G. Ferrari

Secondary Air Injection in the Exhaust After-Treatment System of S.I. Engines: 1D Fluid Dynamic Modeling and Experimental Investigation

The paper describes the experimental and simulation work recently carried out to investigate the effects of secondary air injection on the emission conversion in the exhaust after-treatment system of a S.I. automotive engine. The modeling of the 1 D unsteady reacting flows in the complete exhaust system of a spark ignition engine, designed to satisfy the Euro IV limits, has been performed including the secondary air injection system, to predict the possible shortening of catalyst light-off time and the speed-up of the after-treatment system warm-up. The transport of chemical species with reactions in gas phase (post-oxidation of unburned HC in the exhaust manifold) and in solid phase (conversion of pollutants in the catalyst) with and without secondary air has been simulated by the 1D thermo-fluid dynamic model GASDYN, developed by the authors. The code has been extended to simulate the injection of air in the exhaust manifold and predict the consequent post-oxidation of pollutants in the ducts. The main chemical reactions arising in gas phase, in the upper part of the exhaust manifold, have been included, considering the oxidation of C 3 H 6 , C 3 H 8 and CO and the steam-reforming of C 3 H 6 and C 3 H 8 . The heat released in the gas due to the exothermal reactions has been taken into account, to evaluate the exhaust gas temperature along the ducts with injection of air. A Fiat-Alfa Romeo four-stroke, four-cylinder 2.0L automotive S.I. engine complying with the Euro IV regulations has been modeled, in order to predict the chemical specie concentration along the exhaust system. A large set of experimental data concerning this engine (cylinder pressure, pressure pulses, wall and gas temperatures, gas chemical composition along the system) with different secondary air mass flows has enabled a comprehensive comparison between predictions and measurements, in order to validate the model in different operating conditions.

Inlet boundary conditions for incompressible LES: A comparative study

Abstract In this paper, a comparison between inlet boundary conditions for Large Eddy Simulation is carried out. The geometry considered is the case n. 83 of the Ercoftac database; an incompressible and fully turbulent flow reaches a wall-mounted hump, that is followed by a separation region with recirculation. Three different inflow boundary conditions (fixed velocity profile, plane mapping and synthetic turbulence inlet) have been tested in an open-source CFD code and their influence on mean flow quantities, such as vortex separation and reattachment points, pressure coefficient and turbulence has been analyzed. Results show a satisfying agreement with experiments for the prediction of the mean pressure coefficient and the vortex separation point, despite which, some discrepancies still exist with respect to the channel velocity profiles, vortex size and reattachment point.

High resolution central schemes for multi-dimensional non-linear acoustic simulation of silencers in internal combustion engines

Because of their small numerical viscosity even when very small time steps are enforced, central schemes look very suitable for acoustic simulations of silencers in internal combustion engines. In this work, a high resolution central scheme has been used with ad-hoc developed boundary conditions for the generation of different acoustic perturbations (white noise, sweep, impulse) in the OpenFOAM^(R) technology. The temporal solution, carried out by a first-order integration of the conservation laws by the explicit Eulers method, has been first transferred into the frequency domain using FFT and then it has been processed to evaluate the transfer function of different geometries of silencers for internal combustion engines. The results obtained from the simulations have been compared with experimental data.