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The current work presents the results of an investigation on the impact of renewable fuels on the combustion and emissions of a turbocharged compression-ignition internal combustion engine. An experimental study was undertaken and the engine settings were not modified to account for the fuel's chemical and physical properties, to analyze the performance of the fuel as a potential drop-in alternative fuel. Three fuels were tested: mineral diesel, a blend of it with waste cooking oil biodiesel and a hydrogenated diesel. The analysis of the emissions at engine exhaust highlights that hydrogenated fuel allows to reduce CO, total hydrocarbon emissions, particulate matter and NOx.

Concerns about the harmful exhaust emissions of internal combustion engines have imposed the employment of aftertreatment devices to reduce their impacts both on health and environment. System modeling of engine and aftertreatment devices is required not only to provide an accurate assessment of the engine and aftertreatment devices performances as single elements but also to quantify the complex interaction of these components from a thermo fluid perspective. The work focuses on development of a model capable of predicting temporal and spatial evolution of thermo-fluid quantities and chemical species in a diesel oxidation catalyst (DOC). The developed model allows to investigate the influence of thermal characteristics and gas composition on the evolution of the phenomena occurring in the device which deeply reflect on the particulate filter behavior during regeneration phase.

The injection strategy as well as the overall efficiency of the diesel engine are tightly related to the performance of the high-pressure injection pump. The paper deals with the modeling of a latest generation Common Rail injection pump, aiming at the characterization of its performance in terms of volumetric- and torque-efficiency. A lumped parameter approach is adopted; with reference to a commercial pump widely used in the field of light diesel engines, a dynamic model of the piston-cylinder pair is built, taking its mechanical drive, the hydraulic supply and delivery systems into account. Based on in-depth experimental activities that provide the performance diagrams of pump, the lumped-parameter model is built and assessed. Given the current strong interest in the use of alternative fuels that limit CO2 emissions, the pump model has been implemented to simulate, beside the standard diesel, the use of biofuel.

Alternative and renewable fuels play a fundamental role in research and development activities aimed at reducing the environmental impact of internal combustion engines. The possibility of using alternative fuels, whether they are pure or blended, is linked to the flexibility of the injection system, whose behavior depends on the fuel features. In this context, the article reports an investigation on a high-pressure pump for common rail diesel injection systems. Investigations have considered a single-piston pump, widely adopted in the field of light duty diesel engines. The experimental activity has been conducted on an instrumented test rig, equipped with a fluid thermoregulation system. Moving from a conventional fluid (commercial diesel) to a waste cooking oil (WCO) biodiesel, the influence of such alternative fuel on pump behavior has been investigated and discussed, highlighting the link between pump performance (in terms of torque- and volumetric-efficiency) and fuel type.

Relatively recent investigations, basing on experiments as well as on modeling, have highlighted that the needle displacement in common-rail diesel injectors is affected by radial components. The effects of such “off-axis” needle displacement on fuel flow features have been so far investigated within the nozzle, only. The objective of this work is to extend the attention towards the formation of fuel sprays, when needle off-axis condition is encountered. In such a viewpoint, the development of each fuel spray has been modeled taking into account the hole-to-hole variations induced by the needle misalignment. The investigation has been carried out basing on 3D-CFD campaigns, in AVL FIRE environment. The modeling of diesel nozzle flow has been interfaced to the spray simulation, initializing the break-up model on the basis of the transient flow conditions (fuel velocity, turbulence and vapor fraction) at each hole outlet section.

Progress in hole drilling technique is opening new perspectives in diesel nozzle design. In such a scenario, research on unconventional hole shapes looks worthwhile, in order to evaluate their influence on fuel flow features within the nozzle. In the present paper, investigations have been based on modeling. Moving from a standard hole configuration towards oval shaped holes, 3D-CFD campaigns have been devoted to highlight the hole layout influence on diesel nozzle flow.

