Two-Stroke Engine Scavenging Port Timing Offset
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Solution Overview
Problem
Two-stroke engines face the issue of 'blow-by' due to air-fuel mixture collisions at the center of the cylinder, leading to unburned gas emissions, which is not adequately addressed by existing technologies such as the four-flow scavenging type engine with porous shield members or rib configurations.
Innovation Solution
The implementation of a two-stroke engine with four scavenging ports, where the first and second sets of diagonally positioned ports have different opening timings, allowing the air-fuel mixtures to flow into the combustion chamber at offset positions and reducing collisions, thereby minimizing 'blow-by' and unburned gas emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If air-fuel mixture is supplied to the combustion chamber through confronting scavenging ports, then the scavenging process is efficient, but the air-fuel mixtures collide at the center of the cylinder causing blow-by and unburned gas emissions
Solution Approach 1:
The patent applies preliminary action by having the first diagonally paired scavenging ports open before the second diagonally paired scavenging ports. This sequential opening allows the first air-fuel mixture to enter the combustion chamber and establish a flow pattern before the second mixture enters, preventing direct collision at the cylinder center and reducing blow-by emissions while maintaining effective scavenging
2Object-generated harmful factors
If the number of scavenging ports is increased to four pairs (six-flow scavenging), then blow-by is suppressed, but the device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies periodic action through the sequential opening and closing of the two diagonally paired scavenging port sets. The first pair opens and begins scavenging before the second pair opens, creating a time-periodic scavenging action that suppresses blow-by through controlled flow sequencing rather than requiring all ports to be open simultaneously, thus reducing device complexity compared to six-flow scavenging
3Object-generated harmful factors
If shield members with holes are disposed on scavenging passages to reduce flow velocity, then collision between air-fuel mixtures is reduced, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent uses preliminary action through sequential port opening timing rather than physical modifications to the scavenging passages. By controlling the timing of when each diagonally paired port set opens, the system reduces air-fuel mixture collision velocity without requiring shield members, holes, or ribs, thereby maintaining manufacturing simplicity while achieving collision reduction
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 suppresses the 'blow-by' phenomenon, reducing unburned gas emissions by approximately 3.1% to 5.9% and improving output by 2.1% to 2.8% compared to traditional four-flow scavenging type engines, while ensuring complete scavenging of the combustion chamber.
Implementation Method 1
amounts of unburned gas in the exhaust gas flow generated by movement of the piston are removed
Data Source
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AI summary
An engine (2) is a four-flow scavenging type engine. Four scavenging ports (34) include: first right and left scavenging ports (34(lef-1) and 34(ref-1) that lie on a side relatively away from an exhaust port (22) and that lie facing each other with a cylinder (4) in between; and second right and left scavenging ports (34(lef-2) and 34(ref-2) that lie closer to the exhaust port (22) than first right and left scavenging ports do and that lie facing each other with the cylinder (4) in between. The second left scavenging port and the first right scavenging port that make up a first mutually diagonal set (Diag-No. 1) have different opening timings from those of the first left scavenging port and the second right scavenging port that make up a second mutually diagonal set (Diag-No.2).