Split Exhaust Engine System for Combustion Temperature Control
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Solution Overview
Problem
Engine knock occurs due to increased combustion temperatures under boosted conditions, and existing systems face issues with high levels of hydrocarbons and carbon monoxide, leading to reduced emission control device function and increased emissions.
Innovation Solution
A split exhaust engine system with a first exhaust manifold routing exhaust gas recirculation to the engine intake upstream of the turbocharger compressor and a second exhaust manifold routing exhaust to the turbocharger turbine, along with coordinated valve timing to create a positive valve overlap for blowthrough air flow, which reduces combustion temperatures and improves turbine efficiency. Additionally, flowing air from the intake manifold to a junction between emission control devices to increase oxygen levels and maintain a stoichiometric mixture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If boosting devices such as turbochargers are used to increase engine power density, then engine power is improved, but combustion temperatures increase causing engine knock
Solution Approach 1:
The exhaust system is segmented into two separate manifolds: a first exhaust manifold that routes exhaust gas recirculation (EGR) to the intake upstream of the turbocharger compressor, and a second exhaust manifold that routes exhaust to the turbocharger turbine. This segmentation allows independent control of EGR flow and turbine drive, enabling temperature management while maintaining power density.
Solution Approach 2:
The system changes the thermal parameters of the combustion charge by introducing cooled EGR gases upstream of the compressor. The EGR gases are cooled during recirculation, and when mixed with fresh intake air, they reduce the overall charge temperature entering the cylinders, thereby preventing knock while maintaining the boosted power output.
2Temperature
If the engine is over fueled to reduce exhaust valve and turbine temperatures, then temperature is improved, but hydrocarbon and carbon monoxide levels increase
Solution Approach 1:
The harmful effect of excess fuel is extracted and redirected. Instead of allowing over-fueled exhaust to directly enter the turbine and emission control devices, a portion of the exhaust flow is diverted through the first exhaust manifold to recirculate as cooled EGR upstream of the compressor. This removes the hot, fuel-rich gases from the turbine path, protecting the turbine and emission devices while still achieving temperature reduction through EGR cooling.
Solution Approach 2:
The first exhaust manifold acts as an intermediary that separates the EGR flow path from the turbine exhaust path. By routing EGR through this intermediate component upstream of the compressor, the system mediates between the need for temperature reduction and the need to maintain clean exhaust for the turbine and emission control devices.
3Device complexity
If a single exhaust manifold is used, then device complexity is reduced, but the ability to separately control scavenging and blowdown exhaust gases is lost
Solution Approach 1:
The exhaust manifold is segmented into two separate manifolds to enable independent routing of different exhaust gas portions. The first exhaust manifold handles scavenging EGR flow to the intake upstream of the compressor, while the second exhaust manifold handles blowdown exhaust to the turbine. This segmentation provides the versatility needed to separately control these flows for optimized engine performance and temperature management.
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 engine knock, improves efficiency, and maintains emission control device function by lowering combustion temperatures and increasing oxygen levels, thereby reducing emissions.
Implementation Method 1
a first exhaust manifold routes exhaust gas recirculation (EGR) to an intake of the engine, upstream of a compressor of the turbocharger
Implementation Method 2
a second exhaust manifold routes exhaust to a turbine of the turbocharger in an exhaust of the engine
Implementation Method 3
a first exhaust manifold routes exhaust gas recirculation (EGR) to an intake of the engine, upstream of a compressor of the turbocharger
Implementation Method 4
The timing of the first set of cylinder exhaust valves may also be coordinated with a timing of cylinder intake valves to create a positive valve overlap period where fresh intake air (or a mixture of fresh intake air and EGR), referred to as blowthrough, may flow through the cylinders and back to the intake
Data Source
AI summary
Methods and systems are provided for operating a split exhaust engine system that provides blowthrough air and exhaust gas recirculation to an intake passage via a first exhaust manifold and exhaust gas to an exhaust passage via a second exhaust manifold. In one example, an air-fuel control method for the engine system may include flowing air from the intake manifold through a plurality of engine cylinders to a junction of the exhaust passage and a bypass passage in response to a condition, the junction positioned along the exhaust passage between first and second emission control devices. The method may further include flowing exhaust gas to the first emission control device while flowing the air to the junction.