Small Turbojet Engine Research Articles

Effects of isentropic efficiency of turbomachinery components on entropy production for small turbojet engine

PurposeUsage of gas turbine engines has increased by day due to rising demand for military and civil applications. This case results in investigating diverse topics related to energy efficiency and irreversibility of these systems. The purpose of this paper is to perform a detailed entropy assessment of turbojet engines for different flight conditions.Design/methodology/approachIn this study, for small turbojet engines used in unmanned aerial vehicles, parametric cycle analysis is carried out at (sea level-zero Mach (hereinafter phase-I)) and (altitude of 9,000 m- Mach of 0.7 (hereinafter phase-II)). Based on this analysis, variation of performance and thermodynamic parameters with respect to change in isentropic efficiency of the compressor (CIE) and turbine (TIE) is examined at both phases. In this context, the examined ranges for CIE is between 0.78 and 0.88 whereas TIE is between 0.85 and 0.95.FindingsIncreasing isentropic efficiency decreases entropy production of the small turbojet engine. Moreover, the highest entropy production occurs in the combustor in the comparison of other components. Namely, it decreases from 2.81 to 2.69 kW/K at phase-I and decreases from 1.44 to 1.39 kW/K at phase-II owing to rising CIE.Practical implicationsIt is thought that this study helps in understanding the relationship between entropy production and the efficiency of components. Namely, the approach used in the current analysis could help decision-makers or designers to determine the optimum value of design variables.Originality/valueDue to rising isentropic efficiencies of both components, it is observed that specific fuel consumption (SFC) decreases whereas specific thrust (ST) increases. Also, the isentropic efficiency of a compressor affects relatively SFC and ST higher than that of the turbine.

An investigation of euro diesel-hydrogen dual-fuel combustion at different speeds in a small turbojet engine

PurposeThis study seeks the effect on static thrust, thrust specific energy consumption (TSEC) and exhaust emissions of euro diesel-hydrogen dual-fuel combustion in a small turbojet engine.Design/methodology/approachExperimental studies are performed in a JetCat P80-SE type small turbojet engine. Euro diesel and hydrogen is fed through two different inlets in a common rail distributing fuel to the nozzles. Euro diesel fuel is fed by a liquid fuel pump to the engine, while hydrogen is fed by a fuel-line with a pressure of 5 bars from a gas cylinder with a pressure of approximately 200 bars.FindingsAt different engine speeds, it is found that there is a decrease at the TSEC between a range of 1% and 4.8% by different hydrogen energy fractions (HEF).Research limitations/implicationsThe amount of hydrogen is adjusted corresponding to a range of 0–20% of the total heat energy of the euro diesel and hydrogen fuels. The small turbojet engine is operated between a range of 35,000 and 95,000 rpm engine speeds.Practical implicationsOn the other hand, remarkable improvements in exhaust emissions (i.e. CO, CO2, HC and NOx) are observed with HEFs.Originality/valueThis is through providing improvements in performance and exhaust emissions using hydrogen as an alternative to conventional jet fuel in gas turbine engines.

DGEN Aeropropulsion Research Turbofan Core/Combustor-Noise Measurements—Experiment and Modal Structure at Core-Nozzle Exit1

Abstract Data from a recent core/combustor-noise source-diagnostic test (SDT) utilizing a small turbofan engine are analyzed. The campaign continued the exploration begun in a baseline test, but with more extensive acoustic instrumentation. Both tests were aimed at developing a better understanding of propulsion-noise sources and their impact on the farfield noise signature, in order to enable improved turbofan noise-prediction methods and noise-mitigation techniques. Simultaneous high-data-rate acoustic measurements (93 channels in total) were obtained using a circumferential sensor array at the core-nozzle exit in conjunction with sideline and farfield microphone arrays for several relevant engine operational points. Measurements were repeated for different circumferential and sideline array configurations, as well as for redundancy. The unsteady pressure field at the core-nozzle exit is documented in detail. Previous work suggested that the ±1 azimuthal duct mode could be cut on at this location, which would have implications for combustor-noise modeling and prediction. The modal decomposition of the combustor noise at the core-nozzle exit verifies this observation. Select farfield sound pressure level (SPL) spectra are also presented.

