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Weak knock characterisation and detection for knock control

Knock is a fundamental phenomenon in combustion engines, and knock control is central in any engine management system. Better understanding of knock, and weak knock in particular, is searched in two main directions, knock detection and knock characterisation. The aim of the knock detectors is both to detect knock and to estimate the crank angle at knock onset. Focusing on weaker knock than before, it is shown that knock detectors and algorithms have to take into account other characteristics of the knock traces than the standard model. It is shown that the best performing of the investigated knock detectors is one that supervises changes in signal variance, except for low signal to noise ratios where it is advantageous to use also oscillation frequency. Regarding characterisation, an important result is that in a wide range of intensities there is an almost linear dependence between the logarithmic normalised knock energy and the rate of cycles with knock. This means for example that a knock controller can use feedback on the rate of cycles with knock instead of knock intensity and vice versa, and both can in combination with better detection provide possibilities for smoother and more anticipatory control schemes.

Ylva Nilsson, Erik Frisk and Lars Nielsen

Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2009

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