Detonation (knock) produces specific acoustic reverberations within the combustion chamber. These resonant frequencies typically fall within the 2 kHz to 12 kHz range. Understanding these frequencies is essential for configuring knock sensor filtering and digital signal processing in engine management systems.

Estimation Formula#

The resonant frequency of an engine cylinder can be estimated based on the cylinder bore diameter. Use the following formula to calculate the primary detonation frequency:

$$f = \frac{900}{\pi \times r}$$

Variables#

• $f$: Resonant frequency (Hz)
• $r$: Cylinder radius (meters)

Important

Ensure the cylinder radius is converted to meters before performing the calculation. This formula provides a theoretical baseline; actual resonant peaks may vary based on combustion chamber geometry and piston crown design.

Frequency Reference Table#

Tip

When tuning knock detection windows, use a band-pass filter centered around the calculated frequency to isolate detonation events from mechanical engine noise.