Knock Detection in SI Engines by Using the Discrete Wavelet Transform of the Engine Block Vibrational Signals

Abstract In the present work, the Discrete Wavelet Transform (DWT) has been applied on the vibrational signals acquired by an accelerometer placed on the cylinder block of a Spark Ignition (SI) engine, for detecting knock phenomena. In order to collect both vibrational data and in-cylinder pressures, useful for the analysis, a series of experiments on a four cylinder, four stroke Internal Combustion (IC) engine has been carried out. The obtained results show how the presented knock detection algorithm is able to monitor the goodness of the combustion phase in absence of knock phenomena, and otherwise to determine its intensity. This algorithm uses a Multi-Resolution Analysis (MRA) performed on the vibrational signals of the engine block as acquired. The same kind of analysis has been executed by using the traditional index MAPO, which is widely applied on the pressure data, and the results of the two methods have been compared. The comparison, showing how the results are very similar, confirm that the use of the DWT represents a very valid alternative to the traditional knock detection techniques

Acoustic Optimization of an Intake System by Means of Geometry CAD Modifications

Abstract The intake system of internal combustion engines represents the most prominent noise source at high load and low vehicle speeds because of the de-throttling strategies which are realized in order to maximize the cylinders filling. Therefore, a good acoustic performance of intake systems represents a very important challenge in order to respect the overall noise emission, according to the more strict European standards. In general, the most used method for characterizing the acoustic performances of a system is represented by the Transmission Loss computation. In this study, a 3D numerical analysis by using the Finite Element Method onan intake system for a commercial spark ignition engine has been exploited for the Transmission Loss calculation. The numerical findings of the finite element model have been validated by means of experimental investigations. A very good agreement between numerical and experimental data has been reached. For this reason, an optimization procedure, by implementing different CAD modifications on the system, has been investigated, as well. All the foreseen geometry changes do not modify the overall size of the original system

ANN tool for impact detection on composite panel for aerospace application

Fleet maintenance and safety aspects represent a strategic aspect in the managing of the modern aircraft fleets. The demand for efficient techniques of system and structure’s monitoring represent so a key aspect in the design of new generation aircraft. This is even more significant for composite structures that can be highly susceptible to delamination of the ply, which is often very difficult to detect externally and can lead to a dramatic reduction of design strength and service life, as a consequence of impact damage. The purpose of the work is the presentation of an innovative application within the Non Destructive Testing field based upon vibration measurements. The aim of the research has been the development of a Non Destructive Test (NDT) which meets most of the mandatory requirements for effective health monitoring systems while, at the same time, reducing as much as possible the complexity of the data analysis algorithm and the experimental acquisition instrumentation

An Hybrid FE/SEA Approach for Engine Cover Noise Assessment

In this paper a deep numerical analysis on an internal combustion engine’s cover is carried out. An Hybrid numerical model approach to evaluate the acoustic performance of engine's cover, has been used. The Hybrid model is composed of two numerical models: FE and SEA models. The model FE patterns the structural system, whilst model SEA patterns the acoustic environment. As main excitation an experimental data has been used for two considered engine conditions. The comparison in terms of sound pressure levels between the experimental and FEM/SEA analysis results shows a very good agreement, in the whole investigated frequency range. The obtained results encourage to use the numerical model for further investigations aimed at the improvement of its acoustic performances. The implemented numerical procedure can be applied successfully not only in automotive field but also in all problems where material acoustic performances, is due

Vibro-acoustic response of a turboprop cabin with innovative sidewall viscoelastic treatment

In recent years, it's considerably grown the market demand for increasingly performing and comfortable aircrafts as a new mandatory design target. Among the determining factors for the internal comfort, are included the noise and vibrations, the source of which is detected mainly in the propulsion unit especially in the case of turboprop category: the most significant component of the noise perceived inside a cabin is undoubtedly the blade-passage load exerted by the propeller. Recently were therefore tested techniques, both active and passive, of vibration emission reduction and sound absorption, however the goal remains to find solutions by extremely low-weight and easy to apply on the real mock-up. As known, a damping treatment is typically used to reduce noise coming from fuselage structure vibration under acoustic loading excitation. In such research context, the vibro-acoustic performance of the viscoelastic material for replacing the conventional interior blanket of the fuselage sidewall have been investigated for the well-known higher dissipation capacity and energy storage. Starting from experimental tests by means of different measurement techniques carried out on an innovative foam sample, the dynamic parameters were estimated according to identify suitably the material performance database for further finite element analysis on a turboprop fuselage model. The outcomes achieved have emphasized a significant role of the viscoelastic foam than the standard blanket with respect to the internal sound pressure levels abatement as well as the thermal insulation. The developed foam prototype is also easily integrable with an outer layer ensuring a fully removable embedded solution for the maintenance inspections

diagnostic process by using vibrational sensors for monitoring cavitation phenomena in a getoror pump used for automotive applications

