The intake system is one of the components on the internal combustion engine most linked with the achievement of the high volumetric efficiency required of naturally aspirated engines. High performance racing engine intake systems have unusual geometry with separate intake pipes (often known as intake trumpets) housed in a common airbox. These intake trumpets are short pipes that are sometimes cylindrical but often conical. The flow within the intake system is very unsteady with high frequency wave action taking place. A carefully developed intake trumpet can use the wave action to tune the engine and therefore increase the performance distinctly. The intake tuning is strongly dependent on the acoustic properties of the intake system. Two important parameters are the pressure wave reflection coefficient at the open inflow end of the intake pipe (to tune the engine effectively) and the acoustic length of the intake pipe (to tune the engine at the appropriate engine speed). Acoustic measurements show that the open inflow end reflection coefficient decreases with inflow but increases with external (coaxial) flow. CFD calculations show that the vena contract a which gets created at the open inflow to the pipe disappears with coaxial flow. A conical inflow shape decreases the reflection coefficient at certain frequencies and influences the phase angle of the acoustic waves. One dimensional prediction models for the wave transfer inside these conical intake pipes are validated against acoustic measurement results. 4 The airbox decreases the reflection coefficient distinctly due to three dimensional resonances inside the airbox and limits the use of one dimensional prediction models, but the acoustic length can still be predicted accurately. Fuelling inside the intake pipe decreases the speed of sound by 10% and thus increases the acoustic pipe length. Therefore it influences the engine tuning and needs be considered when developing intake systems. A new acoustic measurement method is introduced which allows the measurement of the acoustic pipe length within the conical part of the intake pipe. Finally, the time varying nature of the intake flow and intake acoustics is explored on a running racing engine by means of hot-wire and pressure measurements and shows the influence of intake acoustics on the fluctuating intake airflow velocity especially during the period when the intake valves are closed.

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Στo πρώτο κεφάλαιο της εργασίας αυτής περιγράφεται η τεχνολογία που έχει αναπτυχθεί για την αντιμετώπιση των εκπομπών των αυτοκινήτων. Κατόπιν γίνεται μια ανασκόπηση των τεχνολογιών που εφαρμόζονται για τον έλεγχο των στάσιμων πηγών ρύπων, όπου η ποικιλία και η ποσότητα των εκπομπών είναι πολύ μεγάλη. Περιγράφονται επίσης οι φυσικές και χημικές αρχές στις οποίες βασίζεται μια διαδικασία καταλυτικού μετατροπέα. Οι καταλυτικοί μετατροπείς σχεδιάζονται με στόχο την ελαχιστοποίηση της συγκέντρωσης των ρυπογόνων αερίων, όπως αυτή καταγράφεται σε μια προκαθορισμένη θέση, κατά μήκος της συσκευής. Στο δεύτερο κεφάλαιο διατυπώνεται το σύστημα Μερικών Διαφορικών Εξισώσεων (Μ.Δ.Ε.) του βασικού προτύπου και εξετάζεται το πρόβλημα βέλτιστου ελέγχου που ελαχιστοποιεί την συνάρτηση κόστους J(S) με την επιλογή της βέλτιστης συνάρτησης ελέγχου S(t). Ο βέλτιστος έλεγχος είναι αυτός που ελαχιστοποιεί την παραγωγή των επικίνδυνων αερίων μέσω του καταλυτικού μετατροπέα. Το μαθηματικό πρότυπο προσεγγίζεται μέσω αναγωγής του στο πρόβλημα αρχικών και συνοριακών τιμών της εξίσωσης θερμότητας τόσο σε ημιάπειρο όσο και σε πεπερασμένο διάστημα, χρησιμοποιώντας τις κατάλληλες μεθόδους. Στη συνέχεια, στο Κεφάλαιο 3, που αποτελεί και το κεντρικό μέρος της παρούσας διατριβής, επιλύουμε το βασικό μοντέλο εξέλιξης της θερμοκρασίας του καταλυτικού μετατροπέα, μελετώντας την ομογενή εξίσωση θερμότητας σε μία διάσταση, με μη ομογενή αρχική συνθήκη και μη ομογενή συνοριακή συνθήκη. Αναφερόμαστε σε μεθόδους επίλυσης διαφορετικών περιπτώσεων, μέσω της μεθόδου Μετασχηματισμού Fourier Ημιτόνου και Μετασχηματισμού Fourier Συνημιτόνου και της μεθόδου του Μετασχηματισμού Laplace, διαφωτίζοντας κάθε μία με παραδείγματα που καταδεικνύουν τα προτερήματα και μειονεκτήματά τους. Μελετάμε κατόπιν μέσω της μεθόδου Χωριζομένων Μεταβλητών την μη ομογενή εξίσωση της θερμότητας σε πεπερασμένο διάστημα 0<x<L. Κατόπιν, χρησιμοποιώντας στοιχεία από την όλη θεωρία που περιγράφηκε, επιλύουμε αναλυτικά, στο τέλος του Κεφαλαίου 3, το γραμμικοποιημένο μοντέλο του καταλυτικού μετατροπέα, κοντά σε μια κατάσταση