LES analysis for auto-ignition induced abnormal combustion based on a downsized SI engine

Engine knock and super-knock have become the main barriers to significantly improving engine thermal efficiency. To further study the nature of the abnormal combustion, this work quantitatively investigates engine knock and super-knock using a Large Eddy Simulation framework coupling detailed chemistry solver. Firstly, classical knocking cycles with different knocking intensities have been calculated through adjusting spark-ignition timing. It shows that knocking onset and intensity vary proportionally with the advance of spark-ignition timing, however, super-knock events are not observed under the operation conditions. Then for a given spark-ignition timing, the blends of Primary Reference Fuels are introduced in order to obtain different octane number of mixture, through which super-knock events with stronger knocking intensity are observed. The results show that as the decreases of octane number, knocking onset is significantly advanced due to the enhancement of low-temperature chemical reactivity. Consequently, more auto-ignition centers appear at hot exhaust valve side and even cool intake valve side at very low octane number. But for the knocking intensity, it does not always show a proportional correlation with octane number during super-knock. Further auto-ignition scenarios show that developing detonation wave can be induced by both multiple hot-spots auto-ignition and directly by single hot-spot auto-ignition, with different reaction front curvatures. However, the later seems to produce much stronger knocking intensity, especially when there are several developing detonation waves during super-knock. Therefore, how to effectively regulate local auto-ignition initiation and development seems the key to the avoidance of abnormal combustion in modern engines.

[1]  Gautam Kalghatgi,et al.  Influence of autoignition delay time characteristics of different fuels on pressure waves and knock in reciprocating engines , 2009 .

[2]  G. Shu,et al.  The role of low temperature chemistry in combustion mode development under elevated pressures , 2016 .

[3]  Fabio Bozza,et al.  Potentials of cooled EGR and water injection for knock resistance and fuel consumption improvements of gasoline engines , 2016 .

[4]  M. Jia,et al.  Numerical study on the combustion and emission characteristics of a methanol/diesel reactivity controlled compression ignition (RCCI) engine , 2013 .

[5]  Chih-Jen Sung,et al.  Laminar flame speeds of primary reference fuels and reformer gas mixtures , 2004 .

[6]  Vincenzo De Bellis,et al.  Performance optimization of a spark-ignition turbocharged VVA engine under knock limited operation , 2016 .

[7]  S. Richard,et al.  Analysis of pre-ignition in highly charged SI engines: Emphasis on the auto-ignition mode , 2013 .

[8]  P. Senecal,et al.  Multi-Dimensional Modeling of Direct-Injection Diesel Spray Liquid Length and Flame Lift-off Length using CFD and Parallel Detailed Chemistry , 2003 .

[9]  Ulrich Spicher,et al.  Irregular combustion in supercharged spark ignition engines – pre-ignition and other phenomena , 2010 .

[10]  Wenming Yang,et al.  Application of CFD-chemical kinetics approach in detecting RCCI engine knocking fuelled with biodiesel/methanol , 2015 .

[11]  Jean-Baptiste Michel,et al.  A new LES model coupling flame surface density and tabulated kinetics approaches to investigate knock and pre-ignition in piston engines , 2011 .

[12]  Haiqiao Wei,et al.  Experimental investigation on the knocking combustion characteristics of n-butanol gasoline blends in a DISI engine , 2016 .

[13]  Thierry Poinsot,et al.  LES study of deflagration to detonation mechanisms in a downsized spark ignition engine , 2015 .

[14]  S. Menon,et al.  Effect of subgrid models on the computed interscale energy transfer in isotropic turbulence , 1994 .

[15]  S. Turns.  Introduction to Combustion , 1995, Aerothermodynamics and Jet Propulsion.

[16]  Zhi Wang,et al.  Analysis of pre-ignition to super-knock: Hotspot-induced deflagration to detonation , 2015 .

[17]  Gerardo Valentino,et al.  Application of an entrainment turbulent combustion model with validation based on the distribution of chemical species in an optical spark ignition engine , 2016 .

[18]  A. Ramesh,et al.  Investigation on the effect of concentration of methane in biogas when used as a fuel for a spark ignition engine , 2008 .

[19]  Mingfa Yao,et al.  Development of a Reduced Primary Reference Fuel Mechanism for Internal Combustion Engine Combustion Simulations , 2013 .

[20]  G. Shu,et al.  Interactions of flame propagation, auto-ignition and pressure wave during knocking combustion , 2016 .

[21]  Gequn Shu,et al.  Gasoline engine exhaust gas recirculation – A review , 2012 .

[22]  G. Shu,et al.  Interaction of Flame Propagation and Pressure Waves During Knocking Combustion in Spark-Ignition Engines , 2014 .

[23]  Ming Jia,et al.  Enhancement on a Skeletal Kinetic Model for Primary Reference Fuel Oxidation by Using a Semidecoupling Methodology , 2012 .

[24]  Thierry Poinsot,et al.  LES of knocking in engines using dual heat transfer and two-step reduced schemes , 2015 .

[25]  Ming Jia,et al.  Improvement on a skeletal chemical kinetic model of iso-octane for internal combustion engine by using a practical methodology , 2013 .

[26]  E. Tomita,et al.  Visualization of auto-ignition and pressure wave during knocking in a hydrogen spark-ignition engine , 2009 .

[27]  Norbert Peters,et al.  Super-Knock Prediction Using a Refined Theory of Turbulence , 2013 .

[28]  Alasdair Cairns,et al.  The competing chemical and physical effects of transient fuel enrichment on heavy knock in an optical spark ignition engine , 2016 .

[29]  Xudong Zhen,et al.  Study of knock in a high compression ratio SI methanol engine using LES with detailed chemical kinetics , 2013 .

[30]  Akira Yoshizawa,et al.  A Statistically-Derived Subgrid-Scale Kinetic Energy Model for the Large-Eddy Simulation of Turbulent Flows , 1985 .