Exhaust Purification Catalyst Dynamic Hydrocarbon Control
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Solution Overview
Problem
The NOx purification rate in internal combustion engine exhaust systems decreases at high temperatures due to the degradation of NOx storage catalysts.
Innovation Solution
An exhaust purification system is implemented with a catalyst that carries precious metals like platinum and rhodium, and a basic surface layer, where the concentration of hydrocarbons is periodically varied within a predetermined range to enhance NOx reduction, even at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a NOx storage catalyst is used to store and release NOx, then NOx purification is achieved at low temperatures, but the NOx purification rate falls when the catalyst temperature becomes high
Solution Approach 1:
The patent applies dynamics by periodically varying the hydrocarbon concentration at different stages of the NOx release process. During the heating phase, hydrocarbon concentration is kept low to prevent premature reduction. During the NOx release phase, hydrocarbon concentration is increased to promote reduction reactions. This dynamic control adapts the chemical environment to the temperature evolution, maintaining high NOx purification rates across the full temperature range.
Solution Approach 2:
The patent implements periodic action through cyclic variation of hydrocarbon concentration corresponding to the periodic heating and NOx release cycles. The hydrocarbon feed is controlled to create alternating phases of low concentration (during heating/storage) and high concentration (during release), synchronizing with the thermal and chemical cycles of the catalyst to maximize purification efficiency at all temperature levels.
2Reliability
If hydrocarbon concentration is increased to enhance NOx reduction, then NOx purification improves, but unwanted side reactions and reduced storage capacity may occur
Solution Approach 1:
The patent uses periodic action to cyclically vary hydrocarbon concentration, creating distinct phases: a storage phase with low hydrocarbon concentration that maximizes NOx uptake, and a release phase with high hydrocarbon concentration that promotes NOx reduction. This temporal separation ensures that hydrocarbons are only introduced when needed for reduction, preventing them from competing with NOx for storage sites and maintaining high storage capacity while achieving effective purification during the release phase.
Solution Approach 2:
The patent applies preliminary action by first allowing the catalyst to store NOx at low temperatures and low hydrocarbon concentrations before introducing higher hydrocarbon concentrations to trigger the reduction reaction. This sequential approach ensures that the storage capacity is fully utilized before initiating reduction, preventing premature displacement of stored NOx and maximizing the amount of NOx that can be purified in each cycle.
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 system maintains a high NOx purification rate by producing and holding reducing intermediates on the catalyst surface, effectively reducing NOx emissions even when the catalyst temperature exceeds 400°C.
Implementation Method 1
a precious metal catalyst is carried on an exhaust gas flow surface of the exhaust purification catalyst and a basic exhaust gas flow surface part is formed around the precious metal catalyst
Implementation Method 2
an NOx storage catalyst which stores NOx which is contained in exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean
Implementation Method 3
an oxidation catalyst which has an adsorption function, and which feeds hydrocarbons into the engine exhaust passage upstream of the oxidation catalyst
Data Source
AI summary
A method for purifying exhaust gas of an internal combustion engine, including chemically reducing NOx that is contained in the exhaust gas when a concentration of hydrocarbons flowing into an exhaust purification catalyst is made to vibrate within a predetermined range of amplitude and within a predetermined range of period, wherein, during the chemical reduction, the NOx contained in the exhaust gas is reacted with reformed hydrocarbons to produce a reducing intermediate containing nitrogen and hydrocarbons, a reducing action of the reducing intermediate chemically reduces the NOx, and the NOx is chemically reduced without storing nitrates or with storing a fine amount of the nitrates in a basic layer of the exhaust purification catalyst.