High-Temperature Pressure Sensor Using Optical Stress Birefringence for Distributed Engine Control

Abstract: Brusoni, Prencipe, and Pavitt (2001) posited that the digitization of aircraft engine control systems in the early 1980s caused loose organizational coupling. During this period, the number of control parameters indeed increased significantly with the introduction of full authority digital engine control (FADEC). However, during the period categorized by Brusoni et al. (2001) as the (analog) generation, digital technologies such as analog electronic and supervisory controls were gradually introduced. Moreover, with regard to technological changes in aircraft turbofan engines and control systems, technological improvements in engine power systems were evident in the 1960s and 1970s in terms of the bypass ratio, overall pressure ratio, and turbine inlet temperature. Although engine power systems witnessed negligible technological innovation in the 1980s, control systems improved as the number of control parameters increased due to the advent of FADEC. Subsequently, in the 1990s, great technological strides were made in engine power systems. Hence, technological changes in engine power systems and control systems always occurred alternately. Brusoni et al.'s claim that the decline in organizational coupling was due to the even rate of technological change in engines and control systems or the predictability in their interdependence miss the mark in light of the transition history of engine and control systems.Keywords: analog (hydromechanical), digital, aircraft engine control system, technological imbalance1. IntroductionBrusoni, Prencipe, and Pavitt (2001) categorized aircraft engine control systems from the 1950s to the 1970s as hydromechanical (analog) and those from the 1980s to the 1990s as digital. Brusoni et al. (2001) described the scope for change in the organizational structure and knowledge of three companies1 from the perspective of the evolution of control system technology. However, they barely mentioned the change in control system technology from analog to digital, nor did they focus on the changes in the engine power systems, which are associated with changes in control system technology. Referencing Brusoni et al.'s arguments, this study focuses on the transition of engine control systems from analog to digital and the associated technological changes in the power systems in order to review the technologies analyzed by Brusoni et al.2. Technological Change of Engine Control System:From Hydromechanical to DigitalBrusoni et al. (2001) focused on the control systems of aircraft turbofan and turbojet engines. A turbojet engine comprises an air intake, a fan/compressor, combustion chamber, turbine, afterburner, and tail nozzle. The pilot adjusts the position of the throttle lever to achieve the required thrust. The engine control system provides the necessary thrust by receiving the lever position as input and adjusting the fuel flow, thereby accelerating or decelerating the engine's revolutions per minute (RPM). Furthermore, it confirms whether the thrust corresponds with the pilot's intention and maintains the required thrust levels (Yoshinaka, 2010).Compared with the digital system, the analog system could control only a limited number of items. The following section discusses the evolution of jet engine control technologies based on Endoh (2004), Sugiyama (2004), Sono (2008), and Yoshinaka (2010).2.1. Hydromechanical controlThe jet engine was first adopted as a source of thrust in aircrafts in the 1930s. Simple mechanical fuel controls comprising cams and levers were used in reciprocating engines, which constituted the majority at the time. The control required by jet engines was comparatively complex, and the existing technology was inadequate. Even in the case of early post-war turbojet engines, variables of fuel flow or bleed valve could only be controlled. Subsequently, advances in the level of precision and miniaturization in the areas of mechanics and oil hydraulics led to progress in the control technologies of aircraft engines. …

