SISTEMI DI TRATTAMENTO DEI GAS DI SCARICO PER MOTORI HEAVY DUTY A GAS NATURALE

The aim of this dissertation is to define an experimental procedure for three-way catalyst (TWC) characterization, for Heavy Duty Natural Gas engine applications. The oxygen storage capacity (OSC) , and the pollutants behavior upstream/downstream TWC at different air-to-fuel ratio (AFR) are deeply investigated. Experimental results are carried out from a 13-liter NG engine. First test campaign was performed by means of stationary lambda sweeps: on a defined grid of engine operative points,  values were imposed around the stoichiometric value, from 0.9 (Rich mixture) to 1.1 (Lean mixture). The output of this test is the TWC conversion efficiency evaluation for each pollutant. Second test campaign was performed by means of transient  steps, using rich-to-lean and lean-to-rich step patterns. This test returns the OSC values at different engine operative points. Finally, some guidelines have been issued in order to standardize the TWC characterization processes, valid both for fresh and aged samples. A brief description of the test facilities used for the tests is given.