Ornella Chiavola

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

Coupling Codes for Nozzle Flow Modelling in Diesel Injection System

This paper deals with a numerical investigation of a single cylinder diesel engine equipped with mechanical fuel direct injection system and focuses on the fuel injection system modelling with the aim of predicting the performance of the entire injection system, the spray characteristics, the interaction among spray-cones, combustion chamber flows and geometry. In the simulations, two different codes have been used. With the former one, AMESim code, the complete injection system has been analysed and the single components have been selected and modelled. The results obtained from the injection system simulation, in terms of injection needle lift, injection flow rate, pressure time evolution, have been used to initialize the latter computation tool, FIRE code, in which 3D flow numerical investigation of the internal injector flow has been performed. Since such a flow is directly linked to the spray modelling, the primary break-up effects have been taken into account. The details of the adopted modelling strategy have been shown and the results of each simulation step have been presented. In order to highlight the relationship among the nozzle flow condition and the spray formation-vaporization characteristics, a comparison between two different calculation setups has been shown. Moreover, a qualitative comparison among predictions and experimental data has been discussed.© 2006 ASME

Accelerometer signal to characterize the combustion development in multiple injection diesel engine

This work constitutes one of the last steps of a comprehensive research program in which vibration sensors are used with the purpose of developing and setting up a methodology that is able to perform a real time control of the combustion process by means of non-intrusive measurements.Previous obtained and published results have demonstrated that a direct relationship exists between in-cylinder pressure and engine block vibration signals. The analysis of the processed data have highlighted that the block vibration signal may be used to locate, in the crank–angle domain, the combustion phases (the start of the combustion, the crank angle value corresponding to the beginning of main combustion and to the in-cylinder pressure maximum value) and to quantify the in-cylinder pressure development by evaluating the pressure peak value and the pressure rise rate caused by the combustion process.The aim of this work is to extend and validate the developed methodology when a multiple-injection strategy is imposed on the engine.The paper presents the results obtained during the experimentation of a two cylinder diesel engine equipped with a common rail injection system, that was performed in the Laboratory of the Mechanical and Industrial Department of ‘ROMA TRE’ University. During the tests, a wide variation of the injection parameters settings is imposed on the engine (timing and duration) in its complete operative field.Copyright

On the Influence of the Slot Orifice in Diesel Common Rail Nozzle

Methods: In the research, a solenoid injector for light duty diesel engines is equipped with the novel nozzle prototype and tested. The prototype layout is described, pointing out the features of the nozzle orifices, in which a Slot cross-section is adopted; the investigation is accomplished extending the hydraulic tests and the spray visualizations to a reference nozzle with standard holes. The influence of the hole layout on the mechanical-hydraulic behavior of the nozzle is assessed by experimental analysis based on the rate of injection measurement, in comparison with the reference nozzle. Once the hydraulic behavior of the novel nozzle has been characterized in terms of mass flow rate, the slot influence on the spray shape is assessed analyzing the macroscopic features such as the penetration distance and the spray angle, in non evaporative conditions. The study is carried out under transient injection conditions, for different injection pressures, up to 1400 bar.