Simone Malaguti
RESEARCH THEMES
1. 3D analyses of the in-cylinder flow field for Diesel and gasoline engines;
2. 3D analyses of the injection in quiescent and in-cylinder conditions, for common-rail Diesel and GDI engines;
3. 3D analyses of combustion process for Diesel engines;
4. CFD optimization of coolant circuit for Diesel engines.
5. 3D analyses of the hollow-cone and multi-hole injector for GDI engines.
6. 1D analyses of coolant systems for engines;
7. 1D analyses of injection systems for automotive applications.
Cooperation and contract activities with: Fiat Power-Train, Istituto Motori-CNR Napoli, Lamborghini, Vm Motori, Ferrari Gestione Sportiva, Ferrari Gestione Industriale, Lombardini.
Phone: +39 059 2056114
Address: Dipartimento di Ingegneria "Enzo Ferrari"
Strada Vignolese, 905
40125 Modena
Italy
1. 3D analyses of the in-cylinder flow field for Diesel and gasoline engines;
2. 3D analyses of the injection in quiescent and in-cylinder conditions, for common-rail Diesel and GDI engines;
3. 3D analyses of combustion process for Diesel engines;
4. CFD optimization of coolant circuit for Diesel engines.
5. 3D analyses of the hollow-cone and multi-hole injector for GDI engines.
6. 1D analyses of coolant systems for engines;
7. 1D analyses of injection systems for automotive applications.
Cooperation and contract activities with: Fiat Power-Train, Istituto Motori-CNR Napoli, Lamborghini, Vm Motori, Ferrari Gestione Sportiva, Ferrari Gestione Industriale, Lombardini.
Phone: +39 059 2056114
Address: Dipartimento di Ingegneria "Enzo Ferrari"
Strada Vignolese, 905
40125 Modena
Italy
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Papers by Simone Malaguti
detailed numerical and experimental investigation.
The analyzed system, the Magneti Marelli DDI Direct Diesel Injection, is based on a direct-actuation
solenoid injector. The DDI system operates up to 60.0 MPa injection pressure, with a multi-hole nozzle
resulting in a conventional fuel spray plumes distribution inside the combustion chamber, which suites
the requirements of small industrial and automotive Diesel applications.
In the present research activity, the hydraulic behavior of the DDI system was analyzed in terms of
injected volumes and injection rate time-histories varying the injection pressure from 30.0 MPa to 60.0
MPa with a back pressure of 2.0 MPa. The resulting injection process was also analyzed in terms of
spray global shape evolution along with droplet sizing and velocity in a pressurized (1.0 MPa) test
vessel in quiescent and room temperature conditions.
In order to investigate and to validate the capability of adopted CFD models to reproduce the spray
behavior at such non-conventional injection pressure levels for Diesel applications, an experimental
and numerical comparison was performed, in terms of liquid spray morphology, tip penetration and
droplet sizing.
A numerical methodology, based on a preliminary Eulerian Steady Simulation of the nozzle, has been
developed in order to gain correct flow rates and turbulence data at each of the nozzle holes exit. Then
the Lagrangian spray simulations have been carried out by means of a new atomization approach able
to take into account the cavitation phenomena and the turbulence effects. A tuning campaign has been
performed in order to validate the secondary KH-RT breakup model, and a grid sensitivity analysis has
been carried out.
multi-hole injector of a current production wall-guided gasoline direct injection engine. Particular
care is dedicated to the accurate representation of the spray primary breakup by means of an atomization
model. The model is purposely implemented to take into account cavitation phenomena and
turbulent effects induced by the nozzle geometry through a simplified approach. Because a high primary
breakup rate is expected, an initial distribution of atomized droplets is predicted at the nozzle
hole exit by the numerical approach. The spray is at first experimentally investigated in a test vessel
at non-evaporative ambient conditions and under quiescent conditions, in which commercial gasoline
is injected at two different injection pressures (10.0 and 20.0 MPa). The spray is characterized
in terms of both the instantaneous mass flow rate and morphology. Numerical simulations are performed
and then compared against the experiments in order to evaluate their capability to correctly
predict liquid spray penetration, droplet-size distribution, and spray morphology. The new approach
is a fairly simple, yet reliable, solution that is able to predict the influence of the nozzle hole (in terms
of the discharge coefficient, diameter, and length), neglecting geometrical details that are usually far
from being easily accessed by engine developers.
