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Old 15th August 2016, 13:29   #1
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Default Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

Come September 29th at the 2016 Paris Motor Show (Mondial de l'Automobile), Nissan/Infiniti will take the wraps off it's historic VC-T (Variable Compression-Turbocharged) engine - the world's first production-ready variable compression ratio gasoline powertrain and one of the most advanced internal combustion engine technologies ever created.

Nissan's new gamechanger: VC-T engine with 'variable compression ratios'-infinitivctenginesideview.jpg

More than 20 years in the making, the all-new 2.0L VC-T engine is an inline four-cylinder turbocharged gasoline heart which, according to Nissan, "may make some of today's advanced diesel engines obsolete!"

Roland Krueger, president of Infiniti Motor Company:

Quote:
"VC-T technology is a step change for Infiniti. 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."
Nissan engineers say that the VC-T engine will have a seamless and continuously variable compression ratio anywhere between 8:1 (for high performance) and 14:1 (for excellent fuel economy) by transforming itself and seamlessly raising or lowering the height of the pistons reach, thus transforming itself according to the driving situations. The engine, which uses both port and direct injection, will switch between Atkinson and regular combustion cycles without interruption.

Nissan's new gamechanger: VC-T engine with 'variable compression ratios'-infinitivctenginediagram.jpg

Infiniti has claimed that the 2.0-liter VC-T engine will deliver more than 265 hp and 336Nm of torque developed by the 3.5-liter V-6 currently available in the Infiniti QX60 crossover, with an overall 27 percent boost in fuel efficiency.

Nissan engineers also claim that the 2.0L VC-T is cheaper to build than a Euro-VI compliant diesel engine, and also won't be a big contributor to particulate emissions in Europe when launched. They are also mulling coupling the VC-T technology to gasoline-electric hybrid systems to boost the economy and performance figures even further.

Nissan's new gamechanger: VC-T engine with 'variable compression ratios'-infinitivctengine.jpg

This revolutionary engine will make it's worldwide debut in the Infiniti QX50 crossover in 2018, and will find use in future Infiniti & Nissan models as well.

Official Press Release

Automobile Mag

Last edited by RavenAvi : 15th August 2016 at 13:34.
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Old 15th August 2016, 16:25   #2
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Default re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

When we thought the development of gasoline engines has reached it's denouement, here comes a breakthrough from nissan! Really amazed with the concept. But, I got a confusion in the understanding of the linkages system. The Multi link being the responsible part for this variable compression ratio, how is it possible for the crank shaft to stay in it's axle center(or is the axle center moving as well)? Searched for an animation of VC-T but nothing is available.
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Old 16th August 2016, 14:49   #3
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

Here's a thread about something similar from (Honda patents engine with variable piston strokes (EXlink))Honda
(There are some good videos explaining how it works)

And here's one from 11 years ago, where Saab developed something similar (Variable compression ratio engine!)

And here's two other threads for further reading:
1) Additional Strokes? (Can we add another pair of strokes to the 4 stroke?)
2) Long vs Short Strokes (Power characteristics of long and short stroke engines: Cast in stone?)
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Old 16th August 2016, 14:56   #4
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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Originally Posted by sajusherief View Post
The Multi link being the responsible part for this variable compression ratio, how is it possible for the crank shaft to stay in it's axle center(or is the axle center moving as well)? Searched for an animation of VC-T but nothing is available.
It appears the multi-link rotates around the crankshaft. If you notice in the figure titled 'Infinit VC-T engine' here : automobilemag.com, when the central shaft has moved from efficiency to power mode, the upper link is pulled down in the direction of the multi-link, which suggests the multi-link is rotary, and is likely rotating around the crankshaft. So the crankshaft remains fixed, its the mult-link rotating around it, I think.
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Old 16th August 2016, 15:11   #5
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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Originally Posted by sajusherief View Post
The Multi link being the responsible part for this variable compression ratio, how is it possible for the crank shaft to stay in it's axle center(or is the axle center moving as well)? Searched for an animation of VC-T but nothing is available.
The main bearing of the crankshaft shall be moving in horizontal direction. I mean, there will be blocks housing the main journals of the crankshaft. These blocks will be sliding horizontally (by the harmonic drive) in the cylinder block to change the offset.

