Investigation of the nitrogen oxide reduction characteristics and in-cylinder controls of the regeneration mode of a lean nitrogen oxide trap catalyst in a light-duty diesel engine

Abstract

This investigation focused on an in-cylinder control method to create a rich atmosphere inside a lean nitrogen oxide trap catalyst. The experimental procedures can be summarized as follows. To adjust to the excess air ratio λ values of 0.92 and 0.96, the air mass was fixed using a limited post-injection quantity from an engine management system, the main injection timing was slightly adjusted to create a rich atmosphere inside a lean nitrogen oxide trap catalyst in advance and the precise λ values were adjusted by regulating the post-injection timing together with the post-injection quantity calculated using the logic of the engine control unit. The results were as follows. First, the main-injection quantity was greatly reduced when a post-injection quantity was supplied. Second, it was verified that the post-injection quantity participated in generating the torque. Third, the overall efficiency was 26–63% and included a storage efficiency of 11–51%, a reduction efficiency of 56–89% and a conversion efficiency of 11–50%. Fourth, to control the lean nitrogen oxide trap catalyst temperature and its performance precisely using a small λ value, which was caused by the post-injection quantity, as the speed (r/min) increased, the air mass supply must be increased more during the rich mode than during the lean mode.