Computational design and static-structural analysis of a small-scale turbojet propulsive engine for an unmanned aerial vehicle

This study focused on the computational design and static structural analysis of a small-scale turbojet engine (SSTE) that can power an unmanned aerial vehicle with a thrust of 50 N at a speed of 8000 rpm. SOLIDWORKS 2018 was used to design the CAD geometry of the SSTE, and to carry out a CFD analysis on the compressor to determine the pressure distribution across the compressor and the compressor pressure ratio. The obtained pressure ratio was further used to carry out a structural analysis of the SSTE with emphasis on the turbine component using ANSYS static structural module. This analysis was done to determine the level of deformation of the chosen design material (stainless steel grade 310), the maximum and minimum stresses, factor of safety, and its fatigue life. Design and CFD results obtained shows that the design as well as the pressure distribution in the compressor is reliable. The 50N small scale turbojet engine showed higher optimum performance from structural design and evaluation when compared to that of the 70N thrust jet cat model. Results of the structural analysis shows that the turbine blades will experience minimum and maximum deformation of 0 m and 2.2543×10−5 m at the leading edges and trailing edges of the blade chord respectively. Also, maximum and minimumstresses will occur at 1.0632×105 Pa and 6.7192×107 Pa respectively. Conversely, the factor of safety was within 3.0807 to 15 which show that the design is adequate. Additionally, considering the fatigue life, the SSTE is bound to fail completely at approximately 1.929×107 months. Therefore, the SSTE with the materials suggested above is capable ofpropelling an unmanned aerial vehicle considering the results obtained.
 Keywords: Computational, static-structural, turbojet, UAV, design

The Use of Ethanol as an Alternative Fuel for Small Turbojet Engines

The use of alternative fuels to traditional kerosene-based ones in turbo-jet engines is currently being widely explored and researched. However, the application of alternative fuels in the area of small turbojet engines with thrust ratings up to 2 kilo-newtons, which are used as auxiliary power units or to propel small aircraft or drones, is not as well researched. This paper explores the use of ethanol as a sustainable fuel and its effects on the operation of a small turbojet engine under laboratory conditions. Several concentrations of ethanol and JET A-1 mixtures are explored to study the effects of this fuel on the basic parameters of a small turbojet engine. The influence of the different concentrations of the mixture on the start-up process, speed of the engine, exhaust gas temperature, and compressor pressure are evaluated. The measurements shown in the article represent a pilot study, the results of which show that ethanol can be reliably used as an alternative fuel only when its concentration in a mixture with traditional fuel is lower than 40%, yielding positive effects on the operating temperatures and small negative effects on the speed or thrust of the engine.

Advanced materials and technologies for compressor blades of small turbofan engines

BACKGROUND: Manufacturing costs, along with operational performance, are among the major factors determining the selection of the propulsion system for unmanned aerial vehicles (UAVs), especially for aerial targets. OBJECTIVES: In this paper, the design requirements and operating parameters of small turbofan engines for single-use and reusable UAVs are analysed to introduce alternative materials and technologies for manufacturing their compressor blades, such as sintered titanium, a new generation of aluminium and an alloy based on titanium aluminides. METHODS: To assess the influence of severe plastic deformation (SPD) on the hardening efficiency of the proposed materials, the alloys in the coarse-grained and submicrocrystalline states were studied. Changes in physical and mechanical properties of materials were taken into account. The thermodynamic analysis of the compressor was performed in a finite element analysis system (ANSYS) to determine the impact of gas pressure and temperature on the aerodynamic surfaces of compressor blades of all stages. RESULTS: Based on thermal and structural analysis, the stress and temperature maps on compressor blades and vanes were obtained, taking into account the physical and mechanical properties of advanced materials and technologies of their processing. The safety factors of the components were established based on the assessment of their stress-strength reliability. Thanks to nomograms, the possibility of using the new materials and the technologies was confirmed in view of the permissible operating temperature and safety factors of aerofoils. CONCLUSIONS: The proposed alternative materials and production technologies for the compressor blades and vanes meet the design requirements of the turbofan at lower manufacturing costs.

Advanced Materials and Technologies for Compressor Blades of Small Turbofan Engines

Manufacturing costs, along with operational performance, are among the major factors determining the selection of the propulsion system for unmanned aerial vehicles (UAVs), especially for aerial targets and cruise missiles. In this paper, the design requirements and operating parameters of small turbofan engines for single-use and reusable UAVs are analysed to introduce alternative materials and technologies for manufacturing their compressor blades, such as sintered titanium, a new generation of aluminium alloys and titanium aluminides. To assess the influence of severe plastic deformation (SPD) on the hardening efficiency of the proposed materials, the alloys with the coarse-grained and submicrocrystalline structure were studied. Changes in the physical and mechanical properties of materials were taken into account. The thermodynamic analysis of the compressor was performed in a finite element analysis system (ANSYS) to determine the impact of gas pressure and temperature on the aerodynamic surfaces of compressor blades of all stages. Based on thermal and structural analysis, the stress and temperature maps on compressor blades and vanes were obtained, taking into account the physical and mechanical properties of advanced materials and technologies of their processing. The safety factors of the components were established based on the assessment of their stress-strength characteristics. Thanks to nomograms, the possibility of using the new materials in five compressor stages was confirmed in view of the permissible operating temperature and safety factor. The proposed alternative materials for compressor blades and vanes meet the design requirements of the turbofan at lower manufacturing costs.