Abstract A full experimental investigation on a Gerotor pump used for the lubrication of engines is described in this paper. These pumps, as well known, are widely used on engines for all hydraulic circuits and, for this reason, often they work in some conditions (such as at high speeds and pressure value) which are very challenging. In this paper one of the most unwanted phenomena that often occurs during the pump operation has been investigated: the cavitation. The cavitation can be triggered by many multiple factors such as the sloshing in the tank (translational and rotational motions), high percentage of gas dissolved in the fluid and pressure too low at the pump suction port. Therefore, the characterization of a Gerotor pump in cavitation condition is really interesting. In order to replay the cavitating conditions a pump has been installed on a dedicated test bench of the Department of Industrial Engineering of the university of Naples "Federico II". The pump has been forced to cavitate by placing calibrated orifices on the suction side of the pump. Many decreasing diameters have been located in an aluminum connection block, to measure all the working parameters like the flow-rate, pressure (at the suction and delivery ports), pump speeds and pressure ripple. Cavitating and no-cavitating conditions have been investigated by using an accelerometer sensor in proximity of the pump suction chamber with the aim of monitoring the phenomena in terms of vibration amplitude. As afore mentioned, the pump under investigation has been studied in all operative conditions with and without cavitation phenomena by using a non-intrusive sensor like accelerometer in order to monitoring if cavitation is present. More precisely, the accelerometer sensor has been located close to the pump suction chamber and the vibrations have been acquired contemporarily with pressure signals (intake and outgoing discharge) and properly triggered with tachometer signal by using a multichannel acquisition system (Siemens™). A spectral vibration analysis has been used as diagnostic tool for accurately detecting pump degradation. The results coming from the analysis have shown that in presence of cavitation phenomena the non-intrusive monitoring technique represent a good diagnostic method for assessing pump operability

Experimental and Numerical Validation of an Automotive Subsystem through the Employment of FEM/BEM Approaches

Abstract In this paper a deep numerical analysis on an internal combustion engine cover is carried out. A hybrid numerical model has been used to evaluate the acoustic performance of engine cover. The Hybrid model is composed of two numerical models: FE (Finite Element) and BEM (Boundary Element Method) models. The FE model patterns structural system, whilst BEM model patterns fluid environment. The main aim of the present work is to characterize, through the employment of numerical simulation, the acoustic performance of the engine cover by using the NR (Noise Reduction) parameter. The numerical frequency response analysis has been implemented using acoustic impedance experimental data, measured for four different thicknesses of sound proof material forming the cover system. The spectrum of acoustic impedance has been evaluated in near field with a sophisticated probe, pressure-velocity probe (p-v probe). The analysis of the obtained results have highlighted the weaknesses as regards sound attenuation of the cover system and possible further improvements of cover system acoustic performance

Acoustic optimization of a high-speed train composite sandwich panel based on analytical and experimental Transmission Loss evaluation integrated by FE/Test correlation analysis

Present work purpose is to optimize the acoustic attenuation properties of a composite sandwich panel used for a high-speed train structure, choosing the best panel configuration which allows to improve the performances. Firstly, Nilsson’s analytical formulation for Transmission Loss (TL) evaluation has been implemented and experimentally validated on a typical material used for high-speed railway applications, highlighting the opportunity to use a different material to satisfy the new required design specifications. Different materials and stratifications have been then considered and TL parameter of each configuration have been calculated using Nilsson’s formulation, characterizing acoustic behavior in the frequency domain. Once found the composition which ensures the best compromise between high acoustic insulation and low weight, the panel has been physically realized. Finally, an experimental and a numerical modal analysis have been performed on it. Starting from both FE simulation and impact testing outcomes, a correlation study through the computation of the Modal Assurance Criterion (MAC), has been carried out. A good agreement between numerical and experimental analyses has been found, obtaining a reliable FE model for future improvements

Experimental Acoustic Measurements in Far Field and Near Field Conditions: Characterization of a Beauty Engine Cover

Present work focuses on experimental acoustic characterization of an engine beauty cover in far field and near field conditions. Specifically, a comparison between results coming from the two different experimental measurement techniques is presented. Experimental campaign has been carried out on a car engine compartment at different operating conditions, by using on one hand a typical pressure microphone for far field measurements accordingly the related prescribed standards, and on the other hand the more innovative Microflown p-u intensity probe (pressure – particle velocity sensor) for near field measurements. In the latter case, experimental tests have been conducted adopting the Scan & Paint method, based on the acquisition of sound pressure and particle velocity by manually moving the probe across the sound field whilst filming the event with a camera. Differently obtained results have been then analyzed highlighting the peculiarities of each of the two techniques. Finally, evaluating noise emissions with and without cover presence, it has been possible to verify the acoustic performances of the component, identifying a less performing acoustic behavior of the material at some specific frequencies. Hence, future developments could regard the possibility to implement an optimization process through the analysis of different materials and configurations, in order to improve cover acoustic insulation properties at the frequencies of interests