
Nissan Motor Company has announced a new type of gasoline engine - verdande
http://www.reuters.com/article/us-autos-japan-nissan-engine-idUSKCN10P0IK?il=0
======
asimuvPR
Here is a simple explanation gathered from this image
[http://o.aolcdn.com/hss/storage/midas/de3e84cf46030cd7b3ea39...](http://o.aolcdn.com/hss/storage/midas/de3e84cf46030cd7b3ea39900a1fa7ba/204201576/image1+%281%29.JPG)
:

The difference from a conventional engine is that the engine stroke is
increased or decreased automatically. The stroke is the distance the piston
travels up and down in order to turn the crankshaft. A shorter distance that
is closer to the combustion chamber increases the compression ratio because
there is less space for the fuel/air mixture. When the system is operating in
low compression mode the piston travels more and does not reach as high. The
combustion chamber then ends up being farther away and a lower compression
ratio is achieved.

What is novel about this approach is how the combustion chamber was left in
the same place. Past efforts by SAAB had the engine head moving the combustion
chamber away from the pistons. This drastically changes the characteristics of
the combustion process. Something that makes emissions control challenging.
Any power loss due to a dynamic combustion chamber is removed by pressurising
it with a turbocharger, just like Nissan did.

Possible issues with this design could be:

\- Uneven wear of the cylinder bore due to the piston travel being dynamic.

\- An overboost condition during a high compression cycle could damage the
mechanism and even crack the engine block.

\- Increased NHV due to regular wear and tear making its way into the
valvetrain and transmission input shaft.

This is a good effort and I hope Nissan is able to pull it off. Make sure to
wait two years before you buy a vehicle with this technology. Dont be the
guinea pig. :)

~~~
pdonis
_> A shorter distance that is closer to the combustion chamber increases the
compression ratio because there is less space for the fuel/air mixture. When
the system is operating in low compression mode the piston travels more and
does not reach as high._

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.

~~~
TheSpiceIsLife
I don't follow how the stroke length changes. The conrod (upper-link in the
image) is a fixed length, therefore the stroke length is fixed.

The compression ratio changes because the mechanism changes where TDC (Top
Dead Centre) is.

Or have I misunderstood something?

Edited to add: If TDC moves then the bottom of the stroke moves with it
because the conrod is a fixed length, right?

~~~
TheSpiceIsLife
Never mind, I see now how the mechanism changes the stroke length.

~~~
zglennie
Can you elaborate? I'm trying to figure it out. I'm also confused about where
the crankshaft is supposed to be in this picture.

~~~
TheSpiceIsLife
Erm, I'm not sure I get it. I think I'd need to see an animation. If the
crankshaft is fixed I don't see how that linkage can change the stroke length
because all it shows in that diagram is the piston further along the stroke,
which is what all piston engines do when the crankshaft rotates.

So yeah, I probably need to see an animation to grok it.

------
shawkinaw
From the (much better) Reuters article [0]:

> The higher the ratio, the more efficiently the engine works, producing
> better fuel economy and, with the addition of a turbo-charger, more power.

> Traditionally, design engineers had to fix a gasoline engine's combustion
> compression ratio, essentially deciding whether to go for power or economy.

Everything gets better with higher compression ratio, so where's the
compromise? As I understand it, the only reason engine makers don't crank the
ratio as high as possible is to avoid knocking.

[0] [http://www.reuters.com/article/us-autos-japan-nissan-
engine-...](http://www.reuters.com/article/us-autos-japan-nissan-engine-
idUSKCN10P0IK?il=0)

~~~
Aelinsaar
The drawback is that higher compression ratios require higher octane fuels.
Nissan claims to have solved this by some kind of intelligent feedback system
that allows them to control compression ratios on the fly. Presumably the
compromise there is that it will require more moving parts, be expensive, and
may come with issues of its own.

