Low-Temperature NOx Adsorber Heating for SCR Light-Off
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Solution Overview
Problem
Diesel engines face challenges in reducing cold-start exhaust emissions due to delayed SCR catalyst light-off, leading to NOx storage capacity overload in low-temperature NOx adsorbers, resulting in NOx slip before the SCR can convert it, especially during extended low-load operations.
Innovation Solution
Implementing a method that involves heating the low-temperature NOx adsorber to expedite SCR light-off by reaching specific temperature thresholds, using supplemental heat sources like electrical heating or post-injection, and coordinating with downstream SCR and particulate filter regeneration to manage NOx storage and conversion efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LTNA stores NOx during cold start, then NOx emissions are controlled after warm-up, but the LTNA reaches its storage capacity and NOx slips past before SCR can convert it
Solution Approach 1:
The system performs preliminary heating of the LTNA using a heating element before the SCR catalyst reaches its light-off temperature. This preliminary action ensures that when NOx is released from the LTNA, the SCR catalyst is already active and can immediately convert the released NOx, preventing NOx slip during the cold start period
Solution Approach 2:
The patent introduces an intermediary heating element as a mediator between the cold LTNA and the SCR catalyst. This heating element acts as a bridge to transfer thermal energy to the LTNA, enabling controlled NOx release at the appropriate time when SCR is ready to convert it, thus resolving the timing mismatch
2Productivity
If the LTNA is heated to expedite SCR light-off, then NOx conversion efficiency improves, but additional energy is consumed for heating
Solution Approach 1:
The heating element operates periodically rather than continuously - it is activated only during cold start conditions when the SCR catalyst temperature is below light-off temperature. Once the SCR catalyst reaches operational temperature, the heating element is deactivated. This periodic operation minimizes energy consumption while maintaining high NOx conversion efficiency during the critical cold start period
Solution Approach 2:
The system changes the operational parameters of the heating element based on temperature conditions. The heating power and duration are adjusted according to the SCR catalyst temperature, applying heat only when necessary to reach the light-off threshold, thereby optimizing the balance between conversion efficiency and energy consumption
3Reliability
If post-injection of fuel is used for particulate filter regeneration, then regeneration is achieved, but fuel consumption increases and engine performance is affected
Solution Approach 1:
The system uses the existing exhaust heat and oxygen in the exhaust stream to regenerate the particulate filter, rather than introducing additional fuel. The heated exhaust gas naturally promotes oxidation of accumulated particulates in the filter, allowing the filter to self-regenerate using resources already present in the exhaust system, thus avoiding additional fuel consumption and maintaining engine performance
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 reduces NOx slip during cold starts by ensuring the SCR is operational when NOx is released from the adsorber, maintaining high NOx conversion levels and avoiding the need for post-injection fuel, which improves emission control and engine performance.
Implementation Method 1
storing exhaust NOx in a low temperature NOx adsorber (LTNA)
Implementation Method 2
heating the LTNA until an LTNA outlet temperature reaches a first threshold temperature
Implementation Method 3
converting released NOx in a downstream selective catalyst reduction (SCR) device
Implementation Method 4
heating the LTNA until an LTNA outlet temperature reaches a first threshold temperature
Data Source
AI summary
Methods and systems are provided for a low temperature NOx adsorber (LTNA). In one example, a method includes operating in a first mode, the first mode including storing exhaust NOx in an LTNA, heating the LTNA until an LTNA outlet temperature reaches a first threshold temperature, and then converting released NOx in a downstream selective catalyst reduction (SCR) device; and operating in a second mode, the second mode including heating the LTNA until the LTNA outlet temperature reaches a second threshold temperature, higher than the first threshold temperature, and converting exhaust NOx in the SCR device.