Dual-Stage Catalyst System with Intercooling for NOx Reduction
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Solution Overview
Problem
Existing exhaust aftertreatment systems for internal combustion engines fail to effectively reduce particulate matter, volatile hydrocarbon condensables, and nitrogen oxide emissions, particularly due to high operating temperatures causing NOx reformation and the inability to treat ammonia, while also requiring costly and space-intensive heat exchanger installations.
Innovation Solution
A dual-stage exhaust aftertreatment system incorporating a first catalytic converter, an oxidation catalyst with a storage catalyst, an exhaust gas intercooler, and a gas particulate filter, utilizing parallel radiator cooling fluid circuits to cool exhaust gases and introduce compressed air to enhance oxygen concentration and particulate filtration, thereby reducing emissions and NOx levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high temperature operation is used in catalytic converters, then catalytic activity and conversion efficiency are improved, but NOx reformation occurs and emissions control deteriorates
Solution Approach 1:
The exhaust aftertreatment system is divided into multiple catalytic converters with different functions: a first catalytic converter that operates at high temperature for general emission control, and a second catalytic converter specifically designed for NOx reduction at lower temperatures. This segmentation allows each converter to operate in its optimal temperature range, preventing NOx reformation while maintaining overall conversion efficiency.
Solution Approach 2:
An intercooler is introduced as an intermediary component between the first and second catalytic converters. The intercooler reduces the temperature of exhaust gases from the first converter before they enter the second converter, creating a thermal bridge that enables the second converter to effectively reduce NOx without causing reformation.
2Object-generated harmful factors
If multiple heat exchangers are installed for cooling exhaust gases, then emissions control is improved, but system cost and space requirements increase
Solution Approach 1:
The intercooler is designed to serve multiple functions: it cools exhaust gases for the second catalytic converter, condenses volatile hydrocarbon condensables, and can integrate with the vehicle's existing radiator cooling system. This multi-functionality reduces the need for separate dedicated heat exchangers, lowering system cost and complexity while maintaining effective emissions control.
3Productivity
If volatile hydrocarbon condensables remain in gaseous phase, then they escape filtration, but they form additional particulates downstream
Solution Approach 1:
The intercooler is specifically designed to condense volatile hydrocarbon condensables from the gaseous phase to the liquid phase by cooling the exhaust gases. This phase transition occurs before the exhaust enters the catalytic converters, allowing the condensables to be captured in the oil separator and preventing them from forming additional particulates downstream while maintaining filtration efficiency.
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
The system effectively condenses gaseous hydrocarbons into liquids, captures particulates, and reduces NOx emissions by storing ammonia for reaction with nitrogen oxides, improving emissions control and reducing the need for additional heat exchangers.
Implementation Method 1
an exhaust gas intercooler in thermal communication with the exhaust in the exhaust conduit, the exhaust gas intercooler configured to lower a temperature of the exhaust to about 350° F. to about 500° F.
Implementation Method 2
The system effectively condenses gaseous hydrocarbons into liquids
Implementation Method 3
catalytic converters, such as three-way catalytic (TWC) converters, to convert gaseous CO, NOx, and CxHy into less harmful compounds through oxidation and reduction reactions
Implementation Method 4
an oxidation catalyst comprising a storage catalyst... storing ammonia for reaction with nitrogen oxides
Implementation Method 5
a gas particulate filter... captures particulates
Data Source
AI summary
An exhaust aftertreatment system includes a first catalytic converter, an oxidation catalyst including a storage catalyst, an air injector, and a cooling unit. The exhaust aftertreatment system is fluidly coupled to an output of a spark-ignited internal combustion engine that operates in the rich regime during acceleration and the lean regime during deceleration. In one aspect, the storage catalyst stores ammonia produced while the engine operates in the rich regime. The stored ammonia reacts with nitrogen oxide compounds produced when the engine operates in the lean regime. In another aspect, the nitrogen oxide compounds react with ammonia produced while the engine operates in the rich regime.