Nissan Motor Company has announced a new type of gasoline engine

Haha, this reminded me of a friend who did a summer engineering internship with a U.S. automaker. He came back and related one of the most important things he learned: "never, ever buy a first-run car." I remember hearing him tell about tolerances still being adjusted after all these cars had shipped, cringing to think of all the problems that could cause.

Let's also recognize that shortblock costs will be much, much higher with this design when you need a rebuild. Many engine builders won't touch this, and I'd suspect the Nissan OEMs will say that these engine shortblocks are "factory replaceable only". Who is going to make aftermarket bearings for the multilink setup? How does the engine operate under actuator failure?

I think this is partly inaccurate. The images show the piston at the top of the stroke; when the compression ratio is high the piston is higher at the top of the stroke. But the bottom of the stroke is the same in both cases. That means the actual length of the stroke--the distance the piston travels--is greater in high compression mode. This is consistent with the definition of compression ratio, which is the ratio of cylinder volume at bottom of stroke vs. top of stroke; a larger compression ratio means a larger difference between these volumes, i.e., a longer piston stroke to get the piston higher (closer to the top of the cylinder) at the top of the stroke.

- The added maintenance of turbos

- Added cost might not be worth it compared to a hybrid or electric, especially used

The issues I see:

* Regular gasoline explodes from too much compression, if this engine requires premium gasoline it's sort of dead out the door.

* NOX emissions increase with efficiency and in general efficiency increases with compression, there are two prevailing ways to fix this: cheat and inject urea.

* It greatly complicates where all the force is being generated which will probably lead to more failures.

Variability in something like a combustion chamber is a cool idea, so is variability in the angle of turbo vanes. The issue is how you do it, affordably, and in a way that lasts the way that consumers expect from their cars.

http://www.motortrend.com/news/infiniti-prepares-worlds-firs...

We have a lot of techniques to improve mpg that increase NOx. If you can figure out how to easily inhibit NOx formation inside the combustion chamber you could be a rich man.

Incedentally this is one way direct gasoline injection can improve economy. The injector sprays directly into the cylinder, and can do so in a way that forms a little donut of air/fuel mix that is insulated from the walls by a layer of air. It is then ignited. The air barrier helps keep combustion temperatures down.

One last thing, really high compression tends to result in a chamber that is very flat and narrow, which can counterproductively cause hotspots and incomplete combustion because the flame front is restricted. This can be fixed with undersquare pistons with longer travel, but that leads to big, low-power, slow-revving engines, like diesels!

Higher compression ratio = better combustion = more power with less fuel, regardless of turbo.

Higher compression will always mean better fuel efficiency. My moms Mazda CX-5 runs a 13.5 compression ratio and gets 27mpg. The power/efficiency trade off appears when you're talking about turbocharged engines.

Turbos compress air into the combustion chamber, so when you compress compressed air, you get exponentially compressed air. If you don't adjust the compression ratio for the turbo, you're going to get knock. An engine with a 13.5 compression ratio can run perfectly fine on regular gas, but an engine that runs the same ratio and 20 psi of boost with melt itself even on premium gas.

This is a problem for any kind of work vehicle. They almost always have turbos to give them the power to haul their loads with reasonable ease. But this forces the engineers to design the engine with a lower compression ratio, which means at light engine loads, when the turbo isn't doing anything, the engine isn't fulfilling its full potential. It's still compressing air at a low ratio, even though it's not taking in already compressed air. This is where Nissans innovation comes in. The compression ratio will change according to the degree with which the turbo is compressing air. Allowing the engine to run at peak efficiency through the entire range of engine load.

There are a few other undesirable things about high-compression.

And I just read your message about knocking. same thing. Nevermind.

variable compression is nothing new, just very prone to failure. the other downside was it was much harder to work on the engine, but nobody cares about that anymore.

- Will the ignition need to be cut off before the ratio change happens ?

- Will this apply the change to all the cylinders at the same time ?

It's never been clear to me that they are really all the great of a fit with terrestrial engines. Part count goes up, heat goes way up in spots and there is of course lag.

Attempts to mitigate those, without cheating (e.g., VW), have proven difficult.

I think there isn't much improvements to be had for engines at full power. But lots of room for improvement at partial power. Interesting bit, hybrid cars have really low emissions. Which says to me they're avoiding running their engines at power/rpm ranges that create high emissions.

Certainly there's a give-and-take between lawyers giving advice and clients taking it, but by the "big X" their lawyers essentially do what they are told - lest the big client move elsewhere.

All to say: Lawyers doing a bad thing are often a symptom of an internal disease or conflict.

Which is to summarize a whole host of conflicting emotions: I'm slightly defensive about the profession, wholly sympathetic to the outcomes of wielding lawyers to achieve evil ends, and biased by personal experience – but nevertheless appreciative of comments, like this, that highlight the responsibility that lawyers bear to not only advise and act but to represent the reputations of institutions.

https://en.wikipedia.org/wiki/Microsoft_vs._MikeRoweSoft