The Development of a NOx Reduction System during the Fuel Cut Period for Gasoline Vehicles 2019-01-1292
Generally, vehicles do not need power during deceleration. Therefore, the fuel efficiency can be improved by stopping the fuel injection in this period. However, when the fuel cut is activated, NOx is emitted immediately after fuel cut. During the fuel cut period, a large amount of fresh air flows into the catalytic converter installed on a vehicle since there is no combustion. Thus, the catalytic materials are converted into an oxidizing atmosphere. As a result, NOx purification performance of the catalyst deteriorates, and eventually NOx is emitted when combustion restarts. The quantity of NOx in this period is relatively small. However, in case of increasing fuel cuts, emission problem could arise. Therefore, in order to meet the stringent regulation such as LEV III-SULEV20 or 30, the number of fuel cuts need to be limited. The problem is that this strategy leads to a disadvantage of fuel efficiency. In order to solve this problem, in this study, the principle and process of NOx during the fuel cut period was analyzed in detail and then a new catalyst concept has been proposed, designed and tested. The new catalyst concept has functions of both TWC (three-way catalyst) and NSC (NOx Storage Catalyst). A variety of tests have been conducted to evaluate the purification performances, durability and so on. As a result, NOx emitted after fuel cut was reduced to more than 50% of conventional TWC under the same volume, density and cost(less precious metal quantity) conditions. Therefore, it is possible to increase the number of fuel cuts during FTP-75 and then an I4 LEV III-SULEV30 vehicle has an improvement to more than 2% of fuel efficiency on FTP-75 while meeting the SULEV30 NOx standard.