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Technical Paper

Hybrid URANS/LES Turbulence Modeling for Spray Simulation: A Computational Study

Turbulence modeling for fuel spray simulation plays a prominent role in the understanding of the flow behavior in Internal Combustion Engines (ICEs). Currently, a lot of research work is actively spent on Large Eddy Simulation (LES) turbulence modeling as a replacement option of standard Reynolds averaged approaches in the Eulerian-Lagrangian spray modeling framework, due to its capability to accurately describe flow-induced spray variability and to the lower dependence of the results on the specific turbulence model and/or modeling coefficients. The introduction of LES poses, however, additional questions related to the implementation/adaptation of spray-related turbulence sources and to the rise of conflicting numerics and grid requirements between the Lagrangian and Eulerian parts of the simulated flow.
Technical Paper

Numerical and Experimental Analysis of Diesel Air Fuel Mixing

The air fuel mixing process of a small direct injection (d.i.) diesel engine, equipped with two different re-entrant combustion chambers and two nozzles having unlike spray angles, has been studied by integrated use of in-cylinder laser Doppler velocimetry (LDV) measurements, engine tests, and KIVA simulations. The LDV measurements have been carried out in an engine with optical access motored at 2200 rpm. The engine tests have been performed on a similar engine at the same speed, at fixed start of combustion, and different air-fuel ratio. The KIVA-II simulations have been made using as initial conditions the parameters determined by LDV and engine tests. The re-entrant bowl with higher levels of air velocity and turbulent kinetic energy at the time of injection gives the best performance. The nozzle having a spray angle of 150° which injects the fuel into the regions at higher turbulent kinetic energy lowers the smoke emission levels.
Technical Paper

Assessment of k-ε Turbulence Model in KIVA-II by In-Cylinder LDV Measurements

In-cylinder measurements of turbulent integral length scales, carried out during the last 60 degrees of the compression stroke at 600 and 1,000 rpm by a two-probe volume LDV system, were used to assess the capability of the k-ε model used in KIVA-II code. The objective of the paper is to address the following question: what is the most reasonable definition of turbulent length scale in the k-ε model for engine applications? The answer derived from the comparison between KIVA predictions and experiments that showed a fair agreement between the computed turbulent length scale and the measured lateral integral length scale. The agreement is a result of proper choice of the initial swirl ratio and turbulent kinetic energy at inlet valve closure (IVC) by taking into account the LDV measurements and the value of the constant Cμε in the k-ε model equations that relates the turbulent length scale to k and ε.
Technical Paper

Dynamic Tests of Racing Seats and Simulation with Vedyac Code

Dynamic tests have been performed on carbon fiber racing seats following the FIA regulations. The tests have shown, in rear impact tests, a relatively strong rebound leading to large forward bending of neck, and, in side impact tests, very large lateral displacement of the head, the latter protruding dangerously towards hard portions of the car structure. Stiffening the seat back by steel struts results in reducing strongly both the motion and the acceleration of the head. Simulations of the dynamics of the tests have been done with multi-body models, including the Hybrid III dummy and seat deflection, by means of the program VEDYAC. It has been found that computer simulation can predict very accurately the result of a test, provided the numerical models have been carefully calibrated to match the dummy tolerance bands. Once they have been calibrated and validated with a number of tests, the computer models can be very useful to extend the test results to different test conditions.
Technical Paper

CFD Modeling of Compact Heat Exchangers for I.C. Engine Oil Cooling

This work describes the development of a computational model for the CFD simulation of compact heat exchangers applied for the oil cooling in internal combustion engines. Among the different cooler types, the present modeling effort will be focused on liquid-cooled solutions based on offset strip fins turbulators. The design of this type of coolers represents an issue of extreme concern, which requires a compromise between different objectives: high compactness, low pressure drop, high heat-transfer efficiency. In this work, a computational framework for the CFD simulation of compact oil-to-liquid heat exchangers, including offset-strip fins as heat transfer enhancer, has been developed. The main problem is represented by the need of considering different scales in the simulation, ranging from the characteristic size of the turbulator geometry (tipically μm - mm) to the full scale of the overall device (typically cm - dm).
Journal Article

A Progress Review on Soot Experiments and Modeling in the Engine Combustion Network (ECN)

The 4th Workshop of the Engine Combustion Network (ECN) was held September 5-6, 2015 in Kyoto, Japan. This manuscript presents a summary of the progress in experiments and modeling among ECN contributors leading to a better understanding of soot formation under the ECN “Spray A” configuration and some parametric variants. Relevant published and unpublished work from prior ECN workshops is reviewed. Experiments measuring soot particle size and morphology, soot volume fraction (fv), and transient soot mass have been conducted at various international institutions providing target data for improvements to computational models. Multiple modeling contributions using both the Reynolds Averaged Navier-Stokes (RANS) Equations approach and the Large-Eddy Simulation (LES) approach have been submitted. Among these, various chemical mechanisms, soot models, and turbulence-chemistry interaction (TCI) methodologies have been considered.