Ru Electrode Chip Microstructure for Longer-Life Spark Plugs
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Solution Overview
Problem
The premature wear of spark plugs due to oxidation of ruthenium (Ru) chips in the center and ground electrodes, leading to reduced service life, is addressed by controlling the crystal grain boundaries and porosity in the chip structure.
Innovation Solution
The spark plug design includes Ru-containing chips with controlled crystal grain boundaries and porosity, where the average number of grain boundaries per unit length and the average grain circumference lengths are within specific ranges, reducing oxidation and thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a chip made of simple Ru or Ru alloy is used in the center electrode or ground electrode, then the spark plug can operate at high temperatures, but the Ru easily oxidizes and wears out, reducing service life
Solution Approach 1:
The invention changes the microstructural parameters of the Ru chip by controlling crystal grain size (6.5-320 μm circumference) and grain boundary density (20-400 boundaries/mm). This parameter optimization reduces oxidation susceptibility while maintaining high-temperature operation capability, thereby extending service life without sacrificing thermal performance
Solution Approach 2:
The invention uses Ru as the main constituent (50-100 mass%) but combines it with other elements to form a composite material system. This composite structure provides both the high-temperature stability of Ru and enhanced resistance to oxidation and wear, resolving the contradiction between temperature resistance and service life
2Object-affected harmful factors
If the chip has large crystal grains, then oxidation resistance improves, but thermal stress and mechanical strength deteriorate
Solution Approach 1:
The invention optimizes the crystal grain parameters to a specific range (circumference 6.5-320 μm, density 20-400 boundaries/mm). This intermediate grain size provides a balance: large enough to resist oxidation but small enough to maintain mechanical strength and thermal stress resistance, resolving the contradiction between oxidation resistance and strength
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 configuration significantly reduces wear and extends the service life of the spark plug by minimizing oxidation and thermal stress on the Ru chips.
Implementation Method 1
Since oxidized vapor of Ru is remarkable under high temperature, the chip of the related art easily wears out
Data Source
AI summary
A spark plug includes a center electrode and a ground electrode that are electrically insulated. At least one of the center electrode and the ground electrode includes a chip containing Ru as a main constituent, and the chip includes a discharge surface facing another one of the center electrode and the ground electrode. When a first test line that is 10 μm away from the discharge surface is drawn on a cross-section of the chip, an average of the numbers of crystal grain boundaries of the chip, the crystal grain boundaries being intersected by the first test line, per unit length of the first test line is 20 pieces/mm or more and 400 pieces/mm or less, and an average of the lengths of circumferences of crystal grains intersected by the first test line is 6.5 μm or more and 320 μm or less.