If you see the picture, you will notice the difference in the offset between the two compression ratios.

Sorry for the large blank area on the image. If I had trimmed this area and zoomed the image, the resolution would have got poorer.
Attached Thumbnails
Nissan's new gamechanger: VC-T engine with 'variable compression ratios'-vc.jpg  


Last edited by Rahul Bhalgat : 16th August 2016 at 15:13.
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Old 17th August 2016, 14:45   #6
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

Wow!! So in effect does this engine kind of change the compression on its own depending whether the car needs more power or fuel efficiency while cruising? if petrol engine are going be be efficient doing this I wonder what happens when a common rail diesel does this but then Diesel engine compression is high anyway and low compression won't work so may be not
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Old 17th August 2016, 14:54   #7
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

Fancy tech! Still some time away from being released in the market, lets see how it goes reliability wise. From the pics looks like a complicated piece of engineering.

Still advantage Diesel is the energy density of the fuel which is higher than Petrol.
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Old 17th August 2016, 14:57   #8
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

The Bentley Continental GT comes with the Variable displacement Engine. In Bentley AFAIK half of the cylinders are deactivated while running slow or low load conditions.

The technology was pioneered by Alfa Romeo and Cadillac.

Infiniti has taken the technology to the next level by introducing dynamic compression ratio!
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Old 17th August 2016, 16:02   #9
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

If I recollect correctly then a thread on similar tech albeit from HONDA is present on team-bhp. So this tech is not exclusive to anyone but Nissan is first to come out with a production ready one. Would love to read about the claimed performance figures when it is made available to car reviewers.
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Old 17th August 2016, 16:30   #10
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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Originally Posted by Rehaan View Post
And here's one from 11 years ago, where Saab developed something similar (Variable compression ratio engine!)
I remember back in 2003 I had chosen this very topic i.e. SAAB's variable compression engine for my college seminar. I was quite amazed by the thought of having a variable compression engine in a car. Based on the load or demand put forward the engine dynamically alters the volume of the combustion chamber, thus changing the compression ratio. I thought at that time that there would be a paradigm shift in the IC engine design field after this, going forward. But sadly that did not happen. Due to the huge costs involved in developing such an engine SAAB had shelved the project. Good remembrance though
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Old 17th August 2016, 18:21   #11
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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Originally Posted by sooraj.naik View Post
The Bentley Continental GT comes with the Variable displacement Engine. In Bentley AFAIK half of the cylinders are deactivated while running slow or low load conditions.

The technology was pioneered by Alfa Romeo and Cadillac.

Infiniti has taken the technology to the next level by introducing dynamic compression ratio!


This was introduced by GM and Honda too. I cant really comment if the experiment was successful or not. This article makes an interesting reading.

