variable compression engine ???

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Wolfman
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variable compression engine ???

Post by Wolfman » Wed Nov 22, 2017 8:07 am

I will apologize up front. This ain't about military or Jeep.
But, with the knowledge base represented here, I figure someone knows.
Just read an article on a new engine Nissan has developed. A variable compression engine. A 4 cyl. that produces the power of a 6 and is cleaner burning.
The article said the piston stroke is changed to raise or lower the compression. No further details.
???????????????
How do they do that ?
Pretty vague article. Raise and lower the compression ?? Did not mention a change in over all engine displacement.
Raise or lower the crankshaft ??
Raise or lower the cylinder ???
Increase or decrease combustion chamber area ???
IH did the last several years ago on an Ag. Engine. Cylinder head had two combustion chambers per cylinder connected by a third valve. Third valve open. Larger combustion chamber area. Lower compression. Ran on gas.
Third valve closed. Smaller combustion chamber area. Compression higher. Ran on diesel.
Worked initially but they had a lot of problems as the system aged and finally dropped the idea.
My curiosity has been tweaked.
I figure someone on here has an answer.
Mike Wolford
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Re: variable compression engine ???

Post by ndnile » Thu Nov 23, 2017 12:20 pm

I'm not an authority here, but here is what I "think" I know. I don't know which approach Nissan is going with or if they are indeed playing with actual piston stroke.

The two methods I'm somewhat familiar with are the Atkinson Cycle and Miller Cycle. These have been used for years to control the "effective compression" of engines. The standard piston engine is known as an otto-cycle engine.

Atkinson cycle (invented 1882): Make compression stroke smaller than power stroke.
If you have a 10:1 compression engine, but close the intake valve earlier than an otto-cycle engine would on the intake stroke it will lower the compression pressure seen at TDC and thereby mimic a lower compression engine, lets say 8:1. Since you still have the full 10:1 stroke on the power stroke there is an efficiency gain. This is known as the Atkinson cycle engine. Good for efficiency, but bad for max HP. Toyota Prius uses this.

Miller cycle (patented 1957): Do some of the compression outside of the cylinder where you also have an opportunity to pre-cool it.
I think of this as being the opposite of the Atkinson. You use a super charger and leave the intake valve open a bit longer than usual to give the pressurized intake a chance to pump a bit more air in before closing the intake valve. Since some of the compression occurs via the supercharger you also have the opportunity to cool the charge via an intercooler prior to it going into the engine which helps fight pre-detonation.

Fast-Forward to today. With variable valve timing and a well controlled turbocharger you should be able to operate an engine in Atkinson cycle when you are cruising and in Miller cycle when you are pulling a load up a hill. Best of all worlds. I think that is how the ford ecoboost functions.

I am totally up for corrections to the above.
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Re: variable compression engine ???

Post by Wolfman » Fri Nov 24, 2017 8:13 am

Interesting !!!
To make a long story short, they are screwing with the volumetric efficiency of the cylinder to control compression pressure.
Good chance these engines are turbo or supercharged. And don't forget a computer to control all this.
I guess a jeep L-134 does the same thing with a carburetor throttle plate. :D
The Nissan is on steroids.
Thanks for the intel !!
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Re: variable compression engine ???

Post by Destructo6 » Mon Nov 27, 2017 12:23 pm

The write-up in Jalopnik, and Nissan press releases, say that it changes displacement while changing compression:

https://jalopnik.com/worlds-first-varia ... 1785295848

Interesting system. It also has variable valve timing and a turbo.
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Re: variable compression engine ???

Post by artificer » Mon Nov 27, 2017 1:31 pm

Search "Infiniti VC-T engines" then click on images.
It's all there & will fill us in on the methodology....cantilever arrangement with lots more working parts compared to conventional....:
https://www.google.com.au/search?q=Infi ... 22&bih=758
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Re: variable compression engine ???

Post by Wolfman » Tue Nov 28, 2017 7:04 am

This is getting better as it grows.
Nissan is not just messing with the volumetric efficiency of the cylinder. They are actually variably changing the piston height which is increasing and decreasing the compression ratio. 8:1 to as much as 14:1. Old diesels were only 14.5:1
Interesting concept.
Instead of the connecting rod being fastened to the crankshaft directly, it is fastened to one end of a lever, on the crankshaft rod journal. The other end of the lever is controlled by a variable height link. That explains how they did it. Of course there is a computer involved in all this.
My next thought is, " simple is better ".
I am wondering how far this is going to go before it has a problem.
Something come loose and by the time the pieces stop flying, the fix would be, pull the engine. Throw it in the junk pile and install a new one.
:shock: :shock: $$$$$$$$ :shock: :shock:
An L-134 may not keep up but wonder which will still be going in the long run ??
Tortoise and the Hare thing. Know what I mean Vern ?
Welcome to the 21st Century.
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Re: variable compression engine ???

Post by Donovan » Tue Nov 28, 2017 9:31 am

Engine changing compression is an old technology. My father used to have an old International caterpillar tractor (40-50s era) that you started on gas and then through a lever that cut off the gas, turned on the diesel and changed the compression from low to high compression. I had always wondered how it did that and the concept of a valve open for gas and closed for diesel makes sense. The technology today in the new engines is incredible. I like the simplicity of the flat head four cylinder in my vehicle although there are a few times I wish I had more power.

