Motor Volumetric Efficiency

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Motor volumetric efficiency, abbreviated as \(\eta_v\), a dimensionless number, is a measure used in the automotive industry to assess how well an internal combustion engine can draw in and expel air during the intake and exhaust strokes, respectively.  It is a factor in determining the engine's overall performance and efficiency.  Volumetric efficiency is expressed as a percentage and represents the ratio of the amount of air an engine draws in or expels compared to its theoretical maximum.  The theoretical maximum is calculated based on the engine's displacement and the density of air under specific conditions.

A high volumetric efficiency indicates that the engine is effectively utilizing its displacement to draw in and expel air, which is crucial for combustion and power generation.  Factors that can affect volumetric efficiency include the design of the intake and exhaust systems, valve timing, and the efficiency of the combustion process.  Improving volumetric efficiency is a common goal in engine design and tuning, as it can lead to increased power output and fuel efficiency.


Motor Volumetric Efficiency Formula

\( \eta_v \;=\;  ( AF_a \;/\; AF_t ) \;100 \)     (Motor Volumetric Efficiency)

\( AF_a \;=\;   \eta_v \; AF_t \;/\; 100 \)

\( AF_t \;=\;  AF_a \; 100 \;/\; \eta_v \)

Symbol English Metric
\( \eta_v \)  (Greek symbol eta) = volumetric efficiency \(dimensionless\)  
\( AF_a \) = actual air flow \(ft \;/\; sec\)   \(m \;/\; s\) 
\( AF_t \) = theoretical air flow \(ft \;/\; sec\)   \(m \;/\; s\) 


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Tags: Efficiency Motor