In automobile catalytic converters, the surface conditions of the precious metals—the catalyst materials—have a large effect on their ability to clean emissions. Conventionally, precious metal particles are adhered to a base material. However, heat from the exhaust gas causes the particles to collect together and agglomerate to form larger particles. This reduces the surface area of the precious metals and deteriorates their performance as catalysts. To counter this effect, large amounts of precious metals must be used in conventional catalytic converters. As an alternative, Mazda takes advantage of single nanotechnology to realize a unique and new catalyst structure in which precious metal particles are individually embedded into the base material.
The new catalyst has two main features.
1. It inhibits the thermal deterioration caused by the agglomeration of precious metal particles
2. It offers a significant improvement in oxygen absorption and release rates for enhanced emissions cleaning
With these features, the amount of precious metals needed to ensure the same level of effectiveness is reduced by 70 to 90 percent compared to previous products. At the same time, the performance of the catalytic converter is almost unaffected by harsh driving styles.
This technology can significantly reduce the amounts of expensive precious metals such as platinum, palladium and rhodium needed for three-way catalysts to effectively clean exhaust emissions from gasoline engines.
The key to improving fuel efficiency lies in raising an engine’s thermal efficiency. This can be done by increasing the expansion ratio. The expansion ratio is the amount of work the engine does each time the air-fuel mixture in the cylinders detonates. However, in conventional engines the expansion ratio is the same as the compression ratio, so increasing the expansion ratio will also raise the compression ratio. This is a problem because a high compression ratio causes abnormal combustion, or knocking.
The answer is the Miller-cycle engine. By delaying the closure of the intake valves, compression actually begins part way through the compression stroke, which results in a reduced compression ratio. At the same time, changing the shape of the piston crown decreases the combustion chamber minimum volume, resulting in a larger expansion ratio. In this way we can decrease the compression ratio and while increasing the expansion ratio. In other words, the Miller-cycle engine has a higher expansion ratio than compression ratio.
Mazda’s naturally-aspirated MZR 1.3L Miller-cycle engine delays the closure of the intake valves to improve the thermal efficiency (high expansion ratio). Sequential-valve timing (S-VT) is also employed to optimize intake valve timing and ensure sufficient torque for cruising and accelerating. Furthermore, the engine is mated to a continuously variable transmission (CVT) for a perfect blend of responsive acceleration, smooth gear shifts and top-class fuel economy.