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Engineering Analysis of Air Intake System - Open vs Enclosed Filter

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Engineering Analysis of Air Intake System - Open vs Enclosed Filter

 
Old 04-02-2018, 10:35 PM
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Lightbulb Engineering Analysis of Air Intake System - Open vs Enclosed Filter

Background:
I wanted to do a little engineering study of running to an open element air filter vs an enclosed filter that ducts air from a cooler source near the fender liner. Test was performed did not have the intake shield or top cover for the box which would have helped some with the open filter configuration.

Test Procedure:
The test was performed at Buttonwillow Raceway in Ca. Testing was done on the race track to simulate real world air distribution effects that cannot be recreated properly on a DYNO.
The section of data used in the analysis was taken 15 min into the session where temps have stabilized and on the same section of straight on the track.
Data analysis uses the same RPM, CFM and Boost level.

Test Equipment:
Data was captured using Banks iDash 1.8 with Megasquirt ECU data input and Banks 4 channel analog sensor modules and Banks Ambient Air Density module.
The iDash Gauge will calculate Air Density, delta pressure and delta temperature on the fly and log data at 10 Hz to micro SD card.
Sensor location for the data used is Ambient Air Pressure and Temperature recorded at the grill of the vehicle and Pressure and Temperature recorded at the inlet to the compressor.

Results:




Analysis:
The first critical element is temperature. Hot air is less dense and worse for performance.
The open element filter inhaled air that was 43 deg F higher than the ambient air available at the grill of the vehicle. This is expected since it is near the hot turbo and behind the radiator.
The enclosed filter was able to inhale air only 20 degrees hotter than ambient temperatures. This is a big improvement but still is not perfect. The closer the temperature is to ambient the better.

The second critical element is pressure. An enclosed filter system can be more restrictive and that loss in pressure needs to be taken into account.
The open air filter element saw and pressure drop of 0.35 psi at 215 CFM.
The enclosed element was more restrictive and saw a pressure drop of 0.53 psi at the same CFM.
This may be because the duct that it pulls air from may be too small in diameter, or the filter may be more restrictive (more plys of filter media), or the housing design may not be well engineered. Also the amount of dirt on the filter will also affect flow restriction of a filter.

The open element filter was less restrictive which is good for performance, but it was inhaling hotter air which is bad for performance, so how do you know which system is overall the best?
The answer is to calculate the Air Density change in the system. Density is a measurement of how much air mass can fit in a fixed volume size. The higher the density of the air, the more oxygen molecules in that air, which means more fuel can be added resulting in more power. Density utilizes both pressure and temperature into a single calculated value that can be used to determine the overall winner.
The analysis shows that the open element filter saw a density loss or 6.9 lb/1000ft^3 vs a 5.0 lb/1000ft^3 loss for the enclosed element.

For Air Intake Systems, since you cannot reduce temperature below ambient and since we don't have any "Ram-Air" pressure effect, the closer the intake density loss is to zero the better.
So for this comparison, the enclosed element system overall resulted with more available air mass at the inlet to the compressor and will result in more oxygen to the engine and more HP at the wheels.

Potential Follow Up Study:
Since the enclosed element had a higher delta pressure the intake system can be further improved by finding a less restrictive system.
Adding the intake shield and cover to isolate the open filter from the engine bay heat and re-test.
Add hood vents to measure effect on intake air temperature for open filter configurations.
An system with an over the radiator routing and an open element filter in front of the radiator might give the best of both world for best temperature and lowest restriction.

Other Analysis:
Air Density studies can be used to analyze a variety of components.
It's especially powerful for evaluating an intercooler by comparing the temperature reduction (intercooler effectiveness) vs the pressure loss in the IC (restriction).

Pressure loss through a filter is a function of CFM. As you increase boost pressure or engine RPM, you will see more airflow and therefore more pressure drop. At some point the pressure loss will increase exponentially and really hurt your power. This analysis gives you a good idea of when it's time to up-size your air intake system.

Air filters get more restrictive as they collect dust. By monitoring the delta pressure across the filter you will know when you need to clean or replace your air filter.











Open Element Filter and sensor modules


Enclosed Filter (K&N Apolo)


Location of Compressor Inlet Pressure and Temperature Sensors


Banks iDash Gauge and Data Logger used to record data


Data (Open Filter)



Data (Enclosed Filter)


Last edited by cyotani; 04-06-2018 at 02:20 PM.
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Old 04-03-2018, 07:34 AM
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Nice data collection. Makes me feel better about my cowl induction.
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Old 04-03-2018, 07:58 AM
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yeah, great work!
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Old 04-03-2018, 09:03 AM
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Great work.

It'd be interesting to see intake manifold temps taken into account as well. I've seen claims on here several times that intake temps are irrelevant because the intercooler is dropping temps to near ambient temps anyway. Maybe some data to the contrary this will inspire me to come up with an actual intake rather than just a filter clamped to the turbo.
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Old 04-03-2018, 11:57 AM
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Very cool indeed, thank you for posting it so well organized and neat.
It'd be interesting to see intake manifold temps taken into account as well. I've seen claims on here several times that intake temps are irrelevant because the intercooler is dropping temps to near ambient temps anyway. Maybe some data to the contrary this will inspire me to come up with an actual intake rather than just a filter clamped to the turbo.
Not as cut and dry as that. Esp at sustained boost when even the best intercoolers start heating up. Of course then the argument becomes "is the gain worth the trouble/effort" which I think is the real question in that scenario.
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Old 04-03-2018, 12:40 PM
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Very cool test and I appreciate the methodology. This is something I have wondered about for a long time.
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Old 04-03-2018, 02:43 PM
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Great data... I'd have like to see that enclosed filter inlet routed to somewhere that it can get cool air. Perhaps pull air from the same location as where you want to run the unenclosed filter to.
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Old 04-03-2018, 03:21 PM
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Originally Posted by pdexta View Post
Great work.

It'd be interesting to see intake manifold temps taken into account as well. I've seen claims on here several times that intake temps are irrelevant because the intercooler is dropping temps to near ambient temps anyway. Maybe some data to the contrary this will inspire me to come up with an actual intake rather than just a filter clamped to the turbo.
Originally Posted by 18psi View Post
Very cool indeed, thank you for posting it so well organized and neat.
Not as cut and dry as that. Esp at sustained boost when even the best intercoolers start heating up. Of course then the argument becomes "is the gain worth the trouble/effort" which I think is the real question in that scenario.

You are correct, you will see a reduced benefit at the manifold because the intercooler will pull a larger portion of the temp increase out of the air. But you will see a density gain and mass airflow improvement nonetheless.
I looked at my data and unfortunately the 6 deg variation in ambient data throws off the analysis too much. Too many variables in my real world test to give an idea of what is happening there.

But through the power of physics we can get a good idea of what is actually going on.
I used a hypothetical 10 deg F temp increase for enclosed element and 40 deg F temp increase for open Filter.
But I kept everything else constant (Ambient Air Pressure, Ambient Air temp, Pressure Ratio, Compressor Efficiency, Intercooler Effectiveness, etc.)

Using density you can track the effect of the higher air inlet temperature throughout each component in the system.
The end result is a a 5.5% Density improvement at the compressor inlet vs only 1.4% improvement at the manifold.
So as we expected, the intercooler helped cover up the poor air intake configuration.

A 1.4% improvement in air density roughly translates to a 1.4% Power increase.
If you were making 250 WHP with this hypothetical open to enclosed filter change could net you a 3.5 whp gain.

So marginal benefits. But the 8 deg lower Manifold Temp might help with knock limitation and other factors could play a role in overall performance.


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