Alessandro Montanaro

Innovative Lift Direct Command to Inner Hydraulic Circuit Injector Comparison for Diesel Engines

In this paper a comparative investigation between two different injectors for Common Rail diesel apparatus has been carried out in terms of transient response and spray pattern for different injection strategies. Performances of an innovative Magneti Marelli (MM) gasoline derived injector have been evaluated against the Bosch generation injectors for multiple strategies. Both injectors have operated on an automotive apparatus controlled by a Programmable Electronic Control Unit to set injection strategies in terms of pulses number, duration and dwell time. The working mode of the two injectors is completely different: the Bosch injector is activated by the inner fuel hydraulic circuit while the Magneti Marelli one operates a direct control of the needle lift through the solenoid currents. The Bosch nozzle characteristics are 5 holes, 150° spray angle, and 0,13 mm diameter. The MM injector main characteristics are low hydraulic losses, simple component structure and ready use of the fuel at the nozzle opening being able to control small fuel flow rates (0.1 mg/str) in the injection pressures range 20–70 MPa. The geometry of the nozzle is quite similar to the Bosch one being a 5 hole, 150° spray angle, 0.12 mm diameter. Single, pilot+main and pilot+split main strategies have been explored for the two injectors at 50 and 60 MPa injection pressures investigating the spray behavior for two amounts of injected fuel (5.0 and 6.5 mg/str). The systems have been characterized in terms of injected fuel rate as well spatial and temporal behavior of the emerging jets from the nozzle. Images of the spray have been collected by a synchronized CCD camera at different time from the start of injection. The jets have evolved in an optically accessible high pressure vessel at ambient temperature as well in an optically accessible single-cylinder 2-stroke Diesel engine extracting the fuel spray parameters from the collected images applying a digital processing techniques. Due to the diverse mechanism of the injector actuation, a different temporal and spatial fuel distribution has been registered for the two apparatuses. These could strongly influence the air/fuel mixture formation and combustion process with effect on the emissions. Preliminary engine tests performed on a light duty direct injection diesel engine, equipped with the MM injector, have highlighted the potential of the MM injector to handle acceptable engine performances.Copyright

Combined Experimental and Numerical Investigation of the ECN Spray G under Different Engine-Like Conditions

A detailed understanding of Gasoline Direct Injection (GDI) techniques applied to spark-ignition (SI) engines is necessary as they allow for many technical advantages such as increased power output, higher fuel efficiency and better cold start performances. Within this context, the extensive validation of multi-dimensional models against experimental data is a fundamental task in order to achieve an accurate reproduction of the physical phenomena characterizing the injected fuel spray. In this work, simulations of different Engine Combustion Network (ECN) Spray G conditions were performed with the Lib-ICE code, which is based on the open source OpenFOAM technology, by using a RANS Eulerian-Lagrangian approach to model the ambient gas-fuel spray interaction. Foremost, the main scope of the activity was to identify the most accurate numerical set-up in terms of atomization ad secondary break-up models, thanks to a validation of the computed results against experimental data available for the ECN Spray G baseline condition. Specifically, attention was focused on spray penetration along with an analysis of spray morphology and effects of plume-to-plume interaction. Afterwards, the reference set-up was tested and validated under different operating conditions, characterized by detailed experimental measurements specifically provided for this work. In particular, Mie scattering and Schlieren techniques allowed the quasi-simultaneous acquisition of both vapor and liquid penetrations, while a customized imageprocessing procedure, developed in Matlab environment, was used for the outline of the spray contours of both fuel phases to measure the parameters characterizing the jet development. A robust reference numerical set-up was identified, capable to reproduce with good accuracy the injection process of a multi-hole GDI spray under the wide range of tested operating conditions.

Schlieren and Mie scattering techniques for the ECN “spray G” characterization and 3D CFD model validation

Purpose This paper aims to study the heat transfer phenomenon occurring between heated walls and impinging fuel, showing the strict relationship between cooling effect after impingement and enhancing of wallfilm formation. The study focuses on a fundamental task in terms of pollutant emissions in internal combustion engines, aiming at giving a major contribution to the optimization of energy conversion systems in terms of environmental impact. Design/methodology/approach The paper is based on experimental campaigns relevant at taking measurements of an impinging spray over a heated wall in a confined vessel. The results, in both qualitative and quantitative terms (measurements of liquid and vapour radial penetration and thickness), are numerically reproduced by a computational model based on a Reynolds Averaged Navier Stokes approach, properly validated through customized sub-models. Findings The paper provides quantitative results about the agreement between radial penetration and vapour thickness between measurements and simulation, achieved by taking into account the cooling effect determined by the fuel impingement. This validation of the numerical model allows the author to give more considerations about the link between wall temperature and wallfilm formation. Originality/value This paper presents an original approach for the simulation of wall heat transfer, by imposing a boundary condition at the wall that may consider the heat conduction and temperature cooling given by fuel impingement in both lateral and normal directions. The classical Dirichlet boundary condition, characterized by imposing a fixed temperature value, is, instead, replaced by an approach based on calculating the unsteady process that couples the heat fluxes between the fluid and the solid material and within the solid itself.

