F2010A023
Feasibility Study of NOx Reduction with the Active Exhaust Control System when Engine Starting
In recent years emission regulations have become more stringent as a result of increased environmental awareness in each region of the world. While gasoline engines typically use three-way catalysts to improve emmissions, this approach is not possible for diesel engines. As a result NOx emission reduction is a difficult challenge for diesel engines. To respond to these strict regulations, exhaust gas after-treatment systems for diesel engines have been developed. These systems typically feature lean NOx catalyst (LNC) which uses a characteristic chemical reaction mechanism to reduce NOx. [1][2][3] The LNC system reduces NOx through a selective catalytic reduction (SCR) with ammonia, in which NOx adsorbed on the catalyst during lean mixture condition is converted to ammonia during rich mixture condition and reduced in the subsequent lean mixture condition. Thus, the LNC system allows for effective reduction of NOx. However, NOx reduction is still difficult for the LNC system in a cold start situation (immediately after the diesel engine is started). In order to reduce NOx in this situation, various developments are progressing. These include engine combustion control for short time after engine start until the catalyst reaches activation temperature, catalyst material which can be activated at lower temperature, etc.
As an alternative to the approaches described above, this report examines the possibility of a new after-treatment system for exhaust gas, especially NOx. This system combines a fuel reformer with a De-NOx converter containing NOx-adsorption material which acts at low temperature, and a LNC converter is equipped downstream. Experiments on this improved LNC system were conducted, and the possibility of NOx reduction immediately after engine start was verified. The experimental system is shown in Fig. 1. Immediately after engine start, the fuel reformer begins to manufacture a reducing agent in which the main ingredients consist of hydrogen and carbon monoxide and introduces it into the exhaust line. Simultaneously the De-NOx converter begins to adsorb NOx at low temperature. After LNC is activated, introduction of reformed gas is stopped, and the desorbed NOx on the De-NOx converter is reduced by the LNC system operation. Through this experiment, it was clearly shown that NOx discharged in early stages of engine start could be fully reduced through the use of these new technologies added to the LNC system (Fig. 2).
This abstract is supplemented by a PDF, which can be viewed here.
Session: Consumption and Emission Reduction