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 challenges in controlling the air-fuel ratio downstream of emissions control devices, particularly in achieving stoichiometric mixtures for optimal catalyst operation.
Innovation Solution
A split exhaust engine system with a scavenge manifold routing air downstream of an emissions control device and a blowdown manifold routing exhaust gases to the turbine, where the timing of cylinder exhaust valves is coordinated with intake valves to create a positive valve overlap, allowing blowthrough air to flow through the cylinders and recirculate exhaust gases, and excess air is supplied to maintain a stoichiometric mixture and enable emissions control device regeneration.
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 to the turbocharger turbine, and a second exhaust manifold that routes exhaust to the intake manifold upstream of the compressor. This segmentation allows selective routing of exhaust gases to achieve both power enhancement and temperature control
Solution Approach 2:
Exhaust gases from the second exhaust manifold serve as an intermediary substance (EGR) that is introduced into the intake manifold to cool the combustion charge. This mediator reduces combustion temperatures and prevents knock while maintaining the power benefits of turbocharging
2Device complexity
If a single exhaust manifold routes all exhaust to the turbine, then the system is simpler, but the air-fuel ratio downstream of emissions control devices cannot be precisely controlled
Solution Approach 1:
The exhaust system is divided into two separate manifolds with distinct functions: one dedicated to turbine power generation and another dedicated to EGR and air-fuel ratio control downstream of emissions devices, enabling precise control of exhaust composition
Solution Approach 2:
By independently controlling the routing of exhaust gases through the two manifolds, the system can change the parameters of the exhaust mixture downstream of emissions control devices, achieving desired air-fuel ratios for optimal catalyst operation and regeneration
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 combustion temperatures, improves engine efficiency, and allows for precise control of the air-fuel ratio, reducing engine emissions and enhancing the operation of downstream emissions control devices.
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
by flowing a first portion of the exhaust gas (e.g., higher pressure exhaust) through the turbine and a higher pressure exhaust passage and flowing a second portion of the exhaust gas (e.g., lower pressure exhaust) and blowthrough air to the compressor inlet
Implementation Method 3
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, a method may include supplying air to an exhaust system at a location downstream of an emissions control device via the first exhaust manifold, the air not having participated in combustion in the engine, the first exhaust manifold in fluidic communication with a first exhaust valve of a cylinder and an intake manifold, the cylinder including a second exhaust valve in fluidic communication with the second exhaust manifold. The method may further include adjusting an amount of fuel injected to the engine in response to output of a first oxygen sensor, the first oxygen sensor positioned in the exhaust system upstream of the emissions control device.