Innovations in the use of thin film SMA materials have enabled the development of a harsh environment pressure sensor useful for combustion monitoring and control. Development of such active combustion control has been driven by rising fuel costs and environmental pressures. Active combustion control, whether in diesel, spark ignited or turbine engines requires feedback to the engine control system in order to adjust the quantity, timing, and placement of fuel charges. To be fully effective, sensors must be integrated into each engine in a manner that will allow continuous combustion monitoring (turbine engines) or monitoring of each discrete combustion event (diesel and SI engines). To date, the sensors available for detection of combustion events and processes have suffered from one or more of three problems: 1) Low sensitivity: The sensors are unable to provide and adequate signal-to-noise ratio in the high temperature and electrically noisy environment of the engine compartment. Attempts to overcome this difficulty have focused on heat removal and/or temperature compensation or more challenging high temperature electronics. 2) Low reliability: Sensors and/or sensor packages have been unable to withstand the engine environment for extended periods of time. Issues have included gross degradation and more subtle issues such as migration of dopants in semiconductor sensor materials. 3) High cost: The materials that have been used, the package concepts employed, and the required support electronics have all contributed to the high cost of the few sensor systems available. Prices have remained high due to the limited demand associated with the poor reliability and the high price itself. Ternary titanium nickel alloys, with platinum group metal substitution for the nickel, are deposited as thin films on MEMS-based diaphragms and patterned to form strain gages of a standard metal film configuration. The strain induced phase transformation of the SMA is used as a natural signal enhancement. These sensors are maintained at a temperature just in excess of the austenite finish temperature (Af). When the diaphragm is deformed by an applied pressure, the film undergoes the reversible martensite phase transformation. The fraction of the austenite transformed to martensite is a fraction of the applied pressure. The large difference in the resistivity of the two phases results in a very sensitive strain gage, and hence a pressure sensor with a very high gage factor. The combination of the thin film and the fact that the transformation is strain induced (rather than thermally induced) results in a sensor with very high response rate. In fact, the response rate of the sensor has been shown to be strictly a function of the mechanical response of the diaphragm. Unlike other sensor systems, the temperature of the SMA sensor is controlled above the temperature of the local environment. By controlling above the temperature of the environment, the sensor is largely immune to temperature fluctuations that can affect the response of other sensors. This technology has been demonstrated for a variety of target temperature regimes and a variety of pressure regimes. Sensor design and testing to date has ranged from 180C to >500C; and design pressures of 50 to 3500 psi, with higher pressures achievable. Characterization has included analysis of the response rate, the temperature sensitivity, reliability, and the effect of gross alloy changes. Sensor performance has also been evaluated in a diesel engine test cell. Ongoing work includes the sensitivity to minor composition changes, sensitivity to film thickness, and extended reliability and engine testing.

The Navy Landing Craft Air Cushion (LCAC) Service Life Extension Program (SLEP) upgrades the current TF40B gas turbine engine and analog control system on the LCAC to an Enhanced TF40B (ETF40B) gas turbine with a Full Authority Digital Engine Control (FADEC) system. This upgrade and enhancement will provide additional engine horsepower, increased engine reliability, and modern digital engine control equipment to the LCAC. The success of the ETF40B engine development program has been an ongoing effort between the Navy, the LCAC craft builder Textron Marine & Land Systems (TM&LS), and the engine manufacturer Honeywell Engine and Systems. This paper will document and outline the differences between the TF40B and ETF40B and the efforts of the ETF40B 150 hour endurance qualification test.

The control logic of the modern Full Authority Digital Engine Control (FADEC) is comprised of many control loops, each of which has a specific purpose. Typical control loops include (but are not limited to) a high or low rotor speed governor, an Acceleration and Deceleration loop, and various limiting loops for temperature, speed, fuel flow, and rate of change of fuel flow. The logic that determines which of these loops is “in control” at any particular time has a history of being very simplistic. This Selection Logic is usually nothing more that a cascade of minimum and maximum selection logic gates. Since this logic is so simplistic, the control engineer often has to “fine tune” the compensator design for each loop, in order to achieve proper performance. The purpose of this paper is to a present a means of achieving a selection logic design based on Fuzzy Logic principles. Hereafter, this shall be referred to as a Fuzzy Fuel Flow Selector. The paper provides a brief overview of the most typical architecture for real time embedded FADEC control logic, rule development for the Fuzzy Fuel Flow Selector, and a realistic implementation of the Fuzzy Fuel Flow Selector. Also provided is a typical application that is used to contrast the performance between traditional selection logic and the Fuzzy Fuel Flow Selector. An overview of the Fuzzy Logic process is also included for completeness.

