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Automotive Basic Analysis On Air Filter

  1. Oct 28, 2012 #1
    Hello guys,

    I just came out with a new idea for my thesis project which is to improve the air filter system (drop-in type).

    Currently I doing some basic analysis based on the current stock air filter before I proceed to my prototype air filter system.

    Says, I've been given an air filter which the area is 0.25m X 0.15m = 0.0375m^2.

    I assumed the ρ of the air at average temperature (27.5 C ≈ 300 K) is about 1.161 kg/m^3.

    We already know that, mass flow rate = (density)(volumetric flow rate) = (density)(area)(velocity)

    Based on the data given above, how can I determine the velocity of the air going inside the air box?
    - there are several unknowns volumetric flow rate, mass flow rate

    By using this equation, velocity = (volumetric flow rate) / (area) can I assume the velocity of the air is the same with the velocity of the car? (its seems like the velocity of the air (in m/s) too big.

    Hope our engineers and pros may help me by solving this problem together. Thanks.

    ***sorry for my bad language. I trying to make it clear for better understanding***
    Last edited: Oct 28, 2012
  2. jcsd
  3. Oct 28, 2012 #2

    Ranger Mike

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    Science Advisor
    Gold Member

    without going into a lot of emperical data here are a few things to think about...
    todays vehicle design limits where cold air can be piped into todays engine room. With this limiting factor we have to use the air channel as manufactured. Heat is the biggest robber of HP on the intake side. If memory serves me I think at wide open throttle we are moving 40 pounds of air per minute (500cfm). Dyno results tell us we will LOOSE horsepower if we remove the intake air filter....surprise..but true...

    I'll post the reason after we all think about how this can be...

    as far as air velocity..pretty much vehicle dependant relative to speed and location of the intake inlet....the hot setup is to locate it in hugh pressure area to improve performance....K&N air filter are the number one supplier in th espeed world and have done mucho research on this issue..hope it helps
  4. Oct 28, 2012 #3

    Thanks for your detail explanation. From your words, you saying that the air moving at 40 pounds per minute, it means that was the mass flow rate isn't? So that, if convert to SI unit it will be 0.3023949 kg/s.

    ***correct me if I wrong*** :blushing:
  5. Oct 28, 2012 #4


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    Staff: Mentor

    The velocity and therefore mass flow rate are arbitrarily chosen based on the cooling requirements and therefore the size of the fan.
    No. The air circulated through the cabin is circulated by a fan.

    [Edit] Er, wait -- I guess you are talking about the engine air filter, not the cabin air conditioning filter. In that case, the air velocity/volume is determined by the intake of the engine. Similar concept to a fan, though.
  6. Oct 28, 2012 #5
    Thanks for your answer. And yes, I'm talking about the engine air filter (not the air-conditioning filter). :smile:

    By the way, I'm counting the amount of air velocity/volume just before the air pass through the MAF sensor. In other word, the air flow into the filter. ***sorry for my bad language if you don't understand it***

    The simplest way like this :

    AIR (at state 1) --->>> AIR FILTER --->>> AIR (at state 2) --->>> MAF SENSOR --->>> AIR INTAKE
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