Mazda Hydrogen Rotary Hybrid Premacy and RX-8 2009 Review

Mazda Hydrogen concept cars: HRE Hybrid Premacy & HRE RX-8

Not so much
>> Too much noise (Premacy)
>> Too little power (RX-8)
>> Too far off

Overall rating: 2.5/5.0
Powertrain/Chassis: 3.0/5.0
Packaging and Practicality: 2.0/5.0
Behind the wheel: 2.0/5.0
X-factor: 2.5/5.0

About our ratings

If not already, Mazda's loyalty to rotary power has paid off for inspiring a unique formula in enviro-conscious motoring. Arguably Japan's fourth-running automaker has been late to the green car game and these days everybody has some planet-saving offering.

Enter HRE technology. HRE stands for hydrogen rotary engine, utilising Mazda's existing rotary powerplant from the RX-8 and hydrogen fuel to offer near-zero emission motoring. Cars using hydrogen fuel (whether it's burned or converted in a fuel cell) emit only water vapour. Serendipitously for Mazda, rotaries burn hydrogen fuel more efficiently than conventional reciprocating engines.

Due to its flammability, when burned in a 'normal' engine, hydrogen is susceptible to pre-ignition -- usually emanated from the 'hotspot' created by the spark-plug. In rotary engines this tendency is avoided -- the design of the rotary means the combustion chamber is separated from the intake chamber. In short, abnormal combustion is less likely in a rotary than a hydrogen-fuelled conventional engine.

Normally driving the rear wheels of Mazda's RX-8, the rotary engine is mounted transversely in a front-engine, front-wheel drive layout in the HRE Premacy (known as Mazda5 in some markets). The HRE Hybrid's generator, motor and inverter all fit in the engine bay of the two-box peoplemover.

The RX8 HRE meantime retains its traditional layout and has been undergoing testing in Norway since 2008. There it is a relatively high-profile proponent of the country's provision of hydrogen fuelling infrastructure to road users, known as the HyNor highway project. A handful of HRE-powered RX-8 cars are running about Tokyo, which currently has most of Japan's hydrogen stations.

In complete contrast to the high-revving, petrol-only RX-8 the HRE is good for just 80kW and its delivery is slow and metered; missing out on a torque 'sweet spot'.

HRE-powered RX-8s have a driving range of 100km on hydrogen only. In support, a dual-fuel system allows the engine to run on either hydrogen or petrol, and automatically switches to petrol after the onboard load of hydrogen is spent.

The Premacy HRE takes it a step further with an electric motor to promote efficiency via a series hybrid layout. Rather than power the wheels directly, the HRE is coupled to a generator and provides power to an electric motor which drives the front wheels. A 40kW lithium ion battery pack meters current as required.

Mazda told us the company used the series layout because it allows better adaptation to "cleverer components" down the road, which indicates at least a mild or petrol-electric hybrid model will be made available sometime...

In hybrid form, the HRE is rated at 110kW with max torque at 350Nm, and offers 200km driving range running on hydrogen only. The Premacy also uses a dual-fuel system.

Switching from hydrogen to petrol can be done on the run via a dash-mounted switch, while the reverse requires a stationary position, such as waiting at intersection lights. Simple.

Despite its size and extra carrying capability the Premacy HRE doesn't suffer in the response stakes like the RX-8 version, but the hybrid drivetrain adds noise. A lot of noise.

We asked an engineer on board what Mazda execs thought about the noisy operation and he admitted they weren't happy. The excessive noise is apparently due to the electric motor components, and the company has ways to fix to it, he assured.

Normally with three-row accommodation, the Premacy's rearmost space is filled with a large tank for the compressed hydrogen gas which is stored at approximately 5000psi (35MPa). This installation reduces the peoplemover to a five-seater. And forget cargo accommodation, as the tank takes up all but a slim space near the tailgate. Mazda says 230 litres luggage space is still available but it's over the tank so the design needs to incorporate a rear parcel shelf.

Enviro-conscious efforts don't end under the bonnet (or in the boot). Interior-wise, the Premacy shows off Mazda's development in trims using recycled and recyclable materials, and plant fibres.

The seats are trimmed in a smart-looking, durable weave cloth and various dash, console and door components were made using what Mazda terms 'Biotechmaterial'. The trim materials resemble any other type of high quality plastic or cloth.

Mazda intends furthering development in biomaterials for increased use elsewhere in its range, so expect to see the clever cloth and plastic trim in the near future in production models. The Japanese company claims it was the first automaker to develop biomaterials, introducing the original bioplastic, consisting largely of corn, in 2006 and fire-retardant biofabric in 2007. Research for the materials began in 2004.

The Premacy HRE looks like the usual version but the hydrogen-fuelled model is easily identified by its two fuel-filler flaps in either side of the car's rear guards.

We drove the RX-8 and Premacy in a short loop on Yokohama roads. As mentioned the dual-fuel system is easy to operate and the Premacy's dash features a gauge that informs the driver whether energy is being returned to the car's lithium-ion battery, however, designers have left out a consumption readout -- information we were most curious to learn.

Comparing the fuel tank gauge from start to finish, and after drive rotation of a dozen journos the RX-8 and Premacy were almost empty, having spent most of the trips running on hydrogen only. We'd calculate the mileage covered all-up in the RX8 HRE to be close to Mazda's claimed 100km driving range.

The HRE Premacy has more power than the RX-8 version and its performance advantage is obvious behind the wheel. Mazda only had auto-equipped RX-8 HRE models to trial in Tokyo, whereas in Norway the cars are all manual-equipped and, engineers told us, much more responsive.

Apart from the noise, the Premacy is a smooth operator. It will take off using the electric motor alone, like the Toyota Prius, and when the IC engine is required to provide more electric power start-up is fuss-free and noticeable only via a slight tremor in the powertrain.

The Premacy/Mazda 5's usual auto transmission is replaced with a single-ratio version, which made driving a breeze... If a little appliance-like.

Mazda says the company's green motoring objectives must include the signature 'Zoom-Zoom' driving experience but in the case of these early examples, there's not much zooming going on.

And while hydrogen might be one of the greenest solutions yet, for now the HRE models suffer similar infrastructure issues as electric cars. Still, Mazda argues hydrogen filling stations are more viable than plug-in options, and using hydrogen is cleaner.

There's a long way to go before we'll be offered hydrogen-fuelled production cars from Mazda, however. At least, the HRE experience has encouraged Mazda to (finally) take the hybrid route.

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