The new Premacy Hydrogen RE Hybrid is an innovative concept car combining the hydrogen rotary engine and a hybrid system. It was first showcased as a reference exhibit at the 40th Tokyo Motor Show in 2007 and is now under development to begin commercial leasing in fiscal year 2008.
While borrowing some technology from the RX-8 Hydrogen RE, such as the dual-fuel system that also enables the car to run on gasoline, this car boasts a hybrid system that substantially increases its driving range and power.
In the new Premacy Hydrogen RE Hybrid, the power unit output is increased by 40 percent compared to the RX-8 Hydrogen RE, significantly boosting acceleration and improving fuel efficiency.
The core hydrogen rotary engine has been mounted transversely, instead of the conventional longitudinal arrangement. This change, as well as reduced intake and exhaust resistance and improved combustion, resulted in high power output over a wide range of engine speeds.
With the addition of the newly-developed hybrid system mated to the hydrogen rotary engine, torque at low engine speeds, and fuel economy, have also been improved. The driving range in hydrogen fuel mode has also been extended to approximately 200 kilometers, about twice as far as the RX-8 Hydrogen RE. The hybrid system is extremely efficient in converting hydrogen combustion energy into electric energy to drive the motor.
With its high energy efficiency and excellent response, the driver can enjoy a powerful ride with low running costs, while synchronization of the accelerator, rotary engine and electric motor provides a direct feel.
Additionally, Mazda's dual-fuel system, which is highly regarded by RX-8 Hydrogen RE customers because it allows the driver to switch to gasoline fuel, also features on the Premacy HRE Hybrid to maximize convenience.
The new Premacy Hydrogen RE Hybrid is an innovative hydrogen rotary engine vehicle that promotes eco-friendly Zoom-Zoom driving, which is what Mazda has targeted since beginning development of the RX-8 Hydrogen RE.
The main components of the hybrid system are a hydrogen rotary engine, a generator, an inverter, an electric motor and a battery. Power generation, charging and discharging are optimized in accordance with driving conditions.
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Start up: battery power Steady running: Driven by hydrogen rotary engine and generator Acceleration: Driven by hydrogen rotary engine and generator + battery Deceleration: Energy is recovered by the motor when braking and when using the engine as a brake. The recovered energy replenishes the battery. Idling: The engine automatically switches off. If necessary, it will restart and charge the battery. |
 
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Features of the Hydrogen Rotary Engine (RE)
Mazda is focusing on the development of the RENESIS hydrogen rotary engine as one of the steppingstones toward the realization of a more earth-friendly and sustainable society while improving vehicles, maintaining people's interest in cars and benefiting the earth.
This hydrogen engine takes advantage of the characteristics of Mazda's unique rotary engine and maintains a natural driving feeling unique to internal combustion engines. It also achieves excellent environmental performance with zero CO2 emissions.
Further, the hydrogen engine ensures performance and reliability equal to that of a gasoline engine. Since the gasoline version requires only a few design changes to allow it to operate on hydrogen, hydrogen-fueled rotary engine vehicles can be realized at low cost. In addition, because the dual-fuel system allows the engine to run on both hydrogen and gasoline, it is highly convenient for long-distance journeys and trips to areas with no hydrogen fuel supply.
The RENESIS hydrogen rotary engine employs direct injection, with electronically-controlled hydrogen gas injectors. This system draws in air from a side port and injects hydrogen directly into the intake chamber with an electronically-controlled hydrogen gas injector installed on the top of the rotor housing. The technology illustrated below takes full advantage of the benefits of the rotary engine in achieving hydrogen combustion.
- RE features suited to hydrogen combustion
In the practical application of hydrogen internal combustion engines, avoidance of so-called backfiring (premature ignition) is a major issue. Backfiring is ignition caused by the fuel coming in contact with hot engine parts during the intake process. In reciprocal engines, the intake, compression, combustion and exhaust processes take place in the same location—within the cylinders. As a result, the ignition plugs and exhaust valves reach a high temperature due to the heat of combustion and the intake process becomes prone to backfiring.
In contrast, the RE structure has no intake and exhaust valves, and the low-temperature intake chamber and high-temperature combustion chamber are separated. This allows good combustion and helps avoid backfiring.
Further, the RE encourages thorough mixing of hydrogen and air since the flow of the air-fuel mixture is stronger and the duration of the intake process is longer than in reciprocal engines.
- Combined use of direct injection and premixing
Aiming to achieve a high output in hydrogen fuel mode, a direct injection system is applied by installing an electronically-controlled hydrogen gas injector on the top of the rotor housing. Structurally, the RE has considerable freedom of injector layout, so it is well suited to direct injection.
Further, a gas injector for premixing is installed on the intake pipe enabling the combined use of direct injection and premixing, depending on driving conditions. This produces optimal hydrogen combustion.
When in the gasoline fuel mode, fuel is supplied from the same gasoline injector as in the standard gasoline engine.
- Adoption of lean burn and EGR
Lean burn and exhaust gas recirculation (EGR) are adopted to reduce nitrogen oxide (NOx) emissions. NOx is primarily reduced by lean burn at low engine speeds, and by EGR and a three-way catalyst at high engine speeds. The three-way catalyst is the same as the system used with the standard gasoline engine.
Optimal and appropriate use of lean burn and EGR satisfies both goals of high output and low emissions. The volume of NOx emissions is about 90 percent reduced from the 2005 reference level.
- Dual Fuel System
When the system runs out of hydrogen fuel, it automatically switches to gasoline fuel. For increased convenience, the driver can also manually shift the fuel from hydrogen to gasoline at the touch of a button.
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