Study about the link between injection strategy and knock onset in an optically accessible multi-cylinder GDI engine. (15th February 2017)

• Record Type: Journal Article
• Authors: Marseglia, G.; Costa, M.; Catapano, F.; Sementa, P.; Vaglieco, B.M.
• Is Part Of: Energy conversion and management. Volume 134(2017)
• Page Start: 1
• Page End: 19
• Publication Date: 2017-02-15
• Subjects: Gasoline direct injection -- Optical engine -- Flame propagation -- Abnormal combustion -- Knock -- Split injection; Direct energy conversion -- Periodicals; Energy storage -- Periodicals; Energy transfer -- Periodicals; Énergie -- Conversion directe -- Périodiques; Direct energy conversion; Periodicals; 621.3105
• DOI: 10.1016/j.enconman.2016.12.012
• Languages: English
• ISSNs: 0196-8904

Abstract

Highlights: Knock in an optically accessible GDI engine is experimentally and numerically analysed. Gasoline injection is considered in representative single and double events. In cylinder pressure cycles and high temporal and spatial resolution combustion images are collected. Flame front propagation is un-axisymmetric and concavity is affected by injection strategy. Double injection may be a measure for knock reduction and pollutants control. Abstract: The effects of different injection strategies on the mixture formation and combustion processes in a gasoline direct injection (GDI) engine are investigated. A synergic experimental and numerical analysis is realized on an optically accessible multi-cylinder engine under single and double injections, these last delivering the same amount of gasoline in two equal parts, the first during intake, the second during compression. In-cylinder pressure cycles and high temporal and spatial resolution combustion images are collected to highlight the possible occurrence of abnormal phenomena. AVL FIRE simulations are realized to characterize into detail the turbulent reacting flow and to evaluate the influence of mixture formation on flame propagation and the possible formation of zones in the end-gas region with conditions leading to self-ignition. Pollutants formation is also analysed. The flame propagation characteristics are indeed found different for the various injection strategies: for single injection, a faster spread occurs in the opposite side with respect to the injector position and towards the exhaust valves, while under split injection the flame front preferentially moves towards the intake valves. Computational fluid dynamics results give the relevant support to understand these peculiarities as related to in-cylinder equivalence ratio distribution and turbulent kinetic energy. In-chamber knock visualization is related to the numerical results of a simple self-ignition chemical model active in the end-gas zone, not yet reached by the main flame front. Split injection is shown to lead to advantages in terms of reduction of cyclic variability and tendency to knock, hence in increasing energy efficiency and in determining an overall reduction of undesired products of incomplete combustion.