Serge Shcherbanev

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Shcherbanev

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Serge

ORCID

0000-0002-5977-7506

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Publications 1 - 10 of 10

Effect of Mixing on the Anchoring and Combustion Regimes of Pure Hydrogen Flames in Sequential Combustors
Solana Pérez, Roberto; Shcherbanev, Serge; Ciani, Andrea; et al. (2023)
Journal of Engineering for Gas Turbines and Power
In this work, we perform an experimental study of the combustion of pure hydrogen in the sequential stage of a generic combustor. This academic test rig is a simplified model of an industrial sequential combustor. The sequential fuel is injected using different injector geometries. The composition and temperature of the hot stream at the inlet of the sequential burner are defined by the mass flows of the hot combustion products from the first stage (30 kW natural gas–air flame with equivalence ratio of 0.7) and of the dilution air. This temperature is varied between 1100 K and 850 K by modifying the dilution air mass flow in order to study the different combustion regimes of the sequential hydrogen flame. High-speed imaging of OH radicals chemiluminescence is performed with optical emission spectroscopy to measure vitiated gas temperatures. In particular, we investigate the transition from a flame anchored in the sequential combustion chamber, to the situation where it stabilizes upstream into the mixing section, when the inlet flow temperature is increased. Of particular interest is the increasing rate of formation of auto-ignition kernels in this transition process. The underlying combustion regime change is analyzed with 0D reactor simulations, and the limitations of such a simplified low-order model of the flame location are discussed. The effects and importance of the mixing process between fresh fuel and the hot vitiated coflow are examined. Two different injectors are compared under the same operating conditions that create different flow structures along the mixing section. As a result of that, they provide different degrees of mixing between the hydrogen and the hot vitiated flow and allow to demonstrate the impact of mixing quality on the flame morphology.
Jetting axial flow induced by nanosecond repetitively pulsed discharges in quiescent ambient air
Shcherbanev, Serge; Krzymuski, Tanguy; Xiong, Yuan; et al. (2022)
Journal of Physics D: Applied Physics
This study investigates the phenomenon of jetting axial flow induced by nanosecond repetitively pulsed discharges (NRPD) in quiescent ambient air in a pin-to-pin electrode configuration. Axial stratification of discharge parameters (electron number density, temperature, specific energy, etc) influences the hydrodynamic effects leading to directed gas flow from the cathode towards the anode. The experimental results presented in this paper were obtained using schlieren imaging, optical emission spectroscopy (OES), and electrical measurements of the deposited energy. A jetting axial flow was induced for all considered gap distances (0.5-5 mm) and pulse repetition frequencies of >= 10 kHz. The direction of the induced flow is defined by the polarity of the applied high-voltage pulses. It was found that the flow does not arise immediately after the initiation of the first pulse of the applied burst but is induced after a certain number of pulses. Using temporally and spatially resolved OES the electron densities and temperatures were measured in the vicinity of the cathode and anode before and after the generation of the axial flow. A model explaining the generation and maintenance of the axial flow in NRPD and the role of the inhomogeneities of plasma parameters along the plasma channel on hydrodynamic effects is suggested and discussed.
Combustion regime transition of H2 flames during steady and transient operation of a sequential combustor
Solana Pérez, Roberto; Shcherbanev, Serge; Dharmaputra, Bayu; et al. (2023)
Proceedings of the Combustion Institute
The combustion regime transition in a sequential burner (SB) supplied with H (48 kW) is experimentally studied during steady and transient operation. The test rig is a simplified model of an industrial sequential combustor featuring two-staged combustion chambers separated by a mixing section in which dilution air and fuel are injected. The temperature, velocity and composition of the hot vitiated gas flowing through the SB are defined by the products from the first stage (30 kW natural gas-air flame at equivalence ratio 0.7), and by the mass flow of dilution air. To study the combustion regime transition during steady operation of the combustor, is fixed at several values between 22 g/s and 7 g/s. For transient operation investigations, is suddenly changed between 20 and 7 g/s, which triggers a fast transition of the combustion mode. High-speed hydroxyl radicals OH chemiluminescence is used to characterize the combustion process, and optical emission spectroscopy (OES) and tunable diode laser absorption spectroscopy (TDLAS) are respectively used to extract mean and time-resolved temperatures of the vitiated gas in the SB. In particular, we investigate the transition from a propagation-driven turbulent flame anchored at the inlet of the sequential combustion chamber, to a flame stabilized by autoignition inside the mixing section of the burner when the dilution air mass flow is suddenly reduced. Zero-dimensional (0D) simulations are used to analyze the underlying combustion regime transition. A 0D reactor network is developed and calibrated with the experimental data. This simplified low-order model predicts well the flame location for both steady and transient operation. Moreover, the good agreement between the numerical results and the experimental data demonstrates that time-resolved TDLAS successfully