Pre-Chamber Spark Plug Geometry for Stable Low-Load Combustion
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Solution Overview
Problem
Spark ignited engines with pre-chambers face challenges in achieving combustion stability at low engine loads and retarded combustion phasing, particularly during cold starts, which limits their application in road cars.
Innovation Solution
A spark ignited engine design featuring a pre-chamber with a volume ratio between 1.9% and 3.1% of the main combustion chamber volume and a nozzle factor between 0.085 l/cm and 1.15 l/cm, along with a nozzle aspect ratio of 1.7 to 2.2, allows for optimal combustion across the entire operating map, including low engine loads and cold starts, by controlling ignition energy and pressure rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pre-chamber is added to the spark plug, then combustion stability and ignition capability are improved, but device complexity increases
Solution Approach 1:
The pre-chamber is nested within the spark plug structure, with the pre-chamber volume ratio optimized between 1.9% and 3.1% of the main combustion chamber volume. This nesting approach integrates the pre-chamber functionality into the existing spark plug without requiring separate external components, thereby improving combustion stability while limiting the increase in overall device complexity.
Solution Approach 2:
The patent optimizes specific parameters including the pre-chamber volume ratio (1.9%-3.1%), nozzle factor (0.085-1.15 l/cm), and nozzle aspect ratio (1.7-2.2) to achieve optimal combustion performance across the entire operating map. These parameter optimizations allow the pre-chamber design to deliver improved reliability while maintaining reasonable structural complexity through precise dimensional control.
2Reliability
If the pre-chamber volume is increased, then ignition energy and combustion stability are improved, but thermal losses and pressure rise increase
Solution Approach 1:
The patent identifies an optimal pre-chamber volume ratio range of 1.9% to 3.1% of the main combustion chamber volume. Within this range, sufficient ignition energy is generated to ensure stable combustion across all operating conditions, while excessive volume that would lead to increased thermal losses and pressure rise is avoided. This parameter optimization directly addresses the trade-off between ignition energy and thermal losses.
Solution Approach 2:
The pre-chamber volume is optimized to provide just sufficient ignition energy for stable combustion without excessive volume that would cause increased thermal losses. The nozzle factor (0.085-1.15 l/cm) and nozzle aspect ratio (1.7-2.2) are also optimized to control the rate of combustion and pressure rise, ensuring that the pre-chamber provides adequate ignition capability while limiting excessive energy losses.
3Productivity
If the nozzle factor is increased, then combustion speed and pressure rise are improved, but combustion stability at low loads deteriorates
Solution Approach 1:
The patent optimizes the nozzle factor within the range of 0.085 to 1.15 l/cm and the nozzle aspect ratio between 1.7 and 2.2. These parameter optimizations balance the competing requirements of achieving sufficient combustion speed for high productivity while maintaining combustion stability across the entire operating map, including low load conditions. The specific parameter ranges ensure that combustion remains stable without excessive pressure rise that would destabilize low-load operation.
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 design enables stable combustion and efficient operation over a wide range of engine loads and conditions, preventing misfires and thermal losses, and allows for the use of gasoline or other fuels in various vehicle types.
Implementation Method 1
A spark plug with a central axis is arranged in the cylinder head with an ignition end facing the main combustion chamber
Implementation Method 2
during the compression stroke of the engine, charge is forced from the main combustion chamber into the pre-chamber
Implementation Method 3
The ignition of the charge occurs in the pre-chamber and extends through the nozzles via jets of partially combusted charge to the main combustion chamber
Data Source
AI summary
A spark ignited engine is disclosed. The spark ignited engine includes a main combustion chamber and a cylinder head at least partially surrounding the main combustion chamber. A spark plug having a central axis is arranged in the cylinder head and an ignition end of the spark plug faces the main combustion engine. A pre-chamber with at least two nozzles is arranged in the main combustion chamber and connects the ignition end and the main combustion chamber via the at least two nozzles. A pre-chamber volume ratio corresponds to a ratio of a volume of the pre-chamber to a volume of the main combustion chamber at a top-dead-center and is between 1.9% and 3.1%. A nozzle factor corresponds to a ratio of a summed flowed-through area of the at least two nozzles to the volume of the pre-chamber and is between 0.085 l/cm and 1.15 l/cm.