Intresting Engine

New engine to hit the market in 2017.
http://www.autoblog.com/2016/08/14/infiniti-vc-t-engine-variable-compression-official/

Best Regards Tom.
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Howard Beel wrote:

compression-official/

Hmm, my 2009 Honda Civic hybrid has variable intake valve timing, which seems to pretty much accomplish the same thing. They've been doing this for some time, probably dates back to at least 2006 on that model.
By reducing the charge drawn into the cylinders, it reduces the peak pressure, so that seems to be varying the compression, too. A pretty low-tech way to accomplish it, it doesn't make any chages to the lower end. This Infiniti scheme seems to add a LOT more complexity to the lower end. I wonder if this is some way to get around a Honda patent?
Jon
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Or a Peugeot patent? http://www.motortrend.com/news/mce5-to-debut-220hp-15l-engine-with-variable-compression-ratio-at-geneva-3891/ --jsw
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wrote:

I think you're misreading it, Jon. This engine is truly revolutionary. Varying valve timing as you describe just produces a pseudo-Atkinson cycle, used on today's hybrids:
https://en.wikipedia.org/wiki/Atkinson_cycle
What this new Nissan engine does is to actually change the compression ratio of the engine.
The nominal compression ratio of an ordinary engine (say, 10:1) is only achieved at full-throttle operation. At any other condition, the actual compression ratio is less, because less air-gas is let in. This is the chief reason that gasoline engines can't achieve the efficiency of diesels, which are always running at their nominal compression ratio.
If you can vary the compression ratio, you can approach the nominal ratio even at part-throttle operation. To achieve it, you actually have to increase the ratio *above* the nominal amount (say, to 14:1). When you do that, the part-throttle operation, which lets in less air-gas, causes the *actual* compression ratio, or effective compression ratio, to be returned to the optimum 10:1. (These values are just examples.)
You wind up with diesel-like efficiency. Then, the Atkinson cycle extracts more, by effectively extending the expansion stroke.
The Atikinson-cycle part of the operation is incidental to the variable compression ratio. It's the variable compression ratio that's the big deal. A true Atkinson cycle is quite efficient, but the pseudo Atkinson cycle of today's hybrids is less so.
--
Ed Huntress

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"Ed Huntress" wrote in message wrote:

I think you're misreading it, Jon. This engine is truly revolutionary. Varying valve timing as you describe just produces a pseudo-Atkinson cycle, used on today's hybrids:
https://en.wikipedia.org/wiki/Atkinson_cycle
What this new Nissan engine does is to actually change the compression ratio of the engine.
The nominal compression ratio of an ordinary engine (say, 10:1) is only achieved at full-throttle operation. At any other condition, the actual compression ratio is less, because less air-gas is let in. This is the chief reason that gasoline engines can't achieve the efficiency of diesels, which are always running at their nominal compression ratio.
If you can vary the compression ratio, you can approach the nominal ratio even at part-throttle operation. To achieve it, you actually have to increase the ratio *above* the nominal amount (say, to 14:1). When you do that, the part-throttle operation, which lets in less air-gas, causes the *actual* compression ratio, or effective compression ratio, to be returned to the optimum 10:1. (These values are just examples.)
You wind up with diesel-like efficiency. Then, the Atkinson cycle extracts more, by effectively extending the expansion stroke.
The Atikinson-cycle part of the operation is incidental to the variable compression ratio. It's the variable compression ratio that's the big deal. A true Atkinson cycle is quite efficient, but the pseudo Atkinson cycle of today's hybrids is less so.
Ed Huntress =================================================================Saab demonstrated a running variable compression supercharged 5 cylinder in 2000, see https://en.wikipedia.org/wiki/Saab_Variable_Compression_engine for example. Naturally GM killed it sometime after they acquired Saab, citing cost. This was an inline engine with the block split horizontally between crankshaft and cylinders, with a hinge down one side and a mechanism to lift the other side to control the compression.
----- Regards, Carl Ijames
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Ed Huntress wrote:

Right.

Well, getting rid of pumping loss is a really good thing, so maybe this accomplishes the variable output without a throttle, at least under the driving range of operation (might still be needed for idle).

