Spark Plug Center Electrode Composition for Oxide Film Stability
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Solution Overview
Problem
High heat rating in spark plugs leads to increased temperature changes, causing the oxide film on the center electrode to peel off easily, resulting in corrosion and wear due to sulfur in fuel.
Innovation Solution
A spark plug design with a center electrode composed of Ni, Cr, and additional elements like Mn, Si, Al, Ti, rare earth elements, Hf, and Zr, where Ni is the largest proportion, Cr is 12% by mass or more, and at least one element from group B is present in 0.1% by mass or more, along with a tip containing Ir and group A elements, forming a dense oxide film and reducing stress from thermal expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the heat rating of the spark plug is increased, then the temperature change of the center electrode increases, but the oxide film peels off more easily due to thermal expansion
Solution Approach 1:
The invention changes the chemical composition parameters of the center electrode by adding specific elements (Fe: 0.01-2.0 wt%, Mn: 0.01-1.0 wt%, Si: 0.01-0.5 wt%, Al: 0.01-0.5 wt%) to modify the thermal expansion characteristics and oxide film formation behavior, thereby resolving the contradiction between high heat rating and oxide film adhesion
Solution Approach 2:
The invention creates a composite material system by combining Ni-based alloy with multiple alloying elements (Cr, Fe, Mn, Si, Al) to form a center electrode that possesses both high temperature resistance and controlled thermal expansion properties, preventing oxide film peeling while maintaining high heat rating
2Stability of the object's composition
If the oxide film peels off due to thermal expansion, then the center electrode is exposed to sulfur in fuel, but corrosion and wear increase quickly
Solution Approach 1:
The invention applies preliminary anti-action by pre-forming a stable, adherent oxide film through controlled composition that resists peeling under thermal cycling, thereby preventing sulfur from reaching and corroding the metal substrate before corrosion can occur
Solution Approach 2:
The invention uses sacrificial alloying elements (Fe, Mn, Si, Al) that preferentially oxidize to form protective oxide layers, sacrificing these elements to protect the main Ni-Cr structure from sulfur corrosion
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 enhances wear resistance by ensuring the oxide film reforms quickly and inhibits corrosion, even under high temperature changes, while the Ir and group A elements reduce stress and fracture risk.
Implementation Method 1
the center electrode undergoes a larger temperature change, and the oxide film peels off more easily due to the thermal expansion of the center electrode
Implementation Method 2
a tip welded to the front end portion with a fused portion therebetween
Data Source
Figure 1
Figure 2
AI summary
A spark plug including a center electrode with a tip 27 welded to a front end portion 25 with a fused portion 26 therebetween. The front end portion contains Ni, Cr, and at least one element selected from a group B consisting of Mn, Si, Al, Ti, rare earth elements, Hf, and Zr. Ni is present in the largest proportion, and Cr is present in the second largest proportion and in an amount of 12% by mass or more. The at least one element selected from the group B is present in a total amount of 0.1% by mass or more. The front end portion satisfies f/e ≤ 0.15 and m/e ≤ 0.015, where f is the Fe content, e is the sum of the Cr, Si, and Al contents, and m is the Mo content.