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Ultimate Geek
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  Reply # 1614013 18-Aug-2016 22:16
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joker97: http://i.stuff.co.nz/motoring/news/81647671/nissan-develops-major-breakthrough-in-engine-technology

 

 

 

Be aware that some high compression petrol engines start to have diesel like characteristics such as high efficiency (good), and nasty emissions (bad). VW is planning to roll out diesel style particulate filters to its petrol cars to combat this problem. Link

 

 

 

As an engineer I am intrigued how they have managed to vary the stroke length. Do they move the crank shaft relative to the engine block? or do they vary the length of the con rod? Both sound technically difficult to implement, But hats off to Nissan for doing it (assuming it makes it into production.)


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  Reply # 1614016 18-Aug-2016 22:26
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Scott3:

 

As an engineer I am intrigued how they have managed to vary the stroke length. Do they move the crank shaft relative to the engine block? or do they vary the length of the con rod? Both sound technically difficult to implement, But hats off to Nissan for doing it (assuming it makes it into production.)

 

 

That one has me confused too... The only other way to decrease compression is a another valve, but since the article says they change stroke, I can't quite imagine how they do it... Rotatable cam-shaped gudgeon? Sooo many things that could lead to failure though.

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  Reply # 1614072 19-Aug-2016 08:46
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Here:

 


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  Reply # 1614075 19-Aug-2016 08:58
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Scott3:

 

 

 

Be aware that some high compression petrol engines start to have diesel like characteristics such as high efficiency (good), and nasty emissions (bad). VW is planning to roll out diesel style particulate filters to its petrol cars to combat this problem. Link

 

 

 

 

Yeah - I think that's possibly going to be mandatory for stratified direct injection petrol engines to meet Euro 7 regs.

 

As I understand it, the particulate volume may be small, but count of very small "nano" particulates is high.  Rather than gumming up the surface of your lungs with soot which you'll hopefully eventually cough up, these particles are small enough to go directly into your bloodstream. Then it's suggested that they could cause cardiovascular disease, strokes, heart attacks etc - probably other bad chronic disease as well.


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  Reply # 1614089 19-Aug-2016 09:23
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Nissan's not the first to try variable compression.  Even Volvo took a shot at it a few years back. I think by altering combustion chamber volume.

At first glance Nissan's design looks mechanically unwieldy.

But driven by those upcoming emissions and mileage requirements, a melding of advances in materials technology and engine management systems, complicated solutions to gain a bit more efficiency will become viable.

And will allow our existing fuel infrastructure to last a bit longer.


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  Reply # 1614096 19-Aug-2016 09:33
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Fred99:

Scott3:


 


Be aware that some high compression petrol engines start to have diesel like characteristics such as high efficiency (good), and nasty emissions (bad). VW is planning to roll out diesel style particulate filters to its petrol cars to combat this problem. Link


 



Yeah - I think that's possibly going to be mandatory for stratified direct injection petrol engines to meet Euro 7 regs.


As I understand it, the particulate volume may be small, but count of very small "nano" particulates is high.  Rather than gumming up the surface of your lungs with soot which you'll hopefully eventually cough up, these particles are small enough to go directly into your bloodstream. Then it's suggested that they could cause cardiovascular disease, strokes, heart attacks etc - probably other bad chronic disease as well.



Boo hoo ... What are the emissions of nuclear power plant? Maybe that's the answer ... Can't we just dump the nuclear waste into the earth core, space, etc?

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  Reply # 1614135 19-Aug-2016 09:56
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Nissan's new technology seems to have quite a few hard working articulated parts ... 

 

I would have though variable compression can be achieved more simply via a variable boost turbo.  In a variable boost turbo the impeller vanes that are pivoted by a stator - changing the boost pressure to suit operating conditions - e.g more boost for take off, less for cruising.

 

This is used in commercial turbo diesels and some SUvs (e.g. Hyundai).





