Combined Experimental and Numerical Analysis of Knock in Spark Ignition Engines
A detailed analysis of knocking event can help improving engine performance and diagnosis strateg... more A detailed analysis of knocking event can help improving engine performance and diagnosis strategies. The paper aim is a better understanding of the phenomena involved in knocking combustion through the combination of CFD and signals analysis tools. CFD simulations have been used in order to reproduce knock effect on the in-cylinder pressure trace. In fact, the in-cylinder pressure signal holds information about waves propagation and heat losses: for the sake of the diagnosis it is important to relate knock severity to knock indexes values. For this purpose, a CFD model has been implemented, able to predict the combustion evolution with respect to Spark Advance, from non-knocking up to heavy knocking condition. The CFD model validation phase is crucial for a correct representation of both regular and knocking combustions: the operation has been carried out by means of an accurate statistical analysis of experimental in-cylinder pressure data. The simulation results allow relating the combustion characteristics to their effect on the in-cylinder pressure signal. It is then possible to highlight critical issues regarding typical knock detection methodologies, while disclosing novel approaches. One of the main results is the validation of knock detection strategies based on the low-frequency content of the pressure signal. These strategies can be used together with standard high-frequency based techniques in order to improve the detection robustness.
Combined Experimental and Numerical Analysis of the Influence of Air-to-Fuel Ratio on Cyclic Variation of High Performance Engines
ABSTRACT The Cycle by Cycle Variation (CCV) of a SI engine is analyzed by combining experimental ... more ABSTRACT The Cycle by Cycle Variation (CCV) of a SI engine is analyzed by combining experimental tests and numerical investigations. The quantification of CCV is based on the evaluation of the Coefficient of Variance (COV) of IMEP. The analysis of the experimental pressure data shows an increase in CCV towards leaner mixture conditions. The evaluation of the Heat Release Rate from the in-cylinder pressure traces reveals the strong influence of the early stages of combustion on the variability of the flame evolution. In order to evaluate the influence on CCV of local air equivalence ratio cycle-to-cycle variability and mixture homogeneity in the chamber, a numerical CFD methodology for the simulation of the combustion process has been proposed. The results reproduce with reasonable accuracy the increase in CCV with leaner combustions and put the basis for a deeper insight into the complex phenomena involved in the combustion process by the use of parametric analysis.
This study investigates the preliminary propulsive performances of a cathode-less plasma thruster... more This study investigates the preliminary propulsive performances of a cathode-less plasma thruster with air as its propellant. The analysis is carried out through a global model and simulates a thruster over a power range of 0 to 50 W. The developed code considers a set of 177 chemical reactions involving 8 different species and includes empirical equations to account for electronegative effects. The analysis presents the steady-state values of species densities at 10 W, 30 W, and 50 W to gain insights into the key characteristics of plasma dynamics. Moreover, the study estimates the thrust and specific impulse and compares the results to data from models that employ xenon and iodine, aiming to understand the performances of air in low-power thrusters. Lastly, the study examines the effects of varying air inflow concentration on the chemistry, analyzing three different orbit altitudes (i.e., 200, 300, and 400 km).
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Sviluppo DI Una Metodologia Innovativa Per La Misura Della Velocità DI Rotazione DI Un Turbocompressore Automobilistico
Il lavoro presenta lo sviluppo di una metodologia, innovativa e a basso costo industriale, per la... more Il lavoro presenta lo sviluppo di una metodologia, innovativa e a basso costo industriale, per la misura in tempo reale a bordo veicolo della velocit\ue0 di rotazione del turbocompressore per vetture equipaggiate con motori sovralimentati mediante sistemi dinamici. La metodologia si basa sulla ricerca della frequenza di rotazione del turbocompressore nell\u2019emissione sonora, acquisita attraverso un microfono posizionato nel vano motore. La ricerca \ue8 guidata dall\u2019utilizzo della mappa caratteristica del compressore, che permette di ottenere una prima stima orientativa della velocit\ue0 di rotazione del sovralimentatore. Nel lavoro viene descritto come \ue8 possibile ottenere una misura di riferimento della velocit\ue0 del turbocompressore con una tecnica di laboratorio per permettere di valutare l\u2019efficacia dell\u2019algoritmo di ricostruzione, che \ue8 stato potenziato rispetto ad una prima versione. I test sono stati condotti su una vettura equipaggiata con motore Diesel turbocompresso, montata sul banco a rulli e funzionante in condizioni molto vicine a quelle operative. I risultati si sono dimostrati incoraggianti ed \ue8 stata pianificata l\u2019attivit\ue0 di ingegnerizzazione dell\u2019algoritmo in un sistema di prototipazione rapida
This paper is a part of the hereunder thematic dossier published in OGST Journal, Vol. 70, No. 1,... more This paper is a part of the hereunder thematic dossier published in OGST Journal, Vol. 70, No. 1, pp. 3-211 and available online here Cet article fait partie du dossier thématique ci-dessous publié dans la revue OGST, Vol. 70, n°1, pp. 3-211 et téléchargeable ici Do s s i e r
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