Dual Reductant System for Cold-Weather NOx Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing NOx reduction systems, such as SCR, face challenges with DEF freezing in cold temperatures and poor vaporization in cool exhaust streams, leading to reduced effectiveness and compliance issues with emission standards.
Innovation Solution
A dual NOx reduction system comprising a primary urea-based system and a secondary ammonia-based system, with a sensor system and electronic control module to determine operating conditions and activate the appropriate flow control modules for efficient reductant delivery, including a heating element for ammonia canister and injection into the exhaust stream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DEF is used as reductant in SCR system, then NOx reduction is achieved under normal operating conditions, but DEF freezes in cold ambient temperatures making the system inoperative
Solution Approach 1:
The system divides the reductant delivery function into two separate segments: a primary DEF-based SCR system for normal conditions and a secondary ammonia-based system for cold conditions. This segmentation allows each system to be optimized for its specific operating range, with the secondary system activated when the primary system becomes inoperative due to freezing.
Solution Approach 2:
The system changes the physical state parameter of the reductant based on temperature conditions. At cold temperatures, it switches from using liquid DEF (which freezes) to using ammonia in a different physical state that remains operational at low temperatures, thereby adapting to the harmful freezing condition.
2Reliability
If DEF is injected into cool exhaust streams, then NOx reduction is attempted, but poor vaporization leads to deposit formation and reduced effectiveness
Solution Approach 1:
The system changes the reductant selection based on exhaust temperature parameters. When exhaust temperature is below the threshold for effective DEF vaporization, the system switches to ammonia which has different vaporization characteristics suitable for cooler conditions, thereby preventing deposit formation while maintaining NOx reduction effectiveness.
3Adaptability or versatility
If a single reductant delivery system is used, then system complexity is minimized, but the system cannot operate effectively across varying temperature conditions
Solution Approach 1:
The system implements dynamic operation by using sensors to monitor temperature conditions and automatically switching between the primary DEF-based system and the secondary ammonia-based system. This dynamic adaptation allows the system to maintain effectiveness across varying temperature conditions while managing complexity through automated control rather than requiring manual intervention or overly complex mechanical designs.
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
Ensures continuous NOx reduction across varying temperature conditions, preventing DEF freezing and maintaining compliance with emission standards by activating the secondary ammonia system when primary urea-based systems are ineffective, thereby maintaining effective NOx reduction.
Implementation Method 1
a heating element coupled to the refillable canister
Implementation Method 2
an injection system connected to the tubing for injecting ammonia into the vehicle exhaust
Data Source
AI summary
An exhaust after-treatment system is described. Generally speaking, the system includes separate primary and secondary NOx reducing systems for delivering reductant (e.g. urea and ammonia) to an exhaust stream, a sensor system for determining relevant operating conditions and an electronic control module for activating the reducing systems. The two NOx reducing systems include flow control modules coupled to the electronic control module. Methods for reducing NOx in an exhaust stream are also described. Generally speaking, the methods include the steps of determining a need for NOx reduction in an exhaust stream, determining temperature of exhaust stream, and injecting at least one of a primary reductant and a secondary reductant into the exhaust stream based on the determined temperature of the exhaust stream. Typically, the primary reductant comprises urea and the secondary reductant comprises ammonia.