Relationship of Flame Front Pattern to Pressure and High-Speed Knock on Commercial Engines

Chiampo, P.; Cristofaro, Ferdinando De; Gozzelino, R.

doi:10.4271/730087

Cited by 11 publications

(1 citation statement)

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“…The threshold was based on the RMS value of non-knocking cycles. Chiampo et al [149] of FIAT also investigated the correlation between flame-front arrival time from ion sensors and knocking cylinder pressure measurements on a FIAT 125 engine and noted similar results to Allwood. An alternative "kinetic knock index" was proposed by Ferraro [150] of the Polytechnic University of Turin based on wave energy rather than the more typical amplitude or integral methods in use at the time, and indeed still today.…”

Section: The 1970s: Oil Shortages Emissions Control and Unleaded Fuelsmentioning

confidence: 72%

Knock: A Century of Research

Corrigan¹,

Fontanesi²

2021

SAE Int. J. Engines

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Knock is one of the main limitations on increasing spark-ignition (SI) engine efficiency. This has been known for at least 100 years, and it is still the case today. Knock occurs when conditions ahead of the flame front in an SI engine result in one or more autoignition events in the end gas. The autoignition reaction rate is typically much higher than that of the flame-front propagation. This may lead to the creation of pressure waves in the combustion chamber and, hence, an undesirable noise that gives knock its name. The resulting increased mechanical and thermal loading on engine components may eventually lead to engine failure. Reducing the compression ratio lowers end-gas temperatures and pressures, reducing end-gas reactivity and, hence, mitigating knock. However, this has a detrimental effect on engine efficiency.Automotive companies must significantly reduce their fleet carbon dioxide (CO 2 ) values in the coming years to meet targets resulting from the 2015 Paris Agreement. One path towards meeting these is through partial or full electrification of the powertrain. However, the vast majority of automobiles in the near future will still feature a gasoline-fueled SI engine; hence, improvements in combustion engine efficiency remain fundamental.As knock has been a key limitation for so long, there is a huge amount of literature on the subject. A number of reviews on knock have already been published, including in recent years. These generally concentrate on current understanding and status. The present work, in contrast, aims to track the progress of research on knock from the 1920s right through to the present day. It is hoped that this can be a useful reference for new and existing researchers of the subject and give further weight to occasionally neglected historical activity, which can still provide important insights today.

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Section: The 1970s: Oil Shortages Emissions Control and Unleaded Fuelsmentioning

confidence: 72%