Passive NOx Adsorber Cold-Start Emission Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for controlling NOx emissions during cold-starts in diesel vehicles are inefficient due to the inability of oxidative catalysts to store NOx, leading to NOx slipping through the SCR catalyst without conversion, especially at cool operating temperatures.
Innovation Solution
A method involving a passive NOx adsorber (PNA) and SCR catalyst system, where NOx is stored and released at specific temperatures to maintain an optimal NOx species ratio upstream of the SCR catalyst, adjusting EGR rate and fuel injection timing based on NOx loading and release to enhance conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an oxidative catalyst is used to control NOx emissions, then NOx conversion is facilitated, but the catalyst cannot store NOx leading to NOx slipping through during cold-starts
Solution Approach 1:
The PNA performs preliminary NOx storage during the cold-start phase before the SCR catalyst reaches light-off temperature. By adsorbing NOx on the PNA upstream of the SCR catalyst, the system prepares for subsequent NOx conversion once optimal temperature conditions are achieved, preventing NOx slip during the critical cold-start period.
Solution Approach 2:
The PNA acts as an intermediary component between the engine exhaust and the SCR catalyst. It temporarily holds NOx species and releases them when the SCR catalyst is ready, mediating the timing mismatch between NOx generation and catalytic conversion capability during cold-start conditions.
2Object-generated harmful factors
If exhaust flow is regulated away from the oxidative catalyst to control NOx ratio, then NOx availability at the catalyst is controlled, but conversion efficiency decreases during cool operating temperatures
Solution Approach 1:
The PNA performs preliminary NOx storage during the cold-start phase before the SCR catalyst reaches light-off temperature. By adsorbing NOx on the PNA upstream of the SCR catalyst, the system prepares for subsequent NOx conversion once optimal temperature conditions are achieved, preventing NOx slip during the critical cold-start period.
Solution Approach 2:
The PNA acts as an intermediary component between the engine exhaust and the SCR catalyst. It temporarily holds NOx species and releases them when the SCR catalyst is ready, mediating the timing mismatch between NOx generation and catalytic conversion capability during cold-start conditions.
3Device complexity
If the SCR catalyst is used without PNA during cold-starts, then the system is simpler, but NOx slips through without conversion at cool temperatures
Solution Approach 1:
The PNA performs preliminary NOx storage during the cold-start phase before the SCR catalyst reaches light-off temperature. By adsorbing NOx on the PNA upstream of the SCR catalyst, the system prepares for subsequent NOx conversion once optimal temperature conditions are achieved, preventing NOx slip during the critical cold-start period.
Solution Approach 2:
The PNA acts as an intermediary component between the engine exhaust and the SCR catalyst. It temporarily holds NOx species and releases them when the SCR catalyst is ready, mediating the timing mismatch between NOx generation and catalytic conversion capability during cold-start conditions.
4Object-generated harmful factors
If EGR rate and fuel injection timing are adjusted based on PNA storage and release, then NOx species ratio is maintained for optimal conversion, but control system complexity increases
Solution Approach 1:
The control system continuously monitors PNA storage and release states through exhaust gas composition sensors and adjusts EGR rate and fuel injection timing accordingly. This feedback mechanism maintains the optimal NOx species ratio (NO:NO2) upstream of the SCR catalyst, ensuring maximal conversion efficiency while adapting to varying engine operating conditions and PNA saturation levels.
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 improves NOx conversion to non-polluting forms like N2 by maintaining a specific NOx species ratio, reducing vehicle emissions during cold-starts by ensuring optimal catalytic conversion conditions are met.
Implementation Method 1
a passive NOx adsorber (PNA) and a SCR catalyst in the exhaust passage. The method comprises: adjusting one of a fuel injection timing and an EGR rate based on the storage on and release of NOx from a passive NOx adsorber (PNA)
Implementation Method 2
after adsorbing NO, the PNA may oxidize the NO such that the primary species is NO2, stored as nitrates
Implementation Method 3
Nitrogen oxides such as NO and NO2, referred to collectively as NOx, are common constituents of emissions in the exhaust gas of diesel engines. The levels of these pollutants are controlled to meet emissions standards by reducing them to nitrogen gas at a selective catalytic reduction catalyst (SCR catalyst) that uses injected urea or ammonia as a reductant.
Implementation Method 4
reducing them to nitrogen gas at a selective catalytic reduction catalyst (SCR catalyst)
Data Source
AI summary
Methods and systems are provided for reducing engine cold-start emissions. An exhaust system having a passive NOx adsorber (PNA) may store NOx during an engine cold-start until conditions are optimal for release of the stored NOx to a downstream SCR catalyst. Based on PNA conditions, including a NOx load and a PNA bed temperature, adjustments to EGR rate and/or injection timing may be made to achieve a catalytically favorable ratio of NOx species upstream of the SCR catalyst, after the SCR catalyst has reached its light-off temperature.