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1 hour ago, Collimatrix said:

 

There's usually more than one shaft.  The AGT-1500, for instance, has two shafts taking power from the high and low pressure turbines to the compressors, and a third, completely separate power turbine with variable inlet geometry that actually delivers the power to the transmission.  So the power turbine could be at or near stall but the rest of the engine wouldn't necessarily.

Does a turbine give a similar torque curve to electric motors? 

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14 hours ago, Xlucine said:

Turbines also have a neat trick for battlefield mobility, as the turbine generates the most torque when it's stalled. The power output from a turbine more closely approximates the output from a magic constant-power source, whereas a piston engine (petrol or diesel) approximates a magic constant torque source. This means that a turbine puts down a much greater fraction of the peak power at low RPM, which is useful for pulling away.

 

I wonder what the suspension comparison in the first page was to? 9g at half the speed compared to 1g in the merk is a big gulf. Maybe a sherman?

 

Either a Patton or Abrams. It's worth noting that the article was written AFTER the comparative trials between the M1A1 and Merkava 3, where both were tested in the north, where there is a nice range of terrain types - deep mud, hard soil, bazalt boulders, and all kinds of slopes. It's a perfect place to test an AFV for mobility in real conditions, and all IDF AFVs are built to cope with the northern terrain of the Golan area.

During those trials they concluded that the Abrams could only drive in certain routes - i.e avoid the bazalt fields, to avoid extensive damage and injuries, whereas a Merkava 3 tank could drive in relative safety in all areas of the Golan.

 

That's why when officials compare the mobility of the two, they say it's comparable to that of the Abrams, because they are familiar with it. They know how it handles in the Merkava's playfield. 

 

And you do touch a very important subject here. During Yehiam Herpez's last interview (he basically developed all the suspension types in MANTAK for a while, including the Mark 3's which was the most revolutionary of the series, and even a torsion bar suspension for a light tank), he said that while Merkava tanks are equipped with towing gear to rescue immobilized tanks, their engines don't actually allow it, therefore they use D9 for this. Hopefully that will change with the Barak, as it's supposed to get a new powerpack.

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While only tangentially related, I find it interesting that the M1 apparently has issues with the terrain of the Golan Heights, not because that terrain is easy (it is very nasty terrain) - but rather because the US extensively has tested the Abrams on the Yakima Training Center grounds which has lots of similar basalt. I wonder if the YTC gives the Abrams headaches.

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  • 4 months later...
On 7/21/2018 at 11:29 PM, Serge said:

 

 

Hmm, reading that article nothing about this engine really seems to be new - it's a opposed piston two-stroke, trying to run as a gasoline compression engine... none of those are new ideas, and both opposed-piston and gasoline compression engines have proven to be generally pretty bad ones. Rather like rotaries, they are fantastic on paper but rapidly run into big issues in practice. Now a variable compression engine, I'd be interested in. Nissan just put one into commercial production after decades of research and trials (KR20DDET).

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28 minutes ago, TokyoMorose said:

 

 

Hmm, reading that article nothing about this engine really seems to be new - it's a opposed piston two-stroke, trying to run as a gasoline compression engine... none of those are new ideas, and both opposed-piston and gasoline compression engines have proven to be generally pretty bad ones. Rather like rotaries, they are fantastic on paper but rapidly run into big issues in practice. Now a variable compression engine, I'd be interested in. Nissan just put one into commercial production after decades of research and trials (KR20DDET).

Why would Variable Compression (VC) be useful in diesel vehicles?

 

I would like to see a camless engine. Like the one Koenigsegg is developing. 

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18 minutes ago, Xoon said:

Why would Variable Compression (VC) be useful in diesel vehicles? 

Because it self adapts to the exact horsepower you need when driving. 

This way, you can save plenty of fuel. You can save your wages to have better welfare and decrease pollution. 

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39 minutes ago, Xoon said:

Why would Variable Compression (VC) be useful in diesel vehicles?

 

I would like to see a camless engine. Like the one Koenigsegg is developing. 

 

@Walter_Sobchak's father worked on the AVCR 1360, IIRC.  Apparently the engine worked well enough, but the ones tested were hand-produced toolroom prototypes, and the design would have been tricky to mass-produce.

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1 hour ago, Serge said:

Because it self adapts to the exact horsepower you need when driving. 

This way, you can save plenty of fuel. You can save your wages to have better welfare and decrease pollution. 

 

1 hour ago, Collimatrix said:

 

@Walter_Sobchak's father worked on the AVCR 1360, IIRC.  Apparently the engine worked well enough, but the ones tested were hand-produced toolroom prototypes, and the design would have been tricky to mass-produce.

How does it work in a diesel? 

 

Does it just lower the compression ratio to compensate for the higher boost? 

 

 

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13 hours ago, Xoon said:

 

How does it work in a diesel? 

 

Does it just lower the compression ratio to compensate for the higher boost? 

 

 

 

Basically, yes - hydraulic pressure is used to vary piston height to change compression as RPM and boost pressures change. The AVCR-1360 was a really nifty engine and if it was not for the Army's then-obsession with turbine power it really should have been the Abrams' engine. In the spoiler pop-out is a picture of the Continental AVCR-series piston head. It was however complicated, and nobody has over the decades of effort put a variable compression engine into mass production until that just-introduced Nissan KR (and they must be feeling confident in it, they are planning to build over 100k of them per year, for a total run in millions).

Spoiler

y6YZbvw.png

 

 

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18 hours ago, Collimatrix said:

 

@Walter_Sobchak's father worked on the AVCR 1360, IIRC.  Apparently the engine worked well enough, but the ones tested were hand-produced toolroom prototypes, and the design would have been tricky to mass-produce.