Improved Gain Scheduling Control and Its Application to Aero-Engine LPV Synthesis

Issues of gain scheduling control for aero-engines are addressed in this paper. An aero-engine is a system with high nonlinearity, and the requirement on controlling performance is high. Linear Parameter Varying (LPV) synthesis is commonly used to satisfy the requirements. However, the designing procedure of an LPV synthesis controller is complex, and may lead to undesirable design results when the variation rate of scheduling parameter is relatively fast. In this paper, an improved gain scheduling design procedure that can guarantee reliable stability and performance is developed. The method allows arbitrary variation of scheduling parameters, and is a modification for conventional LPV synthesis control. Special cases where traditional LPV synthesis control can still work are also discussed. The modified design procedure is evaluated on a small turbofan engine. Simulations show that for conditions where conventional scheduling fail to stabilize the plant, the proposed modification can ensure reliability and achieve desired performance.

Design of Single Stage Axial Turbine for Mini Turbojet Engine

This paper explains about aerodynamic design of a single stage gas generator turbine for a small turbojet engine. The design requirement is that the turbine must be able to deliver power output of 150 kW at 0.814 kg/s gas mass flow, with turbine inlet temperature of 1200 K, and turbine inlet pressure of 267508 Pa. The design phase consists of 4 steps, which is thermodynamic property analysis using parametric cycle analysis, determination of velocity triangle in 2D plane and 2D blade design using CASCADE software, 3D geometry modeling, and 3D flow analysis at design point using Computational Fluid Dynamics method. In parametric cycle analysis, design points are applied to get the unknown thermodynamics property. The determination of velocity triangles, two conditions are applied: zero inlet swirl and constant nozzle angle design. The design continues with the 2D approach in CASCADE to determine the airfoil type at the hub, mean, and the tip of the blade based on the inlet and outlet flow conditions. The 3D approach flow analysis is done by simulating the 3D geometry that has been made using CAD in full configuration to evaluate the overall performance of the turbine, especially the power generated by the turbine. The observed parameters are clearance, stagger angle, and cambered flat plate substitution in NGV affects the turbine’s output power. The analysis results show that all of those parameters above affect the turbine’s output power in a different way from one to each other. The bigger the clearance, the power output and the efficiency that is generated by the turbine also become bigger. Same as clearance, the stagger angle of turbine’s NGV also affects the turbine power and efficiency. The bigger the stagger angle, the bigger the power, but the efficiency drops.

Evaluation of the Operational State of a Small Turbojet Engine Using Variations in Its Near Magnetic Field

Evaluation of the Operational State of a Small Turbojet Engine Using Variations in Its Near Magnetic Field

Computational Investigation of Flow Control Methods in the Impeller Rear Cavity

In typical median and small aeroengines, the air used to realize the functions such as cooling of turbine blades and disks, sealing of turbine cavities and bearing chambers, adjusting of rotating assembly axial load is normally drawn through the rear cavity of centrifugal impeller, so the thorough understanding of flow characteristics and pressure distribution and the proposal of the corresponding control methods in the cavity are the key to design the rational secondary air system. With an impeller rear cavity in a small turbofan engine as an object, the current study was dedicated to the investigation of flow control methods in the cavity. Two methods, namely, baffle and swirl-controlled orifice, were proposed to regulate the pressure loss and distribution in the cavity. Furthermore, the influence of geometry parameters of the two methods such as the length of baffle, the space between the baffle and rotating disk wall, the orientation, and radial position of swirl-controlled orifice was investigated. The CFD results show that the swirl-controlled orifice which could deswirl the flow is more effective in regulating the pressure loss and its distribution in cavity than baffle. The variation of the radial position of the swirl-controlled orifice had little influence on pressure loss but obvious influence on pressure distribution; therefore, decreasing the radial position could reduce the axial load on the rotating disk without changing the outlet pressure.

Operational analysis of transient characteristics in a small scale turbojet engine

Operational analysis of transient characteristics in a small scale turbojet engine

The field noise measurements of small turbofan engine

The field noise measurements of small turbofan engine

Nonvolatile Particulate Matter Emissions of a Business Jet Measured at Ground Level and Estimated for Cruising Altitudes.

Business aviation is a relatively small but steadily growing and little investigated emission source. Regarding emissions, aircraft turbine engines rated at and below 26.7 kN thrust are certified only for visible smoke and are excluded from the nonvolatile particulate matter (nvPM) standard. Here, we report nvPM emission characteristics of a widely used small turbofan engine determined in a ground test of a Dassault Falcon 900EX business jet. These are the first reported nvPM emissions of a small in-production turbofan engine determined with a standardized measurement system used for emissions certification of large turbofan engines. The ground-level measurements together with a detailed engine performance model were used to predict emissions at cruising altitudes. The measured nvPM emission characteristics strongly depended on engine thrust. The geometric mean diameter increased from 17 nm at idle to 45 nm at take-off. The nvPM emission indices peaked at low thrust levels (7 and 40% take-off thrust in terms of nvPM number and mass, respectively). A comparison with a commercial airliner shows that a business jet may produce higher nvPM emissions from flight missions as well as from landing and take-off operations. This study will aid the development of emission inventories for small aircraft turbine engines and future emission standards.

