Compression-Ignition Engine Control with Stratified Air-Fuel Ratio
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Solution Overview
Problem
Compression-ignition engines face challenges in maintaining stable combustion and reducing NOx generation, especially at low load operating ranges where fuel injection amounts are small, leading to unstable spark ignition and difficult self-ignition due to low temperatures.
Innovation Solution
A control system for compression-ignition engines that accurately controls mixture gas distribution within the combustion chamber using a spark plug to ignite mixture gas, creating a stratified air-fuel ratio with lean conditions near the spark plug and rich conditions around it, combined with a swirl flow to stabilize spark ignition and self-ignition, while maintaining a high geometric compression ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the engine operates within a low load operating range with reduced fuel injection amount, then fuel efficiency is improved, but the temperature inside the combustion chamber decreases making spark ignition difficult and SI combustion unstable
Solution Approach 1:
The patent applies local quality by creating a stratified air-fuel mixture where the region near the spark plug has a richer air-fuel ratio (easier to ignite) while the overall mixture remains lean. This localized enrichment allows reliable spark ignition and stable SI combustion in the low load range without sacrificing overall fuel efficiency, as only a small region requires richer mixture for reliable ignition.
Solution Approach 2:
The patent changes the air-fuel ratio parameter spatially within the combustion chamber. By controlling the fuel injection timing and amount, the system creates a non-uniform air-fuel distribution with richer mixture near the spark plug electrode and leaner mixture in the bulk combustion chamber, enabling stable ignition while maintaining overall lean operation for efficiency.
2Reliability
If the air-fuel ratio of the entire mixture gas is set closer to stoichiometric for stable SI combustion, then combustion stability is improved, but NOx generation increases
Solution Approach 1:
The patent resolves this contradiction by applying local quality - creating a spatially varying air-fuel ratio where only the local region near the spark plug has richer mixture for stable ignition, while the overall bulk mixture remains lean (higher air-fuel ratio than stoichiometric). This ensures both combustion stability and reduced NOx generation since most of the combustion occurs in the lean mixture region.
Solution Approach 2:
The patent segments the combustion chamber into different air-fuel ratio zones: a rich zone near the spark plug for reliable ignition and a lean zone in the bulk combustion chamber for low NOx emission. This segmentation allows each region to operate at its optimal air-fuel ratio for its specific function.
3Reliability
If a high geometric compression ratio is used to facilitate CI combustion, then self-ignition capability is improved, but the complexity of the engine design increases
Solution Approach 1:
The patent changes the compression ratio parameter to a high value (14:1 or higher) to enable reliable compression ignition. This parameter change ensures that the temperature and pressure at the end of the compression stroke are sufficient for self-ignition of the lean mixture, maintaining CI combustion capability while allowing flexible operation across different load ranges.
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
The system achieves stable spark and self-ignition combustion, reduces NOx generation, and improves fuel efficiency by controlling the air-fuel ratio and swirl flow to optimize combustion conditions even at low load ranges.
Implementation Method 1
The spark plug ignites the mixture gas to start SI combustion by flame propagation
Implementation Method 2
the timing of the compression ignition greatly changes. By performing the ignition to cause the SI combustion before the CI combustion
Implementation Method 3
Since the geometric compression ratio of the engine is 14:1 or above, near a top dead center of compression stroke at which the combustion is performed, the mixture gas inside the combustion chamber is subjected to relatively high pressure. The CI combustion starts more easily as this pressure rises.
Implementation Method 4
within this high load segment, a swirl flow is generated inside a cylinder
Data Source
AI summary
A control system for a compression-ignition engine is provided, which includes the engine, a spark plug, a fuel injection valve, an air-fuel ratio control valve, and a control unit. A geometric compression ratio of the engine is 14:1 or above. The control unit includes a processor configured to execute an air-fuel ratio controlling module for, when the engine being in a given operating state is detected, controlling the air-fuel ratio control valve to bring the air-fuel ratio of the entire mixture gas to a given lean air-fuel ratio that is larger than a stoichiometric air-fuel ratio, and an spark plug controlling module for, after this control, outputting the control signal to the spark plug to perform the ignition at a given ignition timing so that the mixture gas starts combustion by flame propagation and then unburned mixture gas self-ignites. The given ignition timing is stored in a memory.