Exhaust Gas Purifying System with HC Generator for NOx Reduction
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Solution Overview
Problem
Conventional methods for purifying exhaust gas from internal combustion engines, particularly lean-burn engines, face challenges in effectively reducing nitrogen oxides (NOx) due to insufficient supply and utilization of reducing gases like hydrogen and carbon monoxide, leading to increased CO2 emissions and degradation of driving performance.
Innovation Solution
An exhaust gas purifying system comprising a NOx purifying catalyst and an HC generator that converts hydrocarbons in the exhaust gas into reducing gases such as acetylene, hydrocarbons with 2-5 carbon atoms, and aromatic hydrocarbons, with an oxygen concentration adjustment of 0.8-1.5 vol% to enhance NOx conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If steam reforming is used to generate hydrogen for NOx reduction, then NOx purification efficiency is improved, but high-temperature heat supply is required which increases energy consumption and cannot be sustained under low driving load conditions
Solution Approach 1:
The invention changes the temperature parameter by using a catalyst that operates effectively at lower temperatures (200-400°C) compared to conventional steam reforming requirements. This allows the system to generate hydrogen from hydrocarbons without requiring high-temperature heat supply, thereby reducing energy consumption while maintaining NOx purification efficiency.
Solution Approach 2:
The invention replaces the thermal field-based steam reforming process with a catalyst-based chemical conversion process. Instead of using high-temperature heat to drive the reforming reaction, the system uses a catalyst to facilitate hydrogen generation from hydrocarbons at moderate temperatures, substituting thermal energy with catalytic action.
2Reliability
If air-fuel ratio is shifted to rich to increase reducing agent for NOx reduction, then NOx conversion rate is improved, but unreacted hydrocarbon emission increases leading to environmental degradation
Solution Approach 1:
The invention extracts and converts harmful hydrocarbons into useful reducing agents (hydrogen and carbon monoxide) through catalytic action. Instead of allowing hydrocarbons to remain unreacted and emit harmfully, the system extracts them and transforms them into effective reducing agents that can be used for NOx reduction, thereby eliminating the harmful emission while maintaining the reducing agent supply.
Solution Approach 2:
The invention converts the harmful unreacted hydrocarbons, which would normally increase emissions, into beneficial reducing agents. By using the catalyst to convert hydrocarbons into hydrogen and carbon monoxide, the system turns what would be harmful emissions into useful substances for NOx reduction, achieving both environmental benefit and purification effectiveness.
3Reliability
If conventional NOx trap catalyst is used with excessive reducing agent, then NOx reduction is achieved, but excessive hydrocarbon release increases CO2 emission and driving performance degrades
Solution Approach 1:
The invention changes the chemical composition parameter by generating hydrogen and carbon monoxide directly from hydrocarbons through catalytic conversion. This provides a controlled source of reducing agents without the need to shift the air-fuel ratio to rich conditions, thereby avoiding excessive CO2 emission and fuel consumption while maintaining effective NOx reduction.
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 significantly improves NOx purification efficiency by generating sufficient reducing gases, reducing NOx emissions, and maintaining driving performance while minimizing CO2 emissions.
Implementation Method 1
an HC generator that is disposed upstream of the NOx purifying catalyst in the exhaust gas flow path to generate at least one of acetylene, a hydrocarbon with a carbon number of 2 to 5 other than acetylene, and an aromatic hydrocarbon from a hydrocarbon contained in an exhaust gas
Implementation Method 2
the NOx trap catalyst releases the trapped NOx to reduce to nitrogen (N2) when the air-fuel ratio is stoichiometric or rich
Data Source
AI summary
An exhaust gas purifying system (100) includes: a NOx purifying catalyst (34) that is disposed in an exhaust gas flow path (3) to purify nitrogen oxide; and an HC generator (33, 133) that is disposed upstream of the NOx purifying catalyst (34) in the exhaust gas flow path (3) to generate at least one of acetylene, a hydrocarbon with a carbon number of 2 to 5 other than acetylene, and an aromatic hydrocarbon from a hydrocarbon contained in an exhaust gas. In addition, an exhaust gas purifying method using the exhaust gas purifying system includes the step of adjusting an oxygen concentration in the exhaust gas supplied to the HC generation catalyst (33A, 133A) to 0.8 to 1.5 vol % when an air-fuel ratio is stoichiometric or rich.