Fast engine model for FMU-less small turbojet engines

The focus of this paper is on small low-cost turbojet engines equipped with a gear-type fuel pump rather than a more traditional fuel metering unit. The incorporation of such type of fuel flow actuation devices introduce additional nonlinearities into the system and therefore make traditional modeling and system identification methods difficult to apply. In this paper, we propose a nonlinear fast engine model structure that can be used for various applications, including identification, modeling and simulation, and controller design of such sub-class turbojet engines. A high-fidelity turbojet engine model including its nonlinear gear-type fuel pump is developed, which is later used to generate the fast engine model. The parameters of the fast engine model are estimated using regression analysis. The identification procedure is also applied to real engine test data to verify the proposed approach.

Design and Research of Electrostatic Sensor Based on Aero-engine Airway Electrostatic Monitoring Technology

Aero-engine airway electrostatic monitoring technology is a new type of aero-engine airway fault monitoring technology, which has a good development prospect. The principle of this technology is to realize the acquisition of the electrostatic signal of solid charged particles in the engine tail nozzle through the electrostatic sensor, and to judge the fault degree of the engine air circuit through the analysis of the electrostatic signal. In this paper, the electrostatic sensor is designed and manufactured according to the principle of electrostatic induction, what’s more, the measurement circuit is designed and manufactured, and the noise and interference in the electrostatic signal are eliminated. The validity of the measurement circuit is verified by simulation test. Finally, according to the self-designed test platform of gas-path electrostatic monitoring based on small turbojet engine, the test of electrostatic sensor and measurement circuit was completed, and the electrostatic signal was collected, which preliminarily verified the feasibility and effectiveness of gas-path electrostatic detection method.

Research on Weight Reduction Design Method for Compressor of a Small Turbojet Engine

Research on Weight Reduction Design Method for Compressor of a Small Turbojet Engine

Robust Control of Small Turbojet Engines

Modern turbojet engines mainly use computerized digital engine control systems. This opens the way for application of advanced algorithms aimed at increasing their operational efficiency and safety. The theory of robust control is a set of methods known for good results in complex control tasks, making them ideal candidates for application in the current turbojet engine control units. Different methodologies in the design of robust controllers, utilizing a small turbojet engine with variable exhaust nozzle designated as iSTC-21v, were therefore investigated in the article. The resulting controllers were evaluated for efficiency in laboratory conditions. The aim was to find a suitable approach and design method for robust controllers, taking into account the limitations and specifics of a real turbojet engine and its hardware, contrary to most studies which have used only simulated environments. The article shows the most effective approach in the design of robust controllers and the resulting speed controllers for a class of small turbojet engines, which can be applied in a discrete digital control environment.

Compressor Design optimization for a High speed Jet engine

This is a study that is focused on developing an individual design methodology for a centrifugal jet and generating a mixed flow jet for a small turbojet engine by using this methodology. The structure of the methodology is based on the design, modelling and the optimization processes, which are operated sequentially. The design process consists of engine design and compressor design codes operated together with a commercial design code. Design of Experiment methods and an in-house Neural Network code is used for the modelling phase. The optimization is based on an in-house code which is generated based on multidirectional search algorithm. The optimization problem is constructed by using the in house parametric design codes of the engine and the compressor. The goal of the optimization problem is to reach an optimum design which gives the best possible combination of the thrust and the fuel consumption for a small turbojet engine. The final combination of the design parameters obtained from the optimization study are used in order to generate the final design with the commercial design code. On the last part of the thesis a comparison of the final design and a standard radial flow jet is made in order to clarify the benefit of the study. The results have been showed that a mixed flow compressor design is superior to a standard radial flow compressor in a small turbojet application.

Intelligent Situational Control of Small Turbojet Engines

Improvements in reliability, safety, and operational efficiency of aeroengines can be brought in a cost-effective way using advanced control concepts, thus requiring only software updates of their digital control systems. The article presents a comprehensive approach in modular control system design suitable for small gas turbine engines. The control system is based on the methodology of situational control; this means control of the engine under all operational situations including atypical ones, also integrating a diagnostic system, which is usually a separate module. The resulting concept has been evaluated in real-world laboratory conditions using a unique design of small turbojet engine iSTC-21v as well as a state-of-the-art small turbojet engine TJ-100. Our results show that such advanced control system can bring operational quality of an engine with old turbocompressor core iSTC-21v on par with state-of-the-art engines.