Spark Plug Annular Space Geometry for Fuel Bridge Recovery
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Solution Overview
Problem
The existing spark plugs face issues with irregular discharges and fuel bridges due to increased distance between the center electrode and insulator, leading to difficult recovery from fuel bridges and compromised ignition properties.
Innovation Solution
A spark plug design with an annular space having a distance of 0.2 mm or larger between the center electrode and insulator, featuring a curved contour line of the ground electrode's lateral surface to facilitate fuel flow away from the spark discharge gap, combined with specific geometric configurations to enhance durability and ignition efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the center electrode and insulator is increased, then irregular discharge is suppressed, but fuel adheres to electrodes to connect between them forming a fuel bridge
Solution Approach 1:
The hydrophobic coating is applied selectively to the inner peripheral surface of the axial hole in the region where fuel accumulation is most likely to occur. This localized treatment creates different surface properties: the coated surface repels fuel to prevent bridge formation, while other surfaces maintain their original characteristics for normal spark plug operation.
Solution Approach 2:
The hydrophobic coating serves as an intermediary layer between the insulator surface and the fuel. This coating modifies the fuel-surface interaction by creating a repellent barrier that prevents fuel from adhering to the annular space surfaces, thereby eliminating the harmful fuel bridge formation while allowing the increased electrode-insulator distance to maintain its beneficial irregular discharge suppression effect.
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
Effectively suppresses irregular discharges, improves ignition properties by ensuring early recovery from fuel bridges, and enhances durability by preventing rapid enlargement of the spark discharge gap.
Implementation Method 1
an increase in the fuel entering the annular space due to a capillary action with the increase in the above distance mainly causes the fuel bridge to be liable to be generated
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
In a spark plug in which a distance between a center electrode and an insulator in an opening of an annular space is set to 0.2 mm or larger, an early recovery from a fuel bridge is enabled. A spark plug 1 includes a center electrode 5 extending in a direction of an axis CL1, a ceramic insulator 2 provided with an axial hole 4 into which the center electrode 5 is inserted, a metal shell 3 disposed on an outer periphery of the ceramic insulator 2, and a ground electrode 27 which is fixed to the metal shell 3 and has a facing surface 27F that faces a leading end surface 5F of the center electrode 5. An annular space 31 is formed between an outer peripheral surface of the center electrode 5 and an inner peripheral surface of the axial hole and is opened toward a leading end side, and when C (mm) is a distance between the outer peripheral surface of the center electrode 5 and the inner peripheral surface of the axial hole 4 in the opening of the annular space 31, C≥0.2 mm is satisfied. In a cross-section which includes the axial line CL1 and is orthogonal to the center axis CL2 of the ground electrode 27A, a contour line of lateral surfaces 27S1 and 27S2 of the ground electrode 27 has a curved shape convexed outward.