Urea Injection Control for SCR Catalyst Temperature Management
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Solution Overview
Problem
Existing SCR systems for nitrogen oxide reduction in vehicles face inefficiencies in urban driving conditions due to low exhaust gas temperatures, leading to insufficient urea injection and ammonia storage issues, which result in incomplete nitrogen oxide conversion and ammonia degassing.
Innovation Solution
A method that dynamically manages urea injection by measuring exhaust gas temperature, activating a heating mode when necessary to maintain optimal reaction conditions, and controlling ammonia storage to ensure efficient conversion of nitrogen oxides while minimizing fuel consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If urea injection is restricted to high temperature conditions only, then urea decomposition and SCR reaction efficiency are improved, but nitrogen oxide conversion is insufficient during low temperature urban driving phases
Solution Approach 1:
The system performs preliminary heating of the exhaust stream using a heating element before the SCR catalyst during cold start-up phases. This preliminary action raises the temperature above the minimum threshold, enabling urea decomposition and SCR reactions to occur effectively during low-temperature urban driving conditions, thus resolving the contradiction between maintaining high conversion efficiency and adapting to cold operating conditions
2Reliability
If continuous heating is applied to maintain minimum temperature, then urea injection capability is ensured, but fuel consumption increases significantly
Solution Approach 1:
The heating element is activated periodically or on-demand based on detected temperature conditions rather than continuously. The control system monitors exhaust temperature and activates heating only when below the minimum threshold, turning it off when the threshold is reached. This periodic action maintains urea injection reliability while minimizing unnecessary energy consumption during normal operating conditions
3Productivity
If ammonia storage in catalyst is increased to ensure reduction capability during cold phases, then nitrogen oxide conversion is improved, but ammonia degassing occurs causing odor and irritation issues
Solution Approach 1:
The system continuously monitors exhaust gas temperature and adjusts urea injection and heating operations accordingly. During cold phases, the feedback control activates heating to maintain temperature thresholds, enabling effective SCR reactions without requiring excessive ammonia storage. This feedback mechanism prevents ammonia saturation and subsequent degassing while maintaining nitrogen oxide conversion capability
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
This approach optimizes nitrogen oxide conversion in both hot and cold phases, reducing ammonia degassing and fuel consumption by strategically activating the heating mode based on ammonia storage levels and vehicle parameters, ensuring compliance with emission standards.
Implementation Method 1
an activation of an exhaust gas heating mode is commanded
Implementation Method 2
the treatment consisting in chemically reducing, in a catalyst, called SCR catalyst, the nitrogen oxides by adding ammonia contained in the urea
Implementation Method 3
a first pyrolysis reaction (NH 2 ) 2 CO -> HNCO + NH 3
Implementation Method 4
then a hydrolysis reaction HNCO + H 2 O -> CO 2 + NH 3
Data Source
Figure 1
Figure 2a~2b
Figure 3~4
AI summary
The invention relates to a process for controlling the injection of urea in a selective catalytic reduction, known as CR, system for treating nitrogen oxides, intended to be installed in the exhaust line (6) of a motor vehicle (1) engine (2), wherein the treatment comprises chemically reducing, in a catalyst (3), known as SCR catalyst, the nitrogen oxides by adding ammonia contained in urea, the process comprising the following steps: - the temperature of the gases in the exhaust line (6) of the engine (2), upstream of the SCR catalyst (3), is measured, - if the temperature measured is above a predetermined minimum value, called minimum injection temperature, an order is given to inject urea (5), - if the temperature measured is below the minimum injection temperature, the following substeps are carried out: - a mass of ammonia stored in the SCR catalyst (3) is determined, - the amount of ammonia required to obtain a nitrogen oxide conversion greater than a predetermined value is determined, if the mass of ammonia stored in the catalyst is below this required amount, an order is given to activate a method of heating the exhaust gases, and to inject urea into the system.