Experimental Research on Aftertreatment SCR Sizing Strategy for a Nonroad Mid–Range Diesel Engine

Abstract

Urea-Selective Catalytic Reduction (SCR) is widely used to reduce nitrogen oxide (NOx) emissions. This paper presents a comprehensive experimental research work on aftertreatment emissions of NOx and ammonia (NH3) slip for three aftertreatment concepts by introducing the SCR sizing strategy on a 6-cylinder mid-range non-exhaust gas recirculation (EGR) diesel engine to meet China non-road Stage IV regulation limits. It can be observed that the three concepts could meet the regulation limits for NOx emissions and NH3 slip by selecting the appropriate length. There is little effect on emission results during a non-road transient cycle (NRTC) when the aftertreatment inlet/outlet with insulation and without insulation and the emission results on both strategies could meet non-road China Stage IV regulation limits. It is recommended to select Concept 2 which could meet regulation requirements considering multiple factors in the SCR sizing strategy. Substrate impact and NH3/NOx molar ratio (ANR) impact are investigated based on Concept 2. The results show that by applying the SCR substrate aftertreatment with a cell density of 600 cpsi, NOx conversion capability is stronger than that with cell density 400 cpsi for the same SCR size. Current dosing strategy is capable and recommended ANR is 0.9–1.1 if considering dosing strategy optimization. The methodology in this study provides an effective guidance and reference for future aftertreatment SCR sizing strategies in real applications.

Thermal Management of Diesel Engine Aftertreatment System Based on Ultra-Low Nitrogen Oxides Emission

“…At lower exhaust temperatures, the NH 3 -NO x reactions were hindered by the low temperature, which is consistent with the article mentioned in [8]. As exhaust temperature increases, the NO x conversion rate gradually increases from 87.07% at 200 • C to 97.81% at 260 • C. Longer SCR carriers can also increase the NH 3 -NO x reaction rate at steady working points at the cost of higher capital cost and ammonia chemical loss, as mentioned in [10].…”

“…As exhaust temperature increases, the NOx conversion rate gradually increases from 87.07% at 200 °C to 97.81% at 260 °C. Longer SCR carriers can also increase the NH3-NOx reaction rate at steady working points at the cost of higher capital cost and ammonia chemical loss, as mentioned in [10]. 2.…”

“…The application of thermal management increased the average exhaust temperature, which increased the NH3-O2 reaction rate in SCR. The urea input shall be adjusted properly to avoid NOx emission during the latter part of WHTC, as mentioned in [10]. From 1500 to 1800 s, there was a significant difference in nitrogen oxide emissions between the EAT system with LO-SCR and the conventional arrangement system of 1500~1600 s. The increase in average exhaust temperature caused by thermal management increases the reaction rate between ammonia and oxygen, resulting in the increase in the ammonia chemical loss.…”

“…Gholami et al [9] reviewed different NO x emission-reduction technologies and introduced the chemical reaction mechanism of NH 3 -SCR (standard SCR) under aerobic and anaerobic conditions. Xie et al [10] conducted experimental research on the NO x conversion efficiency and NH 3 leakage of three aftertreatment schemes by introducing SCR size strategies. Xie used postprocessing systems with different SCR lengths of the same SCR diameter and found that the nitrogen oxide emissions of the three SCR systems were similar, but the average NH 3 leakage varied greatly.…”

“…The application of thermal management increased the average exhaust temperature, which increased the NH 3 -O 2 reaction rate in SCR. The urea input shall be adjusted properly to avoid NO x emission during the latter part of WHTC, as mentioned in [10].…”