Exhaust Gas Purifying Apparatus with Dual Catalysts for Lean Operation
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Solution Overview
Problem
Conventional exhaust gas purifying apparatuses for internal combustion engines face challenges in suppressing NOx emission during lean operation and fuel cut operations, leading to reduced fuel efficiency and drivability issues due to rapid air-fuel ratio changes.
Innovation Solution
An exhaust gas purifying apparatus with first and second catalysts, reducing-agent supply means, and air-fuel ratio control means, where the air-fuel ratio is controlled to a rich ratio during lean transition periods to generate reducing agents and then shifted to a lean ratio, optimizing NOx removal and reducing agent storage to minimize NOx emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the air-fuel ratio is set to a lean ratio to improve fuel efficiency, then fuel efficiency is improved, but NOx emission increases due to reduced NOx removing rate of the three-way catalyst
Solution Approach 1:
The control device stores reducing agents (ammonia or hydrocarbons) in advance during stoichiometric operation before transitioning to lean operation. This preliminary storage ensures that when lean operation begins, the reducing agents are already available to suppress NOx emissions immediately, preventing the harmful effect of increased NOx emission that would otherwise occur during lean operation.
Solution Approach 2:
The exhaust gas purification function is divided into two segments: the three-way catalyst handles purification during stoichiometric operation, while the selective reducing catalyst handles NOx removal during lean operation using stored reducing agents. This segmentation allows each catalyst to operate in its optimal condition, enabling lean operation to proceed without excessive NOx emissions.
2Use of energy by moving object
If the air-fuel ratio is rapidly changed from stoichiometric to lean ratio to extend lean operation period, then fuel efficiency is improved, but drivability deteriorates due to rapid air-fuel ratio change
Solution Approach 1:
The control device performs preliminary storage of reducing agents in the selective reducing catalyst before transitioning to lean operation. This advance preparation allows the system to smoothly transition to lean operation without rapid air-fuel ratio changes, maintaining drivability while extending the lean operation period for improved fuel efficiency.
Solution Approach 2:
The control device dynamically adjusts the air-fuel ratio transition speed based on the storage amount of reducing agents. When reducing agents are sufficiently stored, the transition to lean operation can be smoother and more gradual, maintaining drivability while still achieving fuel efficiency improvements through extended lean operation.
3Object-generated harmful factors
If the air-fuel ratio is set to a rich ratio immediately after lean operation to remove stored oxygen, then NOx emission is suppressed, but fuel efficiency decreases due to enrichment of air-fuel ratio
Solution Approach 1:
Instead of enriching the air-fuel ratio after lean operation, the control device uses reducing agents that were stored in advance during stoichiometric operation. This eliminates the need for post-lean enrichment, suppressing NOx emission without the penalty of reduced fuel efficiency associated with running rich.
Solution Approach 2:
The control device converts the previously harmful effect (stored oxygen in the catalyst causing reduced NOx removal) into a beneficial outcome by using reducing agents to actively neutralize the NOx. The reducing agents, when supplied to the selective reducing catalyst, react with stored oxygen and NOx to form harmless products, turning the problematic stored oxygen into a controlled reaction that suppresses emissions without sacrificing fuel 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
This configuration effectively suppresses NOx emission immediately after switching to lean operation, enhances NOx removal rates, and improves fuel efficiency by extending lean operation periods while maintaining drivability through gradual air-fuel ratio changes.
Implementation Method 1
a first catalyst (7), which is provided in an exhaust passage (6) of the engine, has a function of removing NOx in exhaust gases from the engine
Implementation Method 2
a second catalyst (8), which is provided downstream of the first catalyst (7), has a function of removing NOx in the exhaust gases using a reducing agent
Implementation Method 3
the second catalyst (8), which is provided downstream of the first catalyst (7), has a function of removing NOx in the exhaust gases using a reducing agent
Data Source
AI summary
An exhaust gas purifying apparatus for an internal combustion engine is provided. The apparatus includes a first catalyst and a second catalyst. The first catalyst is provided in an exhaust passage of the engine, and can remove NOx in exhaust gases from the engine when an air-fuel ratio of an air-fuel mixture burning in the engine is in the vicinity of the stoichiometric ratio. The second catalyst is provided downstream of the first catalyst, an can remove NOx in the exhaust gases using a reducing agent. An execution condition of a lean operation in which the air-fuel ratio is set to a lean air-fuel ratio which is leaner than the stoichiometric ratio, is determined. When switching the air-fuel ratio from an air-fuel ratio in the vicinity of the stoichiometric ratio to the lean air-fuel ratio, the air-fuel ratio is controlled to a rich air-fuel ratio which is richer than the stoichiometric ratio, during a lean transition period from the time the execution condition is satisfied. The air-fuel ratio is controlled to the lean air-fuel ratio after the lean transition period has elapsed.