Spark Plug Ground Electrode Slope Angle for Ignitability
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Solution Overview
Problem
Conventional spark plugs with curved ground electrodes perpendicular to airflow direction do not adequately improve ignitability of the air-fuel mixture, as they fail to effectively extend the discharge spark and create sufficient negative pressure to enhance combustion.
Innovation Solution
A spark plug design featuring a ground electrode with a sloped surface that recedes from the center electrode's tip end surface, creating a virtual plane perpendicular to airflow, which regulates airflow and forms negative pressure, allowing the discharge spark to extend away from the center electrode, thereby improving ignitability. The ground electrode's slope angle (10°≤Dg≤70°), thickness (1.0 mm≤Th≤1.5 mm), and width (1.5 mm≤Wd) are critical in achieving this configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the ground electrode is curved perpendicular to airflow direction, then the structure is simple, but the ignitability of air-fuel mixture is not adequately improved
Solution Approach 1:
The ground electrode is designed with an asymmetric cross-sectional shape featuring a sloped surface on the airflow upstream side and a substantially perpendicular surface on the downstream side. This asymmetric configuration creates effective negative pressure to extend the discharge spark, thereby improving ignitability while maintaining manufacturing feasibility through a single-piece construction.
2Reliability
If the ground electrode has a sloped surface receding from center electrode, then discharge spark extension is improved, but the device complexity increases
Solution Approach 1:
The ground electrode's cross-sectional perimeter is divided into distinct functional segments: a sloped surface on the upstream side for creating negative pressure, and substantially perpendicular surfaces on the downstream side for stable spark extension. This segmentation of functional surfaces optimizes each area's contribution to overall ignitability.
Solution Approach 2:
The ground electrode features a curved configuration with a sloped surface that recedes from the center electrode tip end surface. This curved, sloped geometry effectively guides airflow to create negative pressure zones that extend the discharge spark away from the center electrode, improving ignitability.
3Strength
If the ground electrode thickness and width are increased, then durability and wear resistance are improved, but the airflow regulation and negative pressure formation may be compromised
Solution Approach 1:
The ground electrode dimensions are optimized within specific ranges: thickness of 0.5-2.0 mm and width of 1.0-3.0 mm. These parameter ranges balance structural durability with effective airflow regulation, ensuring the electrode maintains sufficient strength while preserving the negative pressure formation capability needed for spark extension.
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 described spark plug design significantly improves ignitability of the air-fuel mixture by stabilizing and extending the discharge spark, increasing the contact area and combustibility, while also enhancing the durability of the spark plug through optimized wear resistance and manufacturability.
Implementation Method 1
A predetermined virtual plane that passes through a center axis of the spark plug along the curved ground electrode faces a flow direction of airflow. The ground electrode includes a main body including: an opposing surface on a first side facing the tip end surface of the center electrode; and a sloped surface on a second side opposite the first side. The main body satisfies 10 [°]≤Dg≤70 [°], 1.0 [mm]≤Th, and 1.5 [mm]≤Wd, where Dg is a slope angle of the sloped surface relative to the opposing surface, Th is a thickness of the main body in an insertion direction of the center electrode, and Wd is a width of the ground electrode in a direction perpendicular to the virtual plane.
Data Source
AI summary
A spark plug includes a ground electrode that is curved to oppose a tip end surface of a center electrode. A predetermined virtual plane that passes through a center axis of the spark plug along the curved ground electrode faces a flow direction of airflow. The ground electrode includes a main body including: an opposing surface on a first side facing the tip end surface of the center electrode; and a sloped surface on a second side opposite the first side. The main body satisfies 10 [°]≤Dg≤70 [°], 1.0 [mm]≤Th, and 1.5 [mm]≤Wd, where Dg is a slope angle of the sloped surface relative to the opposing surface, Th is a thickness of the main body in an insertion direction of the center electrode, and Wd is a width of the ground electrode in a direction perpendicular to the virtual plane.