Vacume and diesel engines

[Matt_Jr]

I love threads that involve theory.

You are all correct. Mostly. Vacuum is an absense of pressure. Scientists at NASA are still trying to make perfect vacuums to test space suits. They can't yet, but come pretty close by our standards using very strong pumps both piston and vein. A perfect vacuum is theorized to exist at 30 inches of mercury. No pump in the world is strong enough to do that. The most effecient running gasoline engines (not including high performance engines) at sea level will have a reading of approximately 18"hg (hg is mercury) at idle. If one was to connect a 1 inch squared tube to the manifold of their gas engine while idling the atmospheric pressure surrounding the bucket of mercury would push the mercury up the tube 18". If this same procedure was done with a diesel engine the mercury may not be pushed up the tube at all. The reason is that there is no throttle plate on a diesel. There is on a gas engine. If you put a rag in front of the throttle body atmospheric pressure will push the rag into the throttle. Although the rag is pushed into the engine by atmospheric pressure we usually describe the rag as being sucked into it. Go ahead guys, let me have it.

As for the plane on a conveyor belt. Once it leaves ground effects will it fall back to the ground.. I mean.. back on the conveyor belt?

 

[Matt_Jr]

Oh, what if the plane was tracked instead of wheeled? Or had skis?

 

[polo1665]

"Scientists at NASA are still trying to make perfect vacuums to test space suits. They can't yet, but come pretty close by our standards using very strong pumps both piston and vein. A perfect vacuum is theorized to exist at 30 inches of mercury"

Inches of mercury is a very rough measure of vacuum. In my industry that measure is only used to confirm that doors have sealed when a chamber is initially pumped down. Our furnaces ultimately achieve vacuum levels that are measured in microns of mercury. Rotary piston pumps and blowers rough the furnace chambers down to around 200 microns, at this point diffusion pumps are brought online to bring the ultimate pressure down to below one micron in some cases. To put that in perspective you have to realize that one atmosphere is equal to 760 Torr or 760,000 Microns. These vacuum levels easily achieved with common equipment, and other industries achieve even finer vacuum levels. You can only begin to realize what vacuum levels are being achieved in a scientific setting.

Sorry, that was totally off topic, but I have always found it fascinating.

 

[Matt_Jr]

"Scientists at NASA are still trying to make perfect vacuums to test space suits. They can't yet, but come pretty close by our standards using very strong pumps both piston and vein. A perfect vacuum is theorized to exist at 30 inches of mercury"

Inches of mercury is a very rough measure of vacuum. In my industry that measure is only used to confirm that doors have sealed when a chamber is initially pumped down. Our furnaces ultimately achieve vacuum levels that are measured in microns of mercury. Rotary piston pumps and blowers rough the furnace chambers down to around 200 microns, at this point diffusion pumps are brought online to bring the ultimate pressure down to below one micron in some cases. To put that in perspective you have to realize that one atmosphere is equal to 760 Torr or 760,000 Microns. These vacuum levels easily achieved with common equipment, and other industries achieve even finer vacuum levels. You can only begin to realize what vacuum levels are being achieved in a scientific setting.

Sorry, that was totally off topic, but I have always found it fascinating.

Thanks for the update. I too find this stuff interesting. What kind of furnaces are you using.

 

[polo1665]

We operate vacuum remelt furnaces, melting and pouring anywhere from 10 to 140 lbs of nickel and cobalt based superalloys. The components we manufacture are used in turbine engines, both for aerospace and land based (power generation) applications.

 

[QRTRHRS]

Back in the days when cars had vacuum windshield wipers, one could argue that gasoline engines were not so good at making vacuum either.

 

[Egon]

Back in the days when cars had vacuum windshield wipers, one could argue that gasoline engines were not so good at making vacuum either.

Made one wish the hand operated ones were still used every time you went up a hill! But on the downside it was different!

 

[SPYDERLK]

I knew the part about NA engines having lower horsepower at lower altitudes, but I've never had much experience with a Turbo. I wasn't sure if the thinner atmosphere would still affect a turbo since it's got lower pressure to start with.

Sounds like it doesn't.

It doesnt affect a turbo system as much, or in particular, as quickly as you might think.

With a turbo an engine sorta pulls itself up by the bootstraps - its exhaust. The more power it produces the more exhaust it makes the faster the turbo goes the more air goes in the cylinders the more fuel it can burn the more power it can make.... At higher altitude the thinner [lower pressure] air that the turbo is compressing presents less of a load to it. This just lets it spin faster and consequently it can put out almost the same pressure as it could at lower altitude.
larry

 

[dqdave1]

Plane will not move regardless of type of gear or tires. Remember this is in therory. Mythbusters cannot duplicate therory.

 

[tallyho8]

Plane will not move regardless of type of gear or tires. Remember this is in therory. Mythbusters cannot duplicate therory.

No fair! You have to go to the "Will it Fly?" thread to post your opinion.






PS Yes it will.