Modello per la previsione delle emissioni di idrocarburi incombusti di un motore a CI ad accensione comandata
Unburned hydrocarbons exhausted by a spark ignition engine are due to an incomplete combustion in... more Unburned hydrocarbons exhausted by a spark ignition engine are due to an incomplete combustion in the cylinder, caused by a complex interaction of different processes. The development work of a numerical code for the simulation of HC emissions is presented in this article. Its purpose is to complete the information given by a comprehensive fluid dynamic model for the simulation of one-dimensional unsteady flows in engine ducts, from the air inlets to the exhaust outlets. The proposed computer code takes into account only the effects produced by the flame quenching at the walls and at the crevices inlets and by the hydrocarbon absorption and desorption from the lubricant oil film. Comparison between predicted and measured data concerning different engines and operating conditions shows the model capability of correctly predicting the trend in exhausted unburned hydrocarbon production as a function of the main engine parameters.
Instationary heat and mass transfer phenomena in additive manufactured open cell polyhedral structures for automotive catalysis
Chemical Engineering Science, 2021
Abstract Additive Manufactured (AM) Open Cell Polyhedral lattices are novel substrates for automo... more Abstract Additive Manufactured (AM) Open Cell Polyhedral lattices are novel substrates for automotive catalytic converters due to promising properties. The present investigation focuses on heat and mass transfer with chemical reactions during cold starts, based on numerical simulations in OpenFOAM and dimensionless analytical analysis. The numerical model consists of a multi-region approach with overlapping meshes for fluid and solid regions, in order to simulate the presence of porous substrates. Experimental results from first vehicle-size AM catalysts are used as a basis. The catalyst heat-up is characterized by two distinguished phases: the initial phase where heat is convected from the inflowing gases to the catalyst and the following phase which is governed by the heat released by the chemical reactions. The impact of different operating parameters, lattice and converter geometries has been quantified. The introduction of dimensionless temperature, time and space, evidences the similarity of the initial warm-up phase.
The implementation and the combination of advanced boundary conditions and subgrid scale models f... more The implementation and the combination of advanced boundary conditions and subgrid scale models for Large Eddy Simulations are presented. The goal is to perform reliable cold flow LES simulations in complex geometries, such as cylinder engines. In the paper, an inlet boundary condition for synthetic turbulence generation is combined with a fully non reflecting Navier Stokes Characteristic Boundary Condition (NSCBC) for the outlet and with the local Dynamic Smagorinsky subgrid scale model, that is not included in the official distribution of OpenFOAM. Validation of the models has been performed separately on two steady state flow benches: a backward facing step geometry [1] and a simple IC engine geometry with one axed central valve [2]. The code developed has been included into a C++ library for multi-dimensional engine modeling based in the OpenFOAM Technology.
Introduction: A surgical table was designed to give opportunity to surgery residents, to study an... more Introduction: A surgical table was designed to give opportunity to surgery residents, to study and experiment on coronary arteries of bovine heart in home alone Objectives: It is aimed to learn and experiment vascular anastomosistechniques in bovine heart model. Materiel/Patients and Methods: In this study, before attempting anastomotic techniques in coronary arteries, the surgical table was designed (Figure 1A). The aorta is closed with a running 3-0 silk suture to prevent leakage from aorta. Then mitral valve was closed with 4-0 running suture. Next the Circumflex coronary artery (Cx) is dissected and harvested as a graft and the side branches are closed with simple sutures. Then the proximal end of right coronary artery was dissected and cannulated to fill the ascending aorta with the water. After that Cx is separated from the left main coronary artery (LMCA) from its bifurcation. The previously separated proximal end of Cx artery is closed in the LMCA bifurcation. The atrial retractors are used as a holder to hang the Cx artery during performing anastomosis. Finally, distal end of Cx artery is anastomosed to the LAD artery as an end to side or sequential fashion by using diagonal branch as a second vessel to be grafted. Subsequently, the proximal end of the Cx artery may be anastomosed to the ascending aorta as an end-to-side fashion. After completing the anastomoses, Aorta was filled with water to control the anastomosis sides whether there is any leakage or not. Results: Not only surgical residents, but also staff members, and surgeons who wish to make training in vascular anastomosistechniques without any assistance can use this model. Conclusion: Transplantation surgery requires well-done vascular anastomosis. Because anastomotic complications may be the most important reason for graft loses. In order to overcome this issue, surgical residents, staff members or surgeons can experiment vascular anastomosis technique. Conflict of Interest: None.
