Urea-SCR System Of Diesel Engine Research Articles

Analysis of deposit formation mechanism and structure optimization in urea-SCR system of diesel engine

A three-dimensional computational model of a diesel engine exhaust post-treatment system is built in the computational fluid dynamics software to simulate the deposit formation process in the mixer area of the diesel engine Urea-SCR (selective catalytic reduction) system. The SCR inlet uniformity, pressure drop in the mixer, urea solid, and three main urea by-products (biuret (biurea), CYA (cyanuric acid), and ammelide (cyanuric acid monoamide)) are investigated in the exhaust post-treatment system of the diesel engine. The results show that in the whole exhaust post-treatment system, the liquid film only appears in the mixer and nozzle areas. It is found that the production of biuret, CYA, and ammelide, which are by-products of urea decomposition, is mainly affected by the NCO− (isocyanate-group) concentration, and liquid film temperature and height. The thicker the liquid film and the smaller the rate of evaporation, the smaller the mass fraction of urea solid and the larger the mass fraction of urea decomposition by-products. According to the analysis results, the optimization scheme of the mixer is proposed, and the simulation analysis is performed. The analysis results show that the NH3 concentration uniformity at the SCR inlet increases, and the pressure drop in the mixer decreases. The deposits, such as urea solids, biuret, CYA, and ammelide decrease. Consequently, the performance of the exhaust post-treatment system is improved.

Square-root unscented Kalman filter for ammonia coverage ratio and input ammonia estimations in diesel-engine urea-SCR system

The selective catalytic reduction (SCR) is a resultful technical approach to diminish the NOx emission in the diesel-engine exhaust. And closed-loop control is of vital importance for SCR system to realize high NOx reduction and low ammonia tailpipe leakage. The input ammonia and the ammonia coverage ratio are two crucial parameters, but the cost of a sensor measuring the former is high, and the latter cannot be obtained by the sensor directly. Thus an observer based on square-root unscented Kalman filter is designed to estimate the two parameters. Meanwhile, a three-state model is established to mathematically describe the SCR system. The simulation results show that the observer can make an outstanding estimation on the state variables, and it shows strong robustness to the external interference.

A Convergence Study on the Effects of NH 3 /NOx Ratio and Catalyst Type on the NOx Reduction by Urea-SCR System of Diesel Engine

Diesel engines have important advantages over its gasoline counterpart including high thermal efficiency, high fuel economy and low emissions of CO, HC and CO2. However, NOx reducing is more difficult on diesel engines because of the high O2 concentration in the exhaust, marking general three way catalytic converter ineffective. Two method available technologies for continuous NOx reduction onboard diesel engines are Urea-SCR and LNT. The implementation of the Urea-SCR systems in design engines have made it possible for 2.5l and over engines to meet the tightened NOx emission standard of Euro-6. In this study, we investigate the characteristics of NOx reduction with respect to engine speed, load, types of catalyst and the NH3/NOx ratio and present the conditions which maximize NOx reduction. Also we provide detailed experimental data on Urea-SCR which can be used for the preparation for standards beyond Euro-6.

Numerical calculation and analysis of diesel Urea-SCR system

The urea selective catalytic reduction (Urea-SCR) system is a after-treatment device to control diesel engine emissions. On the basis of the experiment, a one-dimensional calculation model for the catalytic reduction of the engine is established. Through the one-dimensional simulation, the effect factors such as urea injection, exhaust temperature and length of catalysis converter in the diesel engine Urea-SCR system on NOx conversion efficiency are studied. This study provides a theoretical basis for the selection and matching of catalytic converters.

Experimental studies on the diesel engine urea-SCR system using a double NOx sensor system

SCR has been popularly approved as one of the most effective means for NOx emission control in heavy-duty and medium-duty vehicles currently. However, high urea dosing would lead to ammonia slip. And NH3 sensor for vehicle emission applications has not been popularly used in real applications. This paper presents experimental studies on the diesel engine urea-SCR system by using a double NOx sensor system that is arranged in the downstream of the SCR catalyst based on ammonia cross-sensitivity. It was shown that the NOx conversion efficiency rised as NH3/NOx increases and the ammonia slip started from the NH3/NOx equal to 1.4. The increase of temperature caused high improvement of the SCR reaction rate while the space velocity had no obvious change. The ammonia slip was in advance as catalyst temperature or space velocity increase and the ammonia storage reduced as catalyst temperature or space velocity increase. The NOx real-time conversion efficiency rised as the ammonia accumulative storage increase and reached the maximum value gradually. Keywords: Ammonia slip, Ammonia storage, Cross-sensitivity, Diesel engine, Selective catalytic reduction, Sensor

The characteristics of ammonia storage and the development of model-based control for diesel engine urea-SCR system

This paper investigates the characteristics of ammonia storage in actual SCR catalyst, which indicates that space velocities (SV), the exhaust temperature and NH3:NOX ratio (NSR) have different impacts on the saturated ammonia storage and saturated time. Thus, this paper proposes an embeddable SCR model consisting of a nonlinear ammonia storage model (NAS model) and a multiple variable resistance–capacitance model with time-delay (MVRC model), in order to quantify the ammonia storage and system-out NOX concentration. After that, a model-based ammonia storage control strategy was developed to strike a better balance between high NOX reduction efficiency and low ammonia slip.

Numerical Simulation to Reduce NOx of Diesel Engine Urea-SCR System

By using computational fluid dynamics and chemical reaction dynamics method, the mathematical model of SCR (selective catalytic reduction) system was established. On the basis of the verified feasibility, by CFD numerical analytical method, the reducing agent inside the catalysts concentration distribution was compared under different added urea schemes. Jet direction and the form of fuel injector were studied on the basis of the effects of reducing agent concentration distribution. The simulation result shows good agreement with the experimental data. The simulated results can be utilized in optimization design of the diesel SCR catalyst.

Study on Development of a Urea-SCR System of Diesel Engine

Aimed at the diesel engine, a selective catalytic reduction (SCR) system was developed. In this system, the urea pump is integrated with a urea tank, air and urea mix in the injector, catalyst convertor is based on vanadium. Combining with a self-developed control unit, the urea-SCR system was tested on the engine bench. The ESC experiment results indicate that the NOx emission can be reduced effectively which meets the China stage IV regulation.