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Dans le cadre des travaux du groupe Essais laboratoire de présélectiondépendant du Groupement Français de Coordination (GFC), deux tests d'évaluation, de la tendance d'un lubrifiant pour moteur à former des dépôts à haute température, sont présentés : - Un nouveau test, le microcokage (fig. 1) qui est un essai statique de cokéfaction soumettant l'huile déposée sur une plaque en alliage d'aluminium à des gradients de température élevés et proches des conditions thermiques rencontrées dans la zone de segmentation d'un piston moteur. En fin d'essai, on détermine la température limite de stabilité de l'huile, exprimée par la température d'apparition de dépôts (fig. 2) et l'on évalue l'aspect et la quantité de dépôts existants sous forme de vernis, en attribuant une note, au mérite, à l'aide du système de cotation décrit dans la méthode d'évaluation de la propreté d'un moteur CEC M-02-A-78 (tableau 5 et fig. 5 et 10). L'association des deux méthodes d'appréciation permet de bien discriminer des huiles de différents niveaux. Des résultats d'essais inter-laboratoires concernant des huiles de référence européennes, pour 2 moteurs à essence et Diesel, sont présentés (tableau 7 et figs. 3 et 4). - Une amélioration d'un test de cokéfaction sur plaque inclinée (figs. 6 et 7) dans lequel un volume donné d'huile s'écoule en film mince sur une plaque en acier inoxydable portée à très haute température. Les dépôts formés en fin d'essai sont évalués, selon leur nature (carbone ou vernis) et leur importance, également suivant les principes de la méthode de cotation CEC (fig. 8 et 9). Par ailleurs, un système de cotation vidéo des plaques de microcokage par reconnaissance de couleur est présenté (fig. 11 et 12). Ce système, appelé Vidéo-Cotateur ,, permet de reproduire fidèlement la cotation visuelle (fig. 13), tout en éliminant les facteurs subjectifs de cette cotation. Les résultats obtenus avec ce système constituent une première étape sur la voie de la cotation de pièces de moteurs assistée par ordinateur (fig. 14). Within the framework of the research done by the Essais laboratoire de présélectiongroup, which depends on the Groupement Français de Coordination (GFC), two evaluation tests are described of the tendency of an engine lubricant to form deposits at high temperature :- A new microcoking test (Fig. 1), which is a static coking test subjecting an oil deposited on an aluminium alloy plate to high temperature gradients that are close to the thermal conditions encountered in the piston-ring zone of an engine. At the end of the test, the maximum stability temperature of the oil is determined, as expressed by the temperature at which deposits appear (Fig. 2), and the aspect and quantity of deposits existing in the form of varnish are evaluated by determining a rating by means of the rating system described in the CEC M-02-A-78 method for evaluating the cleanness of a engine (Table 5 and Figs. 5 and 10). The association of the two assessment methods results in a effective discrimination between different level oils. Results of interlaboratory tests concerning European reference oils for gasoline and diesel engines are given (Table 7 and Figs. 3 and 4). - An improvement of a coking test on an inclined plate (Figs. 6 and 7), in which a given volume of oil flows as a thin film over a stainlesssteel plate heated to a very high temperature. The deposits formed at the end of testing are evaluated according to their nature (carbon or varnish), their amount and also according to the principles of the CEC rating method (Figs. 8 and 9). Likewise, a system of video rating of microcoking plates by color recognition is described (Figs. 11 and 12). This system, called Video-Cotateurcan accurately reproduce the visual rating (Fig. 13) while eliminating the subjective factors of this rating. The results obtained with this system make up the first phase in the route to the computer-assisted rating of engine parts (Fig. 14).

Near-field acoustic holography (NAH) is an effective tool for visualizing acoustic sources from pressure measurements made in the near-field of sources using a microphone array. The method involving the Fourier transform and some processing in the frequency-wavenumber domain is suitable for the study of stationary acoustic sources, providing an image of the spatial acoustic field for one frequency. When the behavior of acoustic sources fluctuates in time, NAH may not be used. Unlike time domain holography or transient method, the method proposed in the paper needs no transformation in the frequency domain or any assumption about local stationary properties. It is based on a time formulation of forward sound prediction or backward sound radiation in the time-wavenumber domain. The propagation is described by an analytic impulse response used to define a digital filter. The implementation of one filter in forward propagation and its inverse to recover the acoustic field on the source plane implies by simulations that real-time NAH is viable. Since a numerical filter is used rather than a Fourier transform of the time-signal, the emission on a point of the source may be rebuilt continuously and used for other post-processing applications. [ABSTRACT FROM AUTHOR]

An investigation of structural intensity control associated with flexural vibration in beams using strain sensing is presented in this paper. The instantaneous intensity is completely taken into account in the control algorithm, i.e., all the terms are considered in the real-time control process and, in particular, the evanescent waves are considered in this approach. Previous work has shown the validity of the approach using an array of accelerometers to measure structural intensity. It is the purpose of this paper to present results on the use of strain sensing in the control of structural intensity. A finite difference approach using discrete PVDF strain sensors provides the structural intensity sensing scheme. A feed forward filtered-X LMS algorithm is adapted to this energy-based control problem, involving a nonpositive definite quadratic form in general. In this respect, the approach is limited to cases where the geometry is such that the intensity component will have the same sign for the control source and the primary disturbance. Experimental validation of the approach is conducted on a free-free beam covered with viscoelastic material and excited harmonically by a shaker. A comparison is made between classical acceleration control and structural intensity control and the performance of both approaches is presented. These results tend to indicate that intensity control allows the error sensors to be placed closer to the control source and the primary disturbance, while preserving a good control performance. [ABSTRACT FROM AUTHOR]