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Waste Heat Recovery
Published in Tony Giampaolo, Gas Turbine Handbook: Principles and Practice, 2020
Boilers may be either unfired or fired. Unfired boilers use only the waste heat from the gas turbine exhaust, while fired boilers add additional fuel via afterburners into the hot gas path upstream of the boiler inlet. Afterburners receive their oxygen from the gas turbine exhaust gas, which is sufficiently rich in oxygen to support combustion. The afterburners are activated when the gas & steam turbines are loaded and additional power is required. The power realized from this system can be substantially increased. The limit on supplementary firing, for conventional heat recovery boiler construction, is usually 1400°F but, with installation of higher quality materials in the superheater section and the final stack, 1700°F can be achieved.
Combustion Systems
Published in Ahmed F. El-Sayed, Aircraft Propulsion and Gas Turbine Engines, 2017
The afterburner, as described previously, is a second combustion chamber located downstream of the turbine and is fitted to supersonic aircraft (mostly military) to develop a greater thrust force. An afterburner consists of only two fundamental parts:The spray bars or the fuel nozzleThe flameholderThe afterburner is quite similar to the combustion chamber in ramjet engines as both have a maximum temperature much greater than conventional combustion chambers. For the case of afterburners (in turbojet and turbofan engines), the gases leave the turbine at very high speeds (250–400 m/s), which is far too high for a stable flame to be maintained. Though the flow is diffused before entering the afterburner combustion zone, the gas speed is still high and the diffused air stream would be blown away. For this reason, the afterburner is provided with flameholders downstream of the spray bars. The flameholders have different forms, as shown in Figure 10.21. The vee-gutter flameholder type has been widely used as it has the advantages of low flow blockage, low total pressure loss (dry loss), being simple and lightweight, and having a good development history.
Engine performance
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
Some military jet fighters [9] are equipped with an afterburner. An afterburner† is an additional component added to a jet engine (turbojet or turbofan), primarily those on supersonic aircraft. Its purpose is to provide a temporary increase in thrust, both for supersonic flight and for takeoff. On military aircraft, the extra thrust is also useful for combat operations. This is achieved by injecting additional fuel into the duct downstream of (i.e., after) the turbine. This fuel is burned by the hot exhaust gases and adds greatly to the thrust of the engine. The advantage of afterburning (or re-heating) is significantly increased thrust; the disadvantage of afterburning is its very high fuel consumption. But this is acceptable for a short period of time in which afterburning is usually used. Jet engines are referred to as operating wet when afterburning is being used and dry when the engine is used without afterburning.
Study on full-coverage film cooling on center cone at engine-realistic conditions
Published in Numerical Heat Transfer, Part A: Applications, 2023
Chunhua Wang, Lubo Li, Hai Wang, Jingzhou Zhang
An afterburner is an additional combustion component used in some military jet engines. The afterburning process reheats the exhaust gas by injecting additional fuel into a combustor behind the turbine, which can increase the instantaneous thrust of the aircraft engine effectively. The previous open published data showed that, by introducing afterburner, the thrust of turbojet engine and turbofan engine can be increased by 40–60% and 70–100%, respectively [1, 2]. In a traditional afterburner, the fuel injector and flame stabilizer were placed in the mainstream channel directly, which inevitably generates additional flow resistance and increases the engine weight. An improved scheme called integrated afterburner was developed in recent years. In the integrated afterburner shown in Figure 1, the rear support plate of the turbine, fuel injector, and flame stabilizer were integrated to reduce flow loss and engine weight [3, 4]. As the key component of the integrated afterburner, center cone locating at the rear portion of turbine can increase the mainstream pressure and reduce the mainstream velocity, which is beneficial to ignition and flame stabilization. Nowadays, to pursue high instantaneous thrust, the combustion temperature in integrated afterburner has exceeded the melt point of center-cone material. So, it is necessary to apply advanced cooling technology into the thermal protection of center cone. Moreover, the decrease of center-cone temperature can reduce the backward infrared radiation and increase battlefield survivability of aircraft [5].
Experimental and numerical analysis of film cooling performance of a corrugated surface
Published in Experimental Heat Transfer, 2022
Ashutosh Kumar Singh, Kuldeep Singh, Dushyant Singh, Niranjan Sahoo
The future generation of modern aero-engine gas turbines of high thermal efficiency and power outputs are expected to operate at very high temperatures. To improve the performance of such advanced systems, the turbine inlet temperature reaches up to 2200 K [1]. The afterburner provides additional thrust during some specific situations such as combat, take off, and maneuvering by burning the extra fuel in the exhaust stream of the turbine. At such a high temperature, the structural rigidity of components is jeopardized due to excessive thermal stress. In such a harsh condition, an efficient cooling technique is required to improve the component’s operating life. Among several cooling technologies applied for the afterburner, gas turbine blades, and combustion liner, film cooling is a highly efficient technique. The film cooling on a flat surface with a cylindrical hole is extensively reported by many authors [2–7]. The formation of kidney vortices was one of the main issues with the cylindrical holes. To mitigate the kidney vortices, Goldstein et al. [8] proposed shaped holes. Recent studies on reverse injection found it to be an effective solution to overcome kidney vortices [9].