Determination of Knock Sensor Location on a Heavy-Duty Natural Gas Engine

Knock-induced pressure waves in the combustion chambers of spark-ignited engines cause the engine block to vibrate at the same frequencies. These vibrations have different amplitudes at different locations on the engine block. This paper describes a project to find a location on the engine block where the amplitudes of the knock-induced vibrations are high enough to use in a knock control system. To find this location, six piezoelectric knock sensors were located on suitable regions of the engine block. Data were collected from the sensors at both knocking and non-knocking conditions using a high speed data acquisition system. After the data were transformed into the frequency domain, comparison of the knocking and non-knocking condition data indicated the frequencies and amplitudes of the knock-induced engine block vibrations. The location where knock-induced vibrations were transferred with the greatest amplitude was determined. This location was confirmed at various speeds and air/fuel ratios. The test results indicated that the best location for the knock sensor was the lower-left side of the engine block between the third and fourth cylinders. A horizontally-mounted knock sensor provided a Signal-to-Noise ratio of 3.6.