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A3’s Miller Cycle Engine Shows How Audi Makes A Car Unique

Audi has given the A3 a new personality. More powerful, the 2017 A3 features a Miller cycle engine and seven-speed, dual-clutch gearbox. City mileage is up as are horsepower and torque.
Posted: October 28, 2016 - 12:41AM
Author: Marc Stern

Although this may sound like an advertising come-on, it isn’t. In a moment, it will become apparent. So, here it goes: if you are interested in owning a piece of automotive uniqueness, consider the 2017 Audi A3. It is the only model that of which we have heard that offers the Miller combustion cycle engine.

Patented in 1957, the Miller is a variant of the traditional Otto cycle – four-stroke – engine that has powered vehicles since the first Mercedes-Benz drove on the roads of Germany 130 years ago. The Otto cycle engine features four distinct strokes – intake, compression, power and exhaust. The Miller combustion cycle adds an extra stroke through some clever engineering.

Miller Cycle Described

The Miller cycle keeps the intake valve open for a bit longer than normal to achieve the additional stroke. Typically on the intake stroke, the cylinder draws down to bottom dead center and then starts the compression cycle. On starting, the valve closes so that full compression is obtained before the spark is ignited (or the diesel fuel ignites).

On the Miller cycle, the intake cycle draws the fuel-air charge into the cylinder, as usual. However, instead of closing the intake valve remains open for a bit longer, even as the compression stroke begins. What happens is that because the Miller cycle is usually paired with either turbocharging or supercharging. The turbo or supercharger set up a positive or reverse pressure system so that the fuel-air charge isn’t expelled from the cylinder as the compression stroke starts. The positive pressure portion adds more fuel-air charge to the cylinder for the compression stroke to act on. The valve shuts after about a-fifth of the way into the compression stroke. This is the fifth stroke available on the Miller cycle.

The Miller cycle works with either two- or four-stroke engines and with gasoline or diesel powerplants. It offers more specific power without a mileage tradeoff as the 2017 A3’s mileage is up two mpg – city -- over 2016. Highway mileage is the same at 35 mpg.

In 2016, Audi paired a 1.8-liter four and six-gear dual-clutch gearbox with the front-drive versions of the A3. In 2017, the 2.0-liter Miller cycle four is paired with a seven-speed, dual-clutch gearbox. Power is up to 186 horsepower and 221 pounds-feet of torque, compared to 170 horsepower and 200 pounds-feet on the 2016 A3.

Audi’s Former Best-Seller

The A3 was Audi’s best-selling sedan model last year. Audi sold nearly 36,000 units, beating out the A4 sedan, for the first time. It also outsold the Mercedes CLA sedan. This year, it is a different story at sedan sales have tanked thanks to the crazy demand for crossovers and SUVs. Luxury sedan sales are also off.

Whether it is a wise move or not, pricing is also up for 2017. Entry-level front-drive A3s come with a suggested retail of $32,150. The sedan model starts at $38,550. In 2016, entry-level 2016s had suggested retail pricing of $30,825.

Source: Automotive News