1,721,068 research outputs found
Lubricant oil influence on the combustion process of conventional and Innovative internal combustion engines
Full text linkThe negative impacts of climate change are mounting very fast and bold actions are required, so that significant efforts are needed to improve the current technologies for mobility because of the competitive marketplace as well as of the ever-tightening regulations concerning emissions and fuel economy. In this scenario, internal combustion engines (ICEs) need radical modifications to be still considered a sustainable option for the future.
The motivation for the proposed research stems from evidence reported in the literature, which suggests that lubricant oil droplets are the primary inducer of abnormal combustion modes. Additionally, lubricant oil can represent a major source of very fine soot particles emitted from engines. These adverse effects severely hinder the further development of efficient and cleaner internal combustion engines.
However, the influence of lubricant oil on the combustion process is not yet fully understood as it is often neglected in numerical simulations, due to the assumption that the amount of lubricant oil reaching the combustion chamber is negligible. Thus, there is a need to fill the knowledge lack of lubricant-oil-related auto-ignition processes in engines. In this scenario, the accurate chemical modelling of the fuel-lubricant interaction represents an essential aspect for enabling the further development of the internal combustion engine for providing information difficult or impossible to obtain solely through experiments.
The present work tries to shed light on the criticalities arising from the interaction between fuel and lubricant oil in modern internal combustion engines, through rigorous numerical investigations. A variety of fuels, including traditional fossil fuels (gasoline) as well as carbon-free alternatives (hydrogen), were considered. As a first step a way for considering the presence of trace amounts of lubricant in the combustion chamber was defined, by selecting proper lubricant oil surrogate species. Consequently, several detailed chemical models were developed and validated to isolate the lubricant oil's contribution to abnormal combustion events. However, it is well known that CFD numerical simulations employing detailed chemical models are computationally expensive. In light of this, the detailed chemical models were reduced for the purpose of conducting Three-Dimensional (3D) CFD numerical simulations, in order to reproduce experimental data involving lubricant oil combustion. With the aim to further reduced computational costs, a practical and simple analytical correlation able to predict variations of gasoline ignition delay induced by the presence of lubricant oil, at different temperatures, is presented. Such a correlation was developed by considering both experimental data available in the literature and numerical simulations.
The urgent need to reduce both the environmental impact of mobility and the dependence on fossil fuels has re-ignited the interest toward Hydrogen Internal Combustion Engines (HICEs). However, there are still criticalities that need to be assessed for accelerating the development of this technology. The undesired but unavoidable participation of lubricant oil to the combustion process is considered at the basis of the criticalities that affect the development of a reliable and efficient HICEs. In order to investigate and highlight the role of lubricant oil in the development of HICEs a specific reduced chemical model was developed and validated. The newly developed chemical model was employed in Zero-Dimensional (0D) simulations with the aim to quantify the effects that lubricant oil can have on hydrogen ignition delay time (IDT) in engine-like conditions
A chemical kinetics-based approach to predict uncontrolled self-ignitions in Hydrogen Internal Combustion Engines
Full text linkThe primary objective of the present work is to correlate the hydrogen explosive characteristics with internal combustion engine design parameters, particularly the engine compression ratio. An approach that couples the knowledge about H2 chemical behaviour, and the in-cylinder charge thermodynamic state, has been conceptualized in the form of a unified plot to visually inspect the likelihood of an auto-ignition event. The plot cautions the possible occurrence of autoignition if the state of the charge inside the engine cylinder reaches thermodynamic conditions beyond the explosion limit curve. Having at hand such a tool enables one to cautiously design future experiments to prevent possible damage because of extreme stresses due to an undesired autoignition event.
The results of the analyses in the present work have translated into defining a maximum limit on the compression ratio that can be proposed at pre-defined intake thermodynamic state, mixture composition, engine geometry and engine speed. Predictions based on recently developed chemical mechanisms were employed for the analyses, exploiting the well-established knowledge about the chemical kinetics of hydrogen oxidation.
