Combustion Active Control

To request a copy of a publication send an email to antonio.ficarella02@gmail.com.

2016

"THE NEW FRONTIERS FOR THE CONTROL OF COMBUSTION IN GAS TURBINES", Antonio Ficarella, Invited Lecture at NexTurbine 2016, 12th-13th May 2016, Shanghai, China, 2016.

Research and development in the control of combustion in gas turbines. Combustion processes play a key role in the efficiency of energy use and for the environmental impact of energy systems. The challenging topic of recent scientific and technological research in the field of combustion in gas turbine engines is the control of the fundamental physical and chemical processes, up to the molecular level, affecting the phenomena under investigation. The proposed speech will review the main research areas that actually focus on improvement of injection and vaporization of the fuel, new concepts of atomizers, control and optimization of air - fuel mixing. Moreover, control of oxidation processes with lean combustion, combustion instabilities, micro-scale combustion, control using active systems, development of new combustion concepts. Particularly significant are the results achieved in the investigation of the effects of air-assist atomization, at the combustor inlet of a modern gas turbine engine. The prefilming in airblast atomizer was investigated because the atomization of the fuel influences amongst others the amount of pollutant emissions. The research focused attention to other injection types, as the lean direct injection combustor, or the advanced multi-point fuel injector, analyzing the effects on the flow-field resulting from interactions between low and high-swirl counter-rotating air swirlers. Significant developments have been obtained for the technologies of microcombustion and micro gas turbines, as well as for new combustion concepts. For example, comprehensive experimental investigations were carried out on the flameless oxidation technology for small scale micro gas turbines, or on ultra-compact combustors. The new combustion concepts will offer various advantages in terms of flashback risk, lean blow-out limits and exhaust gas emissions. Particular attention will be payed to the characterization of the behavior of lean liquid fuel gas turbine near the lean blowout limit. The identification of the instability occurrence plays a key role for an efficient flame control. The behavior of high-speed images of the flame under stable and near blowout condition has been analyzed in conjunction with simultaneous optical data in order to better understand the phenomenology of the flame blowout process and the onset of instability. The data collected produce useful features for the development of an efficient tool for the flame control in industrial and aeronautical burners. The thermoacoustic behavior of gas turbine combustors is critical for the reliability and performance of the whole engine. With increasing demand of part load capability, the topic is as important as ever. The burners dynamics have been widely studied to prevent any undesirable behavior such as combustion instabilities, flashback and undesired blow-off. Although lean premixed combustion is very clean and basically soot-free, it has one serious drawback, as tendency to develop thermo-acoustic instabilities. These instabilities can be very violent, at the least causing unwanted noise and vibration, and in more serious cases, complete engine failure. Current research has shown methods to address such instabilities using passive and active control techniques. Finally, the research data can be used to extrapolate the implications on combustion and gas turbine performance and recommendations for the combustor design, considering the substantial impact on the delicate balance between combustor stability and gas turbine performance and emissions.

"Lean Blowout Sensing and Plasma Actuation of Non-Premixed Flames", De Giorgi, MG; Sciolti, A; Campilongo, S; Pescini, E; Ficarella, A; Lovascio, S; Dilecce, G, IEEE SENSORS JOURNAL, vol. 16 n. 10, pag. 3896-3903, 10.1109/JSEN.2016.2538970, 2016.

The aim of this paper is the use of optical sensors to recognize lean blowout in a non-premixed methane/air burner, Bunsen-type, and the use of plasma actuators for flame control and stabilization. The burner is optically accessible to permit the imaging acquisitions of the flame region. The plasma actuation regards alternatively the air flow and the fuel flow. The electric field is generated using a fixed configuration of plasma actuator and the dielectric barrier discharge (DBD) but using two different power supplies: a nanosecond repetitively pulsed high voltage (HV) and a sinusoidal DBD HV. The comparison between the two types of actuation is the core of this paper, together with the analysis of the results obtained when actuation acted on the air or on the fuel. For the analysis, the lean blowout (LBO) limits recorded in the presence and absence of plasma actuation to investigate the plasma actuation success. The flame behavior is acquired using a compact digital camera, an intensified chargecoupled device (CCD) in order to capture the differences between the baseline conditions and the actuated cases. It is shown that the plasma significantly allows stabilizing the flame under lean conditions where it would not exist without plasma.

"Experimental data regarding the characterization of the flame behavior near lean blowout in a non-premixed liquid fuel burner", Maria Grazia De Giorgi, Aldebara Sciolti, Stefano Campilongo, Antonio Ficarella, Data in Brief 6 189–193. DOI http://dx.doi.org/10.1016/j.dib.2015.11.051, 2016.

The article presents the data related to the flame acquisitions in a liquid-fuel gas turbine derived burner operating in non-premixed mode under three different equivalence fuel/air ratio, which corresponds to a richer, an intermediate, and an ultra-lean condition, near lean blowout (LBO). The data were collected with two high speed visualization systems which acquired in the visible (VIS) and in the infrared (NIR) spectral region. Furthermore chemiluminescence measurements, which have been performed with a photomultiplier (PMT), equipped with an OH* filter, and gas exhaust measurements were also given. For each acquisition the data were related to operating parameters as pressure, temperature and equivalent fuel/air ratio.

