Development of a Turbocharger Speed Sensor Using Fiber Optic Coupled Optical Method

Abstract

Abstract Turbochargers play a key role in producing more power for internal combustion engines of small aircrafts operated at altitudes with low air density. However, turbochargers can experience catastrophic failure at specific operating conditions where aeroelastic instability or resonance occurs at extremely high speed, putting the aircrafts at high risk. Therefore, it is critical to avoid turbocharger shaft speeds at these dangerous conditions, requiring accurate and stable turbocharger speed measurements. Currently, turbocharger speed sensors such as eddy-current sensors based on electromagnetic fields are often used for this purpose. However, these devices have limited capabilities such as applicable impeller blade material, maximum measurable speed, and small mounting distance between the sensor and impeller blade. Therefore, the present study focuses on development of a new turbocharger speed measurement method using a Fiber Optic Coupled Optical Speed (FOCOS) sensor and assessment of its capabilities. The FOCOS sensor was installed in the compressor housing of a high-speed turbocharger mounted on an internal combustion engine subjected to altitude conditions. These results were also compared to the performance of eddy-current speed sensors. It was concluded that the FOCOS sensor reliably measured turbocharger speeds over 250 kRPM for a range of impeller blade materials including aluminum and titanium, while the eddy-current speed sensor showed significant limitations.