Giancarlo Chiatti

Analysis of static and dynamic structural problems by a combined finite element-transfer matrix method

Abstract The combined use of the finite element and transfer matrix techniques (FETM) for the study of dynamic problems was proposed a few years ago, in order to overcome the large amount of computer storage and long computation time that the finite element technique often requires. In this paper some interesting applications are emphasized for both static and dynamic problems of structures. A great deal of attention has been paid to the use of shell isoparametric elements for very thin structures, where the usual numerical integration by a two-by-two Gaussian quadrature of the stiffness matrix leads to an ineffective increase of stiffness in the structure. Particularly appealing seems to be the use of quadratic shell elements in the FETM method, because even with a reduction in the total number of elements of the structure it is possible to increase the accuracy of results. Computation time is appreciably reduced by this method, because of the notable lowering of the final matrix order, the manipulation of which gives the solution of the problem. Some results for natural frequencies of a thin plate are finally presented, showing a favourable agreement with those obtained by other proposed methods.

Lattice Boltzmann models for nonideal fluids with arrested phase-separation.

The effects of midrange repulsion in lattice Boltzmann models on the coalescence and/or breakup behavior of single-component, nonideal fluids are investigated. It is found that midrange repulsive interactions allow the formation of spraylike, multidroplet configurations, with droplet size directly related to the strength of the repulsive interaction. The simulations show that just a tiny 10% of midrange repulsive pseudoenergy can boost the surface:volume ratio of the phase-separated fluid by nearly two orders of magnitude. Drawing upon a formal analogy with magnetic Ising systems, a pseudopotential energy is defined, which is found to behave similar to a quasiconserved quantity for most of the time evolution. This offers a useful quantitative indicator of the stability of the various configurations, thus helping the task of their interpretation and classification. The present approach appears to be a promising tool for the computational modeling of complex flow phenomena, such as atomization, spray formation, microemulsions, breakup phenomena, and possibly glassylike systems as well.

Combustion diagnosis via block vibration signal in common rail diesel engine

This article presents a diagnostic technique in which nonintrusive measurements are used with the aim of indirect characterization of the combustion process of an internal combustion diesel engine. The developed technique is based on the vibration signal coming from a mono-axial accelerometer placed in a selected location of the engine block. Such a location is able to guarantee high sensitivity to vibration caused by forces directly linked to the combustion process and low sensitivity to all the other excitation sources. The technique is applied to the signals acquired during two series of experimental tests, carried out on the same kind of engine (multi-cylinder diesel engine, equipped with common rail injection system), in two separate engine test facilities in order to test the engine stand-alone and the engine dressed up with the integrated automatic transmission, aimed at reproducing its real operation condition (it is mainly employed in mini-car sector application). The obtained results suggest the potential applicability of the technique both in the laboratory, during the tuning between the injection parameter settings and the engine, and in the regular running condition of the engine for combustion process diagnosis.

Multicode Prediction of the Influence of the Exhaust System on the Performance of a Turbocharged Engine

A multicode approach, based on the simultaneous use of zero-dimensional, one-dimensional, and three-dimensional models, has been developed and tested, and is here applied to predict the thermodynamic and fluid dynamic phenomena that characterize the unsteady gas flow propagation along the exhaust system of a turbocharged four-cylinder engine. The investigation is carried out by applying each model in a different region of the geometry, allowing to obtain detailed information of the flow behavior in complex elements, such as junctions, avoiding the significant limitations that a one-dimensional scheme always introduces, as well as fast processing typical of one-dimensional ana zero-dimensional models, devoted to the analysis of ducts and volumes. The effect of the influence of different configurations of the exhaust system on the engine performance is analyzed.

DPF soot profile features accounting for engine duty cycle

An investigation of Diesel Particulate Filter (DPF) is performed to obtain deeper insight into the soot loading process. Previous paper has been devoted to the realization of a numerical model to analyse how diesel soot is deposited on the walls of a commercial filter media and to understand the influence of different engine operating conditions on the soot layer growth. The results have been validated by means of experimental data. This paper concerns with the parametrization of particulate deposition profiles and focuses on how soot profile evolves during engine operation in a specified duty cycle, starting from pre-loaded channels. Results of 3D CFD simulations are presented, in which different engine running histories are analyzed.Copyright