A numerical methodology has been developed to improve the prediction of the pure and blends fuel spray. The fuel sprays have been simulated by means of a 3D-CFD code, adopting a multi-component approach for the fuel simulations. The vaporization behavior of the real fuel has been improved testing blends of 7 hydrocarbons and a reduced multi-component model has been defined in order to reduce the computational cost of the CFD simulations. Particular care has been also dedicated to the modeling of the atomization and secondary breakup processes occurring to the GDI sprays. The multi-hole jets have been simulated by means of a new atomization approach combined with the Kelvin-Helmholtz/Rayleigh-Taylor hybrid model. At the nozzle hole exit an initial distribution of atomized droplets has been predicted by the numerical approach taking into account cavitation phenomena and turbulent effects.
Sprays have been investigated using a 6-hole gasoline direct-injection (GDI) injector and injecting fuel into an optically-accessible constant volume vessel at 5.0, 10.0, and 15.0 MPa of injection pressure, at ambient back pressure. Mie-scattering images have been performed using a high-speed camera and a pulsed-wave flash system which is able to track liquid phase in order to estimate the spray development, morphology and cone angle. Moreover fuel injection rates measurements have been carried out using a meter working on the Bosch tube principle to characterize the injected mass. The liquid fuel penetration registered highest values for gasoline fuel with respect to its blends with ethanol at different percentages.
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Results from 3D-CFD simulations are compared to experimental measurements available in literature, in which commercial gasoline at two different injection pressures (10 and 20 MPa) was injected and the spray evolution was analyzed throughout the injection duration. The spray was investigated along the jet axis by phase Doppler anemometry in order to provide droplet size and velocity, in terms of both axial and radial components.
Experimental measurements briefly described above are used to test and validate some lagrangian spray numerical sub-models and numerical parameters such as grid density, numerical setup, primary and secondary fuel breakup and droplet to droplet interaction. Particular care is devoted to the accurate representation of the spray primary breakup, in view of the lack of ad-hoc developed models available in literature. A wide CFD activity is then performed in order to correctly predict both liquid spray penetration and droplet size.
Results from the CFD analyses show a relevant dependency of the spray structure on the adopted CFD model ensemble.
In order to properly investigate and understand the many involved phenomena, experimental visualization of the full injection process by means of an optically accessible engine would be a very useful tool. Nevertheless, the application of such technique, far from being feasible from an industrial point of view, appears to be very difficult even in research laboratories, due to the relevant wall wetting at cranking conditions.
CFD analyses prove therefore to be the sole chance to gain a full insight of the overall process, to correlate spark plug wetting to both the combustion chamber design and the injection profile and eventually address either design modifications or changes in the injection strategies. In order to limit the overall number of modeling uncertainties, and to validate the spray model under actual cranking conditions, comparisons with available experimental data at low temperature and low injection pressure were performed and are reported in the paper. Despite the CFD software continuous improvement and development, low-temperature cranking conditions proved to be an open challenge for the in-cylinder numerical simulations, due to the simultaneous presence of many physical sub-models (spray evolution, droplet-droplet interaction, droplet-wall interaction, liquid-film) and the very low motored engine speed. Furthermore, the high injected fuel quantity as well as the reduced fuel atomization and vaporization lead to very high concentration of liquid fuel droplets in the computational cells, posing a serious challenge to the adoption of a lagrangian approach to the injection simulation. Nevertheless, the use of a properly customized and validated numerical setup led to a good comprehension of the many involved phenomena as well as of the effects of injection strategy modifications on both the air/fuel and fuel/wall interaction.
In order to properly investigate and understand the many complex phenomena, a wide set of engine speeds was experimentally investigated and, as far as the understanding of the physics of spray/wall interaction is concerned, many different injection strategies are tested. Among the wide set of experiments, the present paper focuses on a restricted portion which is then numerically reproduced and further investigated.
UV-visible imaging and spectral measurements are carried out in the engine to investigate the spray characteristics and flame propagation. Measurements are performed in the optically accessible combustion chamber realized by modifying the actual engine. The cylinder head is modified in order to allow the visualization of the fuel injection and the combustion process in the fourth cylinder using a high spatial and temporal resolution ICCD detector.
