Putting a fan on top of air intake?
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Crufty Dusty
Well-Known Member
Re: Putting a fan on top of air intake?
Hmm... I would disagree because you're assuming that the fluid is incompressible, fluid velocity is constant throughout and that the fan blades have no inertia.
Let's say the fan is 10cm (0.1m) in diameter. Circumference = 0.1*pi m. It is spinning at 4600 RPM or 76 revs/sec. Thus the angular velocity is 0.1 * pi * 76 = 23.8716 m/sec. Let's say a split second is 0.1 sec. Deceleration = 23.8716/0.1 = 238.716 m/sec^2 or 24G's. I'm not sure if the fan can withstand such repeated deceleration.
Shaun said:
Hmm... I would disagree because you're assuming that the fluid is incompressible, fluid velocity is constant throughout and that the fan blades have no inertia.
Shaun said:
Let's say the fan is 10cm (0.1m) in diameter. Circumference = 0.1*pi m. It is spinning at 4600 RPM or 76 revs/sec. Thus the angular velocity is 0.1 * pi * 76 = 23.8716 m/sec. Let's say a split second is 0.1 sec. Deceleration = 23.8716/0.1 = 238.716 m/sec^2 or 24G's. I'm not sure if the fan can withstand such repeated deceleration.
Crufty Dusty
Well-Known Member
Re: Putting a fan on top of air intake?
Addressed in previous post.
Don't BMWs come with DBW throttle...?
Shaun said:
Addressed in previous post.
Shaun said:
Don't BMWs come with DBW throttle...?
Crufty Dusty
Well-Known Member
Re: Putting a fan on top of air intake?
Oops! Mea culpa!
Shaun said:
Oops! Mea culpa!
Whisky_Tango
Core Group Members
Re: Putting a fan on top of air intake?
There is a correction in earlier flowrates by 10% reduction.
So its 165CFM @ 6500rev for a 1.8L engine.
snowman said:
There is a correction in earlier flowrates by 10% reduction.
So its 165CFM @ 6500rev for a 1.8L engine.
Re: Putting a fan on top of air intake?
Moving greater mass at pressure through the same pipe, you are compressing the air. Obviously air is compressible. Primary school kids learn that in science class, so why would I assume that it isn't?
Fluid velocity is contant from inches downstream of the fan, to inches before the TB. Of course when the blades kick on or off, there is spring effect as the compression starts or decompression starts but this is momentary. I am not sure why you are trying to obfuscate these simple things which make extremely little difference in how much is sent back out the MAF. The raw number shown has already proved this. The small wave effects within the air column when it is abruptly trapped, are irrelevant at these velocities, pressures. There is no 100 CFM / CF to be backed out through the MAF. I have shown so.
G is half the picture. To complete the picture and find actual loads, you need component mass. 24G is nothing to a low mass fanblade. 24 G applied to large mass amounts to great loads, but the fanblade is not a large mass. Also note I said in earlier post 0.1-0.5 seconds. You are taking the extreme short end. Also, your estimate of 10cm diameter is high. Bilge blowers are not that large in diameter. Computer fans I am not interested in involving, as they have been shown to be lower pressure, lower volumetric flow units, vs bilge blowers.
24G applied to 2gram reed valve is a 48gram load.
24G applied to 30gram impeller is a 720gram load.
24G applied to 500gram piston is a 12,000gram load.
The shaft in a blower is not going to have to support the rough 700 gram load radially since balanced rotation cancels out, but there will be a moment on the shaft. Moment will be reduced somewhat for mass distribution reasons listed above. Even assuming the huge 10cm dia you started out with, 700grams at 10cm makes for a very low moment. approx 0.515 lb-ft torque. A toothpick can take that kind of torque. Even this 0.515 lb-ft figure is on the high side, since mass is distributed not just on the very circumference of the blade, but also all the way along it to the center. To keep things simple, we have assumed that all mass is concentrated on the circumference, artificially raising the torque the shaft has to deal with. Still the force is tiny.
On top of this, shaft speed does not need to reach zero in order for it to stop pressurizing. There is a threshold shaft speed below which there is no meaningful amount of air moved. This is the same for non-positive-displacement blowers whether they be radial, axial, or anything in between. This is demonstrated clearly in turbochargers and centrifugal superchargers that require very high shaft speeds. The first few thousand RPM in those systems produce insignificant amounts or no boost.
