In order to control the emissions from aircraft gas turbines, the International Civil Aviation Organisation (I.C.A.O.) and the U.S. Environmental Protection Agency (E.P.A.) have, through consultations with the various parties over the past decade, made firm proposals for an emission certification scheme, together with mandatory limiting levels for certain pollutants. The compliance with the proposed emission standards requires that a representative sample is collected from the engine exhaust plane and transported without changing its chemical composition to the analysis instruments. Despite clearly defined rules for sample transfer and analysis methods, the emissions measurement will be subject to variability due to the following factors:

a) engine-to-engine variability which will include the impact of dimensional tolerance on the combustor hardware and other components which affect the combustor performance,

b) sampling variation because of the nonuniform distribution of the pollutant species in the exhaust plane (see references 4,5), with the result that engine manufacturers are required to demonstrate “by means of detailed traverse measurements in the sampling plane” that a specific probe design provides a representative sample,

and

c) gas analysis instrumentation scatter that occurs in the actual analysis of identical samples.

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