Engine Cylinder Segmentation for Power and Emissions
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Solution Overview
Problem
Typical spark ignition engines face a trade-off between increasing engine power and reducing vehicle emissions, as strategies to enhance power output, such as global enrichment, lead to decreased catalyst efficiency and increased emissions, while protecting exhaust system components from heat-related degradation limits power gains.
Innovation Solution
The method involves selectively enriching a first set of engine cylinders, leanening a second set, and maintaining a third set at stoichiometry, with exhaust gas recirculation (EGR) provided to the intake passage to increase power without increasing emissions, by cooling exhaust system components and optimizing spark timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If global enrichment strategy is employed to increase engine power, then engine power output increases, but three-way catalyst efficiency decreases and vehicle emissions increase
Solution Approach 1:
The engine cylinders are divided into different groups with different air-fuel ratios. A first set of cylinders operates at a first air-fuel ratio, a second set operates at a second air-fuel ratio, and a third set operates at stoichiometry. This segmentation allows the exhaust streams to be combined to achieve overall stoichiometric composition at the catalyst while individual cylinders can operate in modes that increase power output.
Solution Approach 2:
Different regions of the engine (different cylinder sets) are given different operational characteristics. The first set of cylinders is enriched to provide cooling and power, the second set is leanened or operated at stoichiometry to minimize emissions, and the third set operates at stoichiometry to ensure catalyst efficiency. This local differentiation resolves the contradiction between power and emissions.
2Power
If engine air flow is increased to increase engine power, then engine power output increases, but exhaust system component temperature increases causing degradation
Solution Approach 1:
The air-fuel ratio parameter is changed in different cylinder sets to control exhaust temperature. By enriching the first set of cylinders, unreacted fuel provides cooling effects that reduce exhaust system component temperatures. This allows higher air flow and power output while maintaining temperatures below degradation thresholds.
3Temperature
If unreacted fuel is added to cool exhaust components, then exhaust system component temperature decreases, but three-way catalyst efficiency decreases
Solution Approach 1:
The exhaust system is segmented into multiple streams from different cylinder sets. The first set of cylinders provides enriched exhaust with unreacted fuel for cooling, while the second and third sets provide stoichiometric or lean exhaust to maintain catalyst efficiency. The segmented streams are combined downstream to achieve both cooling and catalytic efficiency.
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 allows for increased engine power while maintaining catalyst efficiency and reducing vehicle emissions, as the enriched EGR provides additional cooling and knock suppression, allowing for advanced spark timing and reduced heat-related degradation.
Implementation Method 1
the additional, unreacted fuel cools exhaust system components, including the turbine and the three-way catalyst
Implementation Method 2
providing exhaust gas recirculation (EGR) to an intake passage of the engine from the first set of cylinders
Implementation Method 3
a three-way catalyst positioned in an exhaust system of the engine
Implementation Method 4
a typical spark ignition engine of a vehicle operates at stoichiometry during most operating conditions, where it is supplied with just enough fuel to react with an amount of air consumed by the engine
Data Source
AI summary
Methods and systems are provided for increasing engine power via partial engine enrichment and exhaust gas recirculation. In one example, a method may include enriching a first set of engine cylinders, enleaning a second set of the engine cylinders, and operating a third set of the engine cylinders at stoichiometry, exhaust gas from all of the engine cylinders producing a stoichiometric mixture at a downstream emission control device, and providing exhaust gas recirculation (EGR) to an intake passage of the engine from the first set of cylinders. In this way, cooling effects from the partial enrichment and the EGR enable engine air flow, and thus engine power, to be increased while an efficiency of the emission control device is maintained, thereby decreasing vehicle emissions.