Figure 5 - uploaded by Ahmed Ghoniem
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High speed CCD images of the flame (blue) and linear photodiode array images (red) in a backward facing step combustor (green) at Re=6300 and φ =0.85 in Case II. Images
Source publication
This paper addresses an experimental investigation of a combustion system using a backward step configuration, with the goal of understanding combustion instability and its control. In order to carry out a systematic study of the various subcomponents of the combustion dynamics including hydrodynamics and heat-release, various sensors and actuators...
Context in source publication
Context 1
... strong instability occurs above Re=7400 or Re=9500 which gives H f =25Hz and 33Hz, respectively, both of which are close to the acoustic frequency, ac f =38Hz. High speed CCD and linear photodiode images in Figure 5 captured at 500 frames/sec confirms strong flame-vortex interactions in Case II. In Case I, no noticeable difference in the heat release or flame structure was observed. ...
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Citations
... Most of the optical measurement techniques available are standard laboratory procedures and equipments [12,13]. Optical probes with a specific use are a current topic of R&D in gas turbines [14,15] or are already in commercial use for power gas turbine applications [16]. ...
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.
... The results in the previous section were measured during steady combustion, which means that the fuel flow is constant. Experiments were also performed with a fuel flow that is perturbed with a MOOG D633-7320 valve [103]. These experiments were performed primarily to determine the flame transfer function. ...
This thesis deals with the interaction between combustion, acoustics and vibrations with emphasis on frequencies below 500 Hz. Extensive literature is available on the interaction between combustion and acoustics and much work is also available on the interaction between acoustics and vibration. The work presented in this thesis attempts to combine these fields in order to calculate the vibrations of the liner.
The development of diagnostic methods suitable for the monitoring of practical flames is an important objective, which is receiving a growing attention and significant research efforts. This is motivated by the need to achieve a more precise description of the process and, ultimately, implement efficient and reliable control and optimisation methods as a key step towards the development of more efficient, flexible, reliable and clean combustion systems. Many and interesting attempts have been proposed, involving widely different approaches in terms of the instrumentation utilized and the concepts proposed to convert sensorial information into various meaningful parameters. This article intends to review the techniques proposed in the literature for the monitoring of flames, either applied to or conceived for the monitoring of practical combustion equipment. It has been divided into four sections, dealing respectively with optical sensors, imaging techniques, pressure transducers and probing methods. A detailed analysis of the works published reveals that probably the main challenge in this field is the definition of the most representative flame signals and of their subsequent processing to derive the meaningful information required to diagnose the state of a flame or to drive a controller in an effective and safe manner. This together with the wide range of diagnostic needs and restrictions imposed by the different combustion situations probably explains the notable heterogeneity observed among the works published. In spite of the great efforts devoted, the techniques proposed for the advanced monitoring of practical flames are still at a development stage. However, significant advances in this field are expected in a near future, fostered by the urgent demands from the combustion industry and facilitated by the continuous progress in sensor technology, signal processing techniques and, not the least, in the understanding of combustion processes.
