Abstract
Natural gas is an alternative fuel to replace partly conventional liquid fuels like diesel or gasoline to improve fuel economy (less CO2) and decrease pollutants (particulates). Mixed stoichiometric–lean combustion has been introduced as a potential way to manage without secondary diesel fuel. This study focused on catalytic methods to oxidize methane, HCs, CO and NO in lean-stoichiometric NG and lean diesel–NG exhaust gases in heavy-duty applications. Lean methane oxidation is the most challenging condition and only methane oxidation catalyst (MOC) developed for lean conditions was able to reach low methane light-off temperatures. MOC was almost as good as three-way catalyst (TWC) in stoichiometric conditions but the heavier ageing and λ oscillating conditions cause problems for MOC (no oxygen storage materials). Diesel oxidation catalysts (DOC) were very poor in TWC reactions but Pt-rich DOC is important to reach in lean higher NO2 utilized in DPF regeneration and SCR. In TWC + MOC, DOC + MOC combinations, the MOC part dominated methane oxidations due to that significant difference in their base activity for methane oxidation. The combinatory systems showed also in deactivation–regeneration cycles promising and interesting results, which can be utilized in transient, heterogeneous exhaust conditions.
Published Version
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