to hydrogen, the only changes Mazda's engineers made to the RX-8's twin rotor engine are the hydrogen injectors, a gas recirculating system to further boost combustion efficiency and a second engine management system to look after the engine when it’s running on hydrogen.
And just how green is this white car?
Well, when it's running on hydrogen, the only thing coming out the exhaust is water vapour. So its green credentials are impeccable. Of course, you also have to take into account the environmental impact of producing the hydrogen in the first place, but even still it's a mighty impressive bit of tomorrow's-motoring-today kit. And it makes our current crop of green cars like the Toyota Prius and Honda Civic IMA look terribly old hat. Talk to Akihiro Kashiwagi, Mazda's Mr Hydrogen, and 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 Mazda will go green.
Excellent, when can I buy one?
Not yet, although Mazda is leasing the RX-8 RE in Japan for around £1900 a month. But it will be a good while before you can wander into a showroom filled with hydrogen-burning Mazdas. 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. CAR Online 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? We know Mazda is no chicken.
Is it exciting to drive?
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. In the cabin, the only 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. The driving experience is exactly the same too, but with less urgency – not helped either by the Japanese-spec four-speed slushbox. 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 107bhp, while torque drops from 162lb ft to 103lb ft. Not ideal, when the RX-8 has always been crying out for more torque.
So it's slow. How disappointing…
Yes. And not very practical either. The hydrogen is stored in liquid form at a very high 350bar pressure, in a 24 gallon tubular aluminium and carbonfibre tank. Which unfortunately takes up the entire boot, and you only get a 60-mile range out of it, too.
The RX-8 RE is a lot like an RX-8, but slower, less practical and it needs filling up twice a day. But don’t be deterred by the RX-8’s looks-fast-goes-slow character - this is the future we are driving here, remember. It is motoring's Holy Grail – imagine clean, conscience-free motoring, with nothing but water coming out your car’s exhaust pipe. One day, all cars will be like this. It'll just take a lot of work to get us there...