MODELLING OF GASOLINE SPRAY IMPACT AGAINST HOT SURFACES AND TRANSIENT HEAT TRANSFER EFFECTS ON PHASE TRANSITION

In gasoline direct injection (GDI) engines, the dynamics of the gasoline spray and the possible spray-wall interaction are key factors affecting the equivalence ratio distribution of the air-fuel mixture at spark timing, hence the development of combustion and the emission of pollutants at the exhaust. Gasoline droplets impact may lead to rebound with consequent secondary atomization or to the deposition in the liquid phase over walls as a wallfilm. This last slowly evaporate with respect to free droplets, leading to local enrichment of the mixture, hence to increased unburned hydrocarbons and particulate matter emissions. Especially in the so-called wall-guided mixture formation mode, complex phenomena characterise the turbulent multi-phase system where heat transfer involves the gaseous mixture (made of air and gasoline vapour), the liquid phase (droplets not yet evaporated and wallfilm) and the solid wall. Therefore, a proper numerical prediction based on a 3D CFD modelling of these in-cylinder phenomena necessarily derives from the correct simulation of the wall cooling effect due to the subtraction of the latent heat of vaporization of gasoline needed for secondary evaporation and of the conductive heat transfer within the solid. Indeed, this heat transfer influences the dynamics of the spray impinging over the heated wall, with a consequent direct effect on the mixing interaction between fuel and air. A proper sub-model is specifically implemented to solve the strongly coupled heat and mass transfer problem and to achieve a correct description of the liquid and vapour phases dynamics after impact. The validation of the developed 3D CFD model is performed by reproducing the experiments performed in a simple configuration within a confined vessel, thanks to a detailed experimental insight of the impact over walls of a multi-hole spray for GDI applications. The collected experimental measurements derive from a combined use of the schlieren and Mie scattering optical techniques.

Analysis of the GDI Spray Dynamics Through Multidimensional Modeling and Flow Visualization in an Optically Accessible SI Engine

Present work is aimed at studying into detail mixture formation and combustion in a gasoline direct injection (GDI) engine working under stoichiometric mixture conditions. The study is performed both numerically and experimentally. From the experimental side, the engine, optically accessible, is characterized by collecting, for various injection strategies, in-cylinder pressure cycles and digital images. From the numerical side, a 3D engine model is developed, that includes proper sub-models for the spray dynamics and the spray-wall interaction. This last phenomenon is studied into detail by resorting to a preliminary 3D simulation of the spray impingement realized in a proper experiment, where the engine injector is mounted at a certain distance from a cold or hot wall.An interesting comparison between numerical and experimental images of the in-cylinder spray dynamics is presented, that also allows individuating the difference in the wallfilm deposition under various injection strategies. This opens the way to understand the difference in the combustion development arising as injection is anticipated or retarded in the engine working cycle.© 2014 ASME

Experimental Study of Injection and Combustion in a Diesel Engine for Heavy Quadricycle Use

An experimental investigation has been carried out on a diesel 1000 cc, two-valve, three-cylinder, engine for heavy quadricycle and off-road applications. The engine was equipped with a unit-pump common rail injection system, automotive derived, with maximum pressure 140 MPa and ECU able to manage multinjection strategies in Euro 4 target for the foreseen applications.Experimental investigations on the fuel spray have been carried out in an optically accessible vessel at engine gas density. Spatial and temporal spray behavior has been studied by image processing of the evolving jet pictures. Spray tip penetrations, cone angles and fuel spatial density analysis have been extracted and correlated to the injection and engine parameters. On the other side, visible flame propagation and soot formation process have been evaluated by digital imaging at high spatial and temporal resolution using a quartz window of the third cylinder obtained modifying the engine head. Strategies consisting of two injections per cycle, pilot and main, and typical of real engine working conditions have been investigated in the pressure range 43–116 MPa both in terms of injection rates and injected fuel dispersion. The effects of different injection strategies on soot formation and exhaust emissions have been evaluated.Copyright