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Experimental Study on Spark Strategy Effects on Knock Mechanism and Combustion Characteristics
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
Engine knock is an abnormal phenomenon due to spontaneous end-gas auto-ignition ahead of propagating flame front, which is one of the major barriers for modern Spark-Ignition (SI) engines to achieve higher thermal efficiency and better performance. In order to understand the knock inception mechanism, various spark strategies (e.g. spark number, spark location) are applied to investigate on the knock intensity, pressure oscillation, combustion characteristics and emissions. The experiment is implemented on a modified Compression-Ignition (CI) engine operated at SI mode with port fuel injection (PFI), and performed with normal aspiration condition and same injection timing (SOI = -330 CAD aTDC). A specialized liner with 4 side spark plugs and 4 pressure sensors are used to trigger various flame propagation processes, which lead to different auto-ignition onsets and knock mechanisms. In addition, based on the multiple channels of pressure signal, both of the auto-ignition sites and the subsequent pressure oscillating processes could be deduced. Moreover, the knock mechanisms regarding various spark strategies are compared and analyzed.