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 Mazda 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.

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