Modeling of gaseous emissions and soot in 3D-CFD in-cylinder simulations of spark-ignition engines: A methodology to correlate numerical results and experimental data

Abstract

In order to reduce development costs and time-to market, 1D and 3D CFD tools can support engine design providing reliable estimations of the tailpipe emissions. In particular, 3D-CFD in-cylinder simulations can evaluate formation of both soot and gaseous pollutants inside the combustion chamber. The main issue in such kind of simulations is the validation against experimental findings. In fact, the complexity of the emission measurements does not allow a straightforward one-to-one comparison between numerical and experimental results. Therefore the present paper aims at providing, on the one hand, a robust numerical framework for both gaseous and solid emissions, on the other hand a dedicated post-processing for a fair comparison between simulations and experiments. From a numerical standpoint, a simplified approach is dedicated to gaseous emissions, while a more detailed one is reserved to soot modeling. The latter is based on the Sectional Method, whose reaction rates are tabulated following 0D chemical kinetic simulations of a purposely designed surrogate in a constant pressure reactor. Simulations and experiments proposed in the present analysis are referred to a high-performance turbocharged direct-injection spark-ignition engine operated at part-load and low rpms. On equal performance, revving speed and mean mixture quality, different injection timings are investigated. The developed numerical approach and post-processing ensure a good agreement between simulations and experiments.

Hydrogen, methane and one of their fuel blends combustion: CFD analysis and numerical-experimental comparisons of fixed and mobile applications

“…Thanks to the reduced computational cost Reynolds Averaged Navier-Stokes (RANS) is the widely used approach for the prediction of normal and abnormal combustion despite more CPU demanding approaches such as LES (Large Eddy Simulation) can be successfully applied to account for cyclic variation of combustion due to turbulent flows [12][13][14][15][16]. Turbulent combustion in RANS of standard and unconventional fuels can be effectively modelled integrating fuel specific chemical characteristics, such as laminar flame speed, ignition delay times and soot tendency without solving online chemistry as demonstrated in [17][18][19][20][21], saving CPU time and preserving accuracy. Despite this, the direct integration of chemical kinetics in the CFD framework is becoming even more attractive thanks to the increase of computing power, especially for the simulation of combustion of fuels which oxidation pathway involves a low number of species and reactions such as hydrogen.…”

Biomimetic swirl device and hydrogen enrichment effects on LPG fueled engine

“…To this end, several research studies are adopted to improve the in-cylinder flow characteristics and therefore the optimization of gaseous engine power output efficiencies. [21][22][23] Moreover, various methods influencing the air-fuel flow dynamics have been used. The first case is investigating the engine piston shape.…”