Dual NOx Catalyst System for Lean Combustion Exhaust
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Solution Overview
Problem
Internal combustion engines fueled by ammonia face challenges in efficiently removing nitrogen oxides (NOX) from exhaust gases, particularly when operating under lean air-fuel ratios, which reduces the effectiveness of three-way catalysts in NOX removal.
Innovation Solution
The implementation of an internal combustion engine with an ammonia feeder and a dual NOX selective reduction catalyst system, featuring an upstream catalyst with zeolite carrying iron and a downstream catalyst with zeolite carrying copper, optimized to maintain a specific ammonia-to-NOX concentration ratio for enhanced NOX removal, allowing for lean combustion without compromising purification performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a three-way catalyst is arranged in the engine exhaust passage to remove NOX, then the NOX removal rate is improved, but precise control of the air-fuel ratio at stoichiometric conditions becomes necessary, increasing system complexity
Solution Approach 1:
The patent changes the operating parameter from stoichiometric air-fuel ratio to lean air-fuel ratio, and simultaneously changes the catalyst type from three-way catalyst to NOX selective reduction catalyst. This parameter change allows the system to achieve NOX removal without requiring precise stoichiometric control, thus resolving the contradiction between NOX removal rate and control complexity
Solution Approach 2:
The NOX selective reduction catalyst is designed to function effectively under lean combustion conditions, serving both the NOX removal function and being compatible with fuel-efficient lean operation. This multi-functionality allows the system to achieve both NOX purification and improved fuel economy without requiring separate systems for each function
2Loss of energy
If the air-fuel ratio is made lean to improve heat efficiency and reduce fuel consumption, then fuel economy is improved, but the NOX removal rate of the three-way catalyst becomes lower
Solution Approach 1:
The patent changes the catalyst type parameter from three-way catalyst to NOX selective reduction catalyst, which is specifically designed to maintain high NOX removal rates under lean air-fuel ratio conditions. This allows the system to operate in the lean regime for improved fuel economy while still achieving effective NOX removal
Solution Approach 2:
The NOX selective reduction catalyst acts as an intermediary that enables the compatibility between lean combustion and NOX removal. It mediates the chemical reactions to reduce NOX effectively even when the air-fuel ratio is lean, thus allowing both fuel efficiency and emission control to be achieved simultaneously
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 achieves high NOX and ammonia removal rates across various operating conditions, eliminating the need for precise stoichiometric air-fuel ratio control and improving overall exhaust purification efficiency.
Implementation Method 1
an upstream side NOX selective reduction catalyst which is arranged in an engine exhaust passage and which selectively reduces the NOX by the feed of a reducing agent constituted by ammonia
Implementation Method 2
a downstream side NOX selective reduction catalyst which is arranged downstream of the upstream side NOX selective reduction catalyst in the engine exhaust passage and which selectively reduces the NOX by the feed of a reducing agent constituted by ammonia
Implementation Method 3
The downstream side NOX selective reduction catalyst has an ammonia oxidation ability which is larger than the upstream side NOX selective reduction catalyst
Data Source
AI summary
The internal combustion engine has an upstream side NOx selective reduction catalyst and a downstream side NOx selective reduction catalyst which are arranged in an engine exhaust passage. The upstream side NOx selective reduction catalyst has a region where the NOx removal rate becomes substantially constant when the ratio of concentration of ammonia to NOx of the inflowing exhaust rises. The internal combustion engine has an operating state in that region where the ratio of concentration of ammonia to NOx is maintained. The downstream side NOx selective reduction catalyst has an ammonia oxidation ability which is larger than the upstream side NOx selective reduction catalyst.