In this thesis, the development and use of a transient heterogeneous 2D model for monolithic catalytic converter is presented. Study on the cold flow hydrodynamics, temperature effect and CO conversion and light off behaviour of different models is developed. Different models are studied based on different parameters such as monolith brick CPSI configuration, size of the converter, inlet cone sizing and inlet velocity of the converter. The results for both steady state and transient modes are presented in detail. It is shown that monolith brick CPSI has a significant effect on pressure drop and light-off behaviour of the converter. Also, converter size has a major effect on the performance of a converter. Inlet cone sizing showed to have a significant effect on the hydrodynamics of the converter but it did not have a major effect on light-off behaviour of the converter. / Chemical Engineering

No description available.

Student Number : 9506932W - MSc research report - School of Mechanical Engineering - Faculty of Engineering and the Built Environment / In this research project, the performance and emissions of a conventional compression ignition engine fuelled on ethanol as main fuel and dimethyl ether as ignition promoter were investigated. Tests were first conducted on diesel fuel, then on ethanol fuel with dimethyl ether and compared. All tests for both fuelling techniques were conducted at the same engine speed and injector pressure. However, engine settings with specific reference to injection timing and injector pressure were optimised to suit diesel fuel, and were left unaltered when the engine was fuelled on ethanol and dimethyl ether. The injector nozzle configuration used for diesel fuel was a standard three-hole type nozzle, whereas for ethanol fuel with dimethyl ether a standard three-hole nozzle as well as a four-hole type nozzle was used. Also investigated was the effect a catalytic converter would have on exhaust emissions, from both fuelling techniques. The performance results of ethanol/dimethyl ether fuel compared favourably to that of diesel fuel. The brake power attained for both fuelling techniques was approximately the same, however the only penalty incurred to this desired result was the simultaneous increase in the brake specific fuel consumption of ethanol/dimethyl ether fuel. The fuel conversion efficiency of ethanol/dimethyl ether fuel was also found to be lower than that of diesel fuel, this largely attributed to the difference in energy release patterns between the two fuels. The emissions results obtained showed that ethanol/dimethyl ether fuel burns cleaner, mainly due to its chemical structure containing oxygen molecules. The NOx, THC, CO and CO2 emissions, produced before the catalytic converter, of ethanol/dimethyl ether fuel were lower than those of diesel fuel. The catalytic converter further produced lower emissions, with the four-hole type nozzle producing the most desired results. In terms of catalytic converter efficiency, THC and CO emissions were more readily removed compared to NOx. In addition, virtually no smoke emissions were detected for ethanol/dimethyl ether fuel combustion.

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.

Biogas as a fuel is attractive from a greenhouse standpoint, since biogas is carbon neutral. To be used as such, increasingly stringent emission standards must be met. Current low-emission technologies meet said standards by precisely controlling the air-fuel ratio. Biogas composition can vary substantially, making air-fuel ratio control difficult. This research was conducted as part of a larger project to develop a sensor that accurately measures biogas composition. Biogas was simulated by fuel mixtures consisting of natural gas and CO2; the effects that fuel composition has on emissions and catalyst performance were investigated. Engine-out THC and NOx increased and decreased, respectively, with increasing CO2 in the fuel mixture. Doubling the catalyst residence time doubled the conversion of THC and CO emissions. The effectiveness of the catalyst at converting THC emissions was found to be dependent on the relative proportions of engine-out THC, NOx and CO emissions.

Biogas as a fuel is attractive from a greenhouse standpoint, since biogas is carbon neutral. To be used as such, increasingly stringent emission standards must be met. Current low-emission technologies meet said standards by precisely controlling the air-fuel ratio. Biogas composition can vary substantially, making air-fuel ratio control difficult. This research was conducted as part of a larger project to develop a sensor that accurately measures biogas composition. Biogas was simulated by fuel mixtures consisting of natural gas and CO2; the effects that fuel composition has on emissions and catalyst performance were investigated. Engine-out THC and NOx increased and decreased, respectively, with increasing CO2 in the fuel mixture. Doubling the catalyst residence time doubled the conversion of THC and CO emissions. The effectiveness of the catalyst at converting THC emissions was found to be dependent on the relative proportions of engine-out THC, NOx and CO emissions.

No description available.

A spark ignition engine was retrofitted to operate on biogas fuel. Biogas was synthetically generated through the mixing of various pure gases. The air-fuel ratio was accurately controlled using a closed feedback system consisting of flow controllers and a wide range oxygen sensor. A natural gas catalytic converter was implemented with the use of biogas fuel. To achieve full NOx and CO reduction the engine was required to run at a slightly rich equivalence ratio. Methane emissions posed to be the hardest to reduce across the catalyst. The biogas fuel composition had no effect on the catalyst performance. The catalyst performance was only affected by exhaust temperature and equivalence ratio. The catalyst requires tight A/F ratio control for optimal performance. A Catalytic converter can be used to reach low emissions but requires the knowledge of the biogas fuel composition.

A spark ignition engine was retrofitted to operate on biogas fuel. Biogas was synthetically generated through the mixing of various pure gases. The air-fuel ratio was accurately controlled using a closed feedback system consisting of flow controllers and a wide range oxygen sensor. A natural gas catalytic converter was implemented with the use of biogas fuel. To achieve full NOx and CO reduction the engine was required to run at a slightly rich equivalence ratio. Methane emissions posed to be the hardest to reduce across the catalyst. The biogas fuel composition had no effect on the catalyst performance. The catalyst performance was only affected by exhaust temperature and equivalence ratio. The catalyst requires tight A/F ratio control for optimal performance. A Catalytic converter can be used to reach low emissions but requires the knowledge of the biogas fuel composition.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Extensive research has gone into developing and modeling the three-way catalyst (TWC) to reduce the emissions of hydrocarbons, NOx and CO from gasoline-fueled engines level. However, much less has been done to model the use of the three-way catalyst to treat exhaust from natural gas-fueled engines. Our research address this gap in the literature by developing a detailed surface reaction mechanism for platinum based on elementary-step reactions. A reaction mechanism consisting of 24 species and 115 elementary reactions was constructed from literature values. All reaction parameters were used as found in the literature sources except for steps modified to improve the model fit to the experimental data. The TWC was simulated as a one-dimension, isothermal plug flow reactor (PFR) for the steady state condition and a continuous stirred-tank reactor (CSTR) for the dithering condition. This work describes a method to quantitatively simulate the natural gas engine TWC converter performance, providing a deep understanding of the surface chemistry in the converter. Due to the depletion of petroleum oil and recent volatility in price, synthesizing value-added chemicals from biomass-derived materials has attracted extensive attention. 1, 3-butadiene (BD), an important intermediate to produce rubber, is conventionally produced from petroleum. Recently, one potential route is to produce BD by dehydration of 2, 3-butanediol (BDO), which is produced at high yield from biomass. This reaction was studied over two commercial forms of alumina. Our results indicate acid/base properties greatly impact the BD selectivity. Trimethylamine can also modify the acid/base properties on alumina surface and affect the BD selectivity. Scandium oxide, acidic oxide or zirconia dual bed systems are also studied and our results show that acidic oxide used as the second bed catalyst can promote the formation of BD, while 2,5-dimethylphenol is found when the zirconia is used as the second bed catalyst which is due to the strong basic sites.