Effect of Exhaust Gas Recirculation Combined with Selective Catalytic Reduction on NO_x Emission Characteristics and Their Matching Optimization of a Heavy-Duty Diesel Engine

Abstract

Exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) have become important technologies to reduce the NO x emission of heavy-duty diesel engines and meet the increasingly stringent emission regulations. This paper studied the effect of EGR combined with SCR on the NO x emission characteristics of a heavy-duty diesel engine based on the engine bench test. The results showed that the NO reduction rate of EGR-coupled SCR increased with the increase of engine load, and the effect was no longer significant when the NO reduction rate exceeded a certain limit under the same working conditions. EGR combined with SCR has little effect on NO 2 emission reduction, and the increase of engine speed can significantly improve the efficiency of the NO 2 reduction rate at 75 and 100% load. 25% opening of the EGR valve (OEV) and 50% OEV have very similar effects on the NO x reduction rate when the engine speed is at a low level. Compared with low engine speeds, increased OEV or ammonia NO x molar ratio (ANR) had a more obvious effect on the NO x reduction rate at high engine speeds. SCR combined with low valve-opening EGR had a more significant effect on the NO x reduction rate. The increase of OEV led to the increase of fuel consumption rate, but the effect on the fuel consumption rate decreased gradually with the increase of diesel engine speed. Meanwhile, this study optimized the matching relationship between OEV and ANR based on the data of the genetic algorithm, which provides a theoretical research method and application basis for diesel engine-matching of EGR and SCR.

Experimental Study on NOx Reduction of Diesel Engine by EGR Coupled with SCR

“…The results showed that NO x conversion efficiency was improved by intake or exhaust throttling or post injection at any altitudes. Lou et al 21 studied the effect of EGR combined with SCR on the NO x emission characteristics of a heavy-duty diesel engine based on the engine bench test. The results showed that the NO reduction rate of EGR-coupled SCR increased with the increase of the engine load, and the effect was no longer significant when the NO reduction rate exceeded a certain limit under the same working conditions.…”

Study on Diesel Engine Selective Catalytic Reduction Performance at Different Atmospheric Pressures Using the Response Surface Method

“…Yue et al 10 studied the influence of ammonia-saturated storage level on SCR performance through experiments, and the results showed that when ammonia saturated storage level was 68.2–73%, the NO x conversion efficiency was the best. Lou et al 11 studied the influence of EGR opening and ammonia-to-nitrogen ratio matching on SCR performance through bench tests combined with genetic algorithm. The results showed that increasing the EGR opening or the ammonia-to-nitrogen ratio could significantly improve NO x conversion efficiency at high speed, and the increase of the EGR opening had little impact on fuel consumption at high speed.…”

A Preliminary Study of a Multifunctional DOC/Wet-Scrubber Capable to Reduce both Chemical and Acoustic Emissions in Marine Field

“…EGR recirculates a portion of the exhaust gas into the engine's combustion chamber, lowering its internal temperature. As a result, NOx emissions are reduced, however causing an increase in fuel consumption and engine efficiency characteristics (Huang et al, 2022;Lou et al, 2022). Therefore, it is preferred to limit the EGR ratio and use other techniques such as the SCR.…”