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.

~~~
paulmd
The obvious precedent for variable-pitch blades are variable-pitch propellers
on aircraft and helicopters. I don't want to say it's a solved problem for
turbos, but there is almost a century's worth of prior art on the topic.
That's one of those things that (in hindsight) really makes you wonder what
took so long to think up.

[https://en.wikipedia.org/wiki/Variable-
pitch_propeller](https://en.wikipedia.org/wiki/Variable-pitch_propeller)

~~~
seanp2k2
Because it has to be cheap and reliable at 1000*C for 200,000 miles over 10
years while constantly accelerating to 280,000RPM and decelerating with no oil
or cooling air circulating when the car is stopped.
[https://garrett.honeywell.com/products/how-a-turbo-
works/](https://garrett.honeywell.com/products/how-a-turbo-works/)

[http://www.epi-
eng.com/piston_engine_technology/turbocharger...](http://www.epi-
eng.com/piston_engine_technology/turbocharger_technology.htm)

------
userbinator
Despite claiming they could replace diesels, I don't see any real numbers
other than comparisons with their own gasoline engines. For internal
combustion engines, the most efficent are still two-stroke diesels, which can
have thermal efficiencies of over 50%:

[https://en.wikipedia.org/wiki/Brake_specific_fuel_consumptio...](https://en.wikipedia.org/wiki/Brake_specific_fuel_consumption#Examples_of_values_of_BSFC_for_shaft_engines)

Seeing as this design includes several more moving parts than conventional
ones, it's an open question how much reliability and longevity are affected; I
remember reading in a book that over the years many have tried to make more
efficient engines and succeeded in achieving that goal, only to be let down
because of real-world reliability issues.

------
AmVess
SAAB was working on one of these years ago before GM flew that company into
the ground. This link gives you an idea of how it works.

[https://en.wikipedia.org/wiki/Saab_Variable_Compression_engi...](https://en.wikipedia.org/wiki/Saab_Variable_Compression_engine)

~~~
tedunangst
Variable compression? So logical next step is variable octane, right? One tank
of 87 and one tank of 93, dynamically mixed in response to changing
compression ratio. :)

~~~
gcb0
not sure if joking or not, but the injection map on your ecu does that.

~~~
Unklejoe
I think you are incorrect. Most production cars (all that I know) have only a
single fuel tank, thus nothing to mix.

~~~
asimuvPR
I think the point of the person you replied to is that any variation in octane
is handled by the fuel injection system. This renders having two tanks
unnecessary (unless you require more distance between fill ups).

~~~
hvidgaard
It can adapt to lower octane fuel by adjusting the timing, it's far from
optimal, and at high enough boost level you need higher octane regardless. At
non boost levels, you need less octane rating to prevent knock, but under
boost you need higher octane rating. So you run the higher octane fuel all the
time, and that is less efficient.

~~~
Unklejoe
Correct. This involves relying on feedback from knock sensors which literally
"listen" for the specific tone that a detonation event produces (usually
somewhere in the 6-7 kHz range depending on cylinder geometry). You will
sometimes hear this phenomenon referred to as "pinging", and it’s actually
audible to the driver if severe enough. There is also another method of knock
detection which involves using the spark plugs to detect the resistance of the
air inside the combustion chamber immediately after an ignition event, which I
believe is an indirect way of measuring cylinder pressure. I’m not positive on
this, but I think the idea is that you want peak cylinder pressure at the
moment of time where the piston is like 20 degrees after top dead center.
Earlier than that, and the majority of the force is wasted pressing directly
down on the crank shaft. This is more advanced and is used only in specific
cars such as the E90 BMW M3.

If the ECU detects knock, it will retard timing. This works to an extent, but
you’re ultimately worse off than if you just ran premium fuel in the first
place. The other issue is that (on systems with conventional knock sensors)
this causes you to basically “bounce” off of the knock threshold. Knocking is
terrible for the bearings inside of the engine and should generally be
avoided, but running regular fuel in a car that calls for premium results in
the ECU constantly trying to creep up timing (or switch to the high octane
map), only to be confronted with knock again.

------
vmarsy
Interesting news, The Reuters article[1] they cite has more content than the
current article[2], but even the Reuters article looks very PR-like.

