Jahn, T., Schuerg, F., and Kempf, S., "Knock Control on Small Four-Two-Wheeler Engines," SAE Technical Paper 2012-32-0052, 2012, doi:10.4271/2012-32-0052.
Today, knock control is part of standard automotive engine management systems. The structure-borne noise of the knock sensor signal is evaluated in the electronic control unit (ECU). In case of knocking combustions the ignition angle is first retarded and then subsequently advanced again.The small-sized combustion chamber of small two-wheeler engines, uncritical compression ratios and strong enrichment decrease the knock tendency. Nevertheless, knock control can effectuate higher performance, lower fuel consumption, compliance with lower legally demanded emission limits, and the possibility of using different fuel qualities.The Knock-Intensity-Detector 2 (KID2) and the Bosch knock control tool chain, based on many years of experience gained on automotive engines, provides an efficient calibration method that can also be used for two-wheeler engines. The raw signal of the structure-borne noise is used for signal analysis and simulation of different filter settings.A feasibility quick test was executed on a water-cooled 125cc small engine of a mass-produced two-wheeler. Although the knock sensor position was not optimized, a satisfactory knock detection quality was achieved across the entire engine speed range up to 10,000 rpm. Without knock control an ignition safety margin of 6°CA to the knock limit is necessary due to tolerances of the compression ratio and different fuel qualities.With active knock control, the following benefits could be achieved at the engine's standard load point of 7,500 rpm: - At moderate ambient temperature (25°C intake-air), a torque increase of 3% with original enrichment or equal torque with 10% less specific fuel consumption at lambda 1. - At high ambient temperature (60°C intake air), the specific fuel consumption could be reduced by 16% - at lambda equals unity and original torque.The benefits that are achieved by merely including knock control to an already existing engine are only given at full load operation. The objective for the near future is to increase the compression ratio of the engine to attain higher performance and reduce the fuel consumption especially at part load, by finding a compromise between performance and fuel economy.