In the face of ever-tightening emissions regulations, the world's car manufacturers are finding innovative ways to cut fuel consumption. In its quest for greater fuel efficiency, Audi has developed a four-cylinder TFSI engine that makes use of a new combustion method, resulting in what Audi claims is the most efficient two-liter gasoline engine in its class.

The combustion method used in Audi's new engine is similar to the Miller cycle, and allows the 2.0-liter turbo unit to produce 140 kW (190 hp), all the while returning a seriously impressive 5.0 L/100km (47 mpg) on the New European Drive Cycle (NEDC). The engine also produces 320 Nm (236 lb-ft) of torque, all of which will be available from just 1,450 rpm, making it perfect for surging into gaps in the traffic from low speeds.

To achieve these figures, Audi has shortened the engine's intake time by taking the crank angle and reducing it from 200 to 140 degrees. Despite the shorter intake time, the engine can still achieve optimal cylinder charges thanks to higher boost pressure on its inlet side. Under the engine's new combustion cycle, the intake valve also closes earlier than it usually would, which allows Audi to run an efficiency-boosting high compression ratio.

"Thanks to this rightsizing approach, the new engine enjoys the consumption benefits of a downsizing engine in partial load operation, while at higher loads it has the advantages of a large-displacement engine," says Stefan Knirsch, Audi's Head of Engine Development. "The result is optimal efficiency and performance characteristics across the entire engine speed range."

The new engine, which is set to debut in the next-generation A4, has also been designed to spend less time in its warm-up phase, and Audi has focused on reducing friction – something Mercedes does with its Nanoslide coating on the inside of its engines.

On top of these efficiency-driven changes to the drive cycle, the new engine is also light, weighing in at just 140 kg (308.6 lb), which should aid the new A4's handling balance as well as its fuel consumption sticker.

The engine was unveiled at the Vienna Motor Symposium, and will be in the new A4 by the end of 2015 before making its way to other model series.

Source: Audi

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