Flow rate imbalances among the nozzle holes are responsible for undesirable effects, as hole to hole differences, that worsen the regular fuel spray development. Multi hole injectors for common rail-equipped small diesel engines have been investigated by 3D-CFD modeling, under ballistic needle motion; simulation campaigns have been devoted to highlight, on one side, how the actual nozzle layout influences the fuel flow pattern upstream the nozzles; on the other side, the role of actual operating conditions of the injector has been studied. Relating to geometrical layout, different factors define the actual injector tip features; here, the effects of specific details have been taken into account; in the modeling of the actual nozzle layout, the effects of hole key-shape, inlet edge radius and hole diameter have been investigated, pointing out their influence on the fuel flow development.

Pilot spray formation process has been analyzed by simulation. Investigating the influence of injection phasing and engine speed on vapor preparation process, the attention has been focused on fuel evaporation within cylinder. Once such a phase had been concluded, the indications on fuel shot evolution have been extrapolated and the obtained results have been used in the lumped parameter modeling of pilot spray evaporation. As the main driving factors regard both the injection system operation (injection pressure, needle opening, nozzle hole diameter and shape, fuel properties) and the in-cylinder conditions (in terms of pressure, temperature and charge motion), different simulation tools have been used.

A diesel injection model for common rail application has been built and extended including a quasi-dimensional, multi-zone, diesel combustion-pollutant emission model (NO x ). In a commercial simulation environment, a lumped parameter electro-mechanical-hydraulic scheme is used to model the injection process. Modeling of spray formation, droplet vaporization, combustion and pollutant emission processes is then implemented in a self developed computation code, accounting for finite thermal conductibility of the liquid phase fuel. The coupling among the models allows for a detailed representation of the involved phenomena at each simulation step; at the same time, it is possible to evaluate the operation of the ensemble injection system-engine on the basis of atomization, combustion and pollutant emission. The results of the numerical prediction are compared to experimental data.

A previously developed injection system model has been enhanced including a quasi-dimensional, multi-zone, direct injection (DI) diesel combustion model, with the aim of taking into account the actual injection process, the spray formation and the droplet heating-vaporization processes. Such a goal is obtained by means of the integration of different modeling approaches. In a commercial simulation environment, a lumped parameter mechanical-hydraulic scheme is used to model the injection process, in terms of fuel flow rate and injection pressure. The spray formation processes and the droplet vaporization phenomena are then implemented in a self developed computation code, accounting for finite thermal conductibility of the liquid phase fuel.

The work aims at developing and setting up a model able to predict the diesel spray evolution to be integrated into a complete thermodynamic model of the engine. Previous papers have been devoted to realize a numerical model for the injection system, in which a lumped parameter + one-dimensional approach is employed. Such a model has been now enhanced by introducing a quasi-dimensional model for fuel break up, diffusion and penetration processes. A self-developed heating sub-model is included in the model, which enables the evaluation of the influence of the fuel properties on the evaporation process. As a result, the injection system simulation model gives indications on the spray formation process and it is used into a lumped parameter model of the combustion process. Results concerning the influence of fuel properties on the evaporation process are presented and discussed, pointing out its effect on engine performance.

The research and development activities on diesel injection systems have focused some key-factors that improve the solenoid actuated injector performance, especially in the frame of the multi-event injection strategies. This paper deals with a 3-D numerical investigation that highlights the nozzle flow features of different injector layouts. A comparison between a last generation standard injector and an optimized unit characterized by an improved dynamics, different number of holes and reduced maximum lift is performed. By means of transient numerical simulations, the behavior of the fuel flows, the tendency to cavitation development and the response to the deviation from the standard operating conditions (highlighted by introducing a radial perturbation on the lift motion) are investigated.

This paper deals with the numerical investigation of a Diesel engine high pressure DI system in which the influence of needle motion characteristics on the internal injector flows is evaluated; a radial perturbation of the axial needle motion has been imposed to analyze its role over the nozzle flow features. The developed model is based on the coupling of two computational tools. With the former one, AMESim code, the injector has been modeled; the results obtained from the injector simulation, in terms of injection needle lift time evolution, have been used to initialize the latter computation tool, FIRE code, in which 3D flow numerical investigation of the internal injector flows has been performed. Details of the adopted modeling strategy are presented and the results of each simulation step are shown.