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aka Hot Wire (or hot film) aeromometer (long)
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Posted by Stephen Goldberger [Email] (more from Stephen Goldberger) on Tue, 1 Apr 2014 07:31:01 Share Post by Email
In Reply to: K & N puts end to rumors of MAF damage, FUEGO, Mon, 31 Mar 2014 14:40:57
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They operate on the principle of heat transfer. The electronics run a tightly controlled current through a wire (or through a conductor on a substrate, or circuit board). The wire resistance changes with temperature. The higher the resistance (usually higher temperature) the greater the voltage measured across the wire. The greater the mass air flow, the greater the heat transfer from the hot wire to the air, the lower the temperature. The voltage changes inversely proportionally to temperature.

Contaminants in the air can build up on the wire, which adds thermal resistance (a smidgen of insulation) that can affect the calibration. Commercially available hot-wire anemometers, as used in a fluid mechanics lab, have a "clean" cycle that runs the wire to red-hot on every start precisely to burn off any contamination. I think I remember from back in the day that the Bosch automotive MAF sensors do the same thing.

1) the oil in the filter is not particularly volatile, and the rate of air flow through a filter is not likely to pick up droplets of oil.

2) If a smidgen of oil gets into the airstream, it is not likely to stick to a hot wire.

3) Even if it did stick to the wire, the burnoff cycle on startup would boil it away.

4) The oxygen sensors and/or trionic measurements provide the final authority on air/fuel ratio, and the 9-5's computer maintains a "trim" calibration factor based on those measurements that it uses to fine-tune the MAF sensor calibration.

I think the statement is true. As to the benefits of the K&N filter, I leave that to others.

posted by 70.126.89...


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