Computational Fluid Dynamics Simulation of Diesel Engines with Sophisticated Injection Strategies for In-Cylinder Pollutant Controls

Abstract

This work presents a computational fluid dynamics (CFD) methodology to simulate diesel combustion in highpressure common-rail engines, which employ sophisticated injection strategies with rate shaping to reduce the in-cylinder pollutant formation and achieve the emission legislation EU6 and US Tier2 Bin 5. The physics of the mixture formation and its effects on combustion and, hence, on emission formation needs to be correctly described by the numerical tool. At the same time, in order to be used in a design and optimization stage of a new engine, the CFD methodology must be very efficient in terms of time requirements. For these purposes, the authors propose and assess the capabilities of the characteristic time-scale combustion model (CTC). The Shell autoignition model is used to predict autoignition, while the standard CTC model was improved by introducing a new expression to compute the characteristic time scale to be applied also in the presence of very high EGR rates. Soot emissions were predicted by the eight reaction step mechanism proposed by Fusco et al., and the extended Zeldovich mechanism was used to estimate NO x concentration. The proposed combustion model was implemented into the Lib-ICE code, which is a set of libraries and applications for internal combustion engine modeling developed by the authors under the OpenFOAM technology. Validation considers two different sets of operating modes, which are representative of common driving conditions and considered to be challenging for the proposed CFD methodology.

Investigation of Biodiesel–Diesel Fuel Blends on Combustion Characteristics in a Light-Duty Diesel Engine Using OpenFOAM

“…19 Heat transfer between the discrete and gas phases is determined using the Ranz−Marshall correlation. 16,17 The Bai and Gosman correlation is used to predict the dynamics characteristics of droplet wall interactions on the piston bowl wall surface. 19 Further details about the spray model constants as well as model implementations and validations are reported elsewhere.…”

“…19 Further details about the spray model constants as well as model implementations and validations are reported elsewhere. [16][17][18][19]23 The spray characteristics of diesel fuel are defined by the thermophysical and transport properties of a C 14 H 30 surrogate. The properties of CME, PME, and SME developed by Ismail et al 19 are utilized for neat biodiesel fuels.…”

“…The initial conditions of the intake pressure and temperature at IVC are 1.23 bar and 300 K, respectively. Here, the dynamic mesh layering utility of the mesh topological change library (Lib-ICE) − is utilized for modeling of the compression and expansion strokes. The mesh with a cell size of 2.0 (radial) × 2.5 (axial) × 2.0 (azimuthal) mm is used throughout this study because it is found to give similar accuracy but with shorter computing time compared to a finer resolution mesh .…”

“…The liquid spray structures are predicted using the Huh injector model to represent the injector and fuel droplets primary spray breakup. , Fuel spray atomization is modeled using the modified Huh and Gosman model. ,, Secondary breakup is computed using the Kelvin-Helmoltz and Rayleigh-Taylor model . Heat transfer between the discrete and gas phases is determined using the Ranz–Marshall correlation. , The Bai and Gosman correlation is used to predict the dynamics characteristics of droplet wall interactions on the piston bowl wall surface . Further details about the spray model constants as well as model implementations and validations are reported elsewhere. − , The spray characteristics of diesel fuel are defined by the thermophysical and transport properties of a C 14 H 30 surrogate.…”

Flame–Wall Interaction Effects on Diesel Post-injection Combustion and Soot Formation Processes

“…Post injection, which involves a short injection of a small quantity of fuel after the main injection, is one of the promising in-cylinder strategies to reduce soot emissions. − The reduction of soot by post injection late in the engine cycle can be achieved through after-treatment system management by increasing the exhaust temperature to promote PM oxidation on DPFs for regeneration purposes. , Post injection is also used, closely coupled with the main injection, to induce different in-cylinder mechanisms for soot reduction purposes, which is the focus of this work. The close-coupled post injection is sometimes referred as “after-injection”, which is used interchangeably with “post injection” defined by this study and many others. ,− It should be noted that this work seeks to advance understanding of the post-injection schedule that is typically required for normal engine operation.…”