OK, that probably requires a degree in thermodynamics to understand.
Jon
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wrote:

Let me try the simple version and see if I can be clear: It is a thermodynamics issue. The higher the compression ratio, the greater is the Carnot efficiency of an engine. You don't need a thermodynamics background to get the idea of the Carnot cycle and efficiency. Wikipedia probably does it.
This is the main reason why diesels are so efficient: they always run at full, nominal compression. There is no throttle on the air. It's only the fuel that's varied as you advance from idle to full throttle.
On a spark-ignition engine, you keep the fuel/air mix as close to uniform as you can, and you vary the amount of the mix that gets into the cylinder, with the throttle. If you vary the fuel/air ratio by much (the ideal is 14.7 pounds of air for a pound of gasoline), the mixture won't ignite with a spark. So at full throttle, the engine will be running at a high compression ratio, the nominal ratio -- maybe 10:1 for example. At part throttle, the lesser amount of fuel/air mix produces a much lower effective compression ratio -- maybe 5:1 at some throttle settings. The Carnot efficiency goes to hell.
So you can see why having a variable compession ratio is such a big deal. Manufacturers have been trying to produce a variable compression ratio system that works well and that doesn't cost an arm and a leg, for close to a century.
The Atkinson cycle is something completely different, but it's another thermodynamics issue. I'll give it a try:
The true, original Atkinson cycle involved a short intake and compression stroke, and a long expansion stroke and exhaust stroke. A true Atkinson did it by means of a complex crank mechanism. The "pseudo Atkinsons," like the engines in today's hybrids, have the same-length stroke for all four parts of the cycle. But they open the intake valve late so the cylinder is less-filled. The expansion stroke, therefore, is *relatively* long for the amount of fuel being burned. You get more efficiency because the charge expands to a greater degree than normal. The nominal compression ratio is very high, but the *actual* compression is normal, because of the lesser cylinder-filling.
This Nissan engine combines both, but it's the compression ratio that's the big deal.
Tell me if this is as clear as mud. <g>
--
Ed Huntress

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Ed Huntress wrote:
The

My only quibble is that the trick, at least on the Honda, is this also means the intake valve CLOSES late, allowing some of the charge to be pushed back into the intake manifold. So, the compression stroke starts with the piston part way up the cylinder. This ends up with pretty low compression (or cylinder pressure, if you prefer) at ignition.
I'm guessing the trick in the Nissan engine is they effectively reduce displacement while still achieving a good cylinder pressure at low horsepower settings. That ought to improve efficiency.
Jon
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wrote:

I've never paid much attention to Atkinson engines, so I don't know what Honda is doing. BTW, the reason usually stated for *not* using the Atkinson cycle in regular engines is that they're not very tractable. I have read that they're slow to respond to the throttle, but beyond that, I don't have a clue.
There must be a lot going on with the Nissan engine, combining the turbocharger, the variable compression, and the Arkinson cycle. They may have published a paper on it with SAE. That's where you get the details.
--
Ed Huntress

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Ed Huntress wrote:

The only reason they'd be slow to respond is if the mechanism that changes the valve timing is slow. I'm sure this is true in the Honda hybrid engine. They put a rotary hydraulic cylinder in the intake cam sprocket, and I'm guessing the control valve on that has a small orifice so that the computer can keep up with the change in valve timing. I assume it has some sensor on the cam so it can measure the valve timing every cam revolution. So, it probably takes a dozen cam revolutions to make a large change in timing.
I can't imagine any other reason why it would be all that slow to respond. If there was some kind of immediate angle sensor in the sprocket so the computer had instant feedback of the valve timing, it could probably respond a lot faster. The hybrid system masks this, you can even see it on the battery gauge. Any time you push down on the gas pedal, the hybrid system applies power until the ICE ramps power up, the revers if you ease up on the pedal. it only takes 1/4 to 1/2 second to respond.

Yup, sounds like a lot to manage.
Jon
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wrote:

I see that Nissan published several papers on the development of this engine, but the last one I saw was from 2006. I just read the abstract.
--
Ed Huntress