A 1D co-simulation approach for the prediction of pollutant emissions of internal combustion engines
Proceedings, 2019
The prediction of pollutant emissions generated by IC engines has been a challenge since the intr... more The prediction of pollutant emissions generated by IC engines has been a challenge since the introduction of the emission regulation legislation. This paper describes the approach followed by the authors to strictly couple two different 1D modeling tools in a co-simulation environment, to achieve a reliable calculation of engine-out and tailpipe emissions. The main idea is to allow an accurate 1D simulation of the unsteady flows and wave action inside the intake and exhaust systems, without resorting to over-simplified geometrical discretization, and to rely on advanced combustion models and kinetic sub-models for the calculation of cylinder-out emissions.
Journal of Computational and Applied Mathematics, 2017
Checkerboard pressure is one of the most significant problems arising from the use of collocated ... more Checkerboard pressure is one of the most significant problems arising from the use of collocated grids for fluid dynamic simulations using the finite-volume method. The original Rhie-Chow momentum interpolation technique, termed Original Momentum Interpolation Method (OMIM) was proposed to eliminate the non-physical saw-tooth pressure oscillations. However, it was soon proved that the steady-state solutions obtained with this technique were under-relaxation factor dependent. Nevertheless, standard OMIM is still commonly used in several CFD codes like OpenFOAM R , the software used for this work. In this paper the OMIM and a possible correction for under-relaxation dependency, which has been implemented in OpenFOAM R , are discussed in detail. The proposed methodology is compared and contrasted with OMIM in terms of accuracy of the solution and speed of convergence for several classical pressure-velocity segregated algo
Development of a CFD Model to Study the Hydrodynamic Characteristics and the Soot Deposition Mechanism on the Porous Wall of a Diesel Particulate Filter
Towards Large-scale Simulations of Moving Boundary Problems in Compressible Flows using OpenFOAM ® : Challenges and Opportunities
Flows involving moving meshes/boundaries occur in myriads of engineering applications such as win... more Flows involving moving meshes/boundaries occur in myriads of engineering applications such as wind and gas turbines, internal combustion engines and solid rocket boosters. Numerical simulations of such flows pose unique challenges not encountered in applications involving fixed boundaries. The advent of leadership-class computers with thousands of processors, provides unique opportunities to conduct high-fidelity, large-scale numerical simulation of these cases. High Performance Computing (HPC) promises to enable high-fidelity, multidimensional simulation of such problems in acceptable wall-times (24 to 48 hours). However, for large-scale simulations on the next generation machines, special attention has to be paid to load-balancing and reducing interprocessor communications for problems involving topologically changing grids to ensure good strong scalability. Existing methodologies for dynamic meshes are not suited for large-scale simulations, since they require considerable amount...
1D Fluid Dynamic Simulation and Experimental Analysis of Lamborghini SI Engines for the Prediction of Silencer Performances and Radiated Exhaust Noise
ABSTRACT This paper describes some recent acoustic experimental and simulation activities develop... more ABSTRACT This paper describes some recent acoustic experimental and simulation activities developed on the GT Lamborghini engines. The research code GASDYN, developed at Politecnico di Milano, has been adopted for the simulation of the engines with their complete intake and exhaust systems. Lamborghini 12 and 10 cylinder V-engines (6.2 L and 5.0 L respectively) have been modeled to calculate the wave motion in the exhaust duct systems and in the silencers, and evaluate the acoustical and fluid dynamic behavior of different silencer configurations. The baseline system, with separated exhaust lines for the two banks, has been compared to the new solution with connected/separated exhaust lines by means of a control valve. The simulation has provided the transmission loss of the silencers and also the spectral content of the radiated tailpipe noise, for each engine order. Finally, a specific procedure has been implemented in the code to predict the tailpipe noise radiated during the pass-by test, considering the contribution of the two exhaust terminations of the Gallardo vehicle during the acceleration. In this case the engine model has been coupled to a simplified model of the vehicle, to account for the operating points and the characteristics of the radiated noise during the simulated pass-by test. The predicted results have been compared to the experimental measurements carried out on the V12 and V10 engines, pointing out a satisfactory agreement.
This work proposes a focus on the simulation of a rotative volumetric expander via a CFD code. A ... more This work proposes a focus on the simulation of a rotative volumetric expander via a CFD code. A customized application of OpenFOAM R has been developed to handle the particular motion of the calculation grid. In particular, a prescribed shape of the stator has been defined in order to adapt the motion of the vanes along the whole cycle. The model uses a mesh to mesh interpolation technique, switching from a calculation grid to the new one on the basis of dynamic mesh quality considerations. This particular approach allows to account for the presence of leakages occurring between the stator and vane tips and also occurring at the top and bottom of the vanes. The fluid considered is the refrigerant R245fa, whose particular properties have been determined resorting to the NIST database. Experimental data, measured at different conditions of mass flow and fluid temperature, are compared to calculation results. Moreover, the CFD analysis has allowed the estimation of the influence of the leakage mass flow occurring at the tip of the vanes on the overall machine performances.
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Papers by A. Onorati