Luenberger-Sliding Mode Observer Based Backstepping Control for the SCR System in a Diesel Engine

Yang Yang,Li Li,Zheng Zheng,Ma Ma

doi:10.3390/en12224270

Abstract

In order to keep the ammonia (NH3) slip of the downstream selective catalytic reduction (SCR) system at a low level and simultaneously achieve a high nitrogen oxide (NOX) conversion rate, a Luenberger-sliding mode observer based backstepping control method is proposed. Considering that the internal working condition of the catalyst cannot be measured by commercial sensors directly, a Luenberger-sliding mode observer is designed to estimate the ammonia concentration at the middle of the catalyst. In addition, based on the stepped distributed characteristic of the surface ammonia coverage ratio along the SCR axial direction, a backstepping control method is utilized for the SCR system, in which the SCR system is decomposed into two subsystems. Firstly, the Lyapunov function is designed to ensure the convergence of the downstream subsystem, and then the virtual control law is obtained. After that, taking the virtual control law as the tracking target of the upstream subsystem, the Lyapunov function of virtual control law is given. Finally, the actual control law of the whole closed loop system is acquired. Simulations under different conditions are conducted to investigate the effect of the proposed control method. In addition, comparisons with the traditional PID (Proportion Integration Differentiation) control are presented. Results show that the proposed method is much better than the PID control method in overshoot, setting time, and tracking error.

Highlights

Diesel engines have attracted more and more attention in recent years due to their high economy, high power, and low CO and HC emissions [1,2,3]
In selective catalytic reduction (SCR) systems, 32.5% of aqueous urea solution is injected into the tail gas pipe of the engine; urea is decomposed into ammonia, which reacts with NOx to generate N2 and H2 O
Several studies have reported that the combination of DOC (Diesel Oxidation Catalyst), diesel particle filters (DPF), and SCR has become one of the most common post-processing applications in heavy diesel engines, which can handle particulate matter (PM) and NOx simultaneously [30,31,32]

Summary

Introduction

Diesel engines have attracted more and more attention in recent years due to their high economy, high power, and low CO and HC emissions [1,2,3]. Various regulations have been legislated against diesel engine. In order to meet stringent regulations, devices such as selective catalytic reduction (SCR) systems and diesel particle filters (DPF) are installed in post-processing systems to reduce emissions. SCR refers to the use of reducing agents to selectively react with NOx in flue gas and generate non-toxic and pollution-free N2 and H2 O under the action of a catalyst. In SCR systems, 32.5% of aqueous urea solution is injected into the tail gas pipe of the engine; urea is decomposed into ammonia, which reacts with NOx to generate N2 and H2 O.

Objectives

Results

Conclusion