Validation and sensitivity analysis of an in-flow water condensation model for 3D-CFD simulations of humid air streams mixing

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.

Section: Sensitivity Studiesmentioning

confidence: 99%

Section: Introduction and Literature Reviewmentioning

confidence: 99%

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

Galindo

Climent

Garcia

et al. 2020

“…[23][24][25] In addition, it can be found in the mixing region between fresh air and EGR gas, due to its high water content. 26,27 Water droplets can produce an important damage to the compressor impeller, severely reducing its durability. In other research fields, such as steam jets 28,29 or nozzles, 30 water condensation is also a problem.…”

Section: Introductionmentioning

confidence: 99%

Development of an experimental test bench and a psychrometric model for assessing condensation on a low-pressure exhaust gas recirculation cooler

Galindo

Garcia

Tarí

et al. 2020

A test bench has been designed to assess condensation formation produced on the interior of a low-pressure exhaust gas recirculation cooler working with hot stream of humid air representing an engine warm-up stage, when its coolant starts from very cold conditions. An experimental campaign has been conducted with three different exhaust gas recirculation mass flow rates, four exhaust gas recirculation inlet temperatures and three different coolant initial temperatures, covering common conditions found in the low-pressure exhaust gas recirculation system of internal combustion engines under cold starts. The transient experimental results are analyzed and compared with a simple psychrometric condensation model, obtaining a good correlation and reproducing the trends of the condensation, even though an overprediction of the condensates of around 20%–40% exists due to the strong hypotheses assumed. The warm-up tests are most sensitive to the initial coolant temperature. For example, an engine starting at –10 °C ambient temperature could require 10 min to stop producing water in the low-pressure exhaust gas recirculation cooler, with an accumulated quantity during the warm-up of about 100 mL of condensates.

“…24 In addition, HP configuration needs less exhaust energy because the compressor operates under lower amount of gas. Moreover, the LP EGR presents troubles related to condensation issues at low ambient temperatures when it mixes with ambient air; this effect was recently studied by JR Serrano et al 25 and J Galindo et al 26 to predict the condensation rate and its effect in the rotor of the compressor, respectively. Nevertheless, at low ambient temperature, condensation issues appear in the whole engine and in all its elements, in the HP EGR line for instance, like JM Luján et al 27…”

Section: Introductionmentioning

confidence: 99%

Cylinder-to-cylinder high-pressure exhaust gas recirculation dispersion effect on opacity and NO_x emissions in a diesel automotive engine

Macián

Luján

Climent

et al. 2020

The objective of the study is to determine the effect of the high-pressure exhaust gas recirculation dispersion in automotive diesel engines in NO x and smoke emissions in steady engine operation. The investigation quantifies the NO x and smoke emissions as a function of the dispersion of the high-pressure exhaust gas recirculation among cylinders. The experiments are performed on a test bench with a 1.6-L automotive diesel engine. In order to track the high-pressure exhaust gas recirculation dispersion in the intake pipes, a valves system to measure CO2, that is, exhaust gas recirculation rate, was installed pipe to pipe. In addition, a valves device to measure NO x emissions cylinder to cylinder in the exhaust was installed. Moreover, a smoke meter device was installed downstream the turbine, to measure the effect of the high-pressure exhaust gas recirculation dispersion on smoke emissions. Five different engine speeds were studied with different torque levels; thus, the engine map was widely studied, from 1250 to 3000 r/min and between 6 and 20 bar of brake mean effective pressure. The exhaust gas recirculation rate varies between 4% and 25% depending on the operating point. The methodology focused on experimental tools combining traditional measuring devices with a specific valves system, which offers accurate information about species concentration in both the intake and the exhaust manifolds. The study was performed at constant raw NO x emissions to observe the effect of the exhaust gas recirculation dispersion in the opacity and fuel consumption. The study concludes that when the exhaust gas recirculation dispersion is low, the opacity presents reduced values in all operating points. However, above a certain level of exhaust gas recirculation dispersion, the opacity increases dramatically with different slopes depending on the engine running condition. This study allows quantifying the exhaust gas recirculation dispersion threshold. In addition, the exhaust gas recirculation dispersion could contribute to increase the fuel consumption up to 3.5%.