MoTeC Knock OKM - Manual (Page 12)

12 Configuration
Test
1. Ensure the engine is at normal operating temperature.
2. Run the engine and listen for any irregularities in engine vibrations
like internal component noise.
3. If all sounds normal bring the engine under some load and carefully
introduce light detonation.
Tip:
To introduce detonation at as light a load as possible, use a low
octane fuel.
4. Proceed with extreme caution and note where detonation can be
introduced. Return to no detonation.
5. Open a new file in Gold Wave and record the data while running the
engine from a normal operating situation to a situation with detonation
at a similar engine speed.
6. Shut down the engine.
Analysis
1. Configure the Gold Wave Software so that the sound recording can
be viewed on a spectrogram (see appendix 4).
2. Play back the Gold Wave audio file.
The Y-axis on the spectrograms chart is the frequency range, the X-
axis is the playback time.
The colours on the chart represent the energy of the recorded sound.
The key to the colours is underneath the X-axis.
3. Look at the spectrogram chart, while listening for detonation. The
colour in the spectrogram changes at the moment detonation occurs.
4. The colour change occurs at the knock frequency, but there are often
reflections of the detonation at other frequencies.
5. Determine the frequency where the difference of the engine sound
with and without detonation is most clear to detect. This will be the
centre frequency setting.