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Re: variable compression engine ???

Post by artificer » Tue Nov 28, 2017 12:00 pm

Having worked on some Cat tractors [in the Military] as just described, they were not variable compression.
What was called a 'donkey or pony' starter engine rather than a starter motor was used to get the diesel running.
A 2 cylinder horizontally opposed 'donkey' engine was started with a pull rope on the smaller models & when warmed up a lever was pulled engaging the donkey with the diesel to get it started. Once the diesel was started the donkey was disengaged & switched off.
The larger models had a conventional 2 cylinder donkey engine, magneto ignition with some electrically started, from memory.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: variable compression engine ???

Post by Donovan » Tue Nov 28, 2017 12:26 pm

John,
I know what a pony motor is and Caterpillar used this technique to start their engine. On an International, there were spark plugs and glow plugs on each cylinder. Very strange setup and always wondered how the lever was changing the compression ratio in the engine. Based on what I have heard in this string, I think I now know how it was done.

The two International caterpillars my Dad owned were a TD-9 and TD-14A.

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Re: variable compression engine ???

Post by artificer » Tue Nov 28, 2017 12:58 pm

With respect 2 different companies International TD series crawler tractors are not related to Caterpillar.
Come to think of it there were a number of supposedly variable compression engines used in agricultural tractors that started on gasoline [petrol] then switched to diesel or kerosene.
http://www.australiansugarcane.com.au/B ... rtales.pdf
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: variable compression engine ???

Post by fiveftsix » Tue Nov 28, 2017 6:31 pm

You might be getting a little confused John,
There were a few tractors running dual fuel
Gas or Petrol then switched to kerosene or TVO as it was known Tractor vaporizing oil once the motor was hot
Otherwise it would not start solely of TVO
Geoff Bull

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Re: variable compression engine ???

Post by artificer » Tue Nov 28, 2017 7:57 pm

Not confused, I remember that era as well.
See what I was talking of in the Chamberlain link, near the middle of page 24.
I was a kid when petrol rationing was still in effect & there were some trucks & cars setup to run that way as well i.e. switch over to kero once they got really hot. Then of course there were vehicles still running around with gas producers....http://consuleng.com.au/Producer%20Gas% ... 939-45.pdf
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: variable compression engine ???

Post by Wolfman » Wed Nov 29, 2017 7:39 am

I have worked on all of the different systems described, Except the new Nissan.
The IH all fuel tractors ( start on gas, switch to TVO ) was used on the old Farmall farm tractors. Had a 1940 "H" in the shop this summer that was set up this way. Two fuel tanks. A small gas tank for starting and the large " All Fuel " or "TVO" tank for running once the engine was warmed up. Both tanks were connected to one carb. through a selector valve. For the day, the all fuel engines were a higher compression engine. Straight gas engine was 5.5:1. The all fuel engine was 6.5:1. Other than this, both were the same. The TVO reminded me of kerosene.
The IH gas/diesel engine had two combustion chambers per cylinder that were connected by a third valve. It also had a complete spark ignition sys. with a carb. and a diesel fuel injection system. The spark plug was in the extra combustion chamber and the diesel fuel injector was in the main combustion chamber.
When the engine was running on gas, the third valve was open, making the combustion chamber area larger and the compression lower.
When the third valve was closed, the second chamber was closed off. The compression increased. The electric ignition system was turned off. Gas to the carb. main jet was blocked and the carb. went to full throttle. The diesel injection turned on and the engine ran on diesel.
And all this was controlled by a single lever. Very temperamental also. Took a lot of maintenance to keep them working correctly.
Pony motors. I have seen Cat dozers with Pony Motors. Never worked on one. My Cat experience was 3165 and 3208 V-8 engines.
Early John Deere "G" and 730, 2 cylinder diesel tractors had pony engines. V-4 gas engines. The later 730D went to electric start.
Starting one was like a ballet.
Start the pony engine. It went to full throttle. Let it warm up. The exhaust pipe from the pony engine was routed through the diesel intake. As the pony engine and exhaust warmed up, the exhaust heated the air in the diesel intake.
Once the pony engine was warm, a decompression pedal was stepped on to hold the diesel exhaust valves slightly open so the pony engine was not working against the diesel compression. A clutch on the pony motor was slowly engaged to spin the diesel engine up to starting RPM. When ready, the decompression pedal was released. and the fuel lever was moved to the run position. If lucky, before the pony motor was pulled down and had to be disengaged, which did not take long, the diesel engine would start and the pony motor shut down. Try teaching this to a new guy. :roll:
None of this had anything to do with a computer.
My guess is with the new Nissan, you insert a card and push a button. :D
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Re: variable compression engine ???

Post by gerrykan » Wed Nov 29, 2017 5:05 pm

Wolfman wrote:
Wed Nov 29, 2017 7:39 am
....None of this had anything to do with a computer.
Well, actually the human was the computer, back when you had to think, instead of mindlessly staring at an I-phone.

Old guy rant over.
Roy

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Re: variable compression engine ???

Post by Wolfman » Fri Dec 01, 2017 7:56 am

I agree, Roy.
The good ole days when people would think and ran the machines.
You only think " Zombie Apocalypse " is a science fiction story.
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