Abstract
A LNT (lean NOx trap) model coupled with EGR (exhaust gas recirculation) was developed based on the Langmuir–Hinshelwood mechanism to investigate the EGR effects on NOx adsorption pathway of LNT catalysts with temperature changed in range 150℃~550℃. Both the nitrate and nitrite adsorption paths were considered for the NOx storage process in the model as well as the spillover of stored NOx between Ba and Pt sites. The data and validation for modelling were from literatures of predecessors and our previous lean-burn gasoline engine experiment*. The model quantified the contributions of both nitrate route and nitrite route to the NOx storage with change of EGR rate (0%~30%) under raw emission atmosphere from tested gasoline engine. The model captured key feature of different trends of nitrate route and nitrite route with increasing temperature (150℃~550℃) under EGR rate varying from 0% to 25%. The LNT model provided insight of reaction mechanism for interpreting the behaviour of NOx storage with change of GER rate and temperature, which contributed to improve the NOx storage capacity when mapping EGR rate for lean-burn engine and catalyst operation strategy optimization.
Highlights
Lean NOx Trap known as NSR (NOx storage and reduction) is one of effective ways to reduce NOx emission of diesel and lean-burn engines with good fuel economy[1]
A detailed lean NOx trap (LNT) adsorption model coupled with exhaust gas recirculation (EGR) was developed based on the Langmuir–Hinshelwood mechanism, and both the nitrate and nitrite adsorption pathways were considered in the model as well as the NOx spillover steps between Ba\Pt sites
A LNT model coupled with EGR was developed based on the Langmuir–Hinshelwood mechanism to investigate the EGR effects on NOx adsorption pathway of LNT catalysts with temperature changed in range 150°C~550°C
Summary
Lean NOx Trap known as NSR (NOx storage and reduction) is one of effective ways to reduce NOx emission of diesel and lean-burn engines with good fuel economy[1]. Epling W S et al.[13] revealed that the two of major components of lean-burn engine exhaust, CO2 and H2O, compete for the same NOx adsorption sites, resulting in reduction of NOx storage capacity of LNT. Lindholm A et al.[14] through the study, Influence of H2O and CO2 on NOx storage and reduction over Pt based catalysts with hydrogen as the reducing agent, has shown that H2O and CO2 of the inlet stream lead to the formation of hydroxide and carbonate species on adsorption sites. There are few researches combining CO2 and H2O to the overall level of EGR to study detailed mechanism of its effects on LNT catalyst specific work stage such as NOx storage step under raw emission atmosphere from tested gasoline engine, though lots of researches done to study the effects of inlet components CO2\H2O on NO oxidation, NOx trap efficiency and NOx convection. Noting that there were two rows data of inlet gas composition and concentration corresponded to each EGR rate in the first column on left side, the data of above row referred to lean conditions of inlet gas composition, while the below row was belonging to rich condition. (The rest inlet gas is N2 by default)
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