分会场

高效清洁燃烧

摘要

Engine knock has been an inherent problem that limiting the engine efficiency improvement and threatening the engine service life. To trigger the controllable knock, a specialized liner with installing 4 side spark plugs mounted on the cylinder head are used in this study to produce various in-cylinder flame propagation. Various spark strategies (e.g. spark timing, spark number, spark location) are applied to generate different auto-ignition sites and knock characteristics. The multiple channels of pressure signal are collected to analyze the knock intensities regarding different spark strategies. In order to investigate the knock induced fluctuations and heat release, we use the multiple correlation to evaluate the sensitivity of the maximum amplitude of pressure oscillation (MAPO) respecting different influential factors, and build a multiple linear regression (MLR) model for MAPO prediction and validate it against the experiment results. Besides, the Wiebe function and curve-fitting techniques were applied to estimate the energy released by auto-ignition in each individual cycle, and assess its relations with knock intensity. The results show that the average growth of pre-oscillation plays an important role on MAPO value (correlation coefficient, r_s = 0.965), the established MLR model possess high accuracy for MAPO prediction. The pressure oscillation regarding the 1st resonance mode is extracted from the high-pass filtered signal, representing the main in cylinder pressure oscillating process. Advancing the CA50, the heat release fraction produced by knock increases at first then reduces due to the thermodynamic conditions and the flame propagation. Activating two or three spark plugs, the rise rate of heat release rate goes up obviously but the knock induced heat release fraction decreases. Moreover, the primary acoustic resonance mode (1, 0) gives more regular knock vibrations than the mixing form (including mode (1, 0), (0, 1), (2, 0), etc.), the average travelling distance of acoustic wave in the time gap of receiving two continuous signals is very close to the cylinder bore. The results give insights of the knock pressure wave propagation process, as well as the relations between knock conditions, pressure oscillations and heat release.

关键词

Engine knock;Pressure oscillation;Auto-ignition;Multiple linear regression;Wiebe function;Acoustic resonance

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