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Old 09-28-2013, 02:47 PM   #21 (permalink)
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There is no advantage to R134A for cooling, so why bother?
The main disadvantage is pressure. In order for R134A to be a liquid, it must be compressed. That is what makes it a refrigerant.
Using this temp-press calculator: R134a Refrigerant Pressure Temperature Calculator
70F = 71 PSI
140F = 228 PSI
200F = 486 PSI

Imagine the price of components that will required to contain those pressures.

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Old 09-29-2013, 12:38 AM   #22 (permalink)
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Above ~101C (and 4.?? MPa) R134a can't exist as a liquid regardless of the pressure it is under.

In addition, the closer it gets to that temperature, the less heat energy it takes to convert it from liquid to gas i.e. the less effective it is as a coolant.
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Old 10-01-2013, 12:05 AM   #23 (permalink)
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Quote:
Originally Posted by jeff88 View Post
Instead of using a TC, could one use a "smart" clutch hooked into the brake pedal. It wouldn't latch when the car is at speed and the brakes are applied, but if the wheels are stopped (or really close to), then the clutch is applied and the break in the system happens. Or maybe you wouldn't need any of that. Anytime the brake is applied, it would detach the engine/transmission and as soon as you let off the brake (before you press the gas again), the clutch would re-engage the system.
VW and Volvo tried something like this, it was a nightmare.
There is an Alison automatic transmission one of the big ones, bigger than the Alison1000 like this, its a traditional auto trans that slips into neutral before you stop and goes back in gear when you let your foot off the brake.
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Old 10-01-2013, 12:16 AM   #24 (permalink)
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Quote:
Originally Posted by jeff88 View Post
Also as a side note, why do we not use oil as a coolant? (I know that the engine oil does help with cooling, but I'm not talking about that). Couldn't one use a really thin, maybe 0w-10, oil in a coolant loop? I would think (and read) oil is a better vehicle for heat pick-up and removal.
Ever own an older Porsche 911?
They have an oil cooling system, takes like 5 or 7 gallons of oil.
Even Porsche abandoned oil/air cooling in the late 80s or early 90s.
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Old 10-01-2013, 06:17 PM   #25 (permalink)
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It was the late 90s. The 993 was still air-cooled (and oil-cooled); the 996 was the first water-cooled 911. I think that started with the 1998 model year.

Water (and glycol) cools more effectively than oil does, I believe. And air is notoriously difficult to get to where you want it, and does not transfer heat as well as water does. Water also serves as a very effective sound absorber when it is run around some of the noisy parts, like cylinders, parts of the head, etc. And the uneven cooling from oil and air keeps you from controlling the combustion cycle as precisely as you want to make good power and low emissions.

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Old 10-02-2013, 02:53 PM   #26 (permalink)
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Other than cost, why doesn't each cylinder have its own head? It seems like that would make more sense maintenance wise, that way when something happens to one cylinder, you don't have to take the whole thing apart. (I know there is an issue with more gaskets and whatnot, but it just seems like it would make more sense - other than cost)

Also, if they were smaller, the size of a single cylinder rather than 4 or 6, etc. then couldn't you put a "screw-on" head, which would allow for a better seal without the risk of blowing gaskets every xxx,xxx miles. I'm thinking like a soda or water bottle, the screws keep everything in (and everything out), or even similar to the screws of the spark plugs.

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Old 10-02-2013, 08:14 PM   #27 (permalink)
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large diesels do this, as do many aircraft engines.

over head valve systems would get very complex with separate heads. Now you are pretty much stuck with pushrods.

where the cylinders bolt to the crank case is often a constant source of oil leaks.
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Old 10-02-2013, 10:16 PM   #28 (permalink)
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Quite a few early ICE's were constructed as individual cylinders on a common crankshaft too.

Reasons that it is not usually done would include:

Arranging coolant flow is more difficult.

The engine is longer and heavier because fasteners (and the corresponding bosses on the heads) cannot be shared between cylinders.

It would take longer to assemble on a production line.

Screw on heads is an interesting idea. Indexing the alignment of the head and cylinder might be difficult though.

It's not quite the same, but screwing cylinder liners into the head has been tried.
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Old 10-03-2013, 05:42 PM   #29 (permalink)
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Quote:
Originally Posted by jeff88 View Post
Other than cost, why doesn't each cylinder have its own head?
Aircooled 911s do. Each cylinder is separate, each head is separate, and then there is a "cam tower" that is a single piece that goes across the whole set, linking them together. It does make for somewhat modular construction, and the head castings can be smaller and cheaper to make. And I think there are air passages in between the individual heads? I forget...

If you have a single head bridging across the cylinders, you get easier coolant passage layout (when not using air, at least). Plus the single large casting is much stronger and resists deformation a lot better than smaller individual castings. And there are fewer interfaces to leak, just one or two large ones rather than many smaller ones.

A number of aero engines also used separate cylinder heads, and separate rocker boxes as well. But in general those are built using 1920s technology. Aircraft engine development lags astonishingly behind automobile engine development in many ways.

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Old 10-03-2013, 06:28 PM   #30 (permalink)
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A number of aero engines also used separate cylinder heads, and separate rocker boxes as well. But in general those are built using 1920s technology. Aircraft engine development lags astonishingly behind automobile engine development in many ways.

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