A comparative numerical investigation of reactivity controlled compression ignition combustion using Large Eddy Simulation and Reynolds-Averaged Navier-Stokes approaches. (1st December 2019)

• Record Type: Journal Article
• Authors: Liu, Xinlei; Kokjohn, Sage; Wang, Hu; Yao, Mingfa
• Is Part Of: Fuel. Volume 257(2019)
• Publication Date: 2019-12-01
• Subjects: AC8H17 Octyl radical -- AC8H17O2 Octylperoxy radical -- AMR Adaptive Mesh Refinement -- C7H15-2 Heptyl radical -- C7H15O2-2 Heptylperoxy radical -- CA ATDC Crank Angle after Top Dead Center -- CFD Computational Fluid Dynamics -- CH2O Formaldehyde -- CI Compression Ignition -- CO Carbon monoxide -- CR Common Rail -- ECN Engine Combustion Network -- ϕ Equivalence ratio -- GDI Gasoline Direct Injection -- H2O Water -- H2O2 Hydroperoxide -- HCO Formyl radical -- HO2 Hydroperoxyl radical -- HRR Heat Release Rate -- HTHR High-Temperature Heat Release -- IC8H18 Iso-octane -- LES Large Eddy Simulation -- LTC Low-Temperature Combustion -- LTHR Low-Temperature Heat Release -- N2 Nitrogen -- NC7H16 N-heptane -- O2 Oxygen -- OH Hydroxyl radical -- PLIF Planar Laser-Induced Fluorescence -- PRF Primary Reference Fuel -- RANS Reynolds-Averaged Navier-Stokes -- RCCI Reactivity Controlled Compression Ignition -- RCR Representative Creation Reaction -- RDR Representative Destruction Reaction -- RNG Renormalization group -- ROI Rate of Injection -- RREX Representative Exothermic Reaction -- SI Spark-Ignited -- SOI Start of Injection -- Spray H N-heptane spray -- 0D Zero-Dimensional -- 3D Three-Dimensional; Large Eddy Simulation -- RCCI -- Flame structure -- Optical engine -- Chemical kinetics; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2019.116023
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Chemical kinetics process of RCCI combustion was investigated. Both the LES and RANS approaches were adopted and compared. Representative reactions for exothermic heat release were analyzed. More insights into the RCCI combustion feature were provided. Abstract: In this work, a comparative numerical study of Reactivity Controlled Compression Ignition (RCCI) combustion was conducted using both the Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) approaches. In order to clarify the associated chemical kinetic processes, a data processing method that is able to calculate average reaction pathways, and identify representative reactions for the species creation, consumption, and heat release was adopted. The LES case yielded a wrinkled spray-flame structure, in contrast to the smoother and concentrated structure predicted by the RANS case. However, despite the different distribution features, both cases demonstrated similar reaction pathways and heat release characteristics. Modeling results showed that the low-temperature heat releases in RCCI combustion were controlled by the n-heptane spray-combustion process and dominated by the reactions R8 (C7 H15 O2 − 2 = C7 H15 − 2 + O2 ), R95 (CH3 COCH2 + O2 = CH3 COCH2 O2 ), and R285 (HCO + O2 = CO + HO2 ). In addition, low-temperature consumption pathways of n-heptane led to the substantial formation of a hydroxyl radical, which enhanced the consumption of iso-octane. As the combustion process progressed, high-temperature ignition pockets were found near the piston rim edge and squish regions, where heat release was dominated by the reaction R285. Intense high-temperature heat release was observed instantly from the ignition pockets, resulting in a rapid propagation of the reactive surfaces.