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An air flow meter, also known as an air consumption meter, is a device that indicates how much air is flowing through a tube. It does not measure the volume of the air passing through the tube, it measures the speed of the air flowing through the device in a defined time segment. Thus air flow meters are simply an application of mass flow meters for a special medium.

Typically, mass air flow measurements are expressed in the units of kg/h (kilograms per hour).

[edit] Types of air flow meters

[edit] Air flow meter in cars

An air flow meter is used in some cars to measure the quantity of air going to the engine. All modern electronically controlled Diesel engines use air flow meter as it is the only possible means of determining the air intake for them. In the case of a gasoline engine the electronic control unit then calculates how much fuel is needed to inject into the cylinder ports. In the diesel engine the ecu meters the fuel through the injectors into the engines cylinders during the compression stroke.

The vane (flap) type air flow meters (Bosch L-Jetronic and early Motronic EFI systems) actually measure air volume, whereas the later "hot wire" and "hot film" air flow meters measure speed of air flow.

The flap type meter includes a spring which returns the internal flap to the initial position. Sometimes if the spring is tensioned too tight, it can cause restrict the incoming air and it would cause the intake air speed to increase when not opened fully.

[edit] Failures

Air flow meters may fail or wear out. When this happens, engine performance will often decrease significantly, engine emissions will be greatly increased, and usually the Malfunction Indicator Lamp will light. In most places in the United States where emissions inspections are obligatory, a lit MIL is cause for a vehicle to fail the inspection.

[edit] Air flow meter for R&D of cars

In the development process of combustion engines with engine test stands an air flow meter/air flow measuring unit is used for measuring the continuous gravimetric air consumption of combustion engines.

[edit] See also

• air flow bench (aviation)
• Mass airflow sensor

[edit] External links

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