Parametric Detectors for Knock in Spark Ignition Engines

Abstract

The efficiency of spark ignition engines, the favoured engine of today’s passenger cars, can be improved by an increase of its compression ratio. However, for high compression ratio engines the angle of ignition for minimum fuel consumption lies in a region where knock occurs. Knock is an abnormal combustion causing rapid rise of temperature and pressure. The so-called knock limit, i. e. the point where knock begins, varies with speed, load, fuel, age etc. To protect against frequent knock and resulting damage, the spark advance is chosen not optimum in the sense of efficiency. Knock detection and control enable safe operation at the actual knock limit. The performance of detectors in use, e. g. [1], seems to be nonoptimum, mainly due to the poor signal to noise ratio (SNR) of the structural vibrations signal that has to be used in practice. At the cost of increased complexity Härle and Böhme [5,4] developed a more sensitive parametric detector. We present an alternative formulation which seems to be more flexible and robust with respect to hardware constraints like fixed-point arithmetic. Experimental results are given for both versions of the parametric detector and for improved conventional detectors. In addition, we show results of a new nonparametric detector.

Supported by Volkswagen AG, Wolfsburg, FRG.