So take decel time at 0.25 seconds to reach say 15% of max shaft speed, at a realistic 3.0 inch impeller diameter, consider mass distribution from center of rotation.......and the above mentioned 0.515 lb-ft torque, being miniscule to begin with, is reduced to near nothing.
Crufty Dusty said:
Moving greater mass at pressure through the same pipe, you are compressing the air. Obviously air is compressible. Primary school kids learn that in science class, so why would I assume that it isn't?
Fluid velocity is contant from inches downstream of the fan, to inches before the TB. Of course when the blades kick on or off, there is spring effect as the compression starts or decompression starts but this is momentary. I am not sure why you are trying to obfuscate these simple things which make extremely little difference in how much is sent back out the MAF. The raw number shown has already proved this. The small wave effects within the air column when it is abruptly trapped, are irrelevant at these velocities, pressures. There is no 100 CFM / CF to be backed out through the MAF. I have shown so.
G is half the picture. To complete the picture and find actual loads, you need component mass. 24G is nothing to a low mass fanblade. 24 G applied to large mass amounts to great loads, but the fanblade is not a large mass. Also note I said in earlier post 0.1-0.5 seconds. You are taking the extreme short end. Also, your estimate of 10cm diameter is high. Bilge blowers are not that large in diameter. Computer fans I am not interested in involving, as they have been shown to be lower pressure, lower volumetric flow units, vs bilge blowers.
24G applied to 2gram reed valve is a 48gram load.
24G applied to 30gram impeller is a 720gram load.
24G applied to 500gram piston is a 12,000gram load.
The shaft in a blower is not going to have to support the rough 700 gram load radially since balanced rotation cancels out, but there will be a moment on the shaft. Moment will be reduced somewhat for mass distribution reasons listed above. Even assuming the huge 10cm dia you started out with, 700grams at 10cm makes for a very low moment. approx 0.515 lb-ft torque. A toothpick can take that kind of torque. Even this 0.515 lb-ft figure is on the high side, since mass is distributed not just on the very circumference of the blade, but also all the way along it to the center. To keep things simple, we have assumed that all mass is concentrated on the circumference, artificially raising the torque the shaft has to deal with. Still the force is tiny.
On top of this, shaft speed does not need to reach zero in order for it to stop pressurizing. There is a threshold shaft speed below which there is no meaningful amount of air moved. This is the same for non-positive-displacement blowers whether they be radial, axial, or anything in between. This is demonstrated clearly in turbochargers and centrifugal superchargers that require very high shaft speeds. The first few thousand RPM in those systems produce insignificant amounts or no boost.
So take decel time at 0.25 seconds to reach say 15% of max shaft speed, at a realistic 3.0 inch impeller diameter, consider mass distribution from center of rotation.......and the above mentioned 0.515 lb-ft torque, being miniscule to begin with, is reduced to near nothing.
Crufty Dusty
Well-Known Member
Re: Putting a fan on top of air intake?
You don't have to be condescending to get your points across. Remember to attack the point, not the person.
Forgive me, I don't recall any of this from my primary school education. Why is it not possible for a fan rated to flow 300cfm of air into an engine that demands 200cfm of air when we agree that air is compressible? Isn't this the basis of forced induction? In the previous post, you said this:
By that very definition, throttle plate is closed, the fan is still pushing 300cfm of air. That's when you brought in the idea that these fans stop "in a split second", based off TPS etc and that the length of the tubing plus the pressure makes everything negligible. OK, fine. We still need to find out what kind of forces we're talking about right? Isn't this the basis of the exalted scientific method? To at least get an idea of what we're dealing with before embarking on something?
Depends on what your definition of "split second" was. If the fan takes exactly 1 minute at the same rotational speed to come to a stop then I'm completely right and there wouldn't be a need for discussion now would there?
Dude, relax.
How was I supposed to know that your "split second" meant 0.5 seconds? A blink of an eye qualifies as a split second, and it shouldn't take 0.5 seconds to bat an eyelid. Remember, I'm not disputing anything, we're working together to come up with some numbers so that we have a frame of reference. Refer to my original post.
Yes you are absolutely right here.
Shaun said:
You don't have to be condescending to get your points across.
Remember to attack the point, not the person. shaun said:
Forgive me, I don't recall any of this from my primary school education. Why is it not possible for a fan rated to flow 300cfm of air into an engine that demands 200cfm of air when we agree that air is compressible? Isn't this the basis of forced induction? In the previous post, you said this:
Shaun said:
By that very definition, throttle plate is closed, the fan is still pushing 300cfm of air. That's when you brought in the idea that these fans stop "in a split second", based off TPS etc and that the length of the tubing plus the pressure makes everything negligible. OK, fine. We still need to find out what kind of forces we're talking about right? Isn't this the basis of the exalted scientific method? To at least get an idea of what we're dealing with before embarking on something?
