Mazda2 - Demio: 2008 JDM Version Gets New Naturally-Aspirated 1.3-liter Miller-cycle Engine

Rotar powered engines isn’t the only abandoned by others technology that Mazda continues to invest in. The Japanese firm also believes in the Miller-cycle tech developing a brand-new, naturally aspirated MZR 1.3-liter Miller-cycle engine for the 2008 Demio (known as the Mazda2 in overseas markets) when it goes on sale in Japan in July 2007. According to Mazda, the Miller-cycle engine powered Demio will be combined the firm’s first continuously variable transmission (CVT), achieving an avg. fuel consumption figure of 4.3 liters/100 -54.7 mpg (US). That’s a 20% improvement over the 5.2 liters/100 km - 45.2 mpg rating of the current model. As you can see in the press release that follows, Mazda hasn’t given out any power or performance figures.

But what exactly is a Miller-cycle engine? First of all, the name for the Miller-cycle engine was invented by an American engineer, Ralph Miller who patented his version of the forced induction Otto-cycle petrol engine in the 1940s. A traditional Otto cycle petrol engine uses four "strokes", of which two can be considered "high power" – the compression stroke (high power consumption) and power stroke (high power production). In the Miller cycle, the intake valve is left open longer than it would be in an Otto cycle engine. In effect, the compression stroke is two discrete cycles: the initial portion when the intake valve is open and final portion when the intake valve is closed

This two-stage intake stroke creates the so called "fifth" cycle that the Miller cycle introduces. As the piston initially moves upwards in what is traditionally the compression stroke, the charge is partially expelled back out the still-open intake valve. Typically this loss of charge air would result in a loss of power. However, in the Miller cycle, this is compensated for by the use of a supercharger. The supercharger typically will need to be of the positive displacement type due its ability to produce boost at relatively low engine speeds. Otherwise, low-rpm torque will suffer. That does raise a few questions on the Demio’s naturally aspirated 1.3-liter Miller-cycle engine doesn’t it? (Miller-cycle engine info via: Wikipedia)

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PRESS RELEASE: Mazda Develops New Naturally-Aspirated MZR 1.3L Miller-cycle Engine

- The new MZR 1.3L engine powers the all-new Mazda Demio to achieve a fuel economy of 23.0 km/L and qualify for Japan's Green Tax exemptions -

HIROSHIMA, Japan—Mazda Motor Corporation has developed a new, naturally aspirated MZR 1.3L Miller-cycle engine, which will power the all-new Demio (known as the all-new Mazda2 in overseas markets) when it goes on sale in Japan in July 2007. In combination with Mazda’s first continuously variable transmission (CVT), the engine will assist the new Demio to achieve a 10-15 mode fuel economy of 23.0 km/L, an improvement of approximately 20 percent over the 19.2 km/L rating of the current model.

Newly developed from the current MZR 1.3L DOHC aluminum engine, the naturally-aspirated MZR 1.3L Miller-cycle engine employs delayed closing of the intake valves in order to reduce pumping losses and improve thermal efficiency through a higher expansion ratio. Intake valve timing is optimized by the Sequential Valve Timing System to provide improved fuel efficiency over the current MZR 1.3L engine when cruising and accelerating. In conjunction with the CVT, which transfers torque at low speeds without power loss and eliminates gear-shift shock, the setup achieves excellent fuel efficiency as well as a smooth and exhilarating ride.

In addition to this new, highly efficient powertrain, the all-new Demio has been made approximately 100 kg lighter than its predecessor through weight reduction techniques, which have resulted in nimble handling and significantly improved fuel economy.

The Demio model with the naturally aspirated MZR 1.3L Miller-cycle engine combined with the CVT transmission achieves a fuel economy that is rated as 20 percent or better than the level specified by Japan’s 2010 fuel economy standards. Exhaust emissions are also at least 75 percent lower than 2005 standards, which conforms to Japan’s Super Ultra-Low Emissions Vehicle (SU-LEV) standard and qualifies the Demio for Green Tax exemptions.

Through its Sustainable Zoom-Zoom plan that was announced in March 2007, Mazda declared its intention to pursue the harmony felt between driving pleasure and environmental and safety features, and its quest for an advanced Zoom-Zoom world. This includes the ongoing desire to create captivating design, to provide our customers with continual driving pleasure and to develop improved safety and environmental technologies.