The complete engine cycle is reproduced by means of 3D-CFD simulations using a commercial code; due to the many physical sub-models an ad hoc numerical methodology is validated and implemented. The CFD models are validated against experiments and particular care is devoted to the spray and wall film simulations. A lagrangian approach is implemented in order to simulate the GDI multihole spray. The experimental and numerical comparisons, in terms fuel mixing and flame front propagation, give a good understanding of the idle condition.
CFD analyses prove to be a very useful tool to investigate and understand the effects generated by the direct injection into the combustion chamber and they integrate the information provided by the optical investigations.
The paper reports part of a combined numerical and experimental synergic activity aiming at the understanding of the physics of spray/wall interaction within the combustion chamber and particular care is used for air/fuel mixing and the combustion process analyses. In order to properly describe the engine condition, different injection strategies are investigated. Late and early injection strategies are deeply analyzed and compared in terms of combustion stability and pollutant emissions.
UV-visible imaging and spectral measurements are carried out in real engine with wide optical accesses... Measurements are performed in the optically accessible combustion chamber realized by modifying a real engine. The cylinder head was modified in order to allow in the fourth cylinder the visualization of the fuel injection and the combustion process with high spatial and temporal resolution.
The 3D-CFD engine simulations are reproduced by means the commercial code Star-CD. Due to the warm-up condition and the many physical sub-models a numerical methodology is implemented and particular care is used to boundaries conditions analyses. CFD analysis is used to find a possible explanation of the high cycle to cycle variability. The experimental and numerical comparisons, in terms fuel mixing and front flame propagation, give an explanation of the idle condition.
The experimental investigation is carried out using a mechanical injection pump equipped by the heavy duty eight cylinder engine. Only one of its plungers has been activated and the fuel is discharged through a seven holes mechanical injector, 0.40 mm in diameter. Measurements of fuel injection rate have been performed at 900 rpm pump speed by the AVL Bosch tube at engine loads ranging between 10 to 100% that correspond to the injected fuel from 85 to 600 mg/str. Spray tip penetrations have been measured by an imaging technique in an optically accessible high pressure vessel at different instant from the start of injection and different load conditions.
CFD analysis is first focused on in-cylinder flow structure during the intake and compressions strokes to evaluate the swirl and turbulence intensity, as well the tangential profile of the air velocity within two combustion chambers having a different geometry. The prediction of liquid fuel and vapour mass fraction is carried out at 50 and 100% spray load rates considering different jet orientation with respect to the combustion chamber cavities. The predictions are carried to estimate the influence of both shape and jet orientation on the spray behaviour.
2-D imaging technique is used to follow the global evolution of the spray as function of the injection time in order to estimate the jet development, the morphology of the spray, and the instantaneous velocity field of fuel droplets by Particle Image Velocimetry (PIV). A PDA system is used to acquire, simultaneously, both droplet velocity and size (D10), at the same operative conditions as for the PIV ones, close to the nozzle exit.
As far as the numerical investigations, CFD computations are carried out by means of the STAR-CD software. A preliminary evaluation of the fuel droplet velocity at the injector exit is performed in order to define an instantaneous mass flow rate, aiming at capturing the spray temporal evolution throughout the injection process. Pre-spray, transient spray and fully-developed spray are accounted for. The Linearized Sheet Instability Model (LISA), is implemented by the authors within the STAR-CD code. In addition to the LISA, a tuning of the STAR-CD built-in secondary break-up models derived for Diesel-jets is performed to match the experiments.
Results of the simulations are compared to the experiments in terms of spray tip penetration, droplet size, spatial distribution and jet shape. Adequate tuning of the CFD model constants and parameters allow the numerical predictions to accurately represent the actual spray behavior.
In view of the non-conventional engine operating conditions (in terms of injected fuel amount, engine speed, ambient and wall temperature and almost null fuel atomization and breakup), an understanding of the many involved phenomena by means of an optically accessible engine would be of crucial importance. Nevertheless, the application of such technique appears to be almost unfeasible even in research laboratories, mainly because of the relevant wall wetting.