 

Pretty much, yes.  The main advantage was that you could have a higher compression when starting the engine and then lower the compression at high speed.  One of the big issues with military diesel engines is getting them to pass the NATO cold start requirements.  With the higher compression at starting, it was easier to get the engine to start in really low temps.  

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2 hours ago, Walter_Sobchak said:

 

Pretty much, yes.  The main advantage was that you could have a higher compression when starting the engine and then lower the compression at high speed.  One of the big issues with military diesel engines is getting them to pass the NATO cold start requirements.  With the higher compression at starting, it was easier to get the engine to start in really low temps.  

Has integrated exhaust manifolds been considered?

It should help with cold starts and provide a faster way of getting the engine up to the optimal temperature. 

Also it allows you in theory, to reduce the temperature of the exhaust. 

 

Other neat features would be variable twin scroll turbochargers. 

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3 hours ago, Xoon said:

Has integrated exhaust manifolds been considered?

It should help with cold starts and provide a faster way of getting the engine up to the optimal temperature. 

Also it allows you in theory, to reduce the temperature of the exhaust. 

 

Other neat features would be variable twin scroll turbochargers. 

 

Having a variable multi-scroll would be redundant - having multiple scrolls is to allow multiple ratios, which is what variable does anyhow. And running a hot air intake from the exhaust manifolds don't really help on a pure cold start, and once you have the engine running it's just going to sap performance by decreasing intake air density.

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5 hours ago, Xoon said:

Has integrated exhaust manifolds been considered?

It should help with cold starts and provide a faster way of getting the engine up to the optimal temperature. 

Also it allows you in theory, to reduce the temperature of the exhaust. 

 

Other neat features would be variable twin scroll turbochargers. 

 

AVCR-1360 had variable geometry turbos on it, and they were quite problematic.  This was back in the late 70's/early 80's and the mechanical controls they had were not nearly as good as the digital controls what would appear a decade or so later.  In fact, those variable geometry turbo controls would eventually end up in a Teledyne dumpster, by dad fished some of the parts out and eventually used them to build a oscillating sander for his woodworking shop.  True story.  

 

As to integrated exhaust manifolds, I don't think they would have been of much use on an air cooled engine like the AVCR-1360.

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11 hours ago, TokyoMorose said:

 

Having a variable multi-scroll would be redundant - having multiple scrolls is to allow multiple ratios, which is what variable does anyhow.

Variable Geometry turbocharger:

 

 

Twin Scroll turbocharger:

 

 

Variable Twin Scroll Turbocharger:

 

 

Watch these three videos, which will give you a quick explanation of the three turbochargers. 

 

 

 

11 hours ago, TokyoMorose said:

 

And running a hot air intake from the exhaust manifolds don't really help on a pure cold start, and once you have the engine running it's just going to sap performance by decreasing intake air density.

???

 

 

Integrated exhaust manifolds simply make the exhaust manifold a part of the block. This allows it to be water cooled.  And the heat from the exhaust helps heat up the coolant running through the block, helping it reach optimal temperature faster.  It also allows for better turbocharger performance. 

 

 

9 hours ago, Walter_Sobchak said:

AVCR-1360 had variable geometry turbos on it, and they were quite problematic.  This was back in the late 70's/early 80's and the mechanical controls they had were not nearly as good as the digital controls what would appear a decade or so later.  In fact, those variable geometry turbo controls would eventually end up in a Teledyne dumpster, by dad fished some of the parts out and eventually used them to build a oscillating sander for his woodworking shop.  True story.  

The AVCR-1360 sound more and more interesting. 

 

 

9 hours ago, Walter_Sobchak said:

As to integrated exhaust manifolds, I don't think they would have been of much use on an air cooled engine like the AVCR-1360.

Oh, it was air cooled. My bad. 

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7 hours ago, Xoon said:

Watch these three videos, which will give you a quick explanation of the three turbochargers.

 

I know pretty much all there is to know about Turbochargers -  and the reason nobody has put a twin-scroll variable geometry system into mass production is for the reason I mentioned, they are utterly redundant. Variable Geometry solves the problem that twin scroll turbos were introduced for, better than twin scroll turbos do. Twin Scroll is still around because it is simpler and cheaper, but there's no reason to have multiple scrolls if you are going to pay for variable geometry. If you absolutely have to have low end response faster than a pure-VGT option can offer, it's much simpler to use a small electric boost motor attached to the turbine - it's quite common nowadays.

 

8 hours ago, Xoon said:

Integrated exhaust manifolds simply make the exhaust manifold a part of the block. This allows it to be water cooled.  And the heat from the exhaust helps heat up the coolant running through the block, helping it reach optimal temperature faster.  It also allows for better turbocharger performance.

 

Ah, so you want to heat the coolant with the exhaust instead of intake air, sorry. However, even this isn't terribly practical - it adds a bunch of complexity to the block, which is already quite the complicated part, and once the engine is at operational temperature it simply adds more heat to the coolant that has to be diffused by the radiator. The gains in turbo performance are utterly marginal and is much cheaper/simpler to simply use a slightly larger turbo for the same effect. Volkswagen's use of water-cooled exhaust is an extremely oddball development, and probably has to due with Volkswagen's general love of complexity. I mean, they were the crazy guys who put the Twincharger into production. The gains you get from water-cooling the exhaust just aren't worth the costs added unless you are physically out of other ways to get the engine heated in time or can't use a bigger turbo and need the sliver of performance.

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