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Detecting Start of Combustion using Knock Sensor Signals

Author: Mats Järgenstedt Title: Detecting Start of Combustion using Knock Sensor Signals Abstract: The benefits from knowing the start of combustion (SOC) in a direct injection diesel engine are numerous. Examples are the ability to optimize the fuel consumption versus the emissions and an increase in diagnostic features of the injection equipment. By using feedback from SOC it would also be possible to use less expensive electronics and mechanics. Engine management systems of today utilize, at very best, closed loop control of the start of injection with good precision. However, it is the combustion that produces power and emissions and since the delay between the start of injection and the start of combustion varies with several factors, it would be much better to control SOC. A new technique for detecting start of combustion by knock signal evaluation is described. The method is based on measurements from widely used and inexpensive knock sensors which measure a knock signal. The signal is thereafter band pass filtered, the envelope of the resulting signal is calculated and finally compared to a threshold expressed as a percentage of the maximum value of the envelope. SOC is said to occur when the envelope exceeds the threshold. The standard deviation of the delay between the measured start of injection and the detected start of combustion in all experiments is less than 0.1 crank angle degree. The method detects SOC in real time and makes it possible to control SOC with closed loop strategy. The closed loop control strategy makes it possible for the engine control system to correct for changes in for example the air temperature, moisture content, fuel quality and for errors in the accuracy of the injectors. Thereby the differences between individual cylinders and different engines can be minimized.

Mats Järgenstedt


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Last updated: 2021-11-10