Gross starting characteristics of the Vericor Power Systems ETF40B gas turbine engine utilizing diesel fuel for the Republic of Korea Navy LSF-II application indicate inconsistent starting performance, especially in cold ambient temperatures. There is also evidence that cold starting inconsistencies exist on the US Navy LCAC installation of the ETF40B engine. The inconsistencies include late light-offs, failed starts, excessive exhaust smoke, detonative ignition and excessive commanded fuel flow by the full authority digital engine control (FADEC). The starting anomalies experienced on US Navy LCAC have ultimately resulted in the addition of starting requirements to the production engine acceptance test procedure. A detailed review of historical information regarding the TF40B fuel system characteristics resulted in the basis for establishing revised LFMV calibration values and revised FADEC engine start fuel scheduling. Additionally, this review indicated the need for fuel system flow/pressure measurements in order to establish current characteristics and to help refine component requirements and changes (as appropriate). These measurements are required over the entire engine starting and operating range. Cold ambient temperature start testing was performed to establish the engine start characteristics on JP5/JET A fuels with the existing and revised LFMV calibrations. A revised start schedule was developed that provided a reliable, stable starting characteristic (reliable first attempt starting, reducing smoking on starts, eliminating detonative ignition, minimizing large variations in commanded fuel flow during starting). The fuel system pressures and flows were fully characterized in the start and operating regime and start testing validation was performed on Diesel Fuel.

Cerenkov radiation, which is produced by charged particles that pass through optical fibers with a velocity greater than that of light, is frequently regarded as a severe noise signal in a fiber-optic radiation sensor consisting of a scintillator and an optical fiber. Since the spectral range of Cerenkov radiation is very broad and covers that of light outputs from a scintillator, Cerenkov radiation generated in optical fibers is also acquired by a photodetector. However, Cerenkov radiation can be a significant signal when we measure the intensities of Cerenkov radiation generated from fixed length of optical fibers because it is one of the signals induced by interactions between radiations and optical fibers. In this study, gamma-ray induced Cerenkov radiation generated in silica and plastic optical fibers was measured in order to select an efficient optical fiber for producing Cerenkov radiation. The intensities and the spectra of Cerenkov radiation generated in the optical fibers were measured using a spectrometer. As the results, the intensities of Cerenkov radiation generated in silica and plastic optical fibers have peak wavelengths at approximately 500 nm. Also, the intensity of Cerenkov radiation obtained using a plastic wavelength shifting fiber was the highest among all sample optical fibers.

Embedded optical fibers are considered for use in structural monitoring of aircraft fiber-reinforced composite structures, such as wings and stabilizers. However, it is crucial that these optical fibers do not themselves significantly degrade the load-bearing ability of the composite. An embedded optical fiber, having a diameter an order of magnitude larger than the reinforcing fibers of a composite, alters the microstructure of the composite and gives rise to perturbations in the stress fields. The present study is an experimental investigation into how the introduction of embedded optical fibers affects the failure modes of a composite laminate. Quasi-isotropic composites with two realistic embedded optical fiber configurations were investigated, i.e. closely spaced optical fibers and optical fiber loops. Closely spaced optical fibers may be necessary near connectors and in some sensing schemes making use of multiple sensors. Similarly, changing the direction of an optical fiber is necessary in some sensing schemes and in cases where a single optical fiber is to be used to monitor a larger area. Static tensile and compressive experiments, as well as fatigue experiments, were conducted to study effects of the embedded optical fibers. Extensive post-failure fractographic examinations were carried out to identify if any failure modes were related to the presence of the optical fibers. Both room temperature dry, and high temperature (90'C) wet conditions were considered. It was found that the embedded optical fibers did not initiate fiber-dominated failure in the composite, and therefore did not cause any significant deterioration of the composite strength, neither in tension nor in compression. However, the damage evolution process was affected by the optical fibers as they were preferred sites for matrix cracking, especially in the hot-and-wet condition. In fatigue, damage grew from the edges of the specimens, not from the optical fibers, and the fatigue life was not affected by the optical fibers.

