Infiniti (partially) explains the biggest recent revolution in combustion engines: the VC-Turbo

The Paris Motor Show has presented lots of new cars, some of which we still have not written about due to the little time we had. But the most important presentation at the French event will not be easily visible. Not if you don’t pop the hood of the car Infiniti will choose to introduce the VC-Turbo engine. VC stands for Variable Compression, something that has been presented as a concept many times, but never as a production-ready engine. The VC-Turbo is exactly that.

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The new 2.0-liter engine may look quite ordinary, but it is far from that. Especially if you pay careful attention to an unusual element right behind the intercooler in the image above. It is the piece that allows the compression ratio to be variable. It is called Harmonic Drive and its main component is rather simple: a solenoid. It is this electric part that moves the control shaft, as we have already shown in our first article about this engineering marvel.

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Infiniti has made a giant leap in the technology when it imagined a different and much better solution than all other concepts so far. Most of them tried to create a moving cylinder head, with all the technical challenges (and prohibitive costs) it could arise. This is why the idea was almost deemed as impossible to manufacture in high scale. The Japanese carmaker made it possible by interfering with parts that move by nature. And the idea is so simple many engineers must have struck their heads and asked: “Why haven’t I thought of that?”. The video below shows how the engine works in the best way possible.

It is just a pity that, in an effort to be easy to understand, the video commits some mistakes. A lower compression ratio does not mean per se that the engine is more powerful. In fact, that is precisely the opposite. Lower compression ratio engines are known to be more robust, even if much less powerful than engines that endure higher compression ratios. If you look into Infiniti’s press release, you will not find any relevant information to explain that, but the company has been kind enough to provide infographics that help us to explain things in a more accurate way.

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Infiniti manages to get more power with lower compression ratios because it probably works with more turbo pressure in these situations. A lower compression ratio helps the engine avoid knocking under high demand. And the luxury division of Nissan also does that because it injects more fuel on the combustion chamber by using two kinds of fuel injection: multi-point and direct injection. Both of them are probably used in heavy loads. Volkswagen uses just the direct injection, which it names FSI (Fuel Stratified Injection), in order to work with lean mixtures with no risk of detonation. Infiniti probably uses only direct injection for partial or light loads, when a leaner mixture of fuel and air are interesting for a more fuel-efficient ride. It is very interesting that the VC-Turbo shares some characteristics with the new Fiat GSE engine, such as the integrated exhaust manifold and the ability to change its cycle from pure Otto into a Miller/Atkinson cycle, for better fuel consumption. This may well be a trend in engine building.

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This extra power requires some actions in order to ensure the engine will be as reliable as a regular one. So the VC-Turbo has a variable displacement oil pump, which can increase oil pressure as the engine speed increases, and a multi-way control valve for the cooling system. This is because the VC-Turbo has a high specific power. Infiniti discloses the goal in another infographic.

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The company’s objective is to reach 200 kW and amazing 390 Nm with the new engine. And to start selling it in 2018. If you compare it to the one applied to the Mercedes-AMG A 45, which is also a 2.0-liter powerplant, but delivers 280 kW and 475 Nm, that may not seem such an achievement. But Infiniti has not released fuel consumption figures, which must be much better than that of the Mercedes mill. Infiniti says it will be 27% better than that of a regular V6 engine. The model that is more fuel-efficient with a simple V6 on Infiniti’s lineup is the Q50, with 23 mpg, or 10.2 l/100 km in combined cycle. A 27% improvement would lead to a fuel consumption of 29.4 mpg, or 8 l/100 km. And this is just the start for the VC-Turbo. It may eventually deliver much more power and torque in “hotter” versions.

Infiniti will probably replace its V6 engines with its new creation. After all, the company claims it is 20 db more silent than a common 4-cylinder and requires no balance shafts. But it can be in the path of achieving something much bigger. One of the only aspects of combustion that could not vary was the compression ratio. Now that this obstacle has been successfully overcome, there is a myriad of new possibilities ahead, at least for the Japanese carmaker. It can develop, for example, the most efficient flex-fuel engine in the world, with the ideal compression ratio for ethanol, ranging from 8:1 up to 14:1. It can adjust to any fuel quality, from a very low octane gasoline to the highest one available. It can run on any fuel, just like the Lotus Omnivore.

Whatever Infiniti decides to do with the VC-Turbo, which took 20 years of research to emerge, the future looks promising. For its competitors, there is little left to do, since the idea is patented. We see only two possibilities: or they will try to develop something similar in much less time or they will speed up the adoption of electric engines (if battery technology helps them on that). In the meantime, Infiniti will probably become the king of ICE (internal combustion engines). For as long as they last under a bonnet.

Gustavo Henrique Ruffo

I have been an automotive journalist since 1998 and have worked for many important Brazilian newspapers and magazines, such as the local edition of Car and Driver and Quatro Rodas, Brazilian's biggest car magazine. I have also worked for foreign websites, such as World Car Fans and won a few journalism prizes, among them three SAE Journalism Awards and the 2017 IAM RoadSmart Safety Award. I am the author of "The Traffic Cholesterol", a book about bad drivers that you can buy at Hotmart, Google Play, Amazon and Kobo.