Definition
A dimensionless measure of the visible smoke produced by a turbine engine exhaust, determined by drawing a measured sample of exhaust gas through a clean filter paper under standardized conditions and comparing the resulting stain to a reference scale. Higher numbers indicate more soot and a more visible smoke trail; lower numbers indicate cleaner combustion.
Plain English
A score that shows how smoky a jet engine's exhaust is. The dirtier the filter paper after sampling the exhaust, the higher the number.
Context Anchor
Seen in turbine-engine emissions information, engine certification material, and discussions of visible smoke from jet exhaust.
Why Pilots Care
Smoke number reflects combustion quality. A rising smoke number on a particular engine type can indicate combustor wear or fuel nozzle problems, and it is also a regulated emissions value engines must meet for certification.
Grounding Statement
Picture engine exhaust being passed through a white filter; if the filter turns darker, the engine has a higher Smoke Number.
Intuition Check
Smoke Number is not a count of smoke bursts or how many times smoke appears. It is a measured rating of how dark a smoke stain is under a standard test.
Example Sentence 1
The new combustor design lowered the engine's smoke number, reducing the visible exhaust trail at takeoff power.
Example Sentence 2
Technicians record the smoke number after each engine run to verify emissions compliance.