Wiki link for Honda's Variable Cylinder Management.
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Old 17th August 2016, 18:30   #12
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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Originally Posted by RavenAvi View Post
Nissan engineers say that the VC-T engine will have a seamless and continuously variable compression ratio anywhere between 8:1 (for high performance) and 14:1 (for excellent fuel economy) by transforming itself and seamlessly raising or lowering the height of the pistons reach, thus transforming itself according to the driving situations. The engine, which uses both port and direct injection, will switch between Atkinson and regular combustion cycles without interruption.
This might seem like a silly question, but can someone explain to me how different compression ratios affect performance? Why low compression for high performance and high compression for better fuel economy?
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Old 17th August 2016, 23:05   #13
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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This might seem like a silly question, but can someone explain to me how different compression ratios affect performance? Why low compression for high performance and high compression for better fuel economy?
A gasoline engine works based on Otto cycle. An Ideal Otto cycle assumes constant volume combustion which occurs when piston is at top dead center (TDC). But a real engine deviates from constant volume combustion and has a definite combustion duration, typically 30 degree crank angle. This definite combustion duration reduces thermal efficiency compared to an ideal cycle due to the shifting of combustion event from the TDC. Higher compression ratio (CR) results in higher peak temperature and pressure inside the cylinder and results in reduced combustion duration and approaches ideal Otto cycle. But this higher temperature and pressure can also cause air-fuel charge to auto ignite (engine knocking). Hence, the full load (full throttle) performance is restricted by engine knocking and limits the compression ratio. Whereas at part load conditions (partially opened throttle), less charge is entered inside the cylinder and results in reduced effective compression ratio and reduced peak temperature and pressure and hence, less chance of knocking. An engine manufacturer preferred to go for the highest possible compression ratio to give high part load efficiency where an engine is run mostly. But with this high CR, he will have to delay ignition angle to avoid knocking at full load (shifting away from TDC). Such configuration can result in announcing less peak torque and power ( affects vehicle sales). So a flexible compression ratio allows him to go for a higher CR at part load to get the best fuel economy and a lower CR at full load which allows him to announce higher peak and torque figures.
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Old 18th August 2016, 15:42   #14
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Post Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

Quote:
Originally Posted by varunswnt View Post
If I recollect correctly then a thread on similar tech albeit from HONDA is present on team-bhp. So this tech is not exclusive to anyone but Nissan is first to come out with a production ready one. Would love to read about the claimed performance figures when it is made available to car reviewers.
Honda's technology is variable displacement.
Nissan's is variable compression ratio. Both are different.
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Old 19th August 2016, 14:58   #15
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Default Re: Nissan's new gamechanger: VC-T engine with 'variable compression ratios'

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Originally Posted by maker_of_things View Post
This might seem like a silly question, but can someone explain to me how different compression ratios affect performance? Why low compression for high performance and high compression for better fuel economy?
Quote:
Originally Posted by Mohd Faiz View Post
A gasoline engine works based on Otto cycle. An Ideal Otto cycle assumes constant volume combustion which occurs when piston is at top dead center (TDC). But a real engine deviates from constant volume combustion and has a definite combustion duration, typically 30 degree crank angle. This definite combustion duration reduces thermal efficiency compared to an ideal cycle due to the shifting of combustion event from the TDC. Higher compression ratio (CR) results in higher peak temperature and pressure inside the cylinder and results in reduced combustion duration and approaches ideal Otto cycle. But this higher temperature and pressure can also cause air-fuel charge to auto ignite (engine knocking). Hence, the full load (full throttle) performance is restricted by engine knocking and limits the compression ratio. Whereas at part load conditions (partially opened throttle), less charge is entered inside the cylinder and results in reduced effective compression ratio and reduced peak temperature and pressure and hence, less chance of knocking. An engine manufacturer preferred to go for the highest possible compression ratio to give high part load efficiency where an engine is run mostly. But with this high CR, he will have to delay ignition angle to avoid knocking at full load (shifting away from TDC). Such configuration can result in announcing less peak torque and power ( affects vehicle sales). So a flexible compression ratio allows him to go for a higher CR at part load to get the best fuel economy and a lower CR at full load which allows him to announce higher peak and torque figures.

Adding to the above point,

Compression ratio is nothing but the ratio of maximum to the minimum volume in the cylinder. So in simple terms, a lower compression ratio (8:1) means that the TDC is lower. Hence the travel of the piston is shortened and hence the power stroke comes in early. Higher compression ratio (14:1) means that the TDC is higher. The travel is more and due to more compression the combustion is cleaner.

Simply translates to the number of power strokes in a particular amount of time in lower CR is more as compared to the higher CR. Hence the more power.

Higher CR means more compression of fuel air mixture, resulting in better burning and hence a better fuel efficiency.
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