Oil Film Thickness Measurement
Challenge
Oil Film Thickness Measurement for Marine Engine Applications
A leading marine engine manufacturer approached MTI Instruments to design and develop a non-contact oil film thickness measurement sensor capable of accurately measuring the microscopic oil film layer between the engine cylinder wall and the piston ring. This critical measurement is vital for engine performance testing, typically conducted across a wide RPM range (400 to 6000 RPM) with piston linear speeds reaching up to 500 inches/second and various torque settings.
For this application, a measuring system with a high-frequency response and a compact sensor size was essential. The sensor needed to minimize any modifications to the engine’s design while ensuring it didn’t affect the engine’s operating characteristics. MTI Instruments’ Accumeasure™ capacitive sensors excel in measuring the tiny capacitance changes caused by variations in oil thickness, which are then converted into accurate oil film thickness measurements.
Custom Probe Design for Precise Measurements
To achieve precise oil film thickness measurement during engine operation, MTI Instruments designed a custom probe that was significantly smaller than the piston ring width. This allowed the probe to capture dynamic measurement data as the piston ring passes the sensor face, ensuring real-time analysis without interfering with the engine’s function. High-temperature epoxy and specialized materials were used in the probe’s construction to enable operation at temperatures up to 285°C (545°F) and to withstand high-pressure conditions.
High-Frequency Response and Signal Optimization
Given the demanding application, MTI engineers created a custom amplifier filter to handle the high-frequency response required for accurate oil film thickness measurement. The design eliminated signal overshoot while minimizing phase delay in the electronics, using a Bessel filter to ensure stable and reliable performance during engine testing.
Additional Applications of Accumeasure™ Sensors
MTI Instruments’ Accumeasure™ sensors are versatile and can be applied to other critical engine and transmission research applications. For instance, they are used to determine the ratio of oil to air in engine passages, providing real-time feedback on the presence of oil, air, or foam. The system produces a distinct voltage output based on the mixture composition, which helps in analyzing and optimizing engine performance.
In addition to oil film measurement, the system is equally effective in transmission research, where it can detect cavitation in fluids. Any foaming indicates the presence of air in the fluid mixture, resulting in a noticeable change in the output signal. This data is invaluable for researchers looking to understand how additives affect transmission fluids, ultimately helping them design longer-lasting, more durable products.
