Spark Plug Insulator Protrusion for Carbon Deposit Removal
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Solution Overview
Problem
Spark plugs in internal combustion engines face issues with reduced insulation distance due to smaller diameters, leading to lateral or recess sparks and carbon deposits that hinder ignition performance, especially in direct-injection engines where carbon deposits are not effectively removed.
Innovation Solution
A spark plug design with a ceramic insulator that protrudes at least 1 mm from the metal shell, having a specific volume and thermal resistance characteristics to rapidly increase temperature and burn off carbon deposits, ensuring proper ignition and preventing creeping discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the spark plug diameter is reduced to fit smaller installation space, then the installation space requirement is improved, but the insulation distance between the ceramic insulator and the mount fitting decreases leading to lateral sparks and reduced reliability
Solution Approach 1:
The ceramic insulator is designed with different protrusion heights at different locations. The front end portion protrudes more than the rear end portion, creating local quality variation. This allows the front end to maintain adequate insulation distance despite overall spark plug size reduction, preventing lateral sparks while fitting compact installation spaces.
Solution Approach 2:
Instead of maintaining uniform insulation distance throughout the spark plug, the invention introduces axial dimension variation by making the front end protrude more than the rear end. This dimensional change allows the insulation distance to be optimized at the critical front end region where lateral sparks occur, while accommodating smaller overall dimensions.
2Volume of moving object
If the spark plug diameter is reduced, then the installation space is improved, but carbon deposits accumulate more easily on the ceramic insulator surface leading to recess sparks
Solution Approach 1:
The front end portion of the ceramic insulator is designed with greater protrusion and larger surface area compared to the rear end. This local quality enhancement provides more surface area for heat dissipation and carbon deposit removal at the critical front end region, preventing recess sparks caused by carbon accumulation.
Solution Approach 2:
The protruding front end of the ceramic insulator is positioned to be directly exposed to the combustion chamber environment, allowing it to self-clean through thermal effects and combustion gas flow. The design enables the front end to maintain itself by burning off carbon deposits through its exposure to high-temperature combustion gases.
3Reliability
If the ceramic insulator protrusion is increased to prevent lateral sparks, then the insulation distance is improved, but the thermal resistance increases making it difficult to burn off carbon deposits
Solution Approach 1:
The ceramic insulator is designed with selective protrusion where only the front end portion protrudes significantly, while the rear end portion maintains smaller protrusion. This local quality differentiation allows the front end to achieve adequate insulation distance for preventing lateral sparks, while the overall design maintains thermal pathways for carbon deposit combustion.
Solution Approach 2:
The front end portion protrudes excessively compared to the rear end, creating a localized region with enhanced insulation distance. This partial excessive action is applied only where needed (front end) to prevent lateral sparks, while the rear end maintains moderate protrusion to preserve thermal characteristics for carbon burn-off.
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 design effectively raises the ceramic insulator's temperature to burn off carbon deposits, restoring normal ignition performance and maintaining high insulation resistance, preventing lateral or recess sparks, and ensuring stable ignition even in small-diameter spark plug installations.
Implementation Method 1
raise a front end temperature of the ceramic insulator and burn off the carbon deposits from the ceramic insulator
Implementation Method 2
the insulation distance between the ceramic insulator and the mount fitting decreases
Data Source
Figure 1
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AI summary
The present invention provides a spark plug that includes a center electrode extending in an axial direction, a ceramic insulator having an axial hole formed in the axial direction to retain the center electrode in a front side of the axial hole and thereby form an assembly unit of the center electrode and the ceramic insulator, a metal shell surrounding an outer circumference of the ceramic insulator to retain therein the assembly unit, and a ground electrode having one end portion joined to a front end face of the metal shell and the other end portion facing the center electrode to define a spark gap therebetween, wherein the spark plug satisfies the following conditions: H ≥ 1 mm, Vc ≤ 17 mm3 and Ra ≥ 10×10-3 m·K/W where H is a length by which the ceramic insulator protrudes toward the front from the front end face of the metal shell in the axial direction; Vc is a volume of part of the ceramic insulator extending within a range of 2 mm from a front end of the ceramic insulator toward the rear in the axial direction; and Ra is a thermal resistance per unit length, excluding air space, at 20°C at a cross section of the assembly unit taken perpendicular to the axial direction at a position 2 mm away from the front end of the ceramic insulator.