Assessment of the numerical and experimental methodology to predict EGR cylinder-to-cylinder dispersion and pollutant emissions

Abstract

EGR cylinder-to-cylinder dispersion poses an important issue for piston engines, since it increases NOx and particulate matter (PM) emissions. In this work, the EGR distribution on a 6-cylinder intake manifold is analyzed by means of experiments, 0D/1D engine modeling and 3D CFD simulations at three different working points. Using a comprehensive set of measurements, statistical regressions for NOx and PM emissions are developed and employed to quantify the sensitivity of numerical configuration to EGR dispersion and subsequent increase of pollutants. CFD mesh and time-step size independence studies are conducted, taking into account their interrelation through the Courant number. The obtained numerical configuration is validated against experimental measurements, considering different unsteady RANS turbulence submodels ([Formula: see text] and [Formula: see text]) as well as the inviscid case. The agreement of the different approaches is quite sensitive to the operating conditions, obtaining root mean square errors for the average cylinder-to-cylinder EGR distribution between 1% and 17% and for the transient [Formula: see text] traces between 8% and 29%. However, for the worst-case scenario, the error in NOx and PM emissions prediction is below 2%. The regressions are employed to find a greater EGR distribution impact on pollutants when EGR rate or dispersion are increased. Flow investigation reveals the underlying reasons for the discrepancies and similarities between the predictions of the different turbulence submodels. A statistical analysis shows the significant errors that average [Formula: see text] probes make when assessing EGR cylinder-to-cylinder distribution, which is explain by the flow heterogeneity at some operating conditions.

EGR cylinder deactivation strategy to accelerate the warm-up and restart processes in a Diesel engine operating at cold conditions

“…Besides, according with the literature the new exhaust gas recirculation distribution and its dispersion could contribute to increase the NOx and PM emissions depending of the mixing behavior. 24,25…”

Numerical assessment of mixing of humid air streams in three-way junctions and impact on volume condensation

“…There are many engineering fields in which three-way junctions are employed to merge two flows into a single stream, such as nuclear industry [1,2,3], internal combustion engines [4,5] and oil industry [6], to name a few. In all these situations, a main stream meets a secondary flow within the junction, seeking for a quick homogenization or trying to keep the streams separated as much as possible, depending of the considered problem.…”

Analysis of condensation and secondary flows at three-way junctions using optical visualization techniques and computational fluid dynamics

“…HP-EGR is well established in current automotive engines, but manufacturers are lately placing LP-EGR in the spotlight, due to its benefits when compared to HP-EGR. For instance, 30 LP-EGR conducts the mixing between the exhaust gases and fresh air far upstream from the cylinders, which overcomes the issues of uneven EGR cylinder-to-cylinder distributions of HP-EGR [4,5]. Furthermore, LP-EGR does not detract energy from the turbocharger as HP-EGR does, and allows using higher 35 EGR rates than HP-EGR, which increases its benefits on emissions.…”