CFD analyses prove then to be a very useful tool to gain a full insight of the overall process as well as to correlate fuel deposits to both the combustion chamber design and the injection strategy. In order to better understand where, and how thick, these wall films are formed during the intake and compression, a detailed description of the spray interaction with both the piston wall and the intake valves was performed by the authors in a previous paper [1]. Subsequently, a wide set of injection strategies was simulated in order to better understand the physics of spray/wall interaction and to minimize the formation of deposits in the combustion chamber most critical locations [2].
In order to limit the overall number of modeling uncertainties (spray evolution, droplet-droplet interaction, droplet-wall interaction, liquid-film) the spray model was at first validated against experimental data under low injection pressure, and results from the comparison were reported in [1].
In the present paper, cold start operations at decreasing ambient temperatures are modeled and results are analyzed in terms of both fuel film distribution on the combustion chamber walls and resulting fuel/air mixture distribution within the combustion chamber. The use of CFD simulations prove to be useful to investigate and understand the influence of both combustion chamber design and injection profile on the amount and distribution of fuel deposits, showing a high potential to address future engine optimization.
and liquid film formation within the combustion chamber of a
current production automotive Gasoline Direct Injected (GDI)
engine characterised by a swirl-type side mounted injector is
presented.
Particularly, the paper focuses on low-temperature
cranking operation of the engine, when, in view of the high
injected fuel amount and the strongly reduced fuel
vaporisation, wall wetting becomes a critical issue and plays a
fundamental role on the early combustion stages. In fact,
under such conditions, fuel deposits around the spark plug
region can affect the ignition process, and even prevent engine
start-up.
In order to properly investigate and understand the many
involved phenomena, experimental visualisation of the full
injection process by means of an optically accessible engine
would be a very useful tool. Nevertheless, the application of
such technique, far from being feasible from an industrial
point of view, appears to be very difficult even in research
laboratories, due to the relevant wall wetting at cranking
conditions.
A numerical program was therefore carried out in order to
analyze in depth and investigate the wall/spray interaction and
the subsequent fuel deposit distribution on the combustion
chamber walls. The CFD model describing the spray
conditions at the injector nozzle was previously implemented
and validated against experimental evidence.
Many different injection strategies were tested and results
compared in terms of both fuel film characteristics and fuel/air
mixture distribution within the combustion chamber.
Low-temperature cranking conditions proved to be an
open challenge for the in-cylinder numerical simulations, due
to the simultaneous presence of many physical sub-models
(spray evolution, droplet-droplet interaction, droplet-wall
interaction, liquid-film) and the very low motored engine
speed. Nevertheless, the use of a properly customized and
validated numerical setup led to a good understanding of the
overall injection process as well as of the effects of both
injection strategy and spray orientation modifications on both
the air/fuel and fuel/wall interaction.
engines is very attractive for fuel economy and performance
improvements in spark ignition engines. Gasoline direct
injection (GDI) offers the possibility of multi-mode
operation, homogeneous and stratified charge, with benefits
respect to conventional SI engines as higher compression
ratio, zero pumping losses, control of the ignition process at
very lean air-fuel mixture and good cold starting.
The impingement of liquid fuel on the combustion chamber
wall is generally one of the major drawbacks of GDI engines
because its increasing of HC emissions and effects on the
combustion process; in the wall guided engines an increasing
attention is focusing on the fuel film deposits evolution and
their role in the soot formation. Hence, the necessity of a
detailed understanding of the spray-wall impingement
process and its effects on the fuel distribution. The
experimental results provide a fundamental data base for
CFD predictions.
In this paper investigations have been performed using a 7-
hole injector, 0.179 mm in hole diameter, spraying in a
constant volume vessel with optical accesses. To examine the
effects of various factors on development of the spray
impinging on the wall, experiments have been conducted at
different injection pressures, diverse wall inclination angles
and at atmospheric pressure. The acquired images have been
processed for extracting the characteristic parameters of the
impinging fuel at the different operative conditions.
The multi-hole spray has been simulated by Star-CD code
taking into account the commercial gasoline properties and
the real mass flow rate derived from experimental
measurements. In order to correctly reproduce spray
impingement and fuel film evolution, a numerical
methodology has been defined. Lagrangian sub-models and
numerical parameters have been validated against
experimental results.