Diesel Nozzle Flow Investigation in Non-Radial Multi Hole Geometry

Flow features at hole inlet traditionally depend both on injector tip type (Minisac, VCO, Microsac), and on hole drilling & finishing technology (hydro grinding, paste honing); such a topic is going to be faced by researchers for many years, due to the importance of high pressure injection process in current and upcoming diesel engine.In the present paper, investigations have been extended to an unconventional diesel nozzle layout, highlighting its capability on altering the flow structure at hole inlet, and thus influencing the flow development within the nozzle holes. As described in the article, the investigated nozzle is based on a multihole layout but, referring to the injector axis, nozzle holes have a non-radial arrangement.The investigations on nozzle hole flow development have been based on modeling. Moving from the standard nozzle configuration towards non-radial arranged holes, 3D-CFD campaigns have been devoted to highlight the influence of such unusual nozzle layout on diesel nozzle flow.In the modeling process, data concerning spatial distribution of velocity and cavitation behavior at hole exit have been computed; the effect of non-radial multi hole geometry has been investigated both on MicroSac and VCO layouts. Specific attention has been focused on the fuel flow distribution among the holes; the computations have evidenced how the unconventional layout is capable to improve the behavior of VCO geometries when needle eccentric displacement is considered. Results have been synthetized indicating how flow pattern properties are reflected at hole exit, quantitatively.Copyright

Modeling the Effect of Nozzle Hole Geometry on Diesel Injection and Combustion

The performance of the ensemble diesel engine-injection system has been investigated by modeling; different approaches have been combined and integrated in a multi step procedure. In a preliminary phase, the nozzle flow features have been investigated by means of 3D CFD simulation (FIRE), allowing for the evaluation of nozzle hole discharge coefficients. Such values have been used in the subsequent phase, based on a 0/1D approach, in which the complete model of the fuel injection system has been realized and the injected fuel amounts have been evaluated. On the basis of these indications, a further simulation phase has been included and a packet model for the modeling of fuel jet formation, evaporation and combustion has been built and used. In-cylinder pressure trends have been obtained and the effects of different nozzle hole geometries have been investigated.Copyright

Inline Pump Internal Flow Characterization for Optimized Diesel Injection

The injection process optimization plays a key role in diesel engine development activities, both for pollutant formation control and performance improvement. The present paper focuses on relatively small diesel units, equipped with fully mechanical injection systems; in detail, the considered system layout is based on the use of spring injectors; the amount of delivered fuel is controlled by the positioning of the pump plunger groove. The paper highlights the role of the inline pump and the influence of fuel characteristics on the system operation. By means of a three-dimensional numerical flow study, the behavior of pump fuel passages and delivery valve is simulated. Then, on the basis of the system features, a complete lumped/one-dimensional numerical model is realized, in which the discharge coefficients evaluated through the three-dimensional simulation are employed. Fuel injection rate and local pressure time histories are investigated, paying specific attention to the occurrence of the relevant phenomena in the system components. Obtained results are compared with experimental data.Copyright

Lumped parameter approach for dpf management in stationary diesel engines

During the last years, emission standards for diesel engines have got more and more severe not only for light- and heavy-duty road application, but also in the nonroad, locomotive and stationary fields. In this paper, the results of a Lumped Parameter (LP) model for Diesel Particulate Filter (DPF) management in stationary diesel engines are presented. The developed LP model allows to predict the pressure drop and soot layer growth in time along the trap channel. In the model, the equations are tuned by means of a complete CFD analysis of the gas flux through a wall-flow DPF. The difference in flow field due to the radial distance from the filter axis and its effects on the soot growth inside the channel are taken into account as the loading phase proceeds. The temperature evolution during the regeneration process of the device is predicted, too, thus permitting a complete management of the filter in control applications.Copyright

Investigating the influence of highway traffic flow condition on pollutant emissions using driving simulators

In the last 20 years the attention of international organizations towards air pollution has been improved, leading to definition of laws and regulations. In order to evaluate strategies and policies, forecasting tools have been adopted by institutions. Currently, the estimation of traffic emissions is based on static models, in which the amount of pollutant is computed as a function of average parameters obtained on a single road stretch. The well-known traffic increase of recent years has significantly changed the actual flow conditions, producing a strong rise of interferences. As this facet affects the operating condition of each vehicle, the use of a standard emission model at high traffic interference can lead to some inaccuracies. In such cases, instantaneous emission models introduce deeper capabilities; essentially, the pollutant prediction is directly tied to the engine vehicle operation point in reallike traffic condition. This second modelling approach has been adopted in the current work. A complete lumped parameter vehicle model has been built to be used as a virtual on-road emission/fuel consumption test unit. Investigations have highlighted the dependence of emission level and fuel consumption on drivers’ behaviour; indeed, the analysis took advantage of the experiments carried out in the virtual reality laboratory: on a typical highway geometry, characterized by a dual lane carriageway with three lanes each, three different flow conditions have been simulated. Once the relationship between highway interference level and drivers’ behaviour has been evidenced (in terms of emissions and fuel consumption), a relation between highway interference level and emissions/fuel consumption has been highlighted. Finally, in order to assess the differences