Stratified Scavenging Two-Stroke Engine Airflow Control
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Solution Overview
Problem
Stratified two-stroke engines face challenges in maximizing air storage for pre-scavenging to prevent blow-by of unburned gas through the exhaust port, as existing designs often limit the amount of air available for pre-scavenging, leading to inefficiencies in gas separation and combustion processes.
Innovation Solution
The design incorporates a second scavenging passage that communicates with the first scavenging passage via a cutout hole, allowing air to be stored in both passages and supplied to the cylinder, with check valves controlling airflow to prevent reverse flow and mixing of the gaseous mixture with air for pre-scavenging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a single scavenging passage is used with a check valve to prevent reverse flow, then air flow control is improved, but the amount of air stored for pre-scavenging is limited
Solution Approach 1:
The scavenging system is divided into multiple independent scavenging passages (first scavenging passage and second scavenging passage), each capable of storing air separately. This segmentation allows the total air storage capacity to be increased without requiring a single large complex passage, as each passage can be optimized independently while contributing to the overall pre-scavenging air quantity.
Solution Approach 2:
Multiple scavenging passages are combined to work together in the same engine cycle. The first and second scavenging passages both receive air from the air passage and both supply air to the cylinder, merging their contributions to achieve sufficient pre-scavenging air quantity that would be difficult to obtain from a single passage.
2Quantity of substance
If check valves are added to control air flow in multiple scavenging passages, then air storage capacity increases, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The system uses multiple simple scavenging passages rather than one complex passage, allowing each passage to be manufactured independently with standard checking procedures. This segmentation simplifies the manufacturing process for each individual component while achieving the cumulative effect of increased air storage capacity.
Solution Approach 2:
The first and second scavenging passages are designed as similar or identical structures, allowing for standardized manufacturing processes and components. This copying approach reduces manufacturing complexity by using repeated, proven designs rather than creating entirely unique complex passages.
3Reliability
If air is supplied to multiple scavenging passages, then pre-scavenging effectiveness improves, but the risk of gaseous mixture mixing with air increases
Solution Approach 1:
By dividing the scavenging system into separate passages, each passage can be equipped with its own check valve to independently control air flow. This segmentation ensures that the gaseous mixture and air remain separated in different passages, maintaining stratified separation while providing redundant flow control paths.
Solution Approach 2:
Check valves act as intermediary devices between the air passage and scavenging passages, and between the scavenging passages and the cylinder. These intermediaries control the direction of flow to prevent mixing of air and gaseous mixture, ensuring that each substance follows its designated path without contamination.
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 enables a larger amount of air to be stored for pre-scavenging, effectively reducing blow-by of unburned gas and enhancing the stratified scavenging process by maintaining a clear separation between air and gaseous mixtures, thereby improving engine efficiency.
Implementation Method 1
a check valve for controlling open and close of the air passage to the scavenging passage
Implementation Method 2
a gaseous mixture is supplied from an intake passage to the inside of a crankcase by a negative pressure generated inside of the crankcase
Implementation Method 3
the air, that has been supplied into the scavenging passage during the upward stroke of the piston, is supplied to the inside of the cylinder as air for pre-scavenging
Implementation Method 4
since a layer of air is present between a combustion gas (exhaust gas) produced by combustion and a gaseous mixture that is newly supplied via the scavenging passage, it is possible to prevent the gaseous mixture from being mixed into the combustion gas
Data Source
AI summary
A stratified scavenging two-stroke engine includes a first scavenging passage that extends from a first scavenging intake that opens to the inside of the crankcase to a scavenging port that opens to the inside of a cylinder, and a second scavenging passage that branches from the first scavenging passage and extends to a second scavenging intake that opens to the inside of the crankcase. An air passage is provided to supply air for pre-scavenging into the first scavenging passage at a position closer to the first scavenging intake than a position at which the second scavenging passage branches from the first scavenging passage. A first check valve inhibits a flow of air from the first scavenging passage during an upward stroke of the piston, and a second check valve inhibits a flow of air and a gaseous mixture from the first scavenging passage during a downward stroke of the piston.