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Introduction to Reliability Design of Mechanical System
Published in Seong-woo Woo, Design of Mechanical Systems Based on Statistics, 2021
An aircraft utilizes an onboard propulsion from the mechanical power produced by an aircraft engine, which is either a propeller or jet propulsion. Especially, jet engines supply airplane thrust by taking in the air, compressing the air, and injecting fuel into the hot-compressed air mixture in a combustion chamber, and the accelerated exhaust emits rearwards through a turbine. Modern gas turbine engines are operated by the Brayton cycle that comprises a gas compressor, a combustion chamber, and an expansion turbine (Figures 1.12 and 1.13).
Emergency Generators
Published in Michael F. Hordeski, Emergency and Backup Power Sources:, 2020
Jet engines function as gas generators where the hot gases are expanded either through a turbine to generate shaft power or through a nozzle to create thrust. Some gas generators expand the hot gases only through a nozzle to produce thrust. These units are identified as jet engines or turbojets. The turbojet is the simplest form of gas turbine since the hot gases generated in the combustion process escape through an exhaust nozzle to produce thrust. Jet propulsion is the most common use of the turbojet, but it has been adapted to drying applications, supersonic wind tunnels, and as the energy source in a gas laser.
Aeroacoustics and Low Noise Design
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
The peak noise from an aircraft is generated during its landing and take-off phases. The main sources of noise in conventional aircraft are generated by the engines and airframe. Noise generated by the engines depends on the eighth power of the jet exhaust velocity. In order to achieve the same level of thrust as a turbojet engine, a turbofan jet engine requires a lower exhaust jet velocity due to the additional thrust generated by the fan. This makes turbofan engines more efficient than turbojet engines, as there is a significant reduction of the noise level as well, for the same level of thrust. Moreover, turbofan engines with increasing bypass ratios tend to reduce the noise levels, as cold ducts generate less noise (proportional to the sixth power of the jet exhaust velocity) than combustion chamber-driven ducts.Airframe noise, which is comparable to engine noise, includes noise generated by high lift devices and landing gear.
Market Basis for Salt-Cooled Reactors: Dispatchable Heat, Hydrogen, and Electricity with Assured Peak Power Capacity
Published in Nuclear Technology, 2020
Molten Salt Reactors were originally developed in the late 1950s as part of the U.S. Aircraft Nuclear Propulsion Program that had as its goal a jet-powered bomber of unlimited range to deliver nuclear weapons to the Soviet Union. The reactor was chosen based on its ability to efficiently couple to a jet engine, i.e., a Brayton power cycle. In a jet engine, air is compressed, heated, and exhausted through a turbine that powers the compressor. That requires a reactor that delivers all of its heat at high temperatures significantly above the temperature of the compressed air. In modern gas turbines, that compressed air temperature is above 400°C. Salt reactors efficiently couple to Brayton power cycles with all heat delivered significantly above 400°C.
The effect of using triple bio-fuel blend with Jet-A on engine performance and emissions in mini-scale turbojet engine
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
In recent years, there have been many developments on small-scale gas turbine engines. Small-scale gas turbine engines, with their ability to obtain high power from small volume, high performance and working with various fuels, bring to the forefront unmanned vehicles, especially for the aviation industry (Marcellan, Visser, and Colonna 2016). In jet engine, which is a type of gas turbine, the thrust consists of momentum depending on the kinetic energy (their velocity) of the exhaust gases (Enagi, Al-Attab, and Zainal 2018). The use of small-scale gas turbine engines has increased in unmanned aerial vehicles, especially in the commercial aviation sector in recent years (Turan 2012). One way to improve the performance of gas turbine engines is to make design changes, while another way is to work on the fuels used. Abd Lati et al. (Abd Lati, Ahma, and Nasir 2017) developed a theoretical model using kerosene fuel on the K-180 G micro gas turbine engine, confirming the thrust performance results with an experimental study. Davies et al. (Davies, Gunabalan, and Davies 2016), used eight different fuels (diesel, Jet-A1, palm oil biodiesel, cooking oil biodiesel, 20/80 (PB/Jet A1), 20/80 (COB/Jet-A1), 50/50 (PB/Jet-A1), and 50/50 (COB/Jet-A1) to performed performance tests on a KingTech K140G gas turbine engine. In this study, it was seen that the low thrust was not only due to low calorific values, but also to the combustion time and low combustion efficiency due to the viscosity of different fuels. Bayona-Roa et al. (Bayona-Roa et al. 2019) performed simulations for different biofuel blends of PT6A turbine engine using GasTurb software. In this study, they performed simulations by estimating the fuel calorific values in various ways and stated that there was no difference on the results. At the same time, Badami et al. (Badami et al. 2014), in a similar study, obtained thrust, TSFC and emission values using experimental and semi-empirical equations and ANSYS software and compared them with pure jet fuel.