Piston Pocket Positioning for Two-Stroke Engine Scavenging
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Solution Overview
Problem
In two-stroke internal combustion engines, scavenging losses occur due to contamination of the supply channel with fuel during the scavenging process, leading to deteriorated exhaust-gas values as an air/fuel mixture enters the combustion chamber and escapes, contaminating the fuel-free combustion air.
Innovation Solution
The piston pocket is positioned closer to the transfer window than the supply channel inlet, allowing the air/fuel mixture to be drawn into the crankcase during the upward stroke, preventing its entry into the supply channel, and ensuring scavenging advance air remains fuel-free by maintaining a shorter distance between the piston pocket and the transfer window compared to the supply channel inlet, thereby reducing contamination and scavenging losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the piston pocket is positioned closer to the supply channel inlet, then the air/fuel mixture can be drawn into the crankcase more effectively, but the supply channel becomes contaminated with fuel
Solution Approach 1:
The patent applies dimensional arrangement by positioning the transfer window and supply channel inlet at different axial distances from the piston pocket. The transfer window is arranged closer to the piston pocket in the axial direction, creating a spatial sequence that ensures the air/fuel mixture is drawn into the crankcase through the transfer channel before the supply channel inlet is activated, thus preventing fuel contamination while maintaining scavenging efficiency
2Quantity of substance
If the transfer channel is positioned closer to the piston pocket, then scavenging advance air can be stored more effectively, but the air/fuel mixture may escape through the outlet
Solution Approach 1:
The patent implements preliminary action by positioning the transfer window closer to the piston pocket than the supply channel inlet, enabling the air/fuel mixture to be drawn into the crankcase during the upward stroke before the supply channel is activated. This temporal and spatial sequencing ensures that scavenging advance air is stored in the transfer channel in a controlled manner, preventing mixture escape through the outlet while maintaining effective air storage
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 significantly reduces the contamination of the supply channel with fuel, resulting in improved exhaust-gas values by maintaining the purity of the scavenging advance air and minimizing scavenging losses, thus enhancing the engine's efficiency.
Implementation Method 1
An air/fuel mixture, which has reached the piston pocket during the downward stroke of the piston, can therefore be drawn by suction into the crankcase via the transfer channel during an upward stroke of the piston with which an underpressure arises in the crankcase
Data Source
AI summary
An internal combustion engine has a cylinder (2) wherein a combustion chamber (3) is formed which is delimited by a piston (5) journalled to move back and forth. At least one transfer channel (14) is provided which connects the crankcase (4) of the engine to the combustion chamber (3) in at least one position of the piston (5). The engine has a supply channel (13) which opens with a supply channel inlet (11) at the cylinder bore (34). The supply channel (13) is connected to the transfer channel (14) via at least one piston pocket (22, 42) in at least one position of the piston (5). In order to achieve low exhaust-gas values of the engine, the piston pocket (22, 42) has a distance (a) to a lower edge (27) of the transfer window (15) which is less than the distance (b) to a lower edge (26) of the inlet (11) of the supply channel at bottom dead center of the piston (5). A method for operating an engine provides that the piston pocket (22, 42) is first connected to the transfer window (15) and then to the supply channel inlet (11) during the upward stroke of the piston (5).