Thus, zero-dimensional numerical simulations were performed. Such an approach avoids also the limitations associated with experimental procedures. To evaluate the maximum safe compression ratio, both a static and a time-based approach have been employed to study the vicinity of a thermodynamic state to the autoignition limit i.e., the explosion limit of hydrogen. Three possible criteria for the definition of a maximum safe geometrical compression ratio were developed and analysed. The present work has then been finally ensembled in the form of an empirical correlation involving intake pressure, intake temperature and equivalence ratio as the variables.
Furthermore lubricant oil as a contaminant seeping through the compression rings of a piston in an internal combustion engine, is modelled to evaluate the distribution of mass and temperature inside a droplet of n-hexadecane using 0D- simulations to evaluate the variation of ignition delay time within the droplet in gas-phase and its effect on the local concentration diluting the pure hydrogen in the vicinity and hence increasing the reactivity causing an early source of self- ignition.
A final study concerning developing detonations from hot spots is carried out to understand the effect of a temperature gradient other than ‘linear’ within the hot spot that could change the detonation response diagrams and subsequently the modes of reacting front propagation. Such detonations with high peak pressures are detrimental to components inside an internal combustion engine and therefore the need to study any possibility of its occurrence is crucial to a better understanding of the design
Advanced Sensors for Diesel Engines
Full text linkQuesta tesi descrive il lavoro inerente allo sviluppo di un sensore di qualità diesel. Il lavoro è svolto all'interno di un dottorato industriale in partnership con Bosch e mira a monitorare costantemente la qualità del carburante utilizzato nella maggior parte dei veicoli pesanti, ma non solo. Il motivo che spinge Bosch a questo tipo di misurazione è il deterioramento della pompa del carburante diesel dovuto all'uso di carburante di scarsa qualità.
L'obiettivo finale è, quindi, la prototipazione di un sistema di rilevamento in linea, che viene posto sulle tubazioni per la distribuzione del gasolio, nel sistema di pre-alimentazione, a fianco del serbatoio.
Diverse soluzioni sono state esplorate e analizzate per trovare la tecnica che garantiva il rilevamento dell'acqua nel gasolio. Le tecniche a microonde e ottiche sono state confrontate, simulate e analizzate. Diversi prototipi sono stati realizzati e confrontati tra loro, evidenziando buoni risultati.This thesis describes the work inherent in the development of a diesel quality sensor. The work is carried out within an industrial doctorate in partnership with Bosch and aims to constantly monitor the quality of the fuel used in most heavy vehicles, but not only. The reason that drives Bosch to this type of measurement is the deterioration of the diesel fuel pump due to the use of poor-quality fuel.
The final objective is, therefore, the prototyping of an in-line detection system, that is placed on the pipelines for the distribution of diesel, in the pre-feeding system, next to the tank.
Different solutions have been explored and analyzed to find the technique that guaranteed the detection of water in diesel. Microwave and optical techniques have been compared, simulated and analyzed. Several prototypes were made and compared with each other, highlighting good results
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Costituente italiana e Costituente europea: la prospettiva di Piero Calamandrei
No full textErede di una famiglia di lunga tradizione giuridica, fine avvocato e studioso del diritto, Piero Calamandrei fu antifascista della prima ora, fondatore del Partito d’azione, padre della Costituzione italiana ed europeista convinto. Il suo poliedrico impegno in quanto intellettuale, giureconsulto e uomo politico è stato ripetutamente indagato da storici, giuristi e studiosi del pensiero, ma non si può dire altrettanto del suo sentimento euro-federalista, che sembra essere, per dirla con Angelo Tonnellato, «più noto che conosciuto». A questo scopo si rivolge il presente contributo, che, partendo dalla biografia, intende ricostruire il pensiero europeista dell’avvocato fiorentino e ripercorrerne l’attività svolta nell’immediato dopoguerra a favore della causa europea
Progetto per Fossoli in "schede di presentazione dei progetti"
No full textPrimo incontro con il tema del male assoluto rappresentato dal piano di sterminio nazi-fascsta e restituito dai reperti sopravvissuti come banalità edilizia.
La rasformazione in memoria di frammenti resi innocui e mimetizzati dal tempo ha comportato una riflessione sugli strumenti del progetto, sul rapporto tra architetura ed eloquenza, tra architettura e rappresentazione che sono state la base di quasi tutto il lavoro seguente
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