Lean Burn Gasoline Engine With SCR Aftertreatment
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Solution Overview
Problem
Current gasoline engines with oxidation-reduction catalytic converters are limited to stoichiometric conditions, restricting fuel efficiency and emission control, while lean burn diesel engines can operate at higher air/fuel ratios, making it challenging to achieve both efficient fuel use and emissions compliance in gasoline engines.
Innovation Solution
Implementing a lean burn active ignition engine system with an aftertreatment system that includes an oxidation-reduction catalyst and a selective catalytic reduction (SCR) catalyst, allowing for operation at air/fuel ratios greater than stoichiometric conditions, coupled with a urea SCR system to enhance fuel efficiency and reduce NOx emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gasoline engine uses an oxidation-reduction catalytic converter (TWC) to meet emissions standards, then NOx, HC, and CO emissions are controlled, but the engine is restricted to stoichiometric air/fuel ratio operation which limits fuel efficiency
Solution Approach 1:
The aftertreatment system is segmented into multiple functional components: oxidation catalyst for CO and HC oxidation, SCR catalyst for NOx reduction, and ammonia storage capacity. This segmentation allows each component to specialize in specific emissions control functions, enabling the system to handle lean burn exhaust conditions while maintaining comprehensive emissions compliance.
Solution Approach 2:
Ammonia serves as an intermediary substance that mediates between the lean burn combustion process and NOx reduction. The ammonia is stored during stoichiometric operation and then utilized during lean burn conditions to enable SCR reactions, bridging the gap between different operating modes and allowing fuel efficiency improvement without compromising emissions control.
2Use of energy by moving object
If a gasoline engine operates at lean burn conditions with high air/fuel ratio to improve fuel efficiency, then fuel economy increases, but NOx reduction capability of the oxidation-reduction catalyst decreases due to increased oxygen content
Solution Approach 1:
The system changes the operating parameters by introducing ammonia into the exhaust stream during lean burn conditions. This parameter change enables the SCR catalyst to reduce NOx effectively even in the oxygen-rich environment of lean burn exhaust, where traditional TWC would fail to reduce NOx efficiently.
Solution Approach 2:
The aftertreatment system uses a composite approach combining oxidation catalyst materials and SCR catalyst materials in a integrated system. This composite structure allows the system to perform both oxidation functions (for CO and HC) and reduction functions (for NOx using ammonia), making it effective under lean burn conditions where single-function catalysts would fail.
3Reliability
If the engine operates at stoichiometric conditions to maintain TWC effectiveness, then emissions are controlled, but the operational range and fuel efficiency are restricted
Solution Approach 1:
The system dynamically adapts its operation mode based on engine conditions. During stoichiometric operation, it maintains traditional TWC functionality for emissions control. During lean burn operation, it transitions to utilizing ammonia storage and SCR catalysis for NOx reduction. This dynamic adaptability allows the system to maintain emissions control across a wide range of operating conditions.
Solution Approach 2:
The aftertreatment system is designed with multi-functionality to handle both stoichiometric and lean burn exhaust conditions. It can perform oxidation of CO and HC, reduction of NOx via SCR, and store ammonia for later use. This universal design enables the system to maintain emissions compliance across diverse operating modes, significantly expanding the engine's operational range.
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 significantly increases fuel economy and extends the operational range of gasoline engines, enabling them to meet emissions standards while operating in lean burn conditions, similar to diesel engines.
Implementation Method 1
the TWC provides a reaction function in which NOx is reduced to oxygen and nitrogen, an oxidation reaction in which CO is oxidized to CO 2 , and unburnt HC is oxidized to CO 2 and H 2 O
Implementation Method 2
a selective catalytic reduction (SCR) catalyst fluidly coupled to the oxidation-reduction catalyst and positioned downstream of the oxidation-reduction catalyst
Data Source
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AI summary
An engine system including a lean burn active ignition engine and aftertreatment system, and a method for operating such a system, are disclosed. In a representative embodiment, the lean burn active ignition engine includes an engine block including plural cylinders, an intake manifold adapted to provide charge air to the cylinders, an exhaust manifold, an active ignition source; and fuel and air handling systems that provide fuel/ charge air mixture such that an air-to-fuel ratio of the mixed charge air and fuel in each of the engine cylinders is substantially greater than a stoichiometric quantity to achieve a lean burn condition. An exhaust gas aftertreatment system is fluidly coupled to an outlet of the exhaust manifold and includes an oxidation-reduction catalyst, and a selective catalytic reduction (SCR) catalyst fluidly coupled to the oxidation-reduction catalyst and positioned downstream of the oxidation-reduction catalyst.