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Engine efficiency increases with higher combustion ratio, limited by preignition and Knock. https://en.wikipedia.org/wiki/Engine_knocking
Knock varies with combustion conditions and can be sensed with a microphone sharply tuned to the block's resonant frequency (thus filtering out other sounds) and controlled by backing off the spark advance until it nearly disappears. The old vacuum advance did this open-loop, advancing the spark further at light throttle when intake vacuum is high and releasing it back to the RPM-controlled centrifugal advance position when you floor the pedal. However this is the easy but not the best way.
SAAB's conceptually simple system moves the cylinder block up or down relative to the crankshaft and piston to vary the combustion chamber's size to maintain maximum allowable pressure and the best efficiency at any power demand. http://www.autozine.org/technical_school/engine/tech_engine_4.htm Look at the positions of the orange eccentric shaft to the right of the connecting rod, and the red combustion chamber.
--jsw
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I like the old-timey bizarre mechanical linkages used to acheive the weird motions folks used to really get excited over.
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They're hardly "bizarr". I use such linkages on my machines to make explosive materials. Those 'bizarre' linkages are really a basic part of mechanics.
Look at some of the OLD (say, pre-1960s), purely-mechanical manuals on how to achieve various motions -- it's all in there!
Lloyd
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Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

It also turns out lots of those motions just aren't necessary. On another group there was chat about VHS tape recorders. Granted most machines now have some level of computer in them and mechanical timing stuff isn't needed anymore. The bottom line is cheap, not let's make elegant mechanisms anymore.
Back to VCRs, the original ones had like a half dozen motors. Recent ones, say made in the past 15-20 years were down to like 2 motors.
They designed all the complex mechanical nonsense out of the product. As it turns out, none of that complexity was really needed in the first place.
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But, "complexity" is not a part of an elegant mechanical design! Folks design stuff based on their "art" at the time. Elegance in mechanics peaked about 1930... It has gone down-hill ever since.<urk!>
Lloyd
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Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

I'm sure lost of this knowledge has been lost. For a long time now I've wondered how much effort it would take to design and built one of those giant mechanical calculators like banks used to have. Those things were absulutely insane in how complex they were and how many parts were crammed inside.
Even typewritters are works of art in how the actions feel nice in operation.
a $50 VCR is pretty amazing as well, when compared to an old one side by side. If you consider them black boxes, the new throw away ones do still work better. It's amazing how the the advancements in electronics rendered all the other mechanical parts useless.
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More specifically the advance in cheap computing power obsoleted both mechanical control mechanisms and bulky discrete electronics such as in older televisions. When I was learning communications electronics in the Army in 1970 a phone line modem was the size of a 2-drawer file cabinet. Each circuit card held two discrete transistor NAND gates. The frequency shift modulator and demodulator were cleverly tuned transformer / filter circuits that the instructor didn't understand. They showed us evaluation samples of integrated circuit electronics but we learned to repair the 1960's gear that was in wide use.
In the early 80's I built a similar frequency-shift modem the size of a portable cassette recorder with parts from Radio Shack. The modem and recorder were the mass storage for my home-brew computer.
As soon as fast enough analog to digital converters became affordable, around 1990, a microcomputer could replace the remaining analog circuitry. That enabled the digital radios I prototyped at Mitre, and pocket-sized cell phones. The best A/Ds we could get back then were for the new Tektronix and HP digital oscilloscopes.
On the other hand, when I was working on the color ink jet printer in the mid 80's I halved the complexity of the electronics by a simple mechanical rearrangement of the print head geometry.
The Army had the technology for encrypted voice and data cell phones by 1970. The field-deployable electronics at the "cell tower" filled six interconnected trailer trucks plus a van for the microwave radio link, with a large Diesel generator on a trailer and at least two dozen men and a field kitchen to support it all. We would have been a tempting and easy target for Spetsnaz desantniki (paratroop commandos).
--jsw
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We were running crypto'd voice in 1968 on Navy River Boats, over in 'Nam; and I think they'd been using them for several years by the time I got there.
The unit was about the size of a medium-sized benchtop oscilloscope (like a Tek 525). We changed the 'Cac' code every day, as part of our pre-mission checkouts.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

http://cryptomuseum.com/crypto/usa/index.htm
Tactical crypto machines were smaller, lighter and less secure, since your comms about your mission became 'stale' and useless to ambush you once you returned to base. The good stuff, the KG-13 and KY-3, weighed several hundred pounds.
We were safeguarding Army payroll data, which sounds silly until you realize that -where- troops were paid was important, not how much they made. For example Putin would really like to know if US tank commanders started receiving their pay in Ukraine.
The Navy had a very serious leak back then: https://news.usni.org/2014/09/02/john-walker-spy-ring-u-s-navys-biggest-betrayal
--ave52G
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