ισορροπίας του και συζητάμε τη σημασία της λύσης του για την μελέτη της λειτουργίας του καταλύτη. Αναγνωρίζοντας ότι η πλήρης αναλυτική λύση του μοντέλου δίνεται μέσω μαθηματικών εκφράσεων που είναι δύσκολο να υπολογισθούν απ’ευθείας, αναφερόμαστε στο Κεφάλαιο 4 σε ορισμένες πολύ σημαντικές αριθμητικές μεθόδους για την επίλυση της εξίσωσης της θερμότητας υπό διαφορετικές αρχικές και συνοριακές συνθήκες. Οι τεχνικές αυτές, που είναι γνωστές και ως μέθοδοι πεπερασμένων διαφορών, είναι επιτυχείς μόνο αν χαρακτηρίζονται από τις ιδιότητες της σύγκλισης (σε μοναδική λύση) και της ευστάθειας. Κλείνοντας το κεφάλαιο 4 παρουσιάζουμε το κριτήριο von Neumann μέσω του οποίου μπορεί να εξασφαλισθεί στα προβλήματα αυτά η ευστάθεια και επομένως και η σύγκλιση των εν λόγω αριθμητικών μεθόδων. Τέλος, τα συμπεράσματά μας παρουσιάζονται στο Κεφάλαιο 5. / Catalytic converters are designed with the goal of minimizing the concentration of the polluting gases emitted by automobiles. The developed catalytic converter technologies are described and a mathematical model for optimizing their function is presented. The mathematical model is based on the problem of initial and boundary conditions of the heat equation at the semi-infinite and finite space using the appropriate methods. Methods for solving different cases of the heat equation are sinus and cosine Fourier transform, Laplace transform and the method of divided variables. Using the theory described, we solve in detail the linear model of catalytic converter, close to a condition of balance. The meaning of its solution is studied for the function of the catalytic converter. Finally some very important arithmetic methods for the solution of the heat equation under different initial and boundary conditions are described. These methods are known as “methods of finite differences” and are successful only under the conditions of stability and convergence. The Von Neumann criterion is presented. Using this criterion the stability can be ensured, thus the convergence.

Small automotive plain engine bearings are used to provide the relative motion between the engine block and the crankshaft via the connecting rod. Under rapidly changing engine loads, these bearings may suffer fatigue damage during service. In modern multilayered bearing designs, fatigue resistance is a complex function of engine loading coupled with the layer architecture and a multiphase lining alloy. This research has mostly focussed upon micro-scale fatigue damage initiation on thin (0.2-0.3mm thickness) lining surface and its subsequent growth leading towards gross failure. The systems examined comprise Al alloys and sintered bronze as relatively soft and conformable lining layers. The weight percent composition of Al lining alloy was Al-6.5Sn-2.5Si-1Cu-1Ni-0.25Mn roll bonded to a stiffer and thicker backing steel layer (1.5-1.8mm thick) via an even thinner Al foil (0.04mm) as an interlayer. The other system comprised an Al lining (Al-20Sn–1Cu) alloy spray coated on to a medium carbon steel layer in the form of a flat bar. All these systems were compared with the previously investigated Al based designs with lining compositions: Al-12Sn-4Si-1Cu and Al-20Sn-1Cu-0.25Mn (manufactured by roll bonding processes). The performance evaluation was based upon the investigation of microstructural features involved in early fatigue initiation and their effect upon short crack growth on the surface. Subsurface crack growth through the layers has also been assessed and finally the observed fatigue life of various components linked to these behaviours. A 3-point bend test configuration was adopted for laboratory fatigue tests. Fatigue comparison was made on the basis of lining surface plastic strain amplitude vs. number of cycles to failure according to a uniform predefined criterion for all the systems. Maximum plastic strains developing at the lining surface were estimated using a combination of finite element analysis (FEA) and strain gauge measurements so that the fatigue life of all systems studied was presented as strain-life data. Specimens in the form of both finished bearings and flat bars were tested. Similar fatigue behaviour was observed for the two testing geometries, giving greater confidence in the fatigue evaluation process and allowing detailed observations of small crack initiation and growth processes in flat bars to be related to behaviour of the actual bearing geometry. In the previous research, the coarser Si particles in the Al-12Sn-4Si-1Cu lining and Sn particles in the Al-20Sn-1Cu-0.25Mn