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Growing concerns about the emissions of internal combustion engines have forced the adoption of aftertreatment devices to reduce the adverse impact of diesel engines on health and environment. Diesel particulate filters are considered as an effective means to reduce the particle emissions and comply with the regulations. Research activity in this field focuses on filter configuration, materials and aging, on understanding the variation of soot layer properties during time, on defining of the optimal strategy of DPF management for on-board control applications. A model was implemented in order to simulate the filtration and regeneration processes of a wall-flow particulate filter, taking into account the emission characteristic of the engine, whose architecture and operating conditions deeply affect the size distribution of soot particles.

Besides pollutant emissions, fuel consumption and performance, vehicle NVH constitutes a further object during engine development and optimization. In recent years, research activity for diesel engine noise reduction has been devoted to investigate aerodynamic noise due to intake and exhaust systems and surface radiated noise. Most of the attention has been concerned with the identification and analysis of noise sources in order to evaluate the individual contribution (injection, combustion, piston slap, turbocharger, oil pump, valves) to the overall noise with the aim of selecting appropriate control strategies. Several studies have been devoted to analyze combustion process that has a direct influence on engine noise emission; the impact of injection strategies on the combustion noise has been evaluated and approaches able to separate engine combustion and mechanical noise components have been presented.

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.

In the last years, the increasing concern for the environmental issues of IC engines has promoted the development of new strategies capable of reducing both pollutant emissions in atmosphere and noise radiation. Engines can produce different types of noise: 1) aerodynamic noise due to intake and exhaust systems and 2) surface radiated noise. Identification and analysis of noise sources are essential to evaluate the individual contribution (injection, combustion, piston slap, turbocharger, oil pump, valves) to the overall noise with the aim of selecting appropriate control strategies. Previous paper focused on the combustion related noise emission. The research activity aimed at diagnosing and controlling the combustion process via acoustic measurements. The optimal placement of the microphone was selected, where the signal was strongly correlated to the in-cylinder pressure development during the combustion process.

Many studies have demonstrated that an efficient control of the combustion process is crucial in order to comply with increasingly emerging Diesel emission standards and demanding for reduced fuel consumption. Methodologies based on real-time techniques are imperative and even if newly sensors will be available in the near future for on-board installation inside the cylinder, non intrusive measurements are still considered very attractive. This paper presents an experimental activity devoted to analyze the noise emission from a small displacement two-cylinder Diesel engine equipped by HPCR (high pressure common rail) fuel injection system. The signals acquired during stationary operation of the engine are analyzed and processed in order to highlight the different sources contributing to the overall emission. Particular attention is devoted to the specific samples of the signal that are mainly caused by the combustion process in order to extract the combustion contribution.

To ensure compliance with emerging Diesel emission standards and demands for reduced fuel consumption, the optimization of the engine operation is imperative under both stationary and real operation conditions. This issue imposes a strict control of the combustion process that requires a closed-loop algorithm able to provide an optimal response of the engine system not only to warm-up, accelerations, changes in the slope of the road, etc., but also to engine aging and variations of fuel properties. In this paper, with the final purpose of accomplishing an innovative control strategy based on non intrusive measurement, the engine block vibration signal is used to extract useful information able to characterize the in-cylinder pressure development during the combustion process. In the previous research activity, the same methodology was applied to stationary operation of the engine.

This paper presents the results of an experimental study on the application of an engine block vibration transducer. The aim of the study was to accomplish a real time management of the control unit using the vibration signal as a feedback to correct the injection parameters setting. The continuously strengthened exhaust emission regulations and the constrains related to the fuel consumption and noise, vibration and harshness (NVH) characteristics, have determined increasing interest towards investigation of the potentiality of new combustion technologies and fuel blends capable of reducing particulate matter and NOx emissions. Focus has also been paid to non-intrusive techniques for the combustion process characterization by means of sensors, such as microphones and accelerometers.

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.

