Next Generation All in One Close-Coupled Urea-SCR System 2015-01-0994

Diesel engines provide a solution for the reduction of carbon dioxide (CO₂) from motor vehicles. For diesel engines, however, technology to reduce nitrogen oxide (NOx) emissions is essential. This report focuses on Urea - Selective Catalytic Reduction (SCR) as an aftertreatment system for NOx reduction.

The NOx conversion performance of SCR catalyst depends on exhaust gas temperature and the NO₂/NO_X ratio. In order to raise the NO₂/NO_X ratio, it is essential to raise the temperature of oxidation catalyst. For these purposes, it is necessary to raise the temperature of oxidation catalyst and SCR catalyst to high level in order to enhance NOx conversion. Temperature rising is implemented by in-cylinder fuel injection (post-injection). Consequently, degraded fuel economy becomes an issue at low vehicle speeds that cannot be expected to raise the temperature in catalyst, and particularly in the case of conventional SCR system that is located under the vehicle floor (Under-Floor SCR: UF/SCR). As one technology, a diesel particulate filter (DPF) that is close-coupled to the engine coated with SCR catalyst (SCR coated on DPF : SCR/F) has been proposed to address this issue so that the SCR catalyst temperature will be higher, and therefore reducing the fuel penalty. The present research considered ways to enhance the performance of the hardware element technology of such an SCR/F system, and this paper reports on the results.

As a result, after the characteristics of the element technologies of the SCR/F system had been ascertained, SCR catalyst was added and mixer specifications were improved so as to create a system that combined all the elements in a single converter. This effort successfully identified specifications that enhance NOx conversion performance while finding a balance with soot combustion performance and pressure loss characteristics.