The dual-fuel hydrogen-gasoline hybrid

The hydrogen rotary engine and the hybrid unit are transversely mounted at the front of the car, with the high-voltage battery located beneath the second row seats and the high-pressure hydrogen tank beside the third row seat.

The Premacy concept car has limited hydrogen range: some 100 km, or 62 miles.

Earlier prototypes of the Mazda mild hybrid system included stop-start, power assistance when the engine is at low rpm, and regenerative braking. An 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.

More details will be available at the show, which opens 19 October.

Mazda will also introduce its new Tribute hybrid, based on Ford’s Excape hybrid technology, at the show. (Earlier post.) Ford owns 33.4% of the Japanese automaker. (Both companies are working on hydrogen-fueled combustion engines as well.)

Mazda will also display its “Smart Idling Stop System” and the SENKU—a direct-injection rotary-engine hybrid based on the next-generation 13B DI direct injection gasoline rotary 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).

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.

RENESIS Hydrogen RE

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.