Two-Stroke Engine Scavenging With Separate Air-Fuel Supply
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Solution Overview
Problem
Two-stroke internal combustion engines suffer from air-fuel mixture blow-by, leading to fuel waste and air pollution, and lack precise control over leading air and air-fuel mixture supply to meet varying operating states, especially in portable working machines.
Innovation Solution
A two-stroke internal combustion engine design with a fuel injection valve supplying fuel to the crank chamber, allowing controlled air-fuel mixture generation and scavenging, using a scavenging passage for air stagnation to contribute to scavenging, and separate intake passages for air and fuel, enabling precise control of leading air and air-fuel mixture supply based on engine state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If air and air-fuel mixture are supplied through separate intake passages to reduce blow-by, then scavenging efficiency is improved, but control precision over supply ratio remains insufficient
Solution Approach 1:
The patent employs a negative pressure detection mechanism that monitors the pressure in the combustion chamber and provides feedback control. This feedback system adjusts the supply amounts of leading air and air-fuel mixture based on real-time operating conditions, enabling precise control of the supply ratio across different engine operating ranges while maintaining high scavenging efficiency.
Solution Approach 2:
The patent implements dynamic adjustment mechanisms for the intake passages, allowing the sectional areas and supply ratios of leading air and air-fuel mixture to vary dynamically based on engine operating conditions. This dynamic control enables optimal supply ratio adjustment throughout the entire operating range, resolving the contradiction between maintaining scavenging efficiency and achieving precise control.
2Reliability
If air-fuel mixture supply amount is increased to maintain operation stability across entire rotation range, then operational stability is improved, but fuel waste increases
Solution Approach 1:
The patent applies partial action by supplying air and air-fuel mixture in optimized proportions rather than excessive air-fuel mixture. The leading air supply is controlled to be sufficient for scavenging without requiring an overly rich air-fuel mixture, thereby maintaining operational stability across the rotation range while reducing fuel waste through precise dosing.
Solution Approach 2:
The patent changes the parameter of air-fuel mixture composition by introducing separate control of leading air and air-fuel mixture supplies. This allows the air-fuel ratio to be optimized at different operating points, maintaining stability without consistently using a rich mixture that would waste fuel.
3Measurement precision
If multiple intake passages and control mechanisms are added to achieve precise control, then control precision is improved, but device complexity increases
Solution Approach 1:
The patent achieves multi-functionality by designing the scavenging passage to serve dual purposes: as a fuel injection path and as a leading air supply passage. This universal design allows precise control of air and air-fuel mixture supplies without adding separate complex intake passages, thereby improving control precision while minimizing device complexity.
4Power
If engine is designed for high-rotation-number and high-load operation, then power output is improved, but adaptability to varying operating states deteriorates
Solution Approach 1:
The patent implements dynamic control mechanisms that allow the engine to adapt to varying operating states. The negative pressure-based feedback control and adjustable supply ratios enable the engine to optimize performance across different rotation numbers and load conditions, maintaining high power output capability while improving adaptability to accelerating, decelerating, and light-load operations.
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
Prevents air-fuel mixture blow-by, improves exhaust gas components, enhances control reliability, simplifies engine design, and allows optimal air-fuel mixture supply across varying operating conditions, including high-rotation-number and high-load ranges, accelerations, and light-load operations.
Implementation Method 1
fuel is injected into a crank chamber, allow air which has been sucked through an intake passage to be introduced into the scavenging passage, and allow air stagnant in the scavenging passage to contribute to scavenging
Implementation Method 2
piston which is configured to reciprocate inside the cylinder through combustion and expansion which occur in the combustion chamber
Implementation Method 3
intake passage which is configured to allow only air to be sucked thereinto under a negative pressure generated when the piston is actuated
Data Source
Figure 1
Figure 2(a)~2(d)
Figure 3~5
AI summary
Provided is a two-stroke internal combustion engine, including: a fuel injection valve (25) configured to supply a fuel into a crank chamber (8); an intake passage (17) configured to allow only air to be sucked thereinto under a negative pressure generated when a piston (4) is actuated; and a scavenging passage (18) that allows communication between the crank chamber (8) and a combustion chamber (6). Further, air passing through the intake passage (17) is introduced into the scavenging passage (18), and air stagnant in the scavenging passage (18) at end of air suction contributes to scavenging.