Urea Injection Control for SCR Catalyst NOx Reduction
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Solution Overview
Problem
Current urea injection control systems for internal combustion engines are unable to effectively control urea injection at low flow rates, particularly during engine idle conditions and deceleration, leading to inefficient NOx reduction due to ammonia storage on the SCR catalyst surface.
Innovation Solution
An exhaust aftertreatment system incorporating a NOx sensing device, ammonia sensing device, temperature sensing device, and a control module that monitors signal inputs to precisely control urea injection into the SCR catalyst, enabling both feed-forward and closed-loop dosing strategies to optimize NOx reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional urea injection control systems are used, then urea injection can be controlled at normal flow rates, but urea injection cannot be effectively controlled at very low flow rates during engine idle and deceleration conditions
Solution Approach 1:
The system employs feedback control by monitoring NOx levels downstream of the SCR catalyst and adjusting urea injection rates accordingly. The control module receives signals from NOx sensors and modifies urea dosing to maintain optimal reduction efficiency across all operating conditions, including very low flow rates during idle and deceleration.
Solution Approach 2:
The urea injection system dynamically adjusts injection rates based on real-time engine operating conditions and NOx emissions levels. The control module continuously adapts the injection strategy to match actual NOx production rates, enabling precise control from very low flow rates during idle up to higher flow rates during dynamic driving conditions.
2Duration of action of stationary object
If the SCR catalyst stores ammonia to continue NOx reduction when urea injection is not controlled, then NOx reduction can persist during transient conditions, but the stored ammonia reacts with NOx emissions on the catalyst surface to produce nitrogen, reducing overall NOx reduction efficiency
Solution Approach 1:
The system monitors NOx levels downstream of the SCR catalyst and adjusts urea injection to prevent excessive ammonia accumulation. By feedback control, the system ensures that ammonia storage does not lead to inefficient nitrogen production, maintaining optimal NOx reduction efficiency while allowing temporary persistence during transient conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves precise control of urea injection, ensuring effective NOx reduction even at low engine-out NOx emissions conditions by monitoring and adjusting urea dosing based on real-time NOx and ammonia levels, thereby enhancing the efficiency of the SCR catalyst.
Implementation Method 1
injection of urea into an exhaust gas feedstream upstream of a selective catalytic reduction ('SCR') catalytic device to cause a reduction of NOx exhaust gases to nitrogen and oxygen
Implementation Method 2
urea which has decomposed on the catalyst surface
Implementation Method 3
A urea injection control system currently in use are not capable of controlling urea injection at very low flow rates... The catalyst is able to continue NOx reduction when the urea injection control system is not capable of controlled dosing, i.e., supplying a controlled amount of urea. The stored ammonia reacts with the NOx emissions on the catalyst surface
Data Source
AI summary
An exhaust aftertreatment system and control system is provided, including a urea injecting device, a selective catalyst reduction device, and, a sensing device operative to monitor a forward portion of the selective catalyst reduction device. The sensing device can comprise a NOx sensor, and alternatively, an ammonia sensor. A control module adapted to monitor signal inputs from the engine, the NOx sensing system, the temperature sensing system, and the sensing device operative to monitor a forward portion of the selective catalyst reduction device; and, adapted to control operation of the urea injecting device.