Tuesday, March 22, 2011

Do Clogged Air Filters Restrict Air Flow?

Best Air Filters Review: Air Filter Facts
Air Filter Facts Part 4: Do clogged air filters restrict air flow?

In our previous post, we proved that different air filters can improve (or worsen) air flow when clean. But what is the impact, if any, of a clogged (or very dirty) air filter?

Our friends from Oak Ridge National Lab also investigated the impact of a clogged air filter. To simulate the appropriate level of reduced air flow, the researchers ended up stuffing shop towels (!!!) on the upstream side of the air filter's air box, or wrapping the filter itself in shop towels:

The shop towels had to be stuffed so hard to get to the right level of reduced airflow that the one of the air filters was quite damaged in the process:-) This is representative of the difficulty of getting severely restricted airflow... In the end, the study was able to restrict flow significantly:

It is worth noting that filters are typically considered clogged when pressure drop across the filter increases by 10" H2O, i.e. 2.5kPa. What this means is that the tests were run using significantly higher air flow restrictions. These are truly worst case tests.

  • Clogged air filters significantly reduce air flow

Does this very significantly reduced air flow (to the degree that it sucked a shop towel into the intake) actually worsen fuel economy? Next we investigate how air flow impacts mileage... So come back soon!

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