Nissan announces 2.0L variable compression ratio engine
 

http://ecomodder.com/forum/attachmen...1&d=1471279636

Hmm... very interesting.

The World's-First Variable Compression Ratio Engine Could Kill Diesel Forever

What they fail to mention is this technology could also be used on diesels to further improve their efficiency as well (I would imagine at least). It would help deal with emissions as well as NHV and cold start conditions as well as efficiency... But you can't say that and also have a sensationalistic article title I suppose. ;)

I thought hydraulically actuated valves were going to allow complete and independent control of effective compression ratio?

I think this is slick engineering, but I'm skeptical of it performing well in longevity tests.

Nissan variable compression ratio tech - Insight Central: Honda Insight Forum

Hmm even on wired, see if this goes anywhere or if its like the 90's era Chrysler 2 cycle car.

Imagine trying to rebuild an engine with that thing in there though?

I wonder if the performance gains are worth the cost and complexity penalties?

I don't see wide-spread adoption of this. I don't even see long-term Infinity adoption of it.

I think there are simpler ways to achieve similar goals.

It would have been nice if they would have provided a apples to apples comparison of the mileage improvement. Yay, it makes as much power as a 3.5L. That is great. But, how does it compare fuel economy wise to a run of the mill 2.0L?

Looking at it, it seems complex, but plot out the movement and it's pretty elegant.

First off, the power stroke is offset way to the side, and the conecting rod moves almost completely vertically, limiting side load and minimizing friction. Also, you have less horizontal movement at the bottom of the con rod than in a regular piston with the same stroke, and the counterbalance on the other side of the crank moves even less...

This all means less counterbalancing, less weight, smoother operation and... supposedly... the elimination of balancer shafts.

Sure, it's a little more complex... but with more parts under... presumably... less stress... it should all balance out.

Here's another variable compression scheme:

http://blog.caranddriver.com/wp-cont...cr-876x535.png
(Click on image for link)

Could The World's First Variable Compression Ratio Engine Kill Diesel Forever?

Fixed

Frank, what do you think would be more effective?

The GM-version XM-1 tank had a variable compression ratio diesel engine (AVCR-1360), but ended up getting exactly the same "one-mile per gallon" mileage that the Chrysler XM-1 turbine did...so, the "peanut oil" burning turbine was selected (wink,wink).

Here's a little diagram I worked up last week:

http://www.topgear.com.ph//images/20...c-t_engine.gif

If the crankshaft rotation was counterclockwise - would the power stroke have better mechanical vectors?

The radius of the crank pin is much smaller, and based on that, the torque would seem to be MUCH lower for the left side diagram.

Interesting thought. I see what you mean... this is basically the reverse of a stroker modification... instead, you're getting the engine to act like a short-stroke one with the same effective movement range. I don't know if it's noticeable, but the piston on the VC-T actually accelerates slower at the start of the downstroke than the standard piston, where all the power is supposed to be made... and contrawise, due to the eccentric movement of the upper link, if you reversed the motion, the VC-T piston would indeed move faster on the downstroke, which *should* give more torque. (...uhh... right?)

But I'm assuming Nissan makes it rotate that way due to side loading and efficiency. Plus, it will probably rev higher (if these other considerations outweigh the extra friction caused by the extra link assemblies) Besides... with a turbo, they can probably cover up any torque deficiency inherent in the design... they're claiming V6-like power... meaning 250-300+ hp... though that's not too terribly far out for a two-liter turbo nowadays.

Thanks Daox... interesting bit of news.

This is certainly interesting.

We'll see how well these will last.

It's amazing how far you'll go with money, many cheaper manufacturers haven't even changed to direct injection, and here we have some manufacturers reinventing the wheel (Or should I say crank)

I was thinking along the lines of what Honda (and I am sure others as well) did, which is to offset the centerline of the cylinder to the down (power) stroke side. This puts the connecting rod in a better position at TDC to push the crank more effectively at the beginning of the power stroke.

The way I see it... it's already offset that way... but I don't know how much of that vertical push goes into the crank.

