An Approach to Detect and Mitigate Ice Particle Accretion in Aircraft Engine Compression Systems

The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8% of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes. INTRODUCTION Over the past twenty years, there have been approximately 150 reported cases of aircraft engine power loss due to the accretion of ice crystal particles in the compression system of commercial turbofan engines [1]. The majority of the work in response to this aviation safety concern has focused on understanding the mechanism by which particles in high icewater content (HIWC) conditions can accrete on compressor stator blades, understanding the environmental conditions in which accretion can occur, and related regulatory questions [2]. While redesigning the compressor to prevent ice accretion is the ideal long-term solution, a systems-level analysis highlights some near-term capabilities. Previous work has developed a means to simulate the impact of ice accretion in the low pressure compressor (LPC) using a series of stacked compressor maps [3]. When these maps are integrated into a high-fidelity engine simulation, the overall system response to the presence of ice can be simulated [4]. Using this approach, a method to detect the accretion of ice using only the existing engine sensors is proposed. For this work, the engine simulation known as C-MAPSS40k (the Commercial Modular Aero-Propulsion System Simulation 40,000 lbf) is used [5]. This simulation is written in MATLAB/Simulink and is a generic, modular, physics-based simulation of a 40,000 lbf thrust-class engine. This simulation is used due to the fact that it is based on dynamic flight test data, includes a realistic engine controller [6], and realistic sensor noise models [7]. The stack of “iced” LPC maps is integrated into C-MAPSS40k and the user is given an input through which the ice blockage level of the LPC can be specified (between 0% and 27%). The LPC operating point is then linearly interpolated to lie between the operating points of the two nearest maps. In this manner, the user can change the blockage level as a function of time to simulate the accretion of ice in the LPC second stator row. A previously developed engine ice particle accretion detection technique [8] relied on observing shifts in the engine sensor outputs directly. While this approach was reasonably effective (97.94% true positive rate, 0.10% false positive rate, and mean detection occurs at 5.519% blockage), the false positive rate (false alarm rate) was much too high for use in service. Thus, a detection technique aimed at directly detecting the change in LPC performance is developed. To determine the performance of this new algorithm, it is applied to the C-MAPSS40k engine simulation and a Monte Carlo study is conducted and evaluated against three detection metrics (true positive rate, false positive rate, and mean blockage at detection). https://ntrs.nasa.gov/search.jsp?R=20140006194 2017-09-14T04:12:40+00:00Z