JUN 14

Mazda's new Miller-cycle engine will power the new Mazda2, (named the Demio for the US).

Mazda Motor Corporation has developed a new, naturally aspirated 1.3-liter Miller-cycle gasoline engine, which will power the all-new Mazda2 when it goes on sale in Japan in July 2007. The Miller-cycle engine usually depends on having a really big super charger but Mazda has figured out a way to use the Miller-cycle on a normally aspirated engine.

The Miller-cycle is a fancy name for a simple change in the valve timing for an engine.  It allows the compression stroke of a 4-cycle engine to begin later than typical. Less power wasted on compression means more efficiency. 

In combination with Mazda’s first continuously variable transmission (CVT), the engine enables the new Mazda2 to offer 54 mpg US, an improvement of approximately 20% compared with Mazda’s current 1.3-liter engine model.

In addition to the new powertrain, the all-new Mazda2 has been made approximately 220 lb lighter than its predecessor through a strict weight reduction program, which results in quick handling to go along with the significantly improved fuel economy.

I can see no reason that the Miller-cycle engine can't be used to improve the efficiency of larger engines and/or engines in hybrids.  I wonder what the carbon footprint of a Miller-cycle hybrid car running on cellulosic ethanol would be?

Comments (4)

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written by Michael Pereckas, June 15, 2007

Miller cycle is essentially the same as the Atkinson cycle used by Toyota's hybrids. Normally they are described as the same concept except that with a supercharger it's called Miller, without, Atkinson, so it's not clear how a non-supercharged Miller cycle is supposed to differ from Atkinson. Impressive gas mileage, but I'm sure the US version (if there was to be one) would have five times the power and one fifth the efficiency, unless there are some big changes in the automotive market here.

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15 % + 5 % = 20%
written by Sandman, June 15, 2007

As I have read a Miller-cycle engine leaves the intake valve open during part of the compression stroke, so that the engine is compressing against the pressure of the supercharger rather than the pressure of the cylinder walls. The effect is increased efficiency, at a level of about 15 percent. In the case of the Demio, additional effeciency in the Mazda oxygen sensor at 5 percent make it overall in total 20 percent... As amazing as the car itself...

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But what about the power?
written by Hun Boon, June 15, 2007

No mention of the power figures there, but I'm sure there's a power loss.

Less power, more economical. Nothing surprising there, which explains why it needed to be accompanied by a weight reduction programme.

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More economical = more power.. not less
written by Neale, June 16, 2007

I doubt it'll be less powerful as Hun suggests.

The simple facts are that less power does not make a car more economical. A smaller displacement does, as it reduces the weight of the pistons and/or the distance the pistons get pushed back and forth.

The simple fact is that if the car is now doing 20% more mpg at the same constant speed with the same shaped body, then it's become more economical at producing the same amount of power. Yes.. around town, the lighter weight will help with stop start driving, but not so much as to save 20% on fuel (otherwise a Lotus Elise would do about 60mpg, not 45mpg).

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