Engine Pre-ignition Control via Lean Mixture and Load Limiting
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Solution Overview
Problem
Engines with high compression ratios or boosted to increase specific output are prone to low-speed pre-ignition combustion events, which can cause high in-cylinder pressures and combustion knock, and mitigation strategies for cylinder misfire can inadvertently increase the likelihood of pre-ignition, leading to engine degradation.
Innovation Solution
Implementing a method where, in response to a misfire event, fuel injection is shut off in the affected cylinder while air continues to be pumped, and the remaining cylinders operate with a lean air-fuel mixture, with engine load limiting based on the leanness of the mixture, engine speed, and pre-ignition history to reduce the likelihood of pre-ignition and subsequent component overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If fuel injection is shut off in the misfiring cylinder and remaining cylinders operate lean to prevent catalyst overheating, then exhaust catalyst temperature is controlled, but the likelihood of pre-ignition increases
Solution Approach 1:
The engine control system dynamically adjusts the air-to-fuel ratio in real-time based on detected pre-ignition events. When pre-ignition is detected, the system enriches the air-to-fuel ratio in affected cylinders, transitioning from a static lean operating mode to a dynamic adaptive mode that prevents further pre-ignition while managing catalyst temperature.
Solution Approach 2:
The system changes the air-to-fuel ratio parameter from lean to rich in response to pre-ignition detection. This parameter change directly addresses the pre-ignition condition by increasing fuel content to raise the ignition temperature threshold, while the control system manages the transition to balance catalyst temperature constraints.
2Loss of substance
If cylinders are operated leaner than stoichiometry to reduce unburned fuel, then the amount of unburned fuel is reduced, but the propensity for pre-ignition increases
Solution Approach 1:
The control system uses feedback from pre-ignition detection to dynamically adjust the air-to-fuel ratio. When pre-ignition events are detected, the system responds by enriching the mixture in affected cylinders, creating a closed-loop control that adapts the fuel management strategy to prevent recurrence while managing unburned fuel output.
3Productivity
If engine load is increased to improve productivity, then output increases, but the likelihood of pre-ignition events increases
Solution Approach 1:
The system dynamically adjusts air-to-fuel ratio based on engine load and pre-ignition detection. Under high load conditions where pre-ignition risk increases, the system enriches the mixture in affected cylinders, allowing the engine to maintain higher output while dynamically preventing pre-ignition through adaptive fuel 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 the propensity for pre-ignition events, mitigates engine degradation, and controls exhaust temperatures, thereby protecting the engine from overheating and related component damage.
Implementation Method 1
another cylinder combusts a lean air-fuel mixture
Implementation Method 2
limiting air into the cylinders to be less than a threshold... By limiting the engine load when some cylinders have fuel shut off and other cylinders are operating lean, the propensity for inducing engine pre-ignition can be reduced
Data Source
AI summary
Methods and systems are provided for addressing pre-ignition that may be induced in response to actions taken to mitigate a cylinder misfire. An amount of engine load limiting applied may be adjusted to reduce the likelihood pre-ignition while also addressing component over-temperature issues. By limiting an engine load while shutting off fuel in a misfiring cylinder, and while combusting a lean air-fuel mixture in the remaining cylinders, pre-ignition induced by the misfire-mitigating lean combustion conditions can be reduced.