Will Nissan’s variable compression tech be a game-changer for gasoline engines?

By Bruce Brown August 15, 2016

mikewaters / 123RF Stock Photo

There’s a new gas engine in town. Most recent vehicle powertrain news relates to electric drive designs. However, gasoline and diesel internal combustion engines still run the vast majority of vehicles in the world, and so all the major auto companies are still developing their gas and diesel engine technologies. A brilliant case in point is a new engine design from Nissan Motor Company that changes the rules by enabling variable compression ratios, according to Reuters.

The new engine is set to launch at the Paris Motor Show in September in an Infiniti model. Nissan’s new Variable Compression-Turbo (VC-T) gasoline engine design varies the engine’s displacement and therefore its compression ratio. The company has been working on this technology for a long time, according to Ars Technica, Motor Trend discovered a Nissan patent filing for variable compression technology from 2001.

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Nissan says its new design may render the more expensive turbocharged diesel engines obsolete. The goal of the variable compression engine is to maximize power and efficiency while minimizing emissions.

The compression ratio in internal combustion engines is the measure of the difference between the maximum and minimum volume within a cylinder when the piston travels from bottom to top. If there’s 10 times as much volume when the piston is at the bottom then at the top, the compression ratio is 10:1. Lower compression ratios have more power; higher compression ratios allow greater efficiency.

The way Nissan is able to vary the new engine’s compression ratios is by changing the displacement. If you don’t let the piston travel down so far — in other words, if you give it a false bottom — the resulting compression ratio is lower. With the same engine, if you allow the piston to travel all the way to the ‘real’ bottom, the compression ratio is higher.

Nissan claims the turbocharged four-cylinder, 2-liter VC-T engine has comparable power and torque to the 3.5-liter V6 engine it is replacing, but with an average of 27 percent improved fuel economy, Reuters reported. The VC-T’s compression ratio can vary from 8:1 to 14:1.

Ars Technica quoted Roland Krueger, president of Infiniti Motor Company saying “It is a revolutionary next step in optimizing the efficiency of the internal combustion engine. This technological breakthrough delivers the power of a high-performance 2.0-liter turbo gasoline engine with a high level of efficiency at the same time.”

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