Funnily enough, some readers pointed out Honda's EX-link, which I knew nothing about... which uses almost the exact same multi-link system, only with a continuously moving lower pivot, basically making it an atkinson's engine, with a longer intake stroke achieved mechanically rather than through valve trickery:
https://www.youtube.com/watch?v=P68W5jOR0bA

(the animation is a bit off, though... in the final Honda prototype, the connecting rod also pushes straight down on the power stroke)

Thinking of covering this one, also, since it was mentioned... but that's going to be a pain in the butt to animate. :D

That's a different design than the Nissan engine.

Yes, it is, but interestingly, Honda's final engine uses a very similar multi-link geometry:

http://world.honda.com/news/2011/p11.../images/10.jpg

Interesting that Honda uses that engine for natural gas cogeneration and heat.

Its unfortunate that cogeneration systems (which are just a motor and heat exchanger) can't be mass produced and reasonably priced.

If they were priced at the same rate as any other small engine we could produce energy at home more efficiently than the grid with about the same level of reliability. Solar when you have it NG when you don't and need heat.

Road&Track had it featured nicely:

Variable Compression Engine - How Infiniti VC-T Works

I covered it more thoroughly months ago... :turtle: :p

That's why it doesn't seem so likely to reach production. And with direct injection becoming more widespread, a fixed high compression ratio is actually more suitable than a variable one.

This is not going to help the cause:


https://www.consumerreports.org/fuel...economy-tests/


CR registered 22 mpg in their "real world" test, vs. an EPA rating of 26 mpg combined.

That's too bad for Nissan. The hammer of bad publicity is about to come down on them.

I've come to really dislike CR. They play to the public's overconfidence in its own intelligence with their air of scientific inquiry, when their process is, "Hey, we removed the controls on all the variables that actually allow you to compare things like vehicle fuel economy with any consistency. Now we're going to scream about how our results varied! Oogie boogie!" Meanwhile, John Q. Public thinks that because they write, "...CR runs its own tests to simulate what consumers are more likely to experience in daily use," their results are perfectly valid and applicable to Mr. Public's own use case because they used science-y words like "test" and "simulate."

Whereas I don't like them simply because they hate the Mitsubshi Mirage.

What's not to like in a spiritual successor to the Geo Metro??? :D

I want to give CR some credit for making claims in a somewhat controlled fashion. They're at least doing track driving only, at set speeds, and correcting for temperature variation.

The government’s tests vs. ours

From: https://www.consumerreports.org/cro/...-gap/index.htm



An interesting trend from their conclusions (I believe this refers mainly to city driving):



https://ecomodder.com/forum/attachme...1&d=1546012357

I've never been a fan of diesel. But since we're talking about killing diesels here... It sure wouln't be hard with the current fuel prices.
In my city in AR gas: $1.829 Diesel: $3.039
That pretty much kills diesel right there, even enough for me to consider a gas burning f250 over a diesel version.

Yes Start with the highest compression ratio your fuel can handle, for maximum displacement, and delay the intake valve closing as needed to lower the compression ratio as low as possible for the power needed. Of course, adjust the fuel injection map.

This system has too many reciprocating parts.

Fiat's Multiair system is mechanically a lot simpler and seems to do a pretty good job.

https://www.youtube.com/watch?v=Td9Gz_h7Qpg

I've been very impressed with the cold start gas mileage.

Rumor has it, the turbo GSE 1L engine with multiair II (direct injection) will be replacing the NA 1.4L in the base Fiat 500 in the US for 2020!

I always hoped for the twinair diesel

Does that exist?

Nah just the 1.3 ltr multijet diesel which would still be a good offering with the 6sp stick

Not surprised much. A downsized turbo is only going to be as economical as its acceleration profile. If the "standard consumer behavior" includes hitting the boost more often, it's going to drink more gas than normal.

What I'd like to see is how it drinks in traffic, where a downsized variable compression engine should have an advantage over regular ones... or if the heat issues inherent in turbocharged installations make that a no-starter, as well.

I have driven the 1.3 L multijet punto and the 1.9 multijet doblo. The engines are fairly good. I was pleased with the performance and the fuel consumption of both cars (3.5l and 5.5l respectively in city traffic). I did try to avoid rush hour but my city has 18M other people so there is always traffic.

The petrol and CNG TwinAirs are nothing spectacular in real world driving, returning far worse FE than advertised