66 research outputs found
Statistical Analysis of Knock Intensity Probability Distribution and Development of 0-D Predictive Knock Model for a SI TC Engine
No full textKnock is a non-deterministic phenomenon and its intensity is typically defined by a non-symmetrical distribution, under fixed operating conditions. A statistical approach is therefore the correct way to study knock features. Typically, intrinsically deterministic knock models need to artificially introduce Cycle-to-Cycle Variation (CCV) of relevant combustion parameters, or of cycle initial conditions, to generate different knock intensity values for a given operating condition. Their output is limited to the percentage of knocking cycles, once the user imposes an arbitrary knock intensity threshold to define the correlation between the number of knocking events and the Spark Advance (SA). In the first part of the paper, a statistical analysis of knock intensity is carried out: for different values of SA, the probability distributions of an experimental Knock Index (KI) are self-compared, and the characteristics of some percentiles are highlighted. The innovative contribution of this work is to correlate such KI probability curves with mean combustion parameters (like maximum in-cylinder pressure or combustion phase) through an analytical function. In this way, KI distributions can be predicted by a fully deterministic combustion model, ignoring CCV. In the final part of the paper such relations are implemented in a 1-D environment and tested using a combustion model, previously calibrated via Three Pressure Analysis (TPA) for knock-free operating conditions. Validation is carried out by comparing experimental and simulated KI distributions
Investigation on Pre-Ignition Combustion Events and Development of Diagnostic Solutions Based on Ion Current Signals
No full textPre-ignition combustions are extremely harmful and undesired, but the recent search for extremely efficient spark-ignition engines has implied a great increase of the in-cylinder pressure and temperature levels, forcing engine operation to conditions that may trigger this type of anomalous combustion much more frequently. For this reason, an accurate on-board diagnosis system is required to adopt protective measures, preventing engine damage. Ion current signal provides relevant information about the combustion process, and it results in a good compromise between cost, durability and information quality (signal to noise ratio levels). The GDI turbocharged engine used for this study was equipped with a production ion current sensing system, while in-cylinder pressure sensors were installed for research purposes, to better understand the pre-ignition phenomenon characteristics, and to support the development of an on-board diagnostic system solely based on ion current measurements. In this work, pre-ignition events induced by heavy knocking operation have been analysed. The focus was mainly on ion current signal real-time processing, and on the possibility to correctly and rapidly detect pre-ignition events. In a previous work, destructive effects of this kind of combustion on engine components had been described. As shown in the paper, the development and implementation of an ion current based detection algorithm results to be very effective in identifying pre-ignition combustions, and it could allow an extremely fast reaction of the engine controller that can prevent further anomalous combustions once the first event has occurred. Moreover, pre-ignition phase information extracted from the ion signal and characteristic combustion angles obtained from pressure signal analysis are well correlated, further confirming the ion signal robustness and accuracy
Investigation of Water Injection Effects on Combustion Characteristics of a GDI TC Engine
No full textThis paper presents simulation and experimental results of the effects of intake water injection on the main combustion parameters of a turbo-charged, direct injection spark ignition engine. Water injection is more and more considered as a viable technology to further increase specific output power of modern spark ignition engines, enabling extreme downsizing concepts and the associated efficiency increase benefits. The paper initially presents the main results of a one-dimensional simulation analysis carried out to highlight the key parameters (injection position, water-to-fuel ratio and water temperature) and their effects on combustion (in-cylinder and exhaust temperature reduction and knock tendency suppression). The main results of such study have then been used to design and conduct preliminary experimental tests on a prototype direct-injection, turbocharged spark ignition engine, modified to incorporate a new multi-point water injection system in the intake runners. The experiments allowed to validate the model results, demonstrating the effectiveness of the proposed technology, and to further investigate on the mechanisms that allow controlling thermal load and knocking tendency by varying the water-to-fuel ratio
Investigation of Knock Damage Mechanisms on a GDI TC Engine
No full textThe recent search for extremely efficient spark-ignition engines has implied a great increase of in-cylinder pressure and temperature levels, and knocking combustion mode has become one of the most relevant limiting factors. This paper reports the main results of a specific project carried out as part of a wider research activity, aimed at modelling and real-time controlling knock-induced damage on aluminum forged pistons. The paper shows how the main damage mechanisms (erosion, plastic deformation, surface roughness, hardness reduction) have been identified and isolated, and how the corresponding symptoms may be measured and quantified. The second part of the work then concentrates on understanding how knocking combustion characteristics affect the level of induced damage, and which parameters are mainly responsible for piston failure. For this purpose, steady-state tests have been conducted controlling different and constant levels of knock intensity (i.e., pressure waves oscillation amplitude) and thermal load (i.e., average temperature and pressure levels inside the combustion chamber). Since these parameters are strictly interrelated for a given engine operating condition and for a given fuel, fuels with different knock resistance (i.e., RON number) have been employed, to allow a clearer understanding of the damage distribution in the knock intensity-thermal load domain
Experimental observations of engine piston damage induced by knocking combustion