The TLDR appears to be: The new engine uses _variable compression_ technology,
which [allows] at any given moment to choose an optimal compression ratio for
combustion.

> The [new VC-T engine] averages 27 percent better fuel economy than the
> 3.5-liter V6 engine it replaces, with comparable power and torque. Nissan
> says the new engine matches the diesel engine in torque.

It will be officially unveiled at next month's Paris motor show

[1] [http://www.reuters.com/article/us-autos-japan-nissan-
engine-...](http://www.reuters.com/article/us-autos-japan-nissan-engine-
idUSKCN10P0IK?il=0)

[2] [http://www.thedailynewsgrabber.com/nissan-on-gasoline-
engine...](http://www.thedailynewsgrabber.com/nissan-on-gasoline-engine-
breakthrough-diesel-obsolete/)

------
tonylemesmer
So if this engine changes the compression ratio (the amount the mixture is
compressed) how is all this complexity better than a supercharger which
changes the amount the air is compressed? Surely increasing the compression of
the mixture and compressing the air before it goes in is pretty much the same
thing? Except...that all that variable stroke length mechanism is a lot more
complicated, and patentable?

~~~
ruste
Higher compression ratio allows better fuel efficiency. Supercharging forces
more fuel and air into the same cylinder.

------
reidacdc
I am far from an expert, but there are two ways I know of to do something like
variable compression, one is that Saab technique already mentioned, where the
cylinder head is displaced to change the size of the combustion chamber.

The other related scheme is the Atkinson cycle:
[https://en.wikipedia.org/wiki/Atkinson_cycle](https://en.wikipedia.org/wiki/Atkinson_cycle)

The wiki page shows a complicated mechanical arrangement for having a smaller
intake volume vs. expansion volume, but the "poor man's" way to do this is to
just keep the intake valve open for the first part of the compression stroke.
The upside is that you can then adjust the effective compression ratio with
valve timing. The downside is that it reduces the intake manifold vacuum by
blowing back some of the intake air, not sure how that's handled.

Don't know what the Nissan guys are doing.

~~~
hvidgaard
This is what Mazda is doing with their Skyactive-G engines if I'm not
mistaken. It works reasonably well.

------
Neil44
The way that makes most sense to think about this to me is in terms of dynamic
compression.

At full throttle the turbo is shoving a large mass of air into the cylinder
for every firing. The compression ratio has to be fixed lower to control
detonation under these circumstances.

At light throttle / cruise there is now hardly any mass of air in the
cylinder, so although mecanically nothing has changed (same / fixed
compression ratio) we are hardly compressing the air at all and we're giving
away a load of efficiency for that reason.

The ability to up the compression ratio at cruise / light throttle claims some
of that basic efficiency back.

------
JumpCrisscross
> _" Increasing the fuel efficiency of internal combustion engines is critical
> to automakers. Not all consumers will accept a battery electric vehicle
> solution._

That's the thesis?

------
Annatar
This is still using ignition timing and spark plugs. Additionally, the
connecting shim and the timing advancer/retarder introduce not one, but two
points of failure.

Thanks, but no thanks: I'll just stick to my simple (by comparison) direct
injected turbo diesel cars.

When there is a gasoline engine which can ignite the fuel without spark plugs
and ignition timing, that'll be the right solution. mazda experimented with
this (see "VCCI"), but it never made it into production, because it's not a
trivial problem to solve. This Nissan patent is a mechanical engineer's
equivalent of a duct tape hack.

Or we could just ditch this entire nonsense with pistons and optimize the
Chrysler's super simple turbine car engine until it matches today's exhaust
emission regulations. This was a tough problem to solve in 1978, but should be
doable now with a particulate filter. And that engine isn't picky: since it's
a turbine, it'll run on anything that's combustible, from filtered cooking oil
to cologne.

[https://www.youtube.com/watch?v=b2A5ijU3Ivs](https://www.youtube.com/watch?v=b2A5ijU3Ivs)

~~~
Neil44
Disesl engines have very fine control of ignition timing via injection timing
which is now very complex. There are tiny pilot injections and multiple short
injections over a carefully controlled length of time so I don't agree that
needing to time a spark makes spark ignition a more complex and by implication
worse solution.

