A siren is a robust fast-valve that generates effective flow pulsations and powerful noise levels under well-controlled conditions. It operates under the inlet flow conditions of a gas turbine combustor. Its principle is based on a sonic air jet periodically sheared by a cogged wheel rotating at a given speed. It is used as an alternative to loudspeakers in combustion laboratories when the use of these is made difficult by aggressive flow conditions, such as hot air under pressure, possibly containing impurities. It is also a serious candidate as an effective flow actuator to be deployed on power gas turbine fleets. The authors have gathered more than twenty years of knowledge on siren technology. This pulsator was originally developed for research on thermoacoustics. By scanning through a given frequency range, one detects the acoustic resonance of specific parts of the combustor assembly, or possibly triggers a combustion instability during a sensitivity analysis of a flame to small perturbations. In 2010, Giuliani et al. developed a novel siren model with the capacity to vary the amplitude of pulsation independently from the frequency. In this contribution, the physics, the metrics, and the resulting parameters of the pulsator are discussed. Technical solutions are unveiled about visiting large frequency ranges (currently 6 kHz) and achieving elevated pressure fluctuations (150 dB SPL proven, possibly up to 155 dB SPL) with a compact device. A multimodal excitation is available with this technology, one idea being to dissipate the acoustic energy on nearby peaks. The contribution ends with a summary of the applications performed so far and the perspective of an industrial application.
Additive manufacturing (AM) is a promising technology for producing better burners. Achieving better energy efficiency on a system level (CO2 emissions) and lower NOx, particulate emissions and CO, as directed by the International Civil Aviation Organisation (ICAO) standards, is a priority for all aircraft and aircraft engine manufacturers. At the current state-of-the-art, technologies like Powder Bed Fusion (PBF) offer a certain freedom of design one can make good use of. Instead of starting from an established conventional burner design and improve it using AM, the proposed approach in this paper is to define from scratch a design that maximises the potential benefits of AM towards a better burner. However, there are a few playing rules one must be aware of. The design, manufacturing and testing of a staged premixed burner with separate injection ramp was done as the follow-up of paper GT2018-75165 where new swirler shapes had been assessed. For this paper a monolithic, profiled burner design for premixed injection was tested for low-emission combustion. Additional features were included and assessed. Separately, regarding the fuel injection system a new design of a fuel ramp disconnected from the burner is proposed in a first approach, which combines the injection and pre-heating of the fuel. It serves as a fuel splitter (burning fuel / bypassed flow), as a miniature heat exchanger and as a multipoint injection ramp. A merging of the monolithic burner and the injection ramp is planned at a later stage. The fuel injection system using AM parts is assessed separately from the burner in a first approach. It suggests some novel technical solutions regarding 3D printed burner designs. Early combustion experiments are described and supported with function tests using a carefully selected instrumentation.
In the near future, combustion engineers will shape the burner according to the flame, and not the opposite way anymore. In this contribution, this idea is explored with the help of additive manufacturing (AM). The focus is put on the design and the production of swirlers using advanced materials with the least possible efforts in terms of manufacturing. The material chosen for this study is Inconel 718. There are three motivations to this project. The first one is to design new shapes and assess these in comparison to conventional ones. The second motivation is to be able to manufacture them using additive manufacturing, and to gather know-how on selective laser melting. The third motivation is to elaborate a methodology involving engineering, research and education to promote — only if and when this is desirable — the production of series of premium parts such as high-end components of gas turbine combustor using AM. First-of-a-kind swirler shapes are explained and designed. These are unlikely to be produced using conventional manufacturing. They are then successfully produced in Inconel 718 using AM. The raw parts are directly submitted for testing with no surface post-processing. The paper states why at current state-of-the-art the raw surface quality still needs improvement, and highlights the benefits of the new swirler shape versus conventional.
Jet engines have remained almost entirely mechanical machines for fail-safe reasons, despite the increasing sophistication of modern gas turbines. However, the trend goes toward more electronic devices for a better operation monitoring. This is the late approach called system of systems in aeronautics. New regulations such as the ICAO/CAEP/10 nvPM Standard set limitations on soot emissions. CO reduction is also an issue. One possible strategy toward more efficient combustion and less pollutant emissions is an advanced management of the safety margins. This is combined with an obligation to reduce operation costs. Therefore new measurement techniques are required for precision combustion monitoring during operation. The specific data requested covers the success of ignition, the margin before the lean-blow-out limit, the effective burner load conditions and the stability of combustion. Many optical measurement techniques are available for advanced combustion diagnostics (Warnatz et al 2001). Their main features are precision and non-intrusivity. However, if these techniques are commonly used in a combustion laboratory or on a test-bench, no application had a breakthrough so far on a flying system. The implementation of optical devices in the aggressive environment of a combustor is challenging. Some critical details are for instance the need for a permanently transparent optical interface or the thermal protection of the sensitive parts. In the scope of the project “emotion” subsidised by the FFG, a heat resistant probe combining optic and acoustic sensors was developed for this purpose. This probe will make advanced combustion monitoring possible. It will comply with the above mentioned rules or constraints. It could be mounted on the pressure casing with a view on the liner. It will monitor the presence or absence of a flame, it will report on the ignition success or failure, it will compare the observed flame power to the expected load, and detect the presence of a combustion instability. In this paper, several sensors are considered. Three different circuits for optical light intensity measurement are assessed. A combined optical-acoustic sensor arrangement called the Rayleigh-Criterion probe is introduced. This most promising configuration is tested and validated on an atmospheric combustion test rig. The presented results support the further development of this probe, first for use on test benches where this technology can achieve maturity, then towards deployment first in power gas turbines and eventually in aeroengines.
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