Divided Exhaust EGR Flow Control During Transients
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Solution Overview
Problem
Engines with dedicated exhaust gas recirculation (EGR) cylinders face challenges in controlling the EGR fraction during transient conditions, leading to increased EGR fraction and potential cylinder misfire and combustion instability due to rapid changes in intake manifold pressure compared to exhaust manifold pressure.
Innovation Solution
A system and method for controlling EGR fraction in a divided exhaust engine, utilizing a controller to divert EGR flow to a lower pressure location within the intake or exhaust system, such as the inlet of a compressor or catalyst, to mitigate EGR fraction deviations and maintain the target EGR fraction during transient conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If dedicated EGR cylinders are used with standard fueling and controls, then the system complexity is reduced and hardware is simplified, but the control over EGR fraction during transient conditions is lost
Solution Approach 1:
The patent applies dynamics by making the EGR fraction variable during transient conditions. The controller dynamically adjusts the EGR fraction based on detected transient conditions, transitioning from a fixed ratio (based on cylinder count) to a variable control strategy. This allows the system to maintain simplicity in hardware while achieving dynamic control adaptability during transients, resolving the contradiction between device complexity and ease of operation.
2Speed
If the charge flow pressure changes rapidly during transient conditions, then the engine response is improved, but the EGR fraction deviates from target value causing combustion instability
Solution Approach 1:
The patent applies preliminary anti-action by detecting transient conditions before they cause significant EGR fraction deviation. When a transient condition is detected, the controller proactively adjusts the EGR fraction to prevent overshoot and combustion instability. This anticipatory control counteracts the rapid pressure changes in the charge flow, maintaining combustion stability while preserving the engine's rapid response capability.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the EGR fraction and comparing it to the target value. When transient conditions cause deviation, the controller uses this feedback information to adjust the EGR fraction back toward the target. This closed-loop control ensures that rapid charge flow pressure changes do not lead to sustained combustion instability, while maintaining the speed of engine response.
3Quantity of substance
If the EGR fraction increases during transient conditions, then more exhaust gas is recirculated, but cylinder misfire and combustion instability occur
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the EGR fraction parameter during transient conditions. Instead of maintaining a fixed EGR fraction based on cylinder ratio, the controller modifies this parameter in response to transient conditions. This prevents excessive EGR flow that would cause misfire and combustion instability, while still utilizing exhaust gas recirculation benefits when appropriate.
Data Source
AI summary
Systems, apparatus, and methods are disclosed that include a divided exhaust engine configured to control an EGR fraction in the charge flow to the cylinders in response to an EGR fraction overshoot condition, an exhaust pressure change in the EGR loop, and/or a transient operating condition.