Two-Stroke Engine Intake Passage Design for Blow-by Prevention
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Solution Overview
Problem
Two-stroke internal combustion engines face issues with air-fuel mixture blow-by during scavenging, leading to fuel waste and air pollution, and existing solutions complicate the structure and increase costs with partition walls or separate passages.
Innovation Solution
A two-stroke internal combustion engine design featuring a fuel injection valve that supplies fuel to the crank chamber, allowing controlled air-fuel mixture generation and scavenging, with a simple intake passage structure that prevents blow-by by using stagnant air as leading air in the scavenging process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a partition wall is added to divide the intake passage into air-fuel mixture passage and air passage, then air-fuel mixture blow-by is prevented, but device complexity and manufacturing cost increase
Solution Approach 1:
The intake passage is divided into a first intake passage for air-fuel mixture and a second intake passage for air only, allowing separate control of air and fuel paths. This segmentation prevents air-fuel mixture blow-by while maintaining structural simplicity by using distinct passages rather than complex partition walls.
Solution Approach 2:
The fuel injection function is extracted from the carburetor system and implemented as a separate fuel injection valve that directly injects fuel into the crank chamber. This eliminates the need for partition walls in the intake passage while still achieving blow-by prevention through the two-passage configuration.
2Object-affected harmful factors
If separate air-fuel mixture passage and air passage are used, then air-fuel mixture blow-by is prevented, but device complexity and cost increase due to additional components
Solution Approach 1:
The air passage and scavenging passage are merged into a single second intake passage that communicates with both the crank chamber and scavenging passage. This merging reduces the number of separate components while maintaining the functional separation needed to prevent air-fuel mixture blow-by.
Solution Approach 2:
The second intake passage serves multiple functions: it supplies air to the crank chamber during the intake stroke and supplies air to the scavenging passage during the exhaust stroke. This multi-functionality reduces the need for separate dedicated passages for each function.
3Adaptability or versatility
If fuel is injected toward the first intake passage or crank chamber, then air-fuel mixture generation is controlled, but fuel injection timing and positioning must be precisely controlled
Solution Approach 1:
The fuel injection valve is positioned to inject fuel specifically toward the first intake passage or crank chamber entrance, creating a localized fuel injection zone. This local quality approach ensures proper air-fuel mixture formation without requiring precise control of fuel injection timing, as the fuel is deposited in a specific location where it will naturally mix with incoming air.
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 design effectively reduces air-fuel mixture blow-by, improves exhaust gas components, simplifies the intake passage structure, and enhances the reliability and startability of the engine, while reducing the size and weight of portable working machines.
Implementation Method 1
The air that has been introduced into the crank chamber is mixed with the fuel to generate an air-fuel mixture
Implementation Method 2
a part of air passing through the intake passage is introduced into the crank chamber through the first intake passage, and another part of air is introduced into the crank chamber through the second intake passage and the scavenging passage
Implementation Method 3
The air-fuel mixture in the crank chamber is introduced into the combustion chamber through the scavenging passage by actuating the piston. The air-fuel mixture in the combustion chamber is compressed by the piston
Implementation Method 4
an ignition device configured to ignite an air-fuel mixture in the combustion chamber
Implementation Method 5
The air-fuel mixture is compressed by the piston, and is ignited by the ignition device to cause combustion and expansion
Implementation Method 6
ignited by the ignition device to cause combustion and expansion. Discharge and scavenging are achieved while the piston is being pushed back by the combustion and expansion
Data Source
AI summary
Provided is a two-stroke internal combustion engine, including: a fuel injection valve configured to supply a fuel to a crank chamber; an intake passage configured to allow only air to be sucked thereinto under a negative pressure generated when a piston is actuated; and a scavenging passage that allows communication between the crank chamber and a combustion chamber. The intake passage is branched into a first intake passage and a second intake passage. The first intake passage communicates with the crank chamber. The second intake passage communicates with the scavenging passage. The fuel injection valve is configured to inject the fuel toward at least one of the first intake passage or the crank chamber. Further, air stagnant in the scavenging passage at end of air suction serves as leading air to contribute to scavenging.