Aftertreatment System SCR Reductant Injector
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Solution Overview
Problem
Spark-ignited gasoline engines face challenges in reducing NOx emissions during engine shut-off events due to insufficient NOx reduction capabilities, leading to increased fuel consumption when rich regeneration of the catalyst is required.
Innovation Solution
Incorporating a selective catalytic reduction (SCR) device in the exhaust passage of a spark-ignited engine, with a reductant injector positioned between the three-way catalyst and the SCR, allowing for ammonia injection when the SCR's ammonia load falls below a threshold, enabling NOx reduction without rich engine operation during restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If rich regeneration of the catalyst is executed to reduce NOx emissions during engine restart, then NOx reduction capability is improved, but fuel consumption increases
Solution Approach 1:
A reductant injector is introduced as an intermediary device between the three-way catalyst and the SCR device. This injector delivers reductant directly to the SCR catalyst, enabling NOx reduction without requiring rich engine operation. The intermediary reductant injection system decouples the NOx reduction function from the engine's air-fuel ratio control, resolving the contradiction between emissions control and fuel efficiency.
Solution Approach 2:
The system changes the operational parameters of the aftertreatment system by monitoring ammonia load on the SCR catalyst and adjusting reductant injection accordingly. When ammonia load falls below a threshold, reductant is injected to maintain NOx reduction capability. This parameter-based control allows the engine to operate lean (improving fuel consumption) while maintaining NOx emissions control through SCR.
2Use of energy by moving object
If the engine operates lean during restart to maintain fuel efficiency, then fuel consumption is reduced, but NOx reduction capability deteriorates
Solution Approach 1:
The aftertreatment system is segmented into distinct functional zones: a three-way catalyst for initial treatment, a reductant injector for targeted reductant delivery, and an SCR device for primary NOx reduction. This segmentation allows the engine to operate lean while the SCR device, supplied with reductant from the injector, handles NOx reduction independently. The functional segmentation decouples fuel efficiency from emissions control.
Solution Approach 2:
The reductant injector serves as an intermediary that supplies the SCR catalyst with the necessary reductant (ammonia or urea) to maintain NOx reduction capability during lean engine operation. This intermediary system enables the engine to sustain lean operation (improving fuel consumption) while the SCR device, fed by the injector, ensures continued NOx control.
3Object-generated harmful factors
If reductant is injected continuously to maintain ammonia load on SCR, then NOx reduction efficiency is improved, but reductant consumption increases
Solution Approach 1:
The control system implements feedback control by monitoring the ammonia load on the SCR catalyst and adjusting reductant injection rates accordingly. When ammonia load falls below a threshold, reductant injection is activated or increased. When ammonia load is sufficient, injection is reduced or stopped. This feedback mechanism maintains optimal NOx reduction efficiency while minimizing reductant consumption, avoiding both over-injection and under-injection.
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 approach reduces fuel consumption by allowing the engine to restart lean, maintaining efficient NOx reduction and minimizing the frequency of rich perturbations, thereby enhancing fuel savings and adhering to emissions standards.
Implementation Method 1
a selective catalytic reduction device...configured to reduce NOx emissions
Implementation Method 2
a reductant injector positioned to inject reductant into the exhaust passage
Data Source
AI summary
Methods and systems are provided for an aftertreatment system. In one example, a system comprising a spark-ignited engine comprising a selective catalytic reduction device (SCR) arranged in an exhaust passage downstream of a catalyst, and an injector positioned to inject a reductant directly into the exhaust passage downstream of the catalyst subsequent an engine shut-off event.