ASME Turbo Expo 2017: Make Combustion Great Again!!!!

We are honoured to be part of the renowned ASME Turbo Expo 2017. This year's ASME conference will be held from June 26 - 30 in Charlotte, North Carolina. CBOne will present its latest research about a novel probe concept for advanced combustion monitoring and about a method for the improvement of impaired combustion conditions at off-design operation points.

For more information about the articles & presentations click on the references below

  • Kraft, G. E., Giuliani, F., Pfefferkorn, L., Paulitsch, N., and Andracher, L., 2017. 
    Heat resistant probe combining optic and acoustic sensors for advanced combustion monitoring including detection of flame instabilities. 
    In Proceedings of ASME Turbo Expo, Charlotte, North Carolina, USA.
  • Giuliani, F., Pfefferkorn, L., and Kraft, G. E., 2017. 
    Improvement of impaired combustion conditions at some off-design operation by driving a precisely controlled modulation of the burner air feed. 
    In Proceedings of ASME Turbo Expo, Charlotte, North Carolina, USA.

 

Charlotte likes it hot !!!

For the improvement of impaired combustion conditions a robust acoustic driver (called siren) is used, being able to perform well and last long in an industrial environment. The previous figure suggests how the siren could be implemented on a real power gas turbine.

One could think about a single actuator connected to several burners via a manifold. 

a) The first configuration called blow-down makes use of a separate compressed air feed line, e.g. the one available for flushing the fuel pipes.

b) An alternative way would be to connect the actuator in bleed or discharge configuration, where e.g. the pilot feed air is periodically sucked from the burner upstream from the gas injection, and re-injected at suitable position between two turbine stages. 

 

Heat resistant probe combining optic and acoustic sensors for advanced combustion monitoring including detection of flame instabilities (GT2017-63626)

So far aviation industry uses optical measurement techniques only during the development of new aero-engines. This led Combustion Bay One to the idea of built-in heat resistant probes combining optical and acoustic measurements in order to gain detailed information about the engine's health status. The flame's front position, the emission products and the combustion stability during flight operation can be monitored simultaneously and in real-time.

In collaborative work with the aviation department of FH Joanneum Graz a probe was designed in order to establish a proof of the concept toward the optical instrumentation of the combustor of an aero-engine. Therefore several sets of sensors and circuits were analysed, and it turned out that the non-amplified reverse current circuit offers the best trade-off between simplicity and signal dynamic. A microphone was combined with the probe in order to measure simultaneously the flame’s noise and its intensity of luminescence.

The resulting probe is multi-purpose, it covers simultaneously several features: 

  • flame detection, 
  • ignition success, 
  • qualitative information on the operation, 
  • and combustion stability monitoring. 

A promising design was tested, and the probe features were successfully validated on an atmospheric combustion test rig. The next efforts will focus on the probe operation under more demanding conditions, as well as on the optimisation of the measurement chain.

 

Major project output: the Rayleigh-Criterion Probe (RCP)

One promising output from the explorative project is the so-called Rayleigh Criterion Probe (RCP). It has been shown that it performs very well when placed close to the flame. In this concept, the sensors are cooled and are in the upper part of the probe, the exposed part. 

 

  

The emotion probe concept, also called Rayleigh Criterion Probe (RCP).
Circuit board with the PD and microphone mounted in a probe tube.

 

On this occasion we would like to thank the FFG for enabling the realization of this project. 

A more detailed description of the opto-acoustic measurement probe are given in the references [1] and [2].

See also:

[1] Kraft, G., Giuliani, F., Pfefferkorn, L., and Andracher, L., 2016. 
Toward embedded optical measurement techniques for precision combustion monitoring in aeroengines. 
In Proceedings of the XXIIIth Biannual Symposium on Measuring Techniques in Turbomachinery, Stuttgart, Germany.

