ATS for Spark Ignition Engine Using Segmented Catalysts
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Solution Overview
Problem
Three-way catalysts in spark ignition engines are unable to effectively convert NOx during lean burn operations due to the presence of oxygen, limiting the engine's operational flexibility and fuel efficiency.
Innovation Solution
An After Treatment System (ATS) comprising a three-way catalyst followed by a Selective Catalytic Reduction (SCR) or SCRoF device, with a Diesel Oxidation Catalyst (DOC) coating on the three-way catalyst and a Particulate Filter (DPF/GPF) in between, that adjusts its functioning based on fuel/air mixture and oxygen content in the exhaust gas, using a urea-based agent injection controlled by NOx and oxygen sensors to manage lean burn operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a three-way catalyst is used in a spark ignition engine, then NOx conversion is effective under stoichiometric conditions, but lean burn operation is forbidden due to the inability to convert NOx in the presence of oxygen
Solution Approach 1:
The aftertreatment system is segmented into two distinct functional zones: a three-way catalyst section for stoichiometric operation and a SCR section for lean burn operation. This segmentation allows each catalyst to operate in its optimal environment, with the 3WC handling NOx conversion when oxygen is absent and the SCR handling NOx conversion when oxygen is present, thereby enabling lean burn operation while maintaining effective NOx control
Solution Approach 2:
A urea-based agent (ammonia source) is introduced as an intermediary substance to enable NOx conversion in the SCR section during lean burn operation. The urea decomposes to form ammonia, which then reacts with NOx in the presence of oxygen through SCR chemistry, allowing the system to maintain adaptability across different operating conditions while controlling harmful emissions
2Productivity
If a three-way catalyst is implemented, then NOx conversion is achieved under stoichiometric mixture, but lean burn operation is forbidden due to oxygen presence
Solution Approach 1:
The aftertreatment system dynamically adapts its NOx conversion mechanism based on operating conditions. During lean burn operation, the system transitions from relying solely on 3WC chemistry to utilizing SCR chemistry activated by urea injection. This dynamic adaptation allows the engine to maintain high fuel efficiency through lean burn while the SCR system actively manages NOx emissions that would otherwise be unconverted in the presence of oxygen
3Object-generated harmful factors
If urea-based agent is injected continuously, then NOx conversion is maintained, but unnecessary urea usage increases cost and complexity
Solution Approach 1:
The system employs feedback control through oxygen sensors and NOx sensors that continuously monitor exhaust gas composition. Based on these measurements, the control unit adjusts urea injection rates in real-time, injecting urea only when lean burn conditions are detected and NOx conversion is needed. This feedback mechanism ensures minimal urea consumption while maintaining effective NOx control, avoiding unnecessary substance usage during stoichiometric 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
Enables the spark ignition engine to operate in lean burn conditions with improved NOx conversion and fuel efficiency, reducing unconverted NOx emissions and promoting passive soot regeneration, while avoiding unnecessary urea-based agent usage.
Implementation Method 1
a three-way catalyst is associated to its exhaust pipe to threat the exhaust gas produced by the internal combustion engine
Implementation Method 2
an SCR or SCRoF... An SCR is a well-known acronym indicating Selective Catalytic reduction device
Implementation Method 3
the three-way catalyst is coated such that to operate as a DOC (Diesel oxidation catalyst) and it could be without any coating or if a coating is present, it is suitable to improve CO/HC conversion and NO2 formation
Implementation Method 4
a DPF (which is meant to be a GPF in the sparking ignition engine environment) is arranged. The DPF/GPF is a well known particulate trap
Implementation Method 5
the oxygen sensor is arranged upstream of the three-way catalyst in order to have a first measurement of the oxygen content
Implementation Method 6
the urea-based agent injection is metered on the basis additionally of a NOx sensor arranged downstream of the three-way catalyst
Data Source
Figure 1~2
Figure 3~4
AI summary
After treatment system (ATS) for a sparking ignition engine comprising a three-way catalyst (3WC) and a selective catalytic reduction device (SCR) comprising a doser (J) arranged to introduce an urea-based agent immediately upstream of the SCR, wherein said 3WC is arranged upstream of said SCR according to a gas flow direction.The SCR can also be provided as a SCRT ot SCRoF or in combination with and particle filter. There can be foreseen a bypass system (BP) for the SCR catalyst.