The paper presents a non-intrusive technique in which accelerometers are used to provide information about the metric of the in-cylinder pressure development, with the final aim of using their signal as feedback in a control algorithm for the injection control unit. Previous papers by the authors have been devoted to the evaluation of the potential of using vibration transducers; the analysis in both the time and frequency domain of the accelerometer and in-cylinder pressure signals has allowed for the separation of the vibration components caused by the combustion process from those due to other sources. The combustion related vibration has then been used to characterize the in-cylinder pressure development.

The optimization of the combustion process in diesel engines is one of the challenges to improve performance, emissions, fuel consumption and NVH characteristics. 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 monitor and optimize the combustion process by means of non-intrusive measurements. Previously published results have demonstrated the direct relationship that exists between in-cylinder pressure and engine block vibration signals, as well as the sensitivity of the engine surface vibration to variation of injection parameters when the accelerometer is placed in a sensitive location of the engine block.

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.

This paper presents the results of an experimental analysis on a multi-cylinder diesel engine, in which in-cylinder pressure and accelerometer transducers are used with the purpose of developing and setting up a methodology able to monitor and optimize the combustion behavior by means of non-intrusive measurements. Previously published results have demonstrated the direct relationship existing between in-cylinder pressure and engine block vibration signals, as well as the sensitivity of the engine surface vibration to variation of injection parameters when the accelerometer is placed in sensitive location of the engine block. Moreover, the accelerometer trace has revealed to be able to locate in the crank-angle domain important phenomena characterizing the combustion process (the start of pre-mixed combustion, the crank angle value corresponding to the beginning of diffusive combustion and to the in-cylinder pressure maximum value).

This work fits into a research program in which the multi-cylinder diesel engine block vibration signal is used with the purpose of developing and setting up a methodology able to monitor and optimize the combustion behavior by means of non-intrusive transducer. Previously published results have demonstrated the direct relationship existing between in-cylinder pressure and engine block vibration signals in a fixed frequency band. It was also shown sensitivity of the engine surface vibration to variation of injection parameters, when the accelerometer is placed in sensitive location of the engine block. Moreover, the accelerometer trace has revealed to be able to locate in the crank–angle domain important phenomena characterizing the combustion process.

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.

Many efforts are being currently devoted to the development of diagnostic techniques based on nonintrusive measurements aimed at defining the injection parameters able to optimize the combustion process. Previous papers of the authors have demonstrated a direct relationship between in-cylinder pressure and engine block vibration signals. Besides, it was also shown sensitivity of the engine surface vibration to variation of injection parameters, when the accelerometer is placed in sensitive location of the engine block. Moreover, in the accelerometer signal, a frequency band in which such a relationship is very strict has been selected. The aim of the present work is to establish a reliable relation between the main characteristics of the in-cylinder pressure curve and the vibration trend, by means of a deeper insight into the engine block signal. The final objective is to monitor the combustion behavior by means of a non-intrusive transducer.

This paper presents a lumped parameter (LP) model to compute diesel soot morphology, in terms of radii of gyration and fractal diameters, starting from the engine operating conditions. The global soot production inside the combustion chamber is evaluated, too. Such a model represents an enhancement of a previously developed LP approach in which the loading and regeneration processes inside a Diesel Particulate Filter (DPF) are investigated. The performance of the DPF during loading is evaluated according to soot layer thickness and pressure drop; the characteristics of soot morphology and particulate deposit are accounted for during the regeneration. Results are presented and validated by means of comparison to those obtained by experimental measures and 3D CFD simulations.

Diesel particulate filters are well known for their efficiency and reliability in trapping particulate matter out of diesel engines. In the last years, many efforts have been done to improve their performances, leading to the employment of new materials and architectures, as well as sophisticated regeneration and management strategies. A lumped parameter model has been developed by the authors able to ensure good accuracy and fast processing for DPF control applications. In this paper, the attention is at first addressed towards the loading process; the evolution with time of pressure drop inside the filter structure is computed and basing on the engine operative condition, a parametrization of the deposited soot layer profile is proposed, in which the effect of the flow distribution at the cross section of the filter is accounted for. The regeneration process is then investigated and temperature profile inside the filter channel is analyzed.

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.