Large-Eddy simulation analysis of spark configuration effect on cycle-to-cycle variability of combustion and knock

Abstract

Cycle-to-cycle variability is numerically simulated for high-speed, full-load operation of a turbocharged gasoline direct injection engine. Large-Eddy simulation is adopted to replicate the fluctuations of the flow field affecting the turbulent combustion. Experimental data were provided at knock onset, and large-Eddy simulation was validated for the same condition. In the original engine configuration, the spark plug is displaced toward the exhaust side, while the electrodes orientation is arbitrary. A 90 rotation is imposed to evaluate the effects of the aerodynamic obstruction caused by the electrode with respect to the flow field and the flame kernel growth. A second speculative analysis is performed modifying the position of the spark plug. The electrodes are shifted 2mm toward the intake side since this variation is compatible with the cylinder head layout. For both variations in orientation and position, the effects on the flow field around the spark plug are investigated. Statistical analysis is carried out on early flame kernel formation and knock tendency. The results highlight that the orientation of the electrodes affects the flow field for each cycle but plays a negligible role on the statistical cyclic variability, indirectly justifying the lack of an imposed orientation. As for the spark plug position, the numerical analysis indicate that the shifting of the electrodes toward the intake side slightly improves the knock limit mainly because of a reduction in in-cylinder peak pressure. In general, it is inferred that improvements may be achieved only through a simultaneous modification of the fuel jet orientation and phasing

Cyclic dispersion in engine combustion—Introduction by the special issue editors

“…in practical engine design) with a greatly reduced computational burden. 10,12 Both the review by Richard et al 10 and the article by Fontanesi et al 11 used LES to investigate aspects of cyclic dispersion in SI engines. Long anticipated as a way to simulate cyclic variability in engine flows and combustion, 27 LES is at last becoming a practical tool for engine research (see, for example, Rutland's review 28 ).…”

“…The four articles in this special issue that employ numerical simulation to investigate sources and effects of cyclic dispersion in SI engines 10,11 and in lowtemperature CI engines 12,13 take two contrasting but complementary approaches, as outlined below. In two of these articles, moreover, a major goal is also the development of models with greatly reduced dimensionality that nonetheless capture the essential results of highly detailed simulations and that can be used for parametric investigations of cyclic variability (e.g.…”

“…Conventional spark-ignition (SI) 6,[9][10][11]14 and compression-ignition (CI) (diesel) engines; 7,12 Spray-guided stratified-charge engines; 4,5 Low-temperature combustion (LTC) engines, 8,9,12,13,15,16 including homogeneous charge compression ignition (HCCI) 8,9,15,16 and reactivitycontrolled compression ignition (RCCI). 12,13 In this introductory overview, we place these articles (which include three invited review papers 4,9,10 ) in the larger context of engine research and offer brief but (we hope) tantalizing summaries.…”

“…Numerical simulation of cyclic dispersion; [10][11][12][13] Sensing and controls. [14][15][16] Of course, these categories, while convenient, are neither unique nor orthogonal.…”

Effect of Fuel Injection Strategy on the Carbonaceous Structure Formation and Nanoparticle Emission in a DISI Engine Fuelled with Butanol

“…Wall wetting is directly related to load, meaning that as engine output is increased at fixed rotational speed, larger quantities of fuel need to be injected; several mechanisms during air-fuel mixture formation contribute to complex effects on charge distribution during combustion, that can be identified through combined experimental and numerical investigations [18], [19]. Mixture inhomogeneity plays a significant role during the initial stages of flame kernel development [20], but also influences the occurrence of abnormal combustion phenomena due to autoignition [21], [22], [23]. The use of alternative fuels is another aspect that needs to be considered from a wide perspective [24].…”