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Hooked_on_HP
Veteran Member
John that is the best and simplest answer to my question. Thank You.
Bill
Bill
Vacume and diesel engines
- Thread starter Hooked_on_HP
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Redneck in training
Elite Member
Gasoline engine at idle is 18-22" hg Diesel engine at idle is much less than 1" hg Gasoline engine working hard is 5-9" hg (3/4 throttle lets say going up a big hill pulling a trailer etc) Diesel engine working hard is still under 1" hg (hopefully much less as it's a sign of a clogged air filter.) Gasoline engine at wide open throttle full load is 1" hg Diesel engine at full load is also about 1" hg. jb[/QUOTE said:
As I said "us nerdy tractor types that get all bound up in the details"
Most people (outside of engineers) would assume it was gauge vacuum as they would use a gauge to measure it. Also, about nobody (outside of engineers) knowing the context would assume it was absolute pressure.
Still, you are accurate and correct. (if bound up in the details)
Merry Christmas!
jb
Most people (outside of engineers) would assume it was gauge vacuum as they would use a gauge to measure it. Also, about nobody (outside of engineers) knowing the context would assume it was absolute pressure.
Still, you are accurate and correct. (if bound up in the details
)Merry Christmas!
jb
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How's that old saying go.. the devil is in the details?
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J_J
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Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
Manifold vacuum is an effect of choked flow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of airflow through the engine, and hence of the unused power capacity in the engine. In some engines, the manifold vacuum is also used as an auxiliary power source to drive engine accessories. Manifold vacuum should not be confused with venturi vacuum, which is an effect that is exploited in carburetors to achieve a fixed mix ratio between fuel and air.
[edit] Manifold vacuum in diesel engines
Many diesel engines do not have butterfly valve throttles. The manifold is connected directly to the air intake and the only suction created is that caused by the descending piston with no venturi to increase it, and the engine power is controlled by varying the amount of fuel that is injected into the cylinder by a fuel injection system. This assists in making diesels much more efficient than petrol engines.
If vacuum is required (vehicles that can be fitted with both petrol and diesel engines often have systems requiring it), a butterfly valve connected to the throttle can be fitted to the manifold. This reduces efficiency and is still not as effective as it is not connected to a venturi. Since low-pressure is only created on the over-run (such as when descending hills with a closed throttle), not over a wide range of situations as in a petrol engine, a vacuum tank is fitted.
Most diesel engines now have a separate vacuum pump ("exhauster") fitted to provide vacuum at all times, at all engine speeds.
Many new BMW petrol engines do not use a throttle valve in normal running, but instead use "Valvetronic" variable-lift intake valves to control the amount of air entering the engine. Like a diesel engine, manifold vacuum is practically non-existent in these engines and an exhauster must be added to power the brake servo. Valvetronic requires very high modulus valve springs and results in a heavy valvetrain, so despite its advantages in fuel economy, it is currently unsuitable for high-revving engines
Manifold vacuum is an effect of choked flow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of airflow through the engine, and hence of the unused power capacity in the engine. In some engines, the manifold vacuum is also used as an auxiliary power source to drive engine accessories. Manifold vacuum should not be confused with venturi vacuum, which is an effect that is exploited in carburetors to achieve a fixed mix ratio between fuel and air.
[edit] Manifold vacuum in diesel engines
Many diesel engines do not have butterfly valve throttles. The manifold is connected directly to the air intake and the only suction created is that caused by the descending piston with no venturi to increase it, and the engine power is controlled by varying the amount of fuel that is injected into the cylinder by a fuel injection system. This assists in making diesels much more efficient than petrol engines.
If vacuum is required (vehicles that can be fitted with both petrol and diesel engines often have systems requiring it), a butterfly valve connected to the throttle can be fitted to the manifold. This reduces efficiency and is still not as effective as it is not connected to a venturi. Since low-pressure is only created on the over-run (such as when descending hills with a closed throttle), not over a wide range of situations as in a petrol engine, a vacuum tank is fitted.
Most diesel engines now have a separate vacuum pump ("exhauster") fitted to provide vacuum at all times, at all engine speeds.
Many new BMW petrol engines do not use a throttle valve in normal running, but instead use "Valvetronic" variable-lift intake valves to control the amount of air entering the engine. Like a diesel engine, manifold vacuum is practically non-existent in these engines and an exhauster must be added to power the brake servo. Valvetronic requires very high modulus valve springs and results in a heavy valvetrain, so despite its advantages in fuel economy, it is currently unsuitable for high-revving engines
dqdave1
Veteran Member
So; did that plane take off yet or is it still sitting still under the conveyor?
Ever heard of a MAP sensor?
This is all about the difference between engineers and the rest of the world. To engineers, there is no such thing as a vacuum. They clean their houses with a negative pressure cleaner, the rest of us use a vacuum cleaner.
Years ago, before engineers had as much influence on automotive/engine design (things were simpler then, and a lot of design work was done by "tinkerers", not engineers), some cars even had vacuum gauges in the dash, to assist the driver in achieving better miles per gallon. All cars had vacuum hoses under the hood. Mechanics used vacuum gauges to test engine condition. For years and years, most of the world thought there was such a thing as vacuum. In English, we even have a word for it, "vacuum". I am sure other languages have a similar word. We were all just fat, dumb and happy, thinking there was such a thing as vacuum, and making use of it to clean floors and make engines go.
Then along came electronic fuel injection, which required engineers to perfect. They needed a way to measure what every body else thought was manifold vacuum in the engine, but they didn't come up with a vacuum sensor, they developed the Manifold Absolute Pressure (MAP) sensor. If some simple guy like me had developed that, I would have foolishly called it a vacuum sensor.
So, yes Virginia, there is a vacuum. There is just a group of people out there that don't believe.
This is all about the difference between engineers and the rest of the world. To engineers, there is no such thing as a vacuum. They clean their houses with a negative pressure cleaner, the rest of us use a vacuum cleaner.
Years ago, before engineers had as much influence on automotive/engine design (things were simpler then, and a lot of design work was done by "tinkerers", not engineers), some cars even had vacuum gauges in the dash, to assist the driver in achieving better miles per gallon. All cars had vacuum hoses under the hood. Mechanics used vacuum gauges to test engine condition. For years and years, most of the world thought there was such a thing as vacuum. In English, we even have a word for it, "vacuum". I am sure other languages have a similar word. We were all just fat, dumb and happy, thinking there was such a thing as vacuum, and making use of it to clean floors and make engines go.
Then along came electronic fuel injection, which required engineers to perfect. They needed a way to measure what every body else thought was manifold vacuum in the engine, but they didn't come up with a vacuum sensor, they developed the Manifold Absolute Pressure (MAP) sensor. If some simple guy like me had developed that, I would have foolishly called it a vacuum sensor.
So, yes Virginia, there is a vacuum. There is just a group of people out there that don't believe.
J_J
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ArTrvlr
Maybe you can tell us why most diesel engines need a vacuum pump to operate all the vacuum devises in autos and trucks.
Maybe you can tell us why most diesel engines need a vacuum pump to operate all the vacuum devises in autos and trucks.