This article raises the problem of improving the analysis of the financial condition of an eco-nomic entity and its use in the compliance control system. The main tasks of using the analysis in the compliance control system in order to increase the efficiency of corporate management of the economic activity of an economic entity have been determined. It is emphasized that the analysis of the financial condition is one of the mandatory components of both internal control and compliance control, the differences in the use of the analysis results are analyzed. It is concluded that the role of financial analysis and its use in the compliance control system in order to improve the efficiency of corporate governance is constantly increasing in order to prevent compliance risks and regulatory risks due to external influence of supervisors.

A remote chemical sensor using a single optical fiber has been developed for collecting evanescently excited spectral signals from liquid samples. The sensor is particularly useful for the study of species adsorbed from solution onto the sensor surface. Fluorescence spectra were taken from dye solutions and dye-labeled proteins to demonstrate the evanescent operation of the probe. Raman data from benzene were collected to indicate its sensitivity in the bulk mode.

Direct picture transmission in a single optical fiber with holographic filters

Bismuth (Bi) and Germanium (Ge) co‐doped silica glass and fiber, as advanced gain media with broadband near‐infrared (NIR) emission and amplification, have promise for extending communication bandwidth. However, efficiently modulating the NIR emissions of bismuth to cover the C+L communication bands remain a significant challenge. In the study, a high‐temperature and high‐pressure reduction treatment on Bi/Ge co‐doped silica glass is employed to tailor the coordination environment around bismuth active center. This method facilitated the creation of new bismuth NIR luminescence centers, resulting in the luminescence spectrum with a peak position at 1550 nm and a FWHM exceeding 350 nm. The changes in the bismuth coordination environment are elucidated using HRTEM, photoluminescence decay, temperature‐dependent emission, EXAFS and CW‐EPR. Furthermore, the feasibility of this method in Bi/Ge co‐doped silica fiber is validated, and obtained >5 dB amplification in the range of 1400–1700 nm. This coordination engineering method holds significant potential for widespread application in Bi/Ge co‐doped silica glass and optical fiber is believed. It presents a promising prospect for expanding communication bandwidth by effectively modulating the NIR emissions of bismuth to cover the S to U communication band.

Maintaining continuous performance in the event of failures from aircraft propulsion engines is critical for mission readiness, mission completion, and maintenance cost. In this paper, a Model-Based Control (MBC) approach was developed and demonstrated for a turbine engine application that significantly improved the performance and fault recovery capability of the engine system. In addition, model-based health management techniques were demonstrated and showed encouraging results towards a real-time implementation. A Full Authority Digital Engine Controller (FADEC) with model-based control was successfully integrated with the high performance Turbine Engine Dynamic Simulator (TEDS). This environment was composed of a complete high fidelity Hardware-In- the- Loop (HIL) simulation of an engine with MBC system that provided both pre-flight and post-flight data results for evaluation. This paper will document and discuss key technologies demonstrated with the hardware in the loop simulation, which are: enhanced fault detection, real-time fault accommodation, model optimization for real-time execution, and integration of the control estimator with the high fidelity thermodynamic engine model. The results of this effort show a model-based controller can significantly improve engine transient response and performance.

To address the challenges commonly encountered in civil aircraft operating under multi-mode, strongly coupled closed-loop control—namely scarce fault samples, pronounced distribution shift, and root-cause explanations that are easily confounded by covariates—this paper proposes a root-cause analysis method that integrates ensemble learning with constraint-guided reasoning by large language models (LLMs). First, for Full Authority Digital Engine Control (FADEC) monitoring sequences, a feature system comprising environment-normalized ratios, mechanism-informed mixing indices, and multi-scale temporal statistics is constructed, thereby improving cross-mode comparability and enhancing engineering-semantic expressiveness. Second, in the anomaly detection stage, a cost-sensitive LightGBM model is adopted and a validation-set-based adaptive thresholding strategy is introduced to achieve robust identification under highly imbalanced fault conditions. Furthermore, for Root Cause Analysis (RCA), a “computation–reasoning decoupling” framework is developed: Shapley Additive exPlanations (SHAP) are used to generate segment-level contribution evidence, while causal chains, engineering prohibitions, and structured output templates are injected into prompts to constrain the LLM, enabling it to infer root-cause candidates and produce structured explanations under mechanism-consistency constraints. Experiments on real flight data demonstrate that our method yields an anomaly detection F1-score of 0.9577 and improves overall RCA accuracy to 97.1% (versus 62.3% for a pure SHAP baseline). Practically, by translating complex high-dimensional data into actionable natural language diagnostic reports, the proposed method provides reliable and interpretable decision support for rapid RCA.

