Engine Pre-Ignition Control via Dynamic Air-Fuel Ratio
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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, leading to high in-cylinder pressures and combustion knock, which existing mitigation strategies like immediate in-cylinder rich or lean fuel injections can address but may degrade catalyst efficiency and exhaust emissions.
Innovation Solution
An engine controller adjusts the air-to-fuel ratio dynamically, enriching the cylinder initially to mitigate pre-ignition and then transitioning to a leaner ratio to maintain stoichiometric conditions, compensating for excess fuel and oxygen levels to prevent catalyst degradation, while also limiting engine load and advancing spark timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If immediate in-cylinder rich fuel injection is carried out to mitigate pre-ignition, then pre-ignition combustion events are reduced, but catalyst efficiency and exhaust emission levels are degraded
Solution Approach 1:
The patent implements a periodic fuel injection strategy where rich fuel injection is applied for a limited number of combustion events (e.g., 1-5 events) following pre-ignition detection, then stopped. This periodic application provides sufficient cooling to mitigate pre-ignition while limiting the duration of rich operation to preserve catalyst efficiency, resolving the contradiction between immediate mitigation and long-term catalyst protection.
Solution Approach 2:
The patent applies fuel injection preemptively during the compression stroke upon detecting pre-ignition conditions. By injecting fuel early in the compression stroke rather than waiting for combustion, the system maximizes the cooling effect during the most critical phase while minimizing the total fuel quantity needed, thereby reducing catalyst degradation while maintaining effective pre-ignition mitigation.
2Reliability
If in-cylinder lean fuel injection is carried out to mitigate pre-ignition, then pre-ignition risk is reduced, but catalyst efficiency is degraded due to sudden change in air-to-fuel ratio
Solution Approach 1:
The patent implements a periodic fuel injection strategy where rich fuel injection is applied for a limited number of combustion events (e.g., 1-5 events) following pre-ignition detection, then stopped. This periodic application provides sufficient cooling to mitigate pre-ignition while limiting the duration of rich operation to preserve catalyst efficiency, resolving the contradiction between immediate mitigation and long-term catalyst protection.
Solution Approach 2:
The patent dynamically adjusts the air-to-fuel ratio parameter based on detected pre-ignition conditions. By transitioning from stoichiometric operation to a temporarily enriched mixture and then back, the system achieves the necessary charge cooling effect while minimizing the duration and magnitude of AFR deviation, thereby protecting catalyst efficiency while maintaining pre-ignition mitigation.
3Reliability
If engine load is limited to reduce pre-ignition occurrence, then abnormal combustion events are reduced, but engine power output is decreased
Solution Approach 1:
The patent applies load limiting selectively to specific cylinders that have detected pre-ignition events rather than uniformly limiting load across all cylinders. This localized approach allows the engine to maintain high power output from unaffected cylinders while applying mitigation only where needed, resolving the contradiction between pre-ignition reduction and overall engine power maintenance.
Solution Approach 2:
The patent applies fuel injection preemptively during the compression stroke upon detecting pre-ignition conditions. By injecting fuel early in the compression stroke rather than waiting for combustion, the system maximizes the cooling effect during the most critical phase while minimizing the total fuel quantity needed, thereby reducing catalyst degradation while maintaining effective pre-ignition mitigation.
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 effectively reduces pre-ignition events without degrading catalyst efficiency or exhaust emissions, maintaining average air-to-fuel ratios near stoichiometry and stabilizing engine operation.
Implementation Method 1
by enriching a cylinder in response to an occurrence of pre-ignition, a cylinder air charge cooling effect may be achieved that may reduce the occurrence of further abnormal combustion events
Data Source
AI summary
Methods and systems are provided for mitigating engine pre-ignition based on a feed-forward likelihood of pre-ignition and feedback from a pre-ignition event. In response to an indication of pre-ignition, a cylinder may be enriched while an engine load is limited. The enrichment may be followed by an enleanment to restore exhaust catalyst feed-gas oxygen levels. The mitigating steps may be adjusted based on engine operating conditions, a pre-ignition count, as well as the nature of the pre-ignition.