Centrifugal compressor influence on condensation due to Long Route-Exhaust Gas Recirculation mixing

Abstract

State of the art techniques for reducing pollutant emission in internal combustion engines often require local flow assessment, specially in the air management field. This work addresses the interaction between a turbocharger compressor and the 3-way long-route EGR joint, where exhaust gases of the combustion are mixed with fresh air. A validated methodology for compressor simulation is combined with a validated condensation model for this work. Numerical simulations of two different working points with three flap positions are conducted. The influence of these operating conditions on the flow field is evaluated. Particularly, there is a connection between the mixing of both steams and the generation of water condensates, responsible for the erosion of the impeller and the loss of compressor efficiency. Moreover, neglecting the impact of the compressor presence on the condensation production is shown to be of low magnitude, so that simulations without the compressor are regarded as accurate, thus reducing the computational effort by two orders of magnitude.

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

“…Junction design should minimize condensation mass flow rate to prevent harm to the LP-EGR compressor, as great impeller erosion was found at experimental impeller durability tests when 3D-CFD simulations predicted the highest condensation rates [37], which can be deemed as another prove of the validity of the 3D CFD model. Galindo et al [5,35] have observed that junction geometries that promote strong secondary flows are the ones providing higher condensation mass flow rates, but their research did not go beyond that point. The idea that volume condensation in a three-way junction may be correlated with a quantitative indicator of the mixing of its inlet streams has never been addressed before in the literature, and is the main task of this work.…”

“…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.…”

Influence of the low-pressure exhaust gas recirculation injection point on engine performance

“…14 Since the specific humidity of exhaust gases is high, water condensation could occur if exhaust gases undergo a cooling process. Both the high and low-pressure EGR systems can be affected by condensation, since water from the exhaust gases is susceptible to condense either in the EGR cooler, 15,16 in the mixture between EGR gases and fresh air 17,18 and/or inside the intercooler (for low-pressure EGR circuits), 19 especially when it is water cooled. The main issue for condensation inside the cooler or in the air-EGR mixing for a low-pressure EGR system is related to compressor wear, due to the impact of water droplets or streams with the highly-rotating blades.…”

“…The predictive capability of this approach has been validated in terms of secondary flows and condensation patterns, 23 distribution of condensation mass fluxes, 24 and correspondence of calculated condensation mass flow rate with subsequent impeller damage. 25 With such model, it has been established the impact of LP-EGR junction design, 23 the existence of regulating flaps 17 or the distance between EGR discharge and compressor impeller 18 on secondary flows, and enhanced air-EGR mixing. Galindo et al 18 obtained a strong positive agreement between air-EGR mixing and condensation mass flow rate, which suggests to avoid flow homogeneity at the compressor inducer plane to reduce condensation.…”

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

“…Regarding LP-EGR configuration, it takes exhaust gases downstream the after-treatment devices, so the problems of soot deposition in the EGR line are avoided. Nevertheless, an important issue in this configuration for the operation and homologation in cold conditions 5 is the condensation that can appear before the compressor 6–8 that compromises the compressor integrity. 9 Condensation may be produced with HP-EGR as well, 10 but it is not so harmful as it happens downstream the compressor.…”