While significant attention is being paid to battery-electric and hydrogen fuel-cell powertrains, carmakers are still trying to wring more efficiency out of internal-combustion engines.

Now, Infiniti is poised to introduce a technology into production cars that was previously sidelined by somewhat easier fixes.

The Nissan luxury brand is set to launch a variable-compression engine, which has the ability to alter its compression ratio.

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That's the volume of the combustion chamber when a piston is at the bottom of its stroke, compared to when a piston is at the top of its stroke—something that is fixed in conventional engines.

Called the VC-T (Variable Compression - Turbo) the engine has the ability to effectively shrink its displacement under low loads, allowing it to use less fuel.

When more power is needed, the engine alters its configuration to effect a larger displacement.

Infiniti VC-T (Variable Compression-Turbocharged) engine

Infiniti VC-T (Variable Compression-Turbocharged) engine

The first VC-T engine will be a turbocharged inline-4 that Infiniti claims will offer the performance of a naturally-aspirated V-6.

Its compression ratio can vary anywhere from 8:1 for maximum performance, to 14:1 for maximum efficiency.

The lower 8:1 compression ratio enables higher boost pressure from the turbocharger without the risk of detonation or engine knock.

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Settings are adjusted automatically depending on driving conditions, without any involvement from the driver.

Compression ratio is changed using a rotating apparatus called the Harmonic Drive.

It uses mechanical linkages to alter the connection between a piston and the crankshaft, adjusting the maximum height the piston can reach within the cylinder, and thus the compression ratio.

Infiniti VC-T (Variable Compression-Turbocharged) engine

Infiniti VC-T (Variable Compression-Turbocharged) engine

Infiniti plans to begin rolling out the VC-T engine in 2018, with more details to come at the 2016 Paris Auto Show.

Several carmakers—including General Motors, Mercedes-Benz, and Saab—have experimented with variable-compression engines, but Infiniti is likely the first to put one into production.

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The Mercedes-Benz F700 concept that debuted at the 2007 Frankfurt Motor Show boasted a variable-compression engine called the "DiesOtto."

At the time, Mercedes said the tiny 1.8-liter twin-turbocharged 4-cylinder engine could offer the performance of a 3.5-liter, V-6.

2007 Mercedes-Benz F700 Concept

2007 Mercedes-Benz F700 Concept

The German carmaker was confident that variable-compression technology would ensure the long-term survival of internal-combustion engines.

Since then, though carmakers have largely pushed aside variable-compression engines in favor of less-complex technologies, like direct injection, downsized turbocharged engines, and more-efficient transmission designs.

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But the need to meet ever-stricter fuel-economy standards means carmakers will likely turn to ever more complex technologies for improving efficiency.

Yet a variable-compression engine likely still won't deliver the efficiency of an all-electric car like, say, Infiniti parent Nissan's Leaf.


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