Shaun said:
Depends on what your definition of "split second" was. If the fan takes exactly 1 minute at the same rotational speed to come to a stop then I'm completely right and there wouldn't be a need for discussion now would there?
Shaun said:
Dude, relax.
How was I supposed to know that your "split second" meant 0.5 seconds? A blink of an eye qualifies as a split second, and it shouldn't take 0.5 seconds to bat an eyelid.
Remember, I'm not disputing anything, we're working together to come up with some numbers so that we have a frame of reference. Refer to my original post.Shaun said:
Yes you are absolutely right here.
Crufty Dusty
Well-Known Member
Re: Putting a fan on top of air intake?
Here's the installation diagram.
http://www.autodesigns.com.sg/wiring_diagram.htm
FWIW, reading DBW TPS is not a straightforward affair.
Shaun said:
Here's the installation diagram.
http://www.autodesigns.com.sg/wiring_diagram.htm
FWIW, reading DBW TPS is not a straightforward affair.
Re: Putting a fan on top of air intake?
Better still! Simplifies things greatly. No TPS or engine RPM to watch, just manifold pressure.
So instead of shutting off or greatly reducing shaft speed when TPS shows closed throttle, they just do it when they see low manifold pressure.
Better still! Simplifies things greatly. No TPS or engine RPM to watch, just manifold pressure.
So instead of shutting off or greatly reducing shaft speed when TPS shows closed throttle, they just do it when they see low manifold pressure.
Whisky_Tango
Core Group Members
Re: Putting a fan on top of air intake?
Yah... you should be able to get some good torque and power.
If you install, appreciate your feedback.
Cheers!
snowman said:
Yah... you should be able to get some good torque and power.
If you install, appreciate your feedback.
Cheers!
Wayansurfer
Well-Known Member
Re: Putting a fan on top of air intake?
Eric,
Would you explain it in layman's term?
If for my car?? will it do good? E36 M40
Whisky_Tango said:
Eric,
Would you explain it in layman's term?
If for my car?? will it do good? E36 M40
Whisky_Tango
Core Group Members
Re: Putting a fan on top of air intake?
Hi Andy,
M40 should be a 316i?
If so, then all the more better to have ADM. Cos 1.6L air intake at 6500rev is about 145CFM. So at this point with ADM (238CFM), you should have an extra airflow of 93CFM at high end. So in another words, ur engine will breath better and do not have to worry for lack of air.
You should also get some good torque and power. But dun expect much. Maybe 5hp to 10hp thereabout.
Cheers!
Wayansurfer said:
Hi Andy,
M40 should be a 316i?
If so, then all the more better to have ADM. Cos 1.6L air intake at 6500rev is about 145CFM. So at this point with ADM (238CFM), you should have an extra airflow of 93CFM at high end. So in another words, ur engine will breath better and do not have to worry for lack of air.
You should also get some good torque and power. But dun expect much. Maybe 5hp to 10hp thereabout.
Cheers!
Wayansurfer
Well-Known Member
Re: Putting a fan on top of air intake?
Eric,
M40 is 318....hmmmmmmmmmmmmmm...
So u reckon still feasible to retrofit this little bugger??
Eric,
M40 is 318....hmmmmmmmmmmmmmm...
So u reckon still feasible to retrofit this little bugger??
Whisky_Tango
Core Group Members
Re: Putting a fan on top of air intake?
Opps... paiseh... so its a 318i huh... Then same as snowman liao.
I have not used or tested this ADM, so feasibility is just based on CFM figures.
Its the control module tat Im concern. How accurate it will rev the ADM in accordance to loading via vacuum differentials.
Cheers!
Wayansurfer said:
Opps... paiseh... so its a 318i huh... Then same as snowman liao.
I have not used or tested this ADM, so feasibility is just based on CFM figures.
Its the control module tat Im concern. How accurate it will rev the ADM in accordance to loading via vacuum differentials.
Cheers!
Wayansurfer
Well-Known Member
Re: Putting a fan on top of air intake?
Thanks....
Will consider lahh but not adding it to my hotlist. Still waiting for my sebring.lol
Thanks....
Will consider lahh but not adding it to my hotlist. Still waiting for my sebring.lol
