The Development of a NOx Reduction System during the Fuel Cut Period for Gasoline Vehicles 2019-01-1292
In general, vehicles do not need to make power from engines in deceleration periods. Therefore, fuel cut-off mode can be applied in these periods to improve fuel efficiency.
However, during the fuel cut-off periods, a large amount of fresh air flows from the engine into the catalytic converter equipped with the car because there is no combustion. So, the catalytic materials in the converters are changed into oxidized atmosphere. Eventually the efficiency for the NOx purification of catalytic converter rapidly deteriorates and catalytic converters cannot purify the NOx emitted immediately after the fuel cut-off. So, the conditions of fuel-cut off entries have no choice but to be strict for the cars which should meet stringent regulations such as SULEV 30.
This strategy is not good for fuel efficiency. In this study, NOx emission process at this period was analyzed microscopically. Additionally, in order to reduce it, new concept of catalyst had been developed. This new catalyst material has the functions of both TWC (Three way catalyst) and LNT (Lean NOx trap). This is capable of purifying the NOx after fuel cut-off by using the LNT’s function while sustaining the TWC’s purification performance. NOx purification after fuel cut-off of this is based on LNT of diesel. Thus, the new catalytic convertor has to be equipped with UCC (Underfloor Catalytic Convertor). The purification abilities depend on UCC temperature on car and the temperature is not constant. So, it is necessary that this be positioned in appropriately to meet the corresponding regulation. In Conclusion, it was verified that approximately 2% of fuel efficiency was improved at FTP-75 mode compared with a conventional SULEV vehicle by increasing the number of fuel cut-offs.
Muyoung Choi, Jinwoo Song, Eunsang Lee, Sangjin Ma, Sangmin Lee, Jungmin Seo, Seungbeom Yoo, Jun LEE
Hyundai Motor Company, Heesung Catalysts