Piston Through Holes for Combustion Chamber Cooling
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Solution Overview
Problem
Two-cycle engines face challenges in maintaining combustion chamber and piston temperatures, leading to abnormal combustion and run-on due to inadequate cooling, despite increased air-cooling efforts, which fail to effectively reduce blow-by gas and temperature.
Innovation Solution
The engine design incorporates a piston with a crown portion and peripheral wall featuring through holes and communication passages that allow scavenging gas to flow, creating a pressure difference and cooling the crown portion during the scavenging stroke, while maintaining stratified scavenging and reducing blow-by gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If air-cooling fins area and air-cooling fan size are increased to increase cooling air amount, then cooling effectiveness is improved, but the temperature reduction of combustion chamber and piston interior remains insufficient
Solution Approach 1:
The invention extracts the cooling function from the external air-cooling system and implements it within the piston structure itself. Through holes are provided in the piston peripheral wall to enable direct flow of scavenging gas through the piston body, creating internal cooling passages that directly cool the combustion chamber and piston interior without relying on external air-cooling fins and fans.
Solution Approach 2:
The scavenging gas serves as an intermediary cooling medium. Instead of using external air-cooling systems, the invention utilizes the scavenging gas that already flows through the engine as the cooling medium. The scavenging gas flows through the through holes in the piston peripheral wall, transferring heat from the combustion chamber and piston interior to the scavenging gas, thereby achieving cooling without additional external cooling systems.
2Object-generated harmful factors
If blow-by gas amount is reduced to improve exhaust quality, then exhaust gas degradation is reduced, but combustion chamber and piston temperature increase causing abnormal combustion and run-on
Solution Approach 1:
The invention applies local quality by providing through holes at specific locations in the piston peripheral wall to create localized cooling zones. The cooling effect is concentrated where it is most needed - at the piston crown and combustion chamber interface - while maintaining the overall engine scavenging function. This localized approach allows temperature control without requiring complete changes to the scavenging system.
3Temperature
If scavenging gas flows through combustion chamber to cool it, then temperature control is improved, but scavenging efficiency may be degraded
Solution Approach 1:
The invention implements dynamic control of the cooling flow by making the through holes operational only during specific phases of the engine cycle. The scavenging gas flows through the through holes during the scavenging stroke when the scavenging ports are open, and the cooling flow is naturally regulated by the pressure differential and timing of the engine operation. This dynamic approach ensures cooling occurs when needed without interfering with the scavenging process.
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 effectively cools the piston crown, reduces abnormal combustion and run-on, and enhances engine performance by maintaining temperature control and emission reduction without degrading scavenging efficiency.
Implementation Method 1
the cylinder and the piston are configured so that the through hole overlaps the second opening to communicate with the communication passage at least in a partial interval of a scavenging stroke
Implementation Method 2
scavenging gas to flow, creating a pressure difference and cooling the crown portion during the scavenging stroke
Implementation Method 3
draw heat from the interior of the combustion chamber and sweep past directly to the outside of the cylinder
Data Source
AI summary
A peripheral wall portion of a piston is provided with a through hole penetrating through the peripheral wall portion. A cylinder is provided with a scavenging passage having a first opening being open in a bore surface and configured to make a bore section and a crank chamber communicate with each other and is provided with a communication passage having a second opening being open in the bore surface on the other side with respect to the first opening and configured to make the bore section and the scavenging passage communicate with each other. The cylinder and piston are configured so that the through hole overlaps the second opening to communicate with the communication passage in a partial interval of a scavenging stroke in which the first opening becomes open in the bore surface on one side of the piston with reciprocal motion of the piston.