Design trend in spark ignition (SI) engines aims to improve power density and efficiency to ensure that regulated emissions levels are minimized. From a thermodynamic point of view this involves increased in-cylinder pressure and local mixture conditions that promote autoignition of the end gas, leading to knock. In order to prevent knock, the commonly used technique consists in retarding spark timing and combustion phasing, which results in a lower thermodynamic efficiency and higher exhaust temperature. A delayed spark timing is frequently coupled with over-fueling that allows to reduce the exhaust temperatures as well as knock tendency. This strategy clearly results in worsened fuel economy and increased emissions levels. At present time knock represents a limiting factor for a further development of new generation of high performance spark ignition engines and a number of technological solutions have been proposed by the scientific community and OEMs to overcome the limitations connected to this phenomenon. New engine architectures with optimized combustion chamber geometry shapes and combination of methodologies have been proposed for a reduced combustion time to enhance high-performance engines. Changes in the engine cooling systems have been applied to enhance end gas cooling leading to knock suppression effect. Other favorable options proposed for knock mitigation are water injection and cooled exhaust gas recirculation. Moreover, attention is also paid on renewable alcohol fuels with a research octane number higher than gasoline. This contribution aims to review some of the recent progresses in this topic with detailed analyses of current and promising future technologies to avoid knock and enable the development of future high efficiency SI powertrains with low impact on emissions.
Technologies for Knock Mitigation in SI Engines—A Review
Energy, Environment, and Sustainability
2021-12-14
25 pages
Aufsatz/Kapitel (Buch)
Elektronische Ressource
Englisch
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