Développement d'une méthode expérimentale appropriée à l'étude des adsorbants utilisables pour le contrôle des émissions d'hydrocarbures lors du démarrage à froid d'un moteur
|Abstract:||As regulations for emissions from gasoline engines become stricter, attention has been focused on the start-up phase (cold-start), when about 70-80% of total hydrocarbon (HC) emissions of an engine are released. This phase is a short period of 1-2 min prior to reaching the minimum catalyst operating temperature, around 200°C. In this thesis, the concept of single-file diffusion (in 1-D zeolites) was employed as a feasible approach to control automotive HC emissions during cold-start. This mechanism was investigated over a variety of zeolites with MTW structures for studying their trapping ability for lighter HC molecules, which are often desorbed before the three-way catalyst reaches its light-off temperature. In this thesis, a serie of ZSM-12 zeolites which different conterions (Na⁺, H⁺, Ag⁺) and with different Si/Al molar ratios (52, 64, 80) were synthesized. Temperature-programmed desorption (TPD) of ethylene and toluene, as models of light and heavy hydrocarbon molecules, was employed to screen these synthesized zeolites as potential HC traps. High heating rate desorption experiments were performed using the Phytronix Laser Diode Thermal Desorption system (S-960 LDTD) after desorption of toluene-ethylene mixture. Three heating rates which reflect the actual heating rate of the catalytic muffler have been used for the desorption process: 3, 5 and 9°C/s. For all solids considered in this study, the two HCs desorbed above 240°C. Ag-ZSM-12 was found the most appropriate HCs trapping adsorbent. Numerically, using a transient diffusion boundary value problem coupled with Fick’s law, it was possible to explain all qualitative features of the temperature dependent desorption profiles observed experimentally. Two steps must be considered, a cage to cage jumping followed by an escape from cage to gas phase. The two steps have different activation energies with EΓ> ED. For each component, both activation energies are strongly dependent on Si/Al ratio and radius of counterions. Moreover the effect of thermal vibration of the host lattice on diffusivities was also depicted.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||24 April 2018|
|Collection:||Thèses et mémoires|
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