Detection of Knocking Combustion Using the Continuous Wavelet Transformation and a Convolutional Neural Network

Achilles Kefalas, Andreas Ofner, Gerhard Pirker, Stefan Posch, Bernhard Geiger, Andreas Wimmer

Research output: Contribution to journalArticlepeer-review


The phenomenon of knock is an abnormal combustion occurring in spark-ignition (SI) engines and forms a barrier that prevents an increase in thermal efficiency while simultaneously reducing CO 2 emissions. Since knocking combustion is highly stochastic, a cyclic analysis of in-cylinder pressure is necessary. In this study we propose an approach for efficient and robust detection and identification of knocking combustion in three different internal combustion engines. The proposed methodology includes a signal processing technique, called continuous wavelet transformation (CWT), which provides a simultaneous analysis of the in-cylinder pressure traces in the time and frequency domains with coefficients. These coefficients serve as input for a convolutional neural network (CNN) which extracts distinctive features and performs an image recognition task in order to distinguish between non-knock and knock. The results revealed the following: (i) The CWT delivered a stable and effective feature space with the coefficients that represents the unique time-frequency pattern of each individual in-cylinder pressure cycle; (ii) the proposed approach was superior to the state-of-the-art threshold value exceeded (TVE) method with a maximum amplitude pressure oscillation (MAPO) criterion improving the overall accuracy by 6.15 percentage points (up to 92.62%); and (iii) The CWT + CNN method does not require calibrating threshold values for different engines or operating conditions as long as enough and diverse data is used to train the neural network.

Original languageEnglish
Article number439
Number of pages19
Issue number2
Publication statusPublished - 15 Jan 2021


  • Continuous wavelet transformation
  • Convolutional neural networks
  • Knocking combustion
  • Pressure trace
  • SI engines
  • Time series

ASJC Scopus subject areas

  • Control and Optimization
  • Energy (miscellaneous)
  • Energy Engineering and Power Technology
  • Electrical and Electronic Engineering
  • Fuel Technology
  • Renewable Energy, Sustainability and the Environment


Dive into the research topics of 'Detection of Knocking Combustion Using the Continuous Wavelet Transformation and a Convolutional Neural Network'. Together they form a unique fingerprint.

Cite this