No full textAbnormal combustion leads to a significant increase in combustion speed, pressure and temperature at the surfaces enclosing the combustion chamber. Severe and lasting knock or pre-ignition can permanently damage and, in many cases, destroy engine pistons, due to very high and localised thermomechanical stresses. The deleterious effects of abnormal combustions have led car manufacturers to set extremely precautionary thresholds in spark advance calibration (in terms of temperatures and pressures) of turbocharged spark ignition direct injection engines, often limiting engine performance and efficiency. Since the mechanisms of piston damage due to abnormal combustion are not currently fully understood, the aim of this study was to characterise its effects on Al forged pistons. The more suitable characterisation techniques were evaluated. The results highlighted that roughness measurements, as well as visual, optical and scanning microscopy analyses on specific zones of the top land and piston crown are useful techniques to qualitatively relate piston damage to combustion regime. Moreover, a significant quantitative relationship was observed between the MAPO (Maximum Amplitude Pressure Oscillations) index and residual piston hardness
Combustion and Intake/Exhaust Systems Diagnosis Based on Acoustic Emissions of a GDI TC Engine
No full textDue to increasingly stringent emission regulations and the need for more efficient powertrains, engine control systems that have been developed during the recent years have become more and more sophisticated. Obtaining accurate information about the combustion process and about all the subsystems that compose the engine can be considered key to reach the maximum overall performance. Low-cost in-cylinder pressure and turbo speed sensors are being developed, but they still present long-term reliability issues, and represent a considerable part of the entire engine management system cost. Sound emissions represent an extremely rich information source about the operating conditions of all the subsystems that comprise the entire engine. The paper shows how it is possible to extract fundamental information regarding the combustion process (such as knock and misfire), turbo speed, and air path fault at the same time, by performing an appropriate analysis of the engine acoustic emissions acquired from the very same microphone, which can thus be considered as an innovative, multifunction, and low-cost sensor for automotive applications
Analysis of Pre-ignition Combustions Triggered by Heavy Knocking Events in a Turbocharged GDI Engine
No full textIn this paper, a pre-ignition sequence with detrimental effects on the engine has been analysed and described, with the aim of identifying the main parameters involved in damaging the combustion chamber components. The experiment was carried out in a wider research context, focused on knock damage mechanisms in turbocharged GDI engines. The pre-ignition sequence was a consequence of a high knock condition, induced at high load at 4500 rpm. The abnormal thermal load due to knock caused overheating of the whole combustion chamber, until the spark plug electrodes became a "hot spot", resulting in premature flame initiation in the following cycles, with a self-sustaining mechanism. Slight cylindrical differences, mainly in terms of volumetric efficiency, allowed comparisons and correlations between indicated parameters, pre-ignition sequence and damage. The main responsible in damaging the engine, in this case and for this engine, is the extremely high heat transferred to the walls in the pre-ignited cycles, characterized by higher mean temperatures. Heavy knock triggered the pre-ignited combustions but progressively reduced its intensity as the spontaneous ignition advance increased, thus having a secondary role in damaging directly the combustion chamber
¿Por qué rojo y no verde? La explicación enactiva de las diferencias cualitativas de la experiencia
No full textFil: Recabarren, Nahuel. Universidad Nacional de Córdoba; Argentina.En este trabajo examinaré el enfoque enactivo, específicamente en su intento de dar cuenta
de las diferencias en los aspectos cualitativos de la experiencia. Particularmente, objetaré la
explicación de la experiencia del color propuesta por Noe basada en la interacción entre
movimiento y sensación. Para ello, en primer lugar, describiré tres experimentos que Noe
presenta para mostrar el papel de las contingencias sensoriomotrices en la percepción. Luego,
explicaré cómo se pretende, a través de éstas contingencias, dar cuenta de las diferencias
intermodales, es decir, las diferencias cualitativas entre modalidades sensoriales como, por
ejemplo, la visión y el tacto, y de las diferencias intramodales, es decir, las diferencias
cualitativas dentro de una misma modalidad sensorial como, por ejemplo, la experiencia· de tojo
y la de verde . Finalmente, consideraré nuevamente los experimentos descriptos para mostrar
cómo estos se pueden interpretar como evidencia contraria a dicha explicación en lo concerniente
a la experiencia del color.Fil: Recabarren, Nahuel. Universidad Nacional de Córdoba; Argentina
Damage evolution analysis in a “spaghetti” bridge model using the acoustic emission technique
No full textThis paper applies the Acoustic Emission (AE) Technique to analyze the damage process in a one-meter span bridge model that was built from spaghetti sticks during a loading test. The AE signals are analyzed in terms of four coefficients that are evaluated as predictors of structure failure, with frequency variation appearing to be the strongest indicator of instability. The AE data are also compared to theoretical predictions that are given by the Bundle Model, confirming that underlying general patterns in damage processes are highly influenced by the geometric distribution of the structure and the loading pattern that is applied to it
Modellazione e verifica sperimentale delle dinamiche di aspirazione di un motore turbo GDI
No full textObiettivo di questo elaborato è quello di provvedere alla elaborazione dei dati geometrici necessari alla modellazione dei condotti di aspirazione e scarico di un motore 4 cilindri turbo benzina ad iniezione diretta (GDI) disponibile a banco prove. I dati sperimentali raccolti sono stati elaborati e sintetizzati, con lo scopo di fare avvicinare il più possibile le caratteristiche del modello a quelle del sistema a banco (cercando dunque di rendere il modello il più veritiero possibile). In primo luogo, saranno descritte le principali caratteristiche dei motori a combustione interna, con particolare enfasi rivolta ai componenti ed ai processi che caratterizzano i motori turbo GDI. In un secondo momento, sarà descritto come si è proceduto nella raccolta dei dati necessari alla modellazione e nell’elaborazione degli stessi. Il software cui l’elaborazione dei dati necessari alla modellazione è stata rivolta è GT-Suite, prodotto da Gamma Technologies e largamente utilizzato dalla maggior parte delle aziende del settore automotive
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