Asymmetric Piston Protrusion for Spark-Ignition Engine Tumble Flow
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Solution Overview
Problem
In spark-ignition internal combustion engines with a protrusion on the piston and a cavity associated with the spark plug, the tumble flow is often decelerated, reducing turbulence energy and fuel efficiency.
Innovation Solution
The engine design includes a protrusion with an intake-side and an exhaust-side inclined surface on the piston, where the ratio of the exhaust-side inclined surface length to the intake-side inclined surface length is 1.25 or larger, and a downwardly recessed cavity at the spark plug position, facilitating smooth tumble flow guidance and increased geometric compression ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a protrusion is formed on the piston top surface with a cavity at the spark plug position, then flame propagation is improved and fuel efficiency is increased, but the tumble flow is decelerated and turbulence energy is reduced
Solution Approach 1:
The protrusion is designed with asymmetric inclined surfaces where the exhaust-side inclined surface has a specific length ratio (1.25 or more) compared to the intake-side inclined surface. This asymmetric geometry allows the tumble flow to maintain its speed and turbulence energy while still achieving the flame propagation benefits of the cavity configuration.
2Reliability
If a protrusion is formed on the piston top surface, then the geometric compression ratio is increased, but the tumble flow path is obstructed and combustion promotion effect is reduced
Solution Approach 1:
The protrusion incorporates a cavity at its apex positioned at the spark plug location, creating a local modification that enhances flame propagation without significantly obstructing the overall tumble flow path. The cavity serves as a flame holder and propagation accelerator while the inclined surfaces guide the tumble flow around it.
Solution Approach 2:
The asymmetric inclined surfaces of the protrusion are designed with specific length ratios to optimize both compression ratio and tumble flow guidance. The exhaust-side inclined surface being longer (ratio of 1.25 or more) creates a smoother flow path that reduces turbulence loss while maintaining compression efficiency.
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 enhances flame propagation, increases fuel efficiency by maintaining high turbulence energy, and prevents abnormal combustion due to improved scavenging performance.
Implementation Method 1
combustion is promoted by turbulence, which is generated by collapse of a tumble flow, as a piston approaches a compression top dead center
Data Source
AI summary
In a spark-ignition internal combustion engine in which a protrusion including an intake-side inclined surface and an exhaust-side inclined surface is formed on a top surface of a piston, and a cavity is formed in the protrusion at a position associated with a spark plug, the intake-side inclined surface and the exhaust-side inclined surface are formed in such a way that a ratio of a length of the exhaust-side inclined surface with respect to a length of the intake-side inclined surface is 1.25 or larger in a cross section passing through a center axis of the piston and orthogonal to an axis direction of a crankshaft.