Optical fiber probes able to detect intracellular potential changes in individual cells, in vivo have been developed. One probe uses a single-mode optical fiber to direct laser light onto cells stained with the voltage-sensitive fluorescent dye WW781 and also return part of the resulting fluorescence to a detection system. Fractional changes in fluorescent intensity of 10/sup -3/, obtained from frog heart cells immobilized in zero-calcium Ringer's solution, are comparable to those reported for other optical methods. Even larger signals can be obtained through multimode fiber, but spatial resolution is lost. For hearts in normal-calcium Ringer's solutions, very large reproducible motion-related artifacts were detected. Optical heterodyne fiber probes that have the ability to study cell electrical activity through membrane birefringence without any fluorescent dye are being developed. >

Powder ceramic phosphors are fundamental materials for solid-state lighting and have contributed to the progress of general lighting and liquid crystal displays. The development of phosphors for high-color rendering illumination, wide-gamut displays, and high-brightness illumination with laser excitation continues. In recent years, the single-particle diagnostic method, which can determine the crystal structure and composition of the particles in a synthesized mixture, without obtaining a single phase has made it possible to dramatically improve the efficiency of searching for new phosphors.In this study we established a proximity measurement method that can accurately measure the photoluminescence (PL) spectrum of single phosphor particles using a commercially available multichannel photodetector generally used for power evaluation1. In this method, optical fibers were placed at a distance of less than 1 mm from a single particle sample for measurement. The measured intensity was inversely proportional to the square of the distance. PL excitation spectrum can also be measured using a single optical fiber connected to a monochromatized Xe light source. This method allows accurate spectral calibration because no extra optical components are used. Moreover, by focusing the excitation light using an optical fiber with a spherical tip, the measurement efficiency was significantly improved. The measurement intensity was proportional to the cube of the particle diameter, and even particles as small as 1.2 μm could be measured.Furthermore, we applied the proximity method to the quantum efficiency (QE) evaluation for a single particle phosphor2. Fluorescence spectroscopy by goniometric measurement, which can accurately evaluate the quantum efficiency of powdered phosphors, has been standardized by ISO23946:2020, and thus this method was applied to the evaluation of single particle. The apparatus consisted of a sample holder, an excitation fiber, and a detection fiber. A 150 W xenon lamp was used for excitation, and a multichannel photodetector was used for detection. The sample holder was attached to a 3-axis goniometer head. The samples were rotated using a motor. The excitation fiber was placed above the sample, whereas the detection fiber was driven by a motor to change the detection angle. A single optical fiber with a spherical tip was used for the excitation. Consequently, the diameter of the excitation beam was focused to 18 μm. A single optical fiber with a core diameter of 230 μm was used for the measurement. The small hole with a diameter of 0.5 mm in the sample holder was filled with barium sulfate powder as a white standard. A single phosphor particle of the test sample was then placed on it. The distances between the tips of the excitation/detection fiber and the sample were set to 500 and 700 μm, respectively. The zenith angle and the rotation angle intervals were set so that the measurement hemisphere was evenly covered with the detection fiber core diameter. Two steps were involved in the measurement. First, the particle was aligned with the center of rotation, and the light distributions in the scattering and emission spectra of the phosphor were measured. Next, the center of rotation was moved above the barium sulfate without the phosphor particle, and the scattered light distribution of the excitation light was measured. CaSiAlN3:Eu2+ red phosphor was used as the test sample. The particle picked from the powder sample was measured. The QE was calculated from the spatially integrated spectrum. Good agreement was achieved with the value for the powder sample. K. Takahashi, et al, Jpn. J. Appl. Phys., 62, 016510 (2023)K. Takahashi, et al, ECS J. Solid State Sci.Technol., 12, 076002 （2023）