Detecting Knock in Noisy Spark Ignition Engines

This paper examines three strategies of detecting knock that are less dependent of engine noise. The first strategy uses the exhaust temperature, the second uses a dithering method (systematically advancing and retarding the timing), while the third uses the standard deviation of knock intensity as the indicator of knock intensity.

The first strategy proves to be difficult to detect knock since the exhaust temperature is strongly dependent on the combustion efficiency instead of knock intensity. The second strategy uses a conventional accelerometer but discriminates against mechanical noise by subtracting the knock intensity during the retarded part from that of the advanced part of a dither cycle. This approach is found to require averaging the signals over large number of engine cycles and using large dither amplitude. The third strategy uses the Difference of Knock Intensity strategy where two cycle standard deviation is used. The last strategy was shown to improve the signal to noise ratio by at least a factor of two, even at high engine speed (4800 rpm). The strategy was implemented and was able to keep the timing within 5 CAD.