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 NOx 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 NOx 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 NO2 emission reduction, and the increase of engine speed can significantly improve the efficiency of the NO2 reduction rate at 75 and 100% load. 25% opening of the EGR valve (OEV) and 50% OEV have very similar effects on the NOx reduction rate when the engine speed is at a low level. Compared with low engine speeds, increased OEV or ammonia NOx molar ratio (ANR) had a more obvious effect on the NOx reduction rate at high engine speeds. SCR combined with low valve-opening EGR had a more significant effect on the NOx 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.