Vehicle Exhaust Purification System with Pd-Rh Catalysts for Cold Start NOx Reduction
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Solution Overview
Problem
Conventional exhaust gas purification systems for gasoline engines, particularly three-way catalytic converters, face challenges in effectively removing nitrogen oxides at low temperatures during engine startup, leading to significant emissions of unburned NOx, which complicates compliance with environmental regulations and fuel efficiency standards.
Innovation Solution
An exhaust gas purification system comprising a housing with a palladium (Pd) catalyst for oxidizing hydrocarbons and occluding nitrogen oxides as the front end catalyst, a rhodium (Rh) catalyst for reducing nitrogen oxides as the rear end catalyst, and a controller that adjusts the air-fuel ratio based on exhaust gas temperature and vehicle speed to optimize NOx removal, especially during cold starts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-way catalytic converter is used for exhaust gas post-treatment, then nitrogen oxides can be removed effectively at high temperatures, but nitrogen oxide removal efficiency deteriorates significantly in cold state at engine startup
Solution Approach 1:
The patent applies parameter changes by switching the air-fuel ratio control strategy based on exhaust gas temperature. In cold state (below light-off temperature), the controller enriches the air-fuel ratio to create fuel-rich conditions that promote NOx reduction. When the engine warms up, the system transitions to lean burn mode. This dynamic parameter adjustment allows the TWC to effectively remove NOx across different temperature conditions.
Solution Approach 2:
The patent implements dynamics by making the air-fuel ratio control adaptive rather than static. The controller continuously monitors exhaust gas temperature and vehicle operating conditions, dynamically adjusting the air-fuel ratio to optimize TWC performance. This includes alternating between fuel-lean and fuel-rich conditions to maintain effective NOx removal as the system transitions from cold to warm operation.
2Loss of energy
If the air-fuel ratio is controlled to be fuel lean to improve fuel efficiency, then fuel economy improves, but nitrogen oxide removal performance deteriorates in high load region
Solution Approach 1:
The patent applies periodic action by alternating the air-fuel ratio between lean and rich conditions. The controller periodically switches between fuel-lean mode (for fuel efficiency) and fuel-rich mode (for NOx removal) based on operating conditions. This periodic switching allows the TWC to accumulate reducing agents during rich periods and utilize them during lean periods for effective NOx reduction, thereby maintaining both fuel efficiency and NOx purification performance.
3Productivity
If conventional three-way catalyst with periodic lean-rich alternation is used, then fuel efficiency regulation can be satisfied, but 60% or more of total nitrogen oxides are exhausted through tail pipe in cold state
Solution Approach 1:
The patent applies preliminary action by preparing the TWC system for effective NOx removal before cold engine operation. The controller pre-conditions the catalyst by controlling the air-fuel ratio to ensure adequate reducing agents are available when the engine starts. This preliminary preparation allows the TWC to immediately begin effective NOx removal rather than allowing 60% or more of NOx to pass through unremoved during cold operation.
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 reduces nitrogen oxide emissions in the cold state at engine startup by optimizing the air-fuel ratio, improving exhaust gas purification efficiency and aligning with environmental regulations by ensuring higher NOx removal rates.
Implementation Method 1
a palladium (Pd) catalyst that oxidizes hydrocarbons and carbon monoxide and occludes nitrogen oxides
Implementation Method 2
a palladium (Pd) catalyst that oxidizes hydrocarbons and carbon monoxide and occludes nitrogen oxides
Implementation Method 3
a rhodium (Rh) catalyst for reducing nitrogen oxides
Data Source
AI summary
An exhaust gas purification system for vehicle provided on an exhaust pipe connected to an exhaust side of an engine for purifying an exhaust gas of the engine includes a housing mounted on the exhaust pipe, a front end catalyst incorporated in the housing to primarily purify the exhaust gas flowing into the housing through the front end portion of the housing, a rear end catalyst incorporated in the housing to secondarily purify the exhaust gas passing through the front end catalyst before the exhaust gas flows out to the rear end portion of the housing, and a controller connected to the exhaust pipe at a front end portion of the housing to control the concentration of unburned fuel contained in the exhaust gas according to temperature of exhaust gas flowing into the housing and speed of the vehicle.