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Article

Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine

State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
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Author to whom correspondence should be addressed.
Energies 2020, 13(19), 5039; https://doi.org/10.3390/en13195039
Received: 30 August 2020 / Revised: 19 September 2020 / Accepted: 22 September 2020 / Published: 24 September 2020
Knocking is a destructive and abnormal combustion phenomenon that hinders modern spark ignition (SI) engine technologies. However, the in-depth mechanism of a single-factor influence on knocking has not been well studied. Thus, the major aim of the present study is to study the effects of flame propagation velocity and turbulence intensity on end-gas auto-ignition through a large eddy simulation (LES) and a decoupling methodology in a downsized gasoline engine. The mechanisms of end-gas auto-ignition as well as strong pressure oscillation are qualitatively analyzed. It is observed that both flame propagation velocity and turbulence have a non-monotonic effect on knocking intensity. The competitive relationship between flame propagation velocity and ignition delay of the end gas is the primary reason responding to this phenomenon. A higher flame speed leads to an increase in the heat release rate in the cylinder, and consequently, quicker increases in the temperature and pressure of the unburned end-gas mixture are obtained, leading to end-gas auto-ignition. Further, the coupling of a pressure wave and an auto-ignition flame front results in super-knocking with a maximum peak of pressure of 31 MPa. Although the turbulence indirectly influences the end-gas auto-ignition by affecting the flame propagation velocity, it can accelerate the dissipation of radicals and heat in the end gas, which significantly influences knocking intensity. Moreover, it is found that the effect of turbulence is more pronounced than that of flame propagation velocity in inhibiting knocking. It can be concluded that the intensity of the pressure oscillation depends on the unburned mixture mass as well as the local thermodynamic state induced by flame propagation and turbulence, with mutual interactions. The present work is expected to provide valuable perspective for inhibiting super-knocking of an SI gasoline engine. View Full-Text
Keywords: knocking mechanism; flame propagation velocity; turbulence; auto-ignition; pressure oscillation knocking mechanism; flame propagation velocity; turbulence; auto-ignition; pressure oscillation
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MDPI and ACS Style

Zhou, L.; Zhang, X.; Zhong, L.; Yu, J. Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine. Energies 2020, 13, 5039. https://doi.org/10.3390/en13195039

AMA Style

Zhou L, Zhang X, Zhong L, Yu J. Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine. Energies. 2020; 13(19):5039. https://doi.org/10.3390/en13195039

Chicago/Turabian Style

Zhou, Lei, Xiaojun Zhang, Lijia Zhong, and Jie Yu. 2020. "Effects of Flame Propagation Velocity and Turbulence Intensity on End-Gas Auto-Ignition in a Spark Ignition Gasoline Engine" Energies 13, no. 19: 5039. https://doi.org/10.3390/en13195039

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