Two-Stroke Engine Communication Passage for Scavenging
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Solution Overview
Problem
Two-stroke engines used in portable power machines face inefficiencies in scavenging and combustion due to unburned mixture gas being exhausted along with post-combustion gases, leading to increased hydrocarbon emissions.
Innovation Solution
The engine design incorporates a communication passage with an inclined ceiling and bottom surface, expanding the scavenging flow to disperse mixture gas widely in the combustion chamber, improving scavenging and combustion efficiency by ensuring thorough replacement of gases and reducing unburned gas emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a conventional scavenging passage is used, then the structure is simple, but unburned mixture gas is exhausted along with post-combustion gases causing increased hydrocarbon emissions
Solution Approach 1:
The scavenging passage is divided into two distinct parts: a first scavenging passage that leads to a combustion chamber and a second scavenging passage that leads to an exhaust port. This segmentation allows unburned mixture gas to be directed to the exhaust port separately from post-combustion gases, preventing hydrocarbon emissions while maintaining a relatively simple overall structure.
Solution Approach 2:
The harmful unburned mixture gas is extracted from the combustion chamber through the first scavenging passage and directed through the second scavenging passage to the exhaust port, separating it from the post-combustion gases. This extraction prevents the unburned gas from being re-exhaled into the combustion chamber, reducing hydrocarbon emissions.
2Productivity
If the scavenging passage is simplified, then the device complexity is reduced, but scavenging efficiency and combustion efficiency are insufficient
Solution Approach 1:
A communication passage is introduced that extends in the radial direction of the cylinder, connecting the first and second scavenging passages. This adds a radial dimension to the scavenging flow path, allowing mixture gas to be compressed and expanded in a controlled manner to improve scavenging efficiency and combustion efficiency.
Solution Approach 2:
The communication passage has its ceiling surface inclined toward the cylinder head and bottom surface inclined toward the crank chamber, creating a progressive expansion of the passage cross-sectional area. This parameter change allows the mixture gas to be compressed in the narrow section and then expanded in the wider section, improving atomization and dispersion into the combustion chamber.
3Object-generated harmful factors
If the communication passage cross-section is uniform, then the structure is simple, but mixture gas is not sufficiently dispersed and atomized
Solution Approach 1:
The communication passage has different cross-sectional areas at different locations: a smaller cross-sectional area near the first scavenging passage and a larger cross-sectional area near the second scavenging port. This local variation in geometry allows the passage to first compress the mixture gas and then expand it to promote atomization and wide dispersion into the combustion chamber, preventing unburned gas from being exhausted.
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 power output and response while significantly reducing hydrocarbon emissions by ensuring efficient scavenging and combustion, with a 30% reduction in unburned gas in the exhaust compared to conventional designs.
Implementation Method 1
the mixture gas compressed in the scavenging passage is expanded to a large extent in the communication passage and jetted from the scavenging port into the combustion chamber, so that the mixture gas can be dispersed widely in the combustion chamber
Implementation Method 2
since a scavenging flow (mixture gas) is expanded in the communication passage, atomization of the mixture gas can be promoted and the mixture gas can be guided into the combustion chamber while spreading in the axial direction of the cylinder
Data Source
Figure 1
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AI summary
Two-cycle engine includes cylinder block formed with a cylinder and crank chamber. The cylinder block includes: an exhaust passage leading to a combustion chamber in the cylinder through an exhaust port opened to an inner circumferential surface of the cylinder; a scavenging port opened to the inner circumferential surface of the cylinder; a communication passage extending from the scavenging port in a radial direction of the cylinder; and a scavenging passage extending in an axial direction of the cylinder, communicating with the crank chamber, and having an opening portion formed in a bottom surface of the communication passage. A ceiling surface of the communication passage is inclined toward a cylinder head with increasing distance from a scavenging passage side thereof toward the scavenging port. A bottom surface of the communication passage is inclined toward the crank chamber with increasing distance from a scavenging passage side thereof toward the scavenging port.