Air Flow Rate

       

Air Flow Rate Formula
\( cfm \;=\;  \dfrac{ cid \cdot rpm \cdot \eta_v }{ 3456 } \)     (Air Flow Rate) \( cid \;=\; \dfrac{ cfm \cdot 3456 }{ rpm \cdot \eta_v } \) \( rpm \;=\; \dfrac{ cfm \cdot 3456 }{ cid \cdot \eta_v } \) \( \eta_v \;=\; \dfrac{ cfm \cdot 3456 }{ cid \cdot rpm }  \)
Symbol	English	Metric
\( cfm \) = Cubic Feet per Minute	\(ft^3 \;/\; min\)	-
\( cid \) = Cubic Inch Displacement	\(in^3\)	-
\( rpm \) = Engine Speed	\(r \;/\; min\)	-
\( \eta_v \)  (Greek symbol eta) = Volumetric Efficiency	\(dimensionless\)	-

Air flow rate refers to the amount of air that passes through an opening or a device over a given time period, and is typically measured in units of volume per unit time, such as cubic meters per second (m³/s) or cubic feet per minute (CFM).  In the context of engines, air flow rate is an important parameter that affects the engine's performance, fuel efficiency, and emissions.  The air flow rate into the engine determines the amount of oxygen available for combustion, and therefore affects the engine's power output and fuel efficiency.

Air flow rate is often measured using a device called a flow meter, which uses various techniques such as thermal anemometry, pitot tubes, or mass flow sensors to measure the rate of air flow.  In some cases, air flow rate can also be estimated using mathematical models based on the geometry of the air intake and other factors such as the engine speed and load.  Air flow rate can be affected by a variety of factors, including the size and shape of the air intake, the temperature and humidity of the air, the presence of obstructions or turbulence in the air flow path, and the pressure difference across the air intake.  Engine designers and tuners often optimize the air flow rate and intake design to achieve the desired performance characteristics of the engine, while balancing trade-offs such as noise, emissions, and fuel efficiency.