[2] Kraft, G. E., Giuliani, F., Pfefferkorn, L., Paulitsch, N., and Andracher, L., 2017. 
Heat resistant probe combining optic and acoustic sensors for advanced combustion monitoring including detection of flame instabilities. 
In Proceedings of ASME Turbo Expo, Charlotte, North Carolina, USA. GT2017-63626.

[3] See, size and seize the flame: the emotion project

 

Improvement of impaired combustion conditions at some off-design operation by driving a precisely controlled modulation of the burner air feed (GT2017-64429)

In the course of this work a non-conventional method based on forced-flow combustion oscillations was investigated regarding the improvement of combustion conditions at suboptimal operating conditions.

When it comes to uncontrolled combustion oscillations in the field of gas turbines we speak of combustion instabilities. Low NOx systems that operate in the lean combustion domain are prone to enable combustion instabilities. A common way to investigate combustion instabilities is to reproduce these with help of an acoustic driver, e.g. using a loudspeaker or a fast valve in order to drive forced-flow combustion oscillations. When the oscillations match with one of the natural resonant frequencies of the combustor cavities or of the feeding pipes, the thermoacoustic coupling can occur in a well-controlled way.

Within this work we describe how a flame can be modified by means of an acoustic drive in order to enhance combustion quality. Better combustion performances were observed with the help of pulsating the burner air feed at part-load conditions on a premixed swirling flame, where combustion quality is known to be impaired at steady-state.

 

Test sequence using the in-house MusicPaper control software.
Top: repeated time-sequence starting with 2 frequency ramps followed by 3 frequency steps, at variable amplitudes of pulsation. 
Bottom: simultaneous exhaust gas measurements.

 

With the help of an in-house control software, called MusicPaper, it is possible to pre-program a test sequence with variable frequency and/or variable amplitude of the pulsed air feed. In the figure above, a test sequence includes a ramp in frequency (used to spot the resonant frequencies of the flame) followed by an analysis one-by-one of the significant resonant frequencies that were detected along this ramp. The resonant frequencies are 208, 365-368 and 510-515Hz for this configuration. For the tests carried out only pulsation at a frequency of 368 Hz had a positive influence regarding the pollutant emissions of our burner test rig. This effect is also clearly visible in the figure. It is remarkable because the outlet temperature rises while CO and NO emissions decrease.

Moreover, under forced flow conditions a faster machine heat-up is possible. Of course it must be stated that this observation cannot be generalised for all operations and resonance is only achieved on a limited amount of operation points. Nevertheless, these results could be verified and repeated. In this writing we report on the improvement of fuel burn under suboptimal operating conditions using a pulse-combustion option. Some significant, well-reproducible and positive results were achieved. Thermoacoustic couplings can be driven on purpose and to optimise combustion when needed. The fact that thermoacoustics improve combustion under some conditions can therefore be of interest for the gas turbine community.

The programme MethaNull was financially supported by the JITU-PreSeed Grant (Contract P1302031-PSI01) of the Austrian Federal Ministry for Economy, Family and Youth under guidance of the Austria Wirtschaftsservice GmbH. 

Additional material was gathered for plausibility check during the test sessions of the project ”emotion”, supported by the FFG (Austrian Research Promotion Agency) in the frame of the ”Take-Off” programme (Contract 850470).

See also:

[1] Giuliani, F., Moosbrugger, V., Stuetz, M., and Leitgeb-Simandl, T., 2015. 
Optimisation of support fuel consumption burning low heat value gas using controlled combustion oscillations. 
In Proceedings of ASME Turbo Expo, Montreal, Canada. GT2015-42377.

[2] Giuliani, F., Pfefferkorn, L., and Kraft, G. E., 2017. 
Improvement of impaired combustion conditions at some off-design operation by driving a precisely controlled modulation of the burner air feed. 
In Proceedings of ASME Turbo Expo, Charlotte, North Carolina, USA. GT2017-64429.

[3] Good Vibes Beat Bad Gas

[4] Vanessa Moosbrugger wins the Schmiedl Research Price for MethaNull!