CNG Engine Oxidation Catalyst Regeneration Control
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Solution Overview
Problem
In compressed natural gas (CNG) engines operating under lean-burn conditions, oxidation catalysts with palladium and platinum face efficiency deterioration due to excess oxygen, leading to reduced performance as palladium becomes inactive when oxygen is adsorbed, necessitating a method to regenerate and maintain catalyst activity.
Innovation Solution
An engine control method that determines the necessity of a regeneration mode based on the activation state and operating conditions of the oxidation catalyst, involving increasing the air-fuel equivalence ratio from 1.10 to 1.20 when the catalyst is inactive, particularly at lower engine speeds, and terminating the regeneration when the catalyst is reactivated or temperature exceeds 500°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the engine operates under lean-burn condition to improve fuel efficiency, then fuel consumption is reduced, but oxidation catalyst efficiency deteriorates due to excess oxygen adsorption
Solution Approach 1:
The control method implements periodic switching between lean-burn and rich-burn operations. The oxidation catalyst is subjected to periodic rich-burn conditions (increased fuel injection) to desorb accumulated oxygen and restore catalytic activity, while maintaining overall lean-burn operation for fuel efficiency. This periodic rich-burn treatment removes oxygen from the catalyst surface, preventing permanent deactivation.
Solution Approach 2:
The method dynamically changes the air-fuel ratio parameter based on catalyst activation state. When catalyst efficiency drops below a threshold, the system increases the fuel injection amount to create rich-burn conditions, temporarily changing the operating parameter from lean (λ>1) to rich (λ<1) to regenerate the catalyst and restore its oxygen storage capacity.
2Reliability
If rich-burn condition is applied to regenerate oxidation catalyst, then catalyst activation is recovered, but fuel consumption increases
Solution Approach 1:
Rich-burn regeneration is applied periodically rather than continuously. The control ECU monitors catalyst activation state and only initiates rich-burn regeneration when activation drops below a predetermined threshold. This periodic application minimizes additional fuel consumption while ensuring catalyst performance is restored only when necessary.
Solution Approach 2:
The method applies partial rich-burn action rather than full rich-burn operation. Instead of maintaining continuous rich-burn conditions, the system applies temporary fuel enrichment only during regeneration periods, using the minimum necessary fuel increase to restore catalyst activation to acceptable levels, thereby limiting the impact on overall fuel consumption.
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 method effectively recovers catalytic activation of the oxidation catalyst, enhancing methane conversion efficiency from 60% to 96%, reducing methane emissions, and maintaining compliance with regulatory limits by operating the engine in a rich-burn condition for a predetermined time.
Implementation Method 1
oxidation catalyst including palladium and platinum may be used to purify methane occupying most of the exhaust gas
Implementation Method 2
When oxygen is adsorbed to palladium, palladium may not function as a catalyst property
Implementation Method 3
the oxidation catalyst may be regenerated by increasing the air-fuel equivalence ratio from 1.10 to 1.20
Data Source
AI summary
In an engine control method for maintaining performance of oxidation catalyst, fuel of a compressed natural gas engine under a lean-burn condition with an air-fuel equivalence ratio less than or equal to 1 is burned. Activation of the oxidation catalyst for purifying an exhaust gas of the engine is determined. Necessity of a regeneration mode for recovering catalytic activation of the oxidation catalyst according to an activation state of the oxidation catalyst and an operating condition of the engine is determined. And, the air-fuel equivalence ratio is increased to a range of from 1.10 to 1.20 when the oxidation catalyst is inactive and an engine speed is lower than a predetermined speed.