2015

"Plasma Actuation to Enhance the Flame Stabilization in a Non-Premixed Lean Microburner", Stefano Campilongo, Maria Grazia De Giorgi, Antonio Ficarella, Elisa Pescini, Aldebara Sciolti, Giorgio di Lecce, 1st Workshop on Nanotechnology in Instrumentation and Measurement (NANOfIM 2015), Lecce, Italy, ISBN: 978-1-5108-1501-8, 24-25 July 2015.

The demand of micro-devices is growing up especially for application such as micro-robots and micro-airplanes. The bottleneck for the development of such devices is the low energy density of the most common batteries. Building efficient micro-combustors has proven difficult. The major challenges are connected with the reduced dimensions that produce a high ratio between surface and volume of the device. Both the fluidodynamics and the heat loss are influenced by this ratio. Efforts in R&D are necessary to produce micro systems on a large scale. A promising burner configuration is the plasma assisted combustor. There are numerous works about the application of plasma for flame control, generally applied to macroscale combustor devices. Interesting works are those of Kim et al. [11], Cha et al. [2] and Pilla et al. [3] where a coaxial combustor was chosen for the experiments, with different plasma actuator technology: a dielectric barrier discharge (DBD) in [1], a glow type and the actuation affecting both reactants in [2] and a nanosecond repetitively pulsed plasma in [3]. Based on the aforementioned considerations, in the present work a micro-burner design with a high-frequency DBD  discharge was employed to investigate the influence of plasma actuation to stabilize a lean non-premixed methane/air flame at atmospheric pressure and under different fuel/air ratios. We found that the plasma actuation enhances the flame stability of a micro-burner especially at lean combustion conditions. The plasma action resulted evident in an increase of the flashback and the blowout limits. The fuel/air ratio range in which flame is guaranteed is evidently enlarged by the plasma actuation. Furthermore a change of the flame shape was recorded using visual observations due to the increase of the flame propagation speed. The enlargement of the stability region permits to use ultra-lean mixtures and to emit less pollutants into the atmosphere while maintaining a stable flame. The plasma assisted combustion is shown to be a promising way to answer to the energetic needs of microscale devices.

"Plasma Assisted Flame Stabilization in a Non-Premixed Lean Burner", Maria Grazia De Giorgi, Aldebara Sciolti, Stefano Campilongo, Elisa Pescini, Antonio Ficarella, Luca Matteo Martini, Paolo Tosi, Giorgio Dilecce, Energy Procedia, Volume 82, Pages 410-416, ISSN 1876-6102, http://dx.doi.org/10.1016/j.egypro.2015.11.825, December 2015.

In recent years, the application of plasma actuators in different engineering fields was considered particularly interesting. It was successfully applied for the cold flow control in aero engines and turbo-devices. One important application concerns the use of non-equilibrium plasma for plasma-assisted ignition and combustion control. The reduction of nitric oxides (NOx) in aircraft engines, gas turbines, or internal combustion engines has become a major issue in the development of combustion systems. A way to reduce the NOx emissions is to burn under homogenous lean conditions. However, in these regimes the flame becomes unstable and it leads to incomplete combustion or even extinction. Thus, the major issue becomes to stabilize the flame under lean conditions. In this context the present work aims to demonstrate the possibility to increase the combustion efficiency of a lean flame through the use of nanosecond repetitively pulsed plasma (NRPP). A NRPP produced by electric pulses with amplitude up to 40 kV, pulse rise time lower than 4 ns and repetition rate up to 3.5 kHz has been used to stabilize and improve the efficiency of a lean non premixed methane/air flame in a non-premixed Bunsen-type burner. The burner is optically accessible permitting the imaging acquisitions of the flame region. The flame behavior was acquired using a high rate CCD camera in order to capture the differences between the baseline conditions and the actuated cases. Moreover a post-processing technique showing the jagging of the flame in different conditions was applied to evaluate the changes occurring in presence of plasma actuation in term of flame area weighted respect to the luminosity intensity. It was shown that the plasma significantly allows stabilizing the flame under lean conditions where it would not exist without plasma.

"Effect of Actuation Parameters on Stabilization of Methane Diffusive Flames Using Plasma Actuators", De Giorgi Maria Grazia, Ficarella Antonio, Sciolti Aldebara, Campilongo Stefano, Pescini Elisa, Dilecce Giorgio. In: XXXVIII Meeting of the Italian Section of the Combustion Institute. p. 1-7, napoli:ASICI - Associazione Sezione Italiana del Combustion Institute, ISBN: 978-88-88104-25-6, Lecce, September 20-23, 2015, doi: 10.4405/38proci2015.I5, 2015.

The reduction of nitric oxides (NOx) in aircraft engines, gas turbines, or internal combustion engines is a main issue in the design of novel combustion systems. The reduction of the NOx emissions might be reached by lean combustion. However, the major issue is the stabilization of the flame under lean conditions. In this context, the present work investigates the possibility of increasing the combustion efficiency of a lean flame through the employment of a plasma actuator, operated by both nanosecond repetitively pulsed high voltage (NRPP) and sinusoidal DBD high voltage (HV). Different actuation conditions have been tested to stabilize and improve the efficiency of a lean non premixed methane/air flame in a Bunsen-type coaxial burner with central fuel jet. An image processing approach was used to characterize the flame behavior near blowout conditions.