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Engine Acoustic Impedance Modeled as a Cyclic Series of Passive System Impedances

Report Number: AFWAL TR 80-4203
Author: Lagnese, Thomas J., Jr.
Corporate Author: Materials Laboratory
Laboratory: Materials Laboratory
Date of Publication: 1981-07-01
Pages: 133
Contract: Laboratory Research - No Contract
Project: None Given
AD Number: ADA103931

The objective of this project was to utilize a recently proposed two sensor sampling technique for attaining certain acoustic properties of an internal combustion engine. Particular interest will be in attempting to define the acoustic source impedance characteristics of an internal combustion engine. The two sensor method of analysis incorporates a Digital Signal Analyzer system to analyze the sensor signals and to calculate incident-reflected acoustic properties. The laboratory method of experimentation includes exposure of the engine to a broadband random noise while performing signal analysis using a transfer function technique. The acoustic source impedance results obtained from this analysis for the engine are then interpreted within a format of passive acoustic systems. It was a hypothesis of this experimentation that the operating engine can be modeled as a series of cyclic passive systems. This hypotheses has been assessed from experimental results obtained from impedance studies of the motored and powered engine. Modeling of the engine as a cyclic series of passive systems was found to be quite useful for interpreting experimental acoustic impedances for motored engines. This acoustic engine model was found to be less applicable for powered engine studies.

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