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  Reply # 1614180 19-Aug-2016 10:30
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MikeAqua:

 

Nissan's new technology seems to have quite a few hard working articulated parts ... 

 

I would have though variable compression can be achieved more simply via a variable boost turbo.  In a variable boost turbo the impeller vanes that are pivoted by a stator - changing the boost pressure to suit operating conditions - e.g more boost for take off, less for cruising.

 

This is used in commercial turbo diesels and some SUvs (e.g. Hyundai).

 

 

 

 

Nissan have used variable vane turbo for a long time in diesel - remember the "hand grenade" ZD30?

 

No - variable boost isn't achieving the same thing.  That's giving higher combustion chamber charge when needed, but limited by the need to avoid pre-ignition with the fixed compression ratio.

 

Variable compression can run very high compression ratio, no boost, and "lean burn" at low load using stratified fuel injection - so very high efficiency - but then when you need lots of power, drop the compression ratio and run lots of boost.  You can get the same kind of output (power per litre) out of fixed compression ratio turbo engines, but because they need high levels of boost, they'd preignite and self-destruct if the mechanical compression ratio was 14:1.  So under low load, the fuel efficiency is compromised by the lower compression ratio.  Normally they compromise - I think you'll find that FSI engines from VW/Audi etc run about 11:1 compression ratio and relatively low levels of boost.  A n/a engine like Mazda SkyActiv run about 14:1 compression ratio, but maximum power isn't close to as good as an equivalent capacity VW FSI.  Variable compression allows the efficiency of SkyActiv n/a engine under normal low-load, but with the power on tap when needed of an all-out performance turbo engine.  It's a very good idea - so long as it's mechanically sound enough to not fly to pieces.


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  Reply # 1614205 19-Aug-2016 10:51
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Actually now that you mention it the variable pressure turbo engines I am familiar with are diesel, and use Bosch technology which is very reliable as long as you don't get corrosion (e.g, not so good in small boats).

 

Given the problems Nissan have had with conrod nuts, I would be very skeptical about all the additional pivoting attachment points in the new system.  Nissan used to make really good diesels - then along came Renault ...





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  Reply # 1614280 19-Aug-2016 12:10
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Do harmful small particles have anything to do with quality of fuel? Ie high octane 98 fuel for example?

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  Reply # 1614315 19-Aug-2016 12:39
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Octane isn't really a quality issue.  It may be vehicle suitability issue.  Different cars have different octane specifications.





Mike

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  Reply # 1614319 19-Aug-2016 12:49
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MikeAqua:

 

Octane isn't really a quality issue.  It may be vehicle suitability issue.  Different cars have different octane specifications.

 

 

I meant designing engines around high fuel octane - any benefits


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  Reply # 1614395 19-Aug-2016 15:14
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joker97:

 

MikeAqua:

 

Octane isn't really a quality issue.  It may be vehicle suitability issue.  Different cars have different octane specifications.

 

 

I meant designing engines around high fuel octane - any benefits

 

 

Reduces knocking, supporting higher compression and theoretically better, cleaner combustion.

 

More power too.





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  Reply # 1614396 19-Aug-2016 15:16
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Linuxluver:

 

Loads of torque

 

 

How much torque are we talking?





Mike

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  Reply # 1614398 19-Aug-2016 15:19
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joker97:

 

MikeAqua:

 

Octane isn't really a quality issue.  It may be vehicle suitability issue.  Different cars have different octane specifications.

 

 

I meant designing engines around high fuel octane - any benefits

 

 

Sure! Running on Avgas, Methanol or Toluene mixes prevented our old high compression engines turning into shrapnel..

 

But having to tip additive into every tank of fuel was a pain, economy, emissions weren't a thing.

 

The idea of a variable compression engine is to burn - an existing fixed octane - fuel always at the optimum ratio, ie more cleanly and efficiently.
Nissan (and other manufacturers) start with the premise that you'll purchase fuel that meets their specifications.

 

Where it will really matter is during the mileage and emissions testing regime, which is done on standardised fuels anyway.


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