The Horizon 2020 EU funded HDGAS project, which focusses on advancing Natural Gas technology for HD applications, has published its first document regarding lean burn aftertreatment systems for natural gas applications. The collaborative paper by University of East Finland, Dinex Ecocat and Ricardo has been published in Applied Catalysis B: Environmental. Applied Catalyst B: Environmental is one of the most prestigious catalyst journals.
The paper is titled “Case study of a modern lean burn methane combustion catalyst for automotive applications: What are the deactivation and regeneration mechanisms?”
The increased adoption of alternative fuel vehicles will assist in lowering CO2 emissions of the transportation sector. Natural gas is an alternative fuel which has promising characteristics as a transportation fuel, since its availability is good, and it is easy to apply with present stoichiometric and lean burn engines, which makes it ready-to-use technology. Natural gas contains mainly CH4, which has over 20 times higher greenhouse gas potential than that of CO2. Thus, overall greenhouse gas potential of the vehicle may increase if CH4 cannot be fully converted in exhaust gas after treatment system, due to its stability and requiring high temperatures for oxidation. The main concern in the long-term use of natural gas as a fuel in lean-burn engines is the sulfur poisoning of after treatment system.
Sulfur compounds originated from natural gas and lubricant oils accumulate into the catalyst in long-term use and decrease its low temperature CH4 conversion activity. It is also known, that water alone can deactivate the catalyst, whereas the joint effect with sulfur species has been proposed to accelerate the formation of inactive sulfur species.
The paper gives an alternative explanation for the joint effect of water and sulfur species on the deactivation of the catalyst, and highlights the importance of the active metal state during the regeneration without focusing only on recover in activity. The key research questions discussed are (a) how does sulfur poison the lean-burn methane oxidation catalyst, (b) how the catalyst is regenerating, and (c) what is the consequence of the repetitive regeneration? Aging and regeneration mechanism proposals for lean-burn methane oxidation catalyst were represented and discussed.
The papers shows how to regain the methane activity via regeneration mechanisms, this is crucial for automotive applications. After fully understanding the conditions the catalyst requires for regeneration, the engine and exhaust control strategy of the automotive application can provide these conditions. The temperature and exhaust gas composition can be periodically changed to allow catalyst regeneration to take place with minimal impact on fuel penalty.
Work Package 3 of the HDGAS project is devoted to the design three aftertreatment systems Euro VI emissions legislation for stoichiometric NG, lean NG and dual fuel NG + Diesel engine applications developed in other work packages, and to model the impact and the interaction of catalyst for NG applications including the impact of sulphur poisoning and ageing, as described above; next to that WP3 will specify the three catalyst systems and appropriate ageing conditions to meet Euro VI legislation and designs and delivers the stoichiometric, lean burn NG and dual fuel catalyst systems to meet Euro VI legislation. Finally calibration will take place.
At this moment in time, Dinex has started the catalyst system design activities holding discussions with the various partners responsible for the three engine variants to discuss expected flow rates and emissions levels.
Initial catalyst specification has been delivered for stoichiometric, lean burn and dual fuel engines.