| ACOUSTIC CHARACTERISTICS OF THE ABNORMAL COMBUSTION IN A HIGH-COMPRESSION RATIO, SPARK-IGNITION ENGINE
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| Junghwan Kim |
| Chung-Ang University |
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| ABSTRACT |
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Engine knocking is often identified by an operator based on the combustion sound emanating from the
cylinder block during engine calibration in a test cell. Such human-hearing-based acoustic knock determination is considered
the most reliable real-time knock-monitoring method, and it is necessary for selecting an accurate spark timing. In this study,
the characteristics of this combustion sound were investigated. To this end, a normal engine calibration experiment was
conducted. The engine sound was recorded under various operating conditions by using a copper tube attached to the cylinder
block and the microphone of a smartphone. The measured signals were subjected to acoustic analyses, including Fast Fourier
transform, smoothing, spectral analysis, and autocorrelation, to compare the sounds recorded at the knock borderline with
those recorded in the cases with significantly advanced spark timing. The results of these analyses revealed several features
that distinguished the knock sound from the normal combustion sound. The knock sound exhibited distinctions in a
high-frequency band between 6,000 and 8,000 Hz. These features can be used to develop effective knock classification
models. |
| Key Words:
Engine knocking, Combustion sound, Spectral analysis, Autocorrelation
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Corresponding Author.
Junghwan Kim , Email. 
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