No description available.

Η εργασία αυτή εκπονήθηκε προκειμένου να μελετηθεί η διάγνωση λανθασμένης λειτουργίας μίας μηχανής αυτοκινήτου με μία τεχνική η οποία, ακολούθως, αναλύεται και περιγράφεται. Η μηχανή ΄΄στέλνει΄΄ ένα ημιτονοειδές σήμα το οποίο λαμβάνεται με τη βοήθεια πιεζοηλεκτρικών υλικών. Αυτό καθίσταται δυνατό χάρη στην ιδιότητα που έχουν να μετατρέπουν τη μηχανική τάση ή πίεση σε ηλεκτρική. Αφότου γίνει αυτή η μετατροπή αυτό που πρέπει να ακολουθήσει είναι η δειγματοληψία του σήματος που λαμβάνεται και η επεξεργασία του. Έτσι μπορεί να γίνει η διάγνωση της κατάστασης στην οποία βρίσκεται η μηχανή. Πιο συγκεκριμένα, κατά τη διάρκεια αυτής της εργασίας πραγματοποιείται εξέταση των συστημάτων διάγνωσης λανθασμένης λειτουργίας μίας μηχανής, των χαρακτηριστικών και της χρήσης των σύγχρονων ενσωματωμένων συστημάτων και των μικροελεγκτών και, ειδικά, του μικροελεγκτή ADuC7026 της Analog Devices, ο οποίος και χρησιμοποιείται για την υλοποίηση και εκτέλεση του κώδικα που απαιτείται. Η υλοποίηση της εργασίας βασίστηκε εξ ολοκλήρου σε προσομοίωση που πραγματοποιήθηκε (δεν υπήρξαν εξωτερικές συσκευές ανάπτυξης) και για αυτή την υλοποίηση χρησιμοποιήθηκε προσεγγιστικό ημιτονοειδές σήμα. Κατά την επεξεργασία του σήματος χρησιμοποιήθηκαν FIR (ψηφιακά φίλτρα πεπερασμένης κρουστικής απόκρισης) και αλγόριθμοι εντοπισμού της συχνότητάς του. Για την ανάπτυξη της εφαρμογής που αποσκοπεί στον προγραμματισμό του μικροελεγκτή χρησιμοποιήθηκε το μvision 4 της Keil, το οποίο είναι ένα περιβάλλον ανάπτυξης εφαρμογών και η γλώσσα που χρησιμοποιήθηκε είναι η C. / This work was conducted in order to study the diagnosis of a car's machine malfunction with a technique which is subsequently analyzed and described. The machine sends a sinusoidal signal which is obtained by means of piezoelectric materials. This is made possible thanks to the capacity they have to convert mechanical pressure or voltage to electricity. After this conversion is done what should follow is to sample the signal received and processed. This can make the diagnosis of the condition in which the engine is. More specifically, during this work an examination of diagnostic malfunction of a machine is done, its features and the use of modern embedded systems and microcontrollers and, especially, the microcontroller ADuC7026 of Analog Devices, which is used for the implementation and execution of code required. The implementation work was based entirely on simulation performed (there were no external devices) and this implementation approximate sinusoidal signal was used. In signal processing FIR (Finite Impulse digital response) and frequency detection algorithms were used. For the application aimed at programming the microcontroller what was used is μvision 4 from Keil, which is an environment for development of applications and the language that was used was C.

Controlled Auto Ignition (CAI) combustion is a new combustion principle in internal combustion engines which has in recent years attracted increased attention. In CAI combustion, which combines features of spark ignition (SI) and compression ignition (CI) principles, air/fuel mixture is premixed, as in SI combustion and auto-ignited by piston compression as in CI combustion. Ignition is provided in multiple points, and thus the charge gives a simultaneous energy release. This results in uniform and simultaneous auto-ignition and chemical reaction throughout the whole charge without flame propagation. CAI combustion is controlled by the chemical kinetics of air/fuel mixture with no influence of turbulence. The CAI engine offers benefits in comparison to spark ignited and compression ignited engines in higher efficiency due to elimination of throttling losses at part and idle loads. There is a possibility to use high compression ratios since it is not knock limited, and in significant lower NOx emission (≈90%) and particle matter emission (≈50%), due to much lower combustion temperature and elimination of fuel rich zones. However, there are several disadvantages of the CAI engine that limits its practical application, such as high level of hydrocarbon and carbon monoxide emissions, high peak pressures, high rates of heat release, reduced power per displacement and difficulties in starting and controlling the engine. Controlling the operation over a wide range of loads and speeds is probably the major difficulty facing CAI engines. Controlling is actually two-components as it consists of auto-ignition phasing and controlling the rates of heat release. As CAI combustion is controlled by chemical kinetics of air/fuel mixture, the auto-ignition timing and heat release rate are determined by the charge properties such as temperature, composition and pressure. Therefore, changes in engine operational parameters or in types of fuel, results in changing of the charge properties. Hence, the auto-ignition timing and the rate of heat release. The Thesis investigates a controlled auto-ignition (CAI) combustion in internal combustion engines suitable for transport applications. The CAI engine environment is simulated by using a single-zone, homogeneous reactor model with a time variable volume according to the slider-crank relationship. The model uses detailed chemical kinetics and distributed heat transfer losses according to Woschini's correlation [1]. The fundamentals of chemical kinetics, and their relationship with combustion related problems are presented. The phenomenology and principles of auto-ignition process itself and its characteristics in CAI combustion are explained. The simulation model for representing CAI engine environment is established and calibrated with respect to the experimental data. The influences of fuel composition on the auto-ignition timing and the rate of heat release in a CAI engine are investigated. The effects of engine parameters on CAI combustion in different engine concepts fuelled with various fuels are analysed. The effects of internal gas recirculation (IEGR) in controlling the auto-ignition timing and the heat release rate in a CAI engine fuelled with different fuels are investigated. The effects of variable valve timings strategy on gas exchange process in CAI engine fuelled with commercial gasoline (95RON) are analysed.