alloys were identified as potential crack initiation sites, though the relationship between particle geometry and arrangement/clustering was found to be important. The newly developed Al-6.5Sn-2.5Si-1Cu-1Ni-0.25Mn lining alloy with finer and fewer Sn and Si particles showed a delayed initiation of short fatigue cracks compared to the previous systems. However, a large number of widely scattered intermetallics in the new linings were observed to fracture causing early fatigue initiation at the micro-scale level with some more complex processes of detaching Sn layers from harder intermetallics and Si particles. Using the mechanical property data for bulk lining and secondary phase particles obtained from tensile testing and instrumented hardness testing, stress fields were investigated within the hard particles (intermetallics), surrounding thin layers and the matrix on the basis of the analytical and numerical modelling. On the basis of these modelling results, optimum particle shapes were defined to minimize tensile stresses (within the particles) and hydrostatic stresses (at the particle matrix interfaces). The experimental growth data of a dominant crack when combined with a Hobson type growth model based upon measured particle distributions and experimental crack growth rates, helped in predicting fatigue life of a similar component at different stress levels. Surface crack driving force reduces considerably when subsurface crack deflection occurred within softer Al interlayer. Replacing this interlayer with a harder brazed sheet did not give any significant difference in the observed fatigue life. In the HVOF systems, crack initiation was observed to be from the weaker interface between a harder matrix and softer circular unmelts as well as from various scattered pores. The overall fatigue life of the HVOF systems was comparable to the previous roll bonded systems; however subsurface deflection of crack at the lining-backing interface resulted in the debonding of the lining and hence the observed lining fatigue resistance may not be a good indication of the overall performance in a bearing system. At similar lining surface plastic strain levels, the bronze bearing with very thin Sn and Ni as overlay layers (~7 microns each) showed comparable fatigue resistance to the currently investigated RB Al based designs. However annealing this system resulted in the formation of hard Ni3Sn intermetallics at the Sn-Ni interface, and the observed fatigue resistance of this system was higher than the RB systems. This has been linked to very fine scale local crack deflection in the overlay layers (although these have not been observed clearly). All these layered bearing systems provide a complex fatigue problem. Factors which reduce initiation /early growth behaviour are likely to offer the best service performance enhancements in view of the relatively HCF nature expected in service.

One dimensional, linear, plane-wave modelling of silencer systems in the frequency domain provides an efficient means to analyse their acoustic performance. Software packages are available to analyse silencers within these modelling parameters; however, they are heavily restricted. The thesis develops an algorithm that increases the computational efficiency of the silencer analysis. The thesis concentrates on how data, within a software package, is stored, retrieved and analysed. The computational efficiency is increased as a result of the predictable patterns caused by the repetitive nature of exhaust system analysis. The work uses the knowledge gained from the construction of two previous algorithms of similar parameters; it isolates and maximises their advantages whilst minimising their associated disadvantages. The new algorithm is dependent on identifying consecutively sequenced exhaust components and sub-systems of such components within the whole exhaust system. The algorithm is further generalised to include multiple time-variant sources, multiple radiation points and exhaust systems that have a balance pipe. Another feature of the improved algorithm encompasses the option of modelling secondary noise sources such as might arise from flow generated noise or be included for active noise cancellation systems. The validation of these algorithmic techniques is demonstrated by comparison of the theoretical noise predictions with experimental or known results. These predictions are achieved by writing computational code using object orientated programming techniques in the language of c++ to implement the algorithms.