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Mazda to Lease Rotary H2ICE, Add Mild Hybrid Support

Mazda plans to start to lease bi-fuel vehicles using rotary engines powered by hydrogen or gasoline during the next two years.

Mazda started working with hydrogen-powered vehicles in 1991, and has developed seven such models since then. The company highlighted its latest H2 effort, the RX-8 Hydrogen Rotary Engine (RE) sports concept car, at this year’s North American International Auto Show (NAIAS) after introducing it at the Tokyo Motor Show in 2003. The RX-8 Hydrogen RE features a dual fuel version of Mazda’s new award-winning RENESIS rotary combustion engine.

Rotary combustion engines are less fuel-efficient than conventional reciprocating engines, but they produce higher power output for a given displacement volume. In other words, the same size (displacement) engine produces more power but at the cost of worse fuel economy (and higher emissions). These combustion characteristics, combined with the nature of hydrogen, have also led many for some time have to consider the rotary combustion engine as a good platform for a hydrogen combustion engine (H2ICE)—hence Mazda’s work on them for some 15 years.

Because it offers separate chambers for intake and combustion, the rotary engine is ideal for burning hydrogen without the backfiring that can occur in a traditional piston engine. The separate induction chamber also provides a safer temperature for fitting the dual hydrogen injectors with their rubber seals, which are susceptible to the high temperatures encountered in a conventional reciprocating piston engine. Furthermore, the rotary works well with a lean fuel mixture.

With the basic gasoline-fueled RENESIS engine, also introduced in 2003, Mazda set out to improve fuel economy and to reduce emissions, while retaining the power. The engineers made a number of changes (more detail on that here), including:

  • Changing the location, size, number and timing of the intake and exhaust ports.

  • Reducing the weight of the rotors.

  • Designing new fuel injectors for improved fuel atomization, allowing the RENESIS to run on a leaner fuel mixture than conventional rotary engines from the low to the high-rev range. When idling, the RENESIS consumes 40% less fuel than the latest production rotary engine.

  • Reducing hydrocarbon emissions by recycling exhaust gas in the subsequent combustion cycle.


The RENESIS Hydrogen RE incorporates an electronically controlled hydrogen gas injector system. The system draws air from the side port during the intake cycle and uses dual hydrogen injectors in each of the engine’s twin rotor housings to directly inject hydrogen into the intake chambers. (Diagram at right, Click to enlarge.)

Also helping to maximize the benefits of the rotary engine in hydrogen combustion mode, the RENESIS Hydrogen RE features adequate space for the installation of two injectors per intake chamber. Because hydrogen has an extremely low density, a much greater injection volume is required compared with gasoline, thus demanding the use of more than one injector.

Typically, this can be difficult to achieve with a conventional reciprocating piston engine because of the structural constraints that prevent mounting injectors in the combustion chamber. However, with its twin hydrogen injectors, the RENESIS Hydrogen RE is both practical and able to deliver sufficient volume.

Mazda RENESIS Hydrogen Rotary Engine
Maximum power154 kW (210 hp)
@ 7200 rpm
81 kW (110 hp)
@ 7200 rpm
Maximum torque222 Nm
@ 5000 rpm
120 Nm
@ 5000 rpm

For future versions of the rotary hydrogen cars, Mazda plans to incorporate the RENESIS hydrogen rotary engine with the emerging Mazda Hybrid System and an electric-motor-assisted turbocharger to enhance efficiency as well as the driving experience (zoom zoom).


The Mazda Hybrid System is a mild hybrid solution consisting of an electric motor, an inverter and a 144V battery. The system features include stop-start, power assistance when the engine is at low rpm, and regenerative braking. The electric-motor-assist turbocharger system is used at low rpm, beginning at approximately 1000 rpm. Here, an electric motor assists the turbocharger to increase induction efficiency. At high rpm, the turbocharger is driven in a traditional fashion, by the flow of exhaust gas alone.

Mazda may have this on demonstration in the upcoming Tokyo Motor Show in a few weeks.


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