Aircraft Lubrication System Oil Mist Reduction via PRV Bypass
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Solution Overview
Problem
Aircraft lubricating systems face issues with oil mist escaping through the vent line due to oil being atomized by the pressure regulating valve (PRV) at high velocities, resulting in oil droplets that are too small for the de-oiler to effectively remove, leading to concerns for engine operators despite not causing oil consumption problems.
Innovation Solution
A lube system configuration that bypasses oil around the valve seat area of the PRV, reducing velocities and energies, allowing oil droplets to form at larger sizes that can be efficiently removed by the de-oiler, while maintaining air velocity through the valve seat area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the pressure regulating valve (PRV) operates at high velocities to regulate pressure, then pressure regulation function is improved, but oil is atomized into small droplets that cannot be effectively removed by the de-oiler
Solution Approach 1:
The air-oil flow path is segmented into two separate paths: one path directs air through the PRV valve seat area for pressure regulation, while the other path directs oil through bypass passages around the valve seat. This segmentation prevents oil from being atomized by the high-velocity air flow through the PRV while maintaining the pressure regulation function.
Solution Approach 2:
Bypass passages act as an intermediary structure that redirects oil flow away from the high-velocity zone created by the PRV operation. The passages provide a separate route for oil that avoids direct interaction with the high-speed air flow through the valve seat, preventing atomization while allowing both functions to coexist.
2Productivity
If the de-oiler is designed to remove large oil droplets, then removal efficiency for large droplets is improved, but small oil mist droplets pass through and escape
Solution Approach 1:
The bypass passages perform a preliminary action by redirecting oil away from the PRV high-velocity zone before the air-oil mixture reaches the de-oiler. This preliminary redirection prevents the formation of small mist droplets in the first place, allowing the de-oiler to focus on removing larger droplets that it is designed to handle.
3Stress or pressure
If the PRV restricts air flow to elevate tank pressure, then suction pressure for lube pump is improved, but cavitation risk increases if pressure is insufficient
Solution Approach 1:
The flow paths are segmented to separate oil and air flows through the PRV area. This ensures that sufficient total flow capacity is maintained through the tank while preventing oil atomization, thereby maintaining stable suction pressure and preventing cavitation.
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
Substantially reduces visible oil mist by ensuring oil droplets are large enough to be separated by the de-oiler, maintaining suction pressure and preventing cavitation in the lube pump.
Implementation Method 1
a deaerator configured to remove a first quantity of oil from a first air-oil supply to generate a second air-oil supply having a second quantity of oil
Implementation Method 2
a de-oiler disposed along the air vent line and configured to remove from the second air-oil supply oil mist including oil droplets of a minimum size
Implementation Method 3
a pressure regulating valve (PRV) disposed along the air vent line between the deaerator and the de-oiler to regulate fluid pressures within the air-oil tank
Implementation Method 4
an insert disposed between the deaerator and the PRV to force oil in the second air-oil supply to bypass a valve seat area of the PRV
Data Source
Figure 1
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Figure 3
AI summary
A lube system, 10, is provided and includes an air-oil tank, 20, including a deaerator, 21, configured to remove a first quantity of oil from a first air-oil supply, 110, to generate a second air-oil supply, 130, having a second quantity of oil, which is smaller than the first quantity of oil, the air oil tank, 20, being configured to output the second air-oil supply, 130, to an air vent line, 140, a de-oiler, 40, disposed along the air vent line, 140, and configured to remove from the second air-oil supply, 130, oil mist including oil droplets of a minimum size and a system, 60, disposed between the deacarator, 21, and the de-oiler, 40, which is configured to encourage formation of the oil droplets of at least the minimum size.