Knock analysis in the crank angle domain for low-knocking cicles detection 2020-01-0549
Knock is an abnormal phenomenon which must be avoided to protect the engine from high in-cylinder pressure oscillations. Conventional control algorithms use the spark timing to avoid high knocking rates but such strategy reduces the thermal efficiency and restricts the performance of a gasoline engine. The detection and characterisation of low-knocking cycles is a challenging task, as normal combustion also excites the resonant harmonics, but it might be used for improving knock control algorithms. Most of the methods used to detect knock use 0-dimensional indicators, regardless of the angular evolution of the pressure oscillations.
In this paper, the in-cylinder pressure oscillations evolution during the piston stroke are analysed by using various time-frequency transformations. The analysis highlights the need of a new criteria for knock detection, which must take into account the intensity of the oscillations but also the location where they take place. A new definition of knock is proposed by using resonance to design an indicator of the pressure resonance evolution and constant volume combustion is assumed to determine the minimum oscillation required for end-gas autoignition detection. Several experimental tests with an EURO VI SI engine are used for illustration and validation purposes.
Benjamin Pla, Joaquin De La Morena, Pau Bares, Irina Jiménez