The smoke production of aircraft gas turbine engines is currently characterized by the SAE smoke number and, to a lesser extent, the exhaust transmittance. Quantitative relationships are developed between these characterizations and the optical properties of the engine smoke particles for use in subsequent visibility calculations. These optical properties are the particulate mass concentration and the specific projected particle extinction area.
The SAE smoke number is both the most common smoke characterization and the one farthest removed from optical properties. The inherent stained filter technique is first treated in general, then specifically in terms of the SAE requirements. A relation between the smoke number and the optical properties is achieved. It is shown that the SAE interpolation procedure is unsuitable at low smoke numbers, and an alternative procedure is suggested.
A relation between smoke number and exhaust transmittance is derived which agrees well with experimental data. Next, the optical properties obtained in this work are compared against the one experimental measurement and a theoretical result using Mie theory. The overall agreement is quite good. Particulate agglomeration is considered and shown to have a negligible effect on the optical properties.
Finally, the results are summarized both in words and in graphical form. It is recommended that exhaust transmittance, which is directly related to the smoke visibility, become the industry standard for quantifying smoke emission from aircraft gas turbine engines.