Dual Path Aftertreatment Using Fuel-Borne Reductant
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Solution Overview
Problem
Conventional diesel engine exhaust systems require costly and complex on-board ammonia storage and injection systems for selective catalytic reduction (SCR) to reduce NOx emissions, adding weight and complexity to vehicles.
Innovation Solution
A dual path exhaust aftertreatment system that utilizes fuel as an on-board reductant, where the engine is controlled to produce separate lean and rich exhaust streams to generate ammonia, which is then used by SCR catalysts to reduce NOx, eliminating the need for ammonia storage and injection systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If on-board ammonia storage and injection systems are used for SCR, then NOx reduction is achieved, but system cost, complexity and weight increase
Solution Approach 1:
The patent extracts and eliminates the ammonia storage and injection subsystem from the conventional SCR system. Instead of storing and injecting ammonia, the system uses fuel-borne reductant injected directly into the exhaust stream, reducing system complexity while maintaining NOx reduction capability
Solution Approach 2:
The system uses the fuel already present in the exhaust stream (fuel-borne reductant) to reduce NOx, eliminating the need for separate ammonia storage and injection systems. The exhaust stream itself provides the reductant needed for the SCR reaction
2Object-generated harmful factors
If on-board ammonia storage and injection systems are used for SCR, then NOx reduction is achieved, but vehicle weight increases
Solution Approach 1:
The patent removes the heavy ammonia storage tanks and injection hardware from the vehicle, replacing them with a simpler system that uses fuel-borne reductant already present in the exhaust stream, thereby reducing vehicle weight
Solution Approach 2:
The system leverages the fuel already being burned in the engine (which appears as reductant in the exhaust) to perform NOx reduction, eliminating the need for additional weight from ammonia storage systems
3Quantity of substance
If dual path aftertreatment system with separate lean and rich exhaust streams is used, then ammonia is generated for SCR, but system complexity increases
Solution Approach 1:
The patent divides the exhaust stream into two separate paths: one for lean operation (producing NOx) and one for rich operation (producing ammonia). This segmentation allows independent optimization of each path while maintaining overall system functionality
Solution Approach 2:
Different regions of the exhaust system are given different characteristics - the lean path is optimized for NOx production while the rich path is optimized for ammonia generation through fuel-borne reductant injection, allowing each path to perform its specific function efficiently
4Use of energy by moving object
If lean operation is maximized for fuel economy, then fuel efficiency improves, but NOx emissions increase
Solution Approach 1:
The system alternates between lean and rich operation modes in different exhaust paths, allowing the lean path to maximize fuel economy while the rich path periodically generates ammonia that is then used to reduce NOx from the lean path exhaust
Solution Approach 2:
By segmenting the exhaust system into lean and rich paths, the patent allows the lean path to operate at high efficiency for fuel economy while the rich path handles NOx reduction through ammonia generation, separating the conflicting requirements
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 emissions without the need for ammonia storage or injection systems, simplifying the system, reducing weight and cost, and improving fuel economy by maximizing lean operation and ammonia generation for efficient SCR catalyst operation.
Implementation Method 1
selective catalytic reduction (SCR). SCR provides a method for removing NOx from an exhaust stream through use of an SCR catalyst that facilitates a reaction between the exhaust gas, ammonia and NOx to produce water vapor and nitrogen gas
Implementation Method 2
enabling the oxidation catalyst to oxidize HC and CO that are present in the respective combined exhaust gas streams from the respective rich exhaust gas streams
Implementation Method 3
the second NOx storage and reduction catalyst facilitates a reaction with stored NOx and the rich second exhaust gas stream to regenerate the second NOx storage and reduction catalyst and generate ammonia
Data Source
AI summary
A system and method for utilizing fuel as an on-board reductant for selective catalytic reduction of NOx is provided and includes a controller for controlling an engine to produce a lean first exhaust stream and a rich second exhaust stream that are received in respective first and second passageways of a dual path aftertreatment system. The rich second exhaust stream reacts with NOx stored in a NOx storage and reduction catalyst of the second passageway to regenerate this catalyst and generate ammonia. The first exhaust stream and the second exhaust stream having the generated ammonia are combined in a downstream common passageway to form a combined lean exhaust gas stream where the ammonia carried therein is stored or used by an SCR catalyst of the common passageway for NOx reduction. The engine is subsequently controlled to produce a rich first exhaust stream and a lean second exhaust stream.