~~~
Annatar
First of all, timing by injection is still simpler than timing by spark: in
gasoline engines, the computer must time both the injection and the ignition.

Second, timing by spark means that spark plugs are necessary, so that is more
parts, and more parts means higher probability of failure.

Third, spark plugs are needed to start a chain reaction of igniting fuel,
because gasoline fuel is volatile enough as not to be combustible. Gasoline
fuel is not flammable, but the vapor is, did you know that? That's what makes
it volatile as far as combustibility, otherwise we would have self igniting
gasoline engines by now.

~~~
Neil44
I'd say that modern disel injector problems were more common than spark plug
problems, so I guess we'll have to agree disagree :) I could also draw your
attention to the cost and ease of replacement of a spark plug vs a diesel
injector, or all the extra emissions treatment equipment that modern diesels
need that petrol doesn't, but I don't think we're going to convince each other
here :)

~~~
Annatar
How long have you worked on diesels in order to be able to claim that?

How many cases of diesel engines with injector problems have you had during
your career as a mechanic?

 _How much does, on the average, a diesel injector cost?_

 _How often do they have to be replaced?_

I've worked on diesel engines since I was a little kid, and have yet to work
on one with injector problems.

The following are ultramodern mazda injectors, for instance; if you look at
the spray pattern and the capability of these programmable injectors, it's
pretty obvious it's going to be tough for them to experience problems:

[https://www.youtube.com/watch?v=fDFgiLrEX1o](https://www.youtube.com/watch?v=fDFgiLrEX1o)

modern piezoelectric technology is wonderful, isn't it? And wouldn't you know
it, all modern diesel engines sport piezoelectric injectors.

But let's suppose for a moment that you are correct, and that I'm wrong. Your
logic has one flaw, and that is that in a diesel engine, I will (and have) get
three times the kilometrage that you will get with a gasoline engine. Even if
I had to replace all of the injectors, I will still have come out ahead. How?

Assuming that you are running the simplest, ultramodern gasoline V8 (I picked
V8 in particular because that is the most reliable of the gasoline engines),
if you maintain it according to the extreme maintenance schedule, you might
get about 460,000 km out of it before requiring a rebuild. By that time, I
will have gotten almost 1,300,000 km on the diesel and _maybe_ need an engine
rebuild, and that engine rebuild might not even need new injectors, if I
changed my fuel filter every 15,000 km (which I do), and every 30,000 km added
one liter of biodiesel to my tank!

------
SixSigma
In economics, the Jevons paradox occurs when technological progress increases
the efficiency with which a resource is used (reducing the amount necessary
for any one use), but the rate of consumption of that resource rises because
of increasing demand.

[https://en.wikipedia.org/wiki/Jevons_paradox](https://en.wikipedia.org/wiki/Jevons_paradox)

------
jalada
> The turbo-charged, 2-liter, four-cylinder [VC-T] engine averages 27 percent
> better fuel economy than the 3.5-liter V6 engine it replaces.

You don't say.

~~~
gmac
_... with comparable power and torque._

------
watmough
Any way to know how they accomplish the variable compression?

~~~
qbrass
[https://www.google.com/patents/US7165517](https://www.google.com/patents/US7165517)

~~~
Animats
Oh, so that's how it works. See Fig. 2 of the patent. It's a lot like the
Peugeot MCE-5, an earlier variable-displacement engine. The Nissan mechanism
looks simpler and seems to take up less space inside the engine. Maybe that
will make this workable. Variable-displacement isn't new, but previous
attempts were mechanically clunky. It adds extra moving parts to the highest-
load path in an engine - the piston to crankshaft connection. It has to
deliver large benefits to justify the costs and problems that implies.

Most engines already have knock sensors. They're used to adjust fuel/air ratio
and spark timing to just above/after where the engine starts to knock. A few
engines adjust valve timing while running, which is also complex mechanically,
but not as difficult as adjusting compression. Now there's another variable to
tweak.

It may take a machine learning system to tune such an engine. All those
interdependent variables to adjust make that a hard problem. Different values
required based on engine speed, load, temperature, fuel consumption, and
emissions outputs. All this is usually expressed as precomputed tables which
are interpolated within the engine controller. Those tables have to be
developed somehow.

------
gervase
This should probably link to the original Reuters article:
[http://www.reuters.com/article/us-autos-japan-nissan-
engine-...](http://www.reuters.com/article/us-autos-japan-nissan-engine-
idUSKCN10P0IK?il=0)

------
kposehn
More information: [http://www.autoblog.com/2016/08/14/infiniti-vc-t-engine-
vari...](http://www.autoblog.com/2016/08/14/infiniti-vc-t-engine-variable-
compression-official/)

------
jacknews
This looks cool, but complicated. The problem addressed seems to be that
turbocharged (and supercharged) engines are sub-optimal at lower powers.

IMHO mild electric hybrids, or full serial electric hybrids would be a more
elegant solution - only run the combustion engine when full power is needed,
and use the electric motor otherwise. "full power" could be used to top the
battery if it's not all required for motion.

~~~
dclowd9901
Would an electrically powered, computer-controlled turbo be silly?

~~~
ArkyBeagle
The electric motor to be used would have to be a pretty unusual motor. IMO,
supercharging is "better" because the PTO side of an engine is less ...
trouble than the exhaust side. Superchargers are generally heavier.

~~~
hvidgaard
Super chargers generally result in a fairly large parasitic loss to power it.
Turbo more or less harvest free energy with only a minimal loss due to
increased back pressure.

~~~
ArkyBeagle
So they say. The story I always got is that turbo ( for aviation - where this
all grew up ) was simply lighter.

The old rule of thumb "turbo costs 3x less than super" is true for a lot of
cases. Supercharge provides a linear boost where turbo does not.

~~~
hvidgaard
Some superchargers provide linear boost, others behave much like a turbo. In
any casem FI is used to increase efficiency, so it doesn't make sense to use a
super charger with a must larger parasitic loss. Modern turbo can provide
boost from 1500 rpm, and result in a flat torque curve - the only negative
thing is the lag.

------
Sanddancer
I'm curious as to what, if anything, would preclude variable displacement from
being used in diesels as well as petrol engines. Diesels also have
performance/economy tradeoffs like this gasoline engines, so it stands to
reason that tweaking compression should give similar benefit. I've got a
feeling that rumors of diesel's impending demise are greatly exaggerated.

~~~
dredmorbius
Diesel's fatal flaw is particulate emissions.

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

~~~
Sanddancer
Volkswagen cheated to try to get a less expensive system in place. DPFs and
urea injection are pretty well proven technologies and work pretty well.

~~~
Reason077
They work well enough on new vehicles coming out of the factory.

The real problem is 5-10 years later when these systems need repair or
replacement. For many the economic temptation to have them "nulled" is too
great (fuel efficiency is improved by removing the DPF) - and that once-clean
diesel is now a toxic, polluting nightmare.

This is a huge problem in the UK - and why we need to phase out diesel in
private/light motor vehicles.

~~~
icebraining
How do they pass the emissions test?

~~~
Reason077
In the UK, there is no emissions test for particulate or NOx emissions, other
than the subjective "does it emit visible smoke?".

A visual inspection for the presence of the DPF is required, but this is
easily defeated by installing a look-alike "null" filter.

The people doing the MOT testing can be pretty shady anyway. Since any
mechanic can operate as a testing facility, it's often the same people who
remove DPFs that will then pass them in the MOT inspection.

~~~
icebraining
Seems like fixing that system would be more sensible than outlawing diesel
cars, no?

~~~
Reason077
I agree with you. A strict emissions test regime would be a good first step.
But politicians have known about this for years and little has been done -
apparently it's a too hard (or too expensive) problem to fix.

The thing is, even brand-new "clean" diesels are still worse polluters, for
toxic particulates and NOx, compared to petrol and petrol-electric hybrid
vehicles.

London already has a disincentive on diesels coming into effect by 2019, when
pre-Euro 6 (i.e. older than September 2015) diesel vehicles will be subject to
a £12.50/day charge to drive in London.

There are calls to extend this to cover all diesel vehicles, eventually
leading to a total ban:

[https://www.theguardian.com/environment/2016/jul/18/ban-
dies...](https://www.theguardian.com/environment/2016/jul/18/ban-diesel-cars-
in-london-thinktank-urges)

Licensing of new diesel taxis will also soon be prohibited in London, and all
single-deck busses will be zero-emission by 2020 (and double-deck busses will,
at minimum, be hybrids).

------
nickhalfasleep
This is an excellent implementation of variable valve gear timing that
external combustion steam locomotives have had for about a century and a half.
Impressive to see it put into an internal combustion engine.

Edit: looking at the posted image, they change the stroke depth of the power
linkage. That plus valve timings let them customize the entire combustion
cycle.

------
alacombe
How are they preventing engine knock ? At 14:1 compression you'd have to be
running premium gas, which would pretty much cancel the efficiency saving, in
a $$ perspective.

~~~
Unklejoe
I think direct injection allows engines to run higher compression ratios
without knocking. I'm not sure exactly why, but I assume it's because the fuel
sprays directly on top of the piston which could allow it to cool any hot
spots which would have normally caused detonation.

~~~
jschwartzi
The fuel probably has to fully vaporize before it can ignite. This happens in
the manifold for a normal EFI, or in the carburetor for an older engine.
There's some short period of time that this is happening, and so if you time
the injection to happen with enough time to vaporize the fuel before ignition
it probably doesn't have enough time to pre-ignite before spark.

This is speculation.

------
brownbat
I have a lot of respect for Nissan's engineers, but somewhat less respect for
their lawyers, who hounded Uzi Nissan for a decade trying to get him to turn
over his domain.

[http://www.nissan.com/Lawsuit/The_Story.php](http://www.nissan.com/Lawsuit/The_Story.php)

Cybersquatting is obnoxious, but once they found out it was the guy's actual
name, and that he was using it to run his own business, they should have just
accepted he had a right to the site and worked to buy it from him or moved on.

~~~
bmh_ca
Lawyers are tools. (Being one, I feel I can say so, with a humble degree of
confidence.)

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.

~~~
brownbat
Fellow attorney, I know how it feels to be defensive about the profession.

So I should have said I'm less than enthused with their legal strategy, rather
than placing blame on a specific group of people.

GC definitely has an obligation to provide guidance on legal strategy before
following the board's demands, and maybe they did so. Impossible to say where
things broke down in this case.

------
andrewvijay
"tarnished by Volkswagen's (undefined) emissions cheating scandal." Dear
Reuters time for you guys to use flow in your js code.

------
Rexxar
It will interesting to see if this can be combined with electric power to have
a very efficient hybrid engine.

------
codeulike
This is all moot. Battery technology and charging infrastructure for EVs will
improve so much over the next 5 to 10 years that engines running on dinosaur
juice will no longer be worth the hassle for mainstream vehicles.

~~~
lutefisk
So all companies related to gas technology should just close up shop?
Something that may or may not work is on the horizon, so all the engineers
that have been researching gas technology for years should throw in the towel
and quit? There is no chance that electric overtakes gas in 5 years.

~~~
codeulike
er, electric cars work fine. They just need to get cheaper and have longer
range. That will happen easily in the next 5 to 10 years.

~~~
barney54
...But it hasn't happened in the last 100 years--it also hasn't happened over
the last 5-10 years. The Nissan Leaf, for example, is over 5 years old.

There are good reasons why EVs haven't dominated yet--cost, range,
flexibility, etc. Battery technology hasn't changed all that much either:
[http://www.cnet.com/news/why-batteries-arent-getting-
better/](http://www.cnet.com/news/why-batteries-arent-getting-better/)

Someday EVs may dominate, but it's doubtful that will happen in the next 5-10
years unless there is a large technological leap.

