Engine NOx Control via Reference Value Calculation
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Solution Overview
Problem
Internal combustion engines face challenges in maintaining NOx emission compliance during transient operating behaviors, such as cold starts, due to inadequate NOx conversion rates in SCR catalytic converters and inefficient control of exhaust gas aftertreatment systems, leading to increased emissions and prolonged start times.
Innovation Solution
An engine control device calculates a continuous NOx reference value based on a predetermined period to ensure compliance with NOx emission targets, adjusting fuel mixture and catalyst control to maintain target NOx levels without delaying engine start or increasing emissions, using a combination of engine and catalyst control devices to optimize NOx reduction and reducing agent consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If dynamic enrichment of the air-fuel mixture is applied during engine start-up to reduce start time, then the starting time is shortened, but the NOx content in exhaust gases increases
Solution Approach 1:
The control device performs preliminary calculations to determine a time-dependent NOx reference value before the SCR catalyst becomes active. This reference value is calculated based on the target average NOx value and the expected activation time, allowing the system to plan reducing agent injection in advance to compensate for upcoming high NOx periods.
Solution Approach 2:
The system dynamically adjusts the reducing agent injection rate based on real-time catalyst temperature and the calculated NOx reference value. The control adapts continuously to changing engine operating conditions, transitioning from a cold state with no catalytic activity to a warm state with full catalytic function.
2Object-generated harmful factors
If the SCR catalyst is used to reduce NOx emissions during cold start, then NOx conversion is attempted, but the conversion rate is insufficient due to low catalyst temperature
Solution Approach 1:
The control device continuously monitors the SCR catalyst temperature and uses this feedback to adjust the reducing agent injection strategy. When the temperature is below the activation threshold, the system calculates a compensating reducing agent amount based on the time-dependent NOx reference value, ensuring that emissions remain controlled despite low catalytic activity.
3Device complexity
If the catalyst control system responds slowly to changing operating conditions, then control simplicity is maintained, but incorrect reducing agent amounts are supplied leading to excessive NOx or NH3 in exhaust
Solution Approach 1:
The control device calculates a time-dependent NOx reference value in advance, anticipating future NOx levels based on the current catalyst temperature and expected warm-up rate. This allows the system to proactively adjust reducing agent injection before transient conditions occur, preventing both NOx and NH3 excursions.
Solution Approach 2:
The control system dynamically adjusts the reducing agent injection rate based on real-time catalyst temperature and the calculated NOx reference value. The control adapts continuously to changing engine operating conditions, transitioning from a cold state with no catalytic activity to a warm state with full catalytic function.
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 allows for compliance with NOx emission targets during transient operations without extending start times, minimizing reducing agent consumption, and improving engine efficiency by maintaining optimal NOx levels over longer periods.
Implementation Method 1
Compliance with emission limits with regard to the NOx content is made possible during thermally steady-state operation of the internal combustion engine by the provision of an SCR catalyst ('Selective Catalytic Reduction'), in which a reducing agent (usually urea) is converted.
Implementation Method 2
Often, an oxidation catalyst is also provided, which is located upstream or downstream of the SCR catalyst with respect to the direction of exhaust gas flow.
Implementation Method 3
Additionally or alternatively, an ammonia slip catalyst (ASC) can be provided downstream of and/or upstream of the SCR catalyst.
Data Source
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AI summary
An internal combustion engine (1), with an engine regulating device (3) and an exhaust gas aftertreatment device (16) with an SCR catalytic converter (4) for the reduction of at least one NOx component, and with a catalytic converter regulating device (6), wherein the engine regulating device (3) is prescribed a target value for an NOx mean value of the NOx component of the exhaust gases, which mean value results at an outlet point (7) of the exhaust gas aftertreatment device (16) in relation to a predefinable time period, and the engine regulating device (3) is configured at least in one operating mode to continuously calculate an NOx reference value for the catalytic converter regulating device (6) with consideration of NOx components which have already been emitted and the predefined target value, which reference value is selected in such a way that the predefined target value results at the outlet point of the exhaust gas aftertreatment device (16) at the end of the predefinable time period when the calculated NOx reference value of the catalytic converter regulating device (6) is fed as NOx setpoint value to the regulating means.