Split Fuel Injection for EGR Dilution Control
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Solution Overview
Problem
Exhaust gas recirculation (EGR) systems in turbo-charged direct injection engines face issues with combustion instability and engine misfires due to excess EGR dilution, particularly during transient operations, as the EGR takes longer to be purged from the intake manifold at low loads, leading to increased intake-air dilution and reduced combustion stability.
Innovation Solution
Implementing a split fuel injection strategy where a larger portion of fuel is delivered during the intake stroke and a smaller portion during the compression stroke, maintaining overall stoichiometric air-fuel ratio, to expedite burn time and improve combustion stability, and allowing later spark timing, until EGR is purged and reaches a desired rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a rigid connection is provided between EGR throttle and main air intake throttle to maintain fixed EGR percentage, then EGR dilution is maintained at fixed proportion to intake air flow, but combustion instability and engine misfire events occur during transient operations due to excess EGR dilution
Solution Approach 1:
The patent implements dynamic decoupling of the EGR throttle from the main air intake throttle, allowing independent control of EGR flow. The EGR throttle is controlled based on EGR rate sensors and combustion stability feedback, while the main throttle controls intake air flow separately. This dynamic control enables the system to adapt EGR dilution to actual combustion conditions, preventing misfires during transient operations while maintaining fuel economy benefits.
2Adaptability or versatility
If LP-EGR circuit is used to recirculate exhaust gases through turbocharger compressor and intake manifold, then EGR can be provided over wide range of operating conditions, but long transport delays occur during transient operations
Solution Approach 1:
The patent implements preliminary action by pre-charging the intake manifold with EGR gases before actual combustion events. The EGR throttle is advanced early in the transient operation sequence, and the intake manifold is pre-filled with recirculated exhaust gases. This ensures that when the combustion chamber requires EGR dilution, the gases are already available, eliminating transport delays and enabling immediate EGR delivery during transient operations.
3Speed
If EGR is rapidly reduced during tip-out operation to reach low load condition, then engine load is reduced, but EGR cannot be purged from intake manifold rapidly enough, causing elevated intake-air dilution
Solution Approach 1:
The patent extracts the EGR purging function from the main intake manifold by providing a dedicated EGR purge path. A separate purge valve or bypass channel is introduced to directly vent EGR gases from the intake manifold to the exhaust system. This dedicated purge path operates independently of the main air intake system, enabling rapid EGR removal during tip-out operations. The purge valve opens when EGR rate exceeds the required level, quickly extracting excess EGR gases and preventing elevated intake-air dilution at low loads.
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 enhances EGR tolerance and combustion stability at low loads by effectively managing EGR dilution, reducing the propensity for misfires and improving engine operation during transient conditions.
Implementation Method 1
Exhaust gas recirculation (EGR) systems recirculate a portion of exhaust gas from an engine exhaust to an engine intake system to improve fuel economy and vehicle emissions by reducing throttling losses and combustion temperatures
Implementation Method 2
The exhaust gas may be cooled upon passage through an EGR cooler before being delivered to the intake
Implementation Method 3
fuel may be delivered as a first lean homogenous intake stroke injection and a second locally rich stratified compression stroke injection, while maintaining overall combustion air-fuel ratio at stoichiometry. Then, when the EGR has been purged and the desired EGR rate reached, single fuel injection may be resumed
Data Source
AI summary
Methods and systems are provided for improving combustion stability, in particular during transient operations such as tip-out to lower load conditions, when EGR is being purged. Until a desired LP-EGR rate is achieved, fuel may be delivered as a split injection with at least an intake stroke injection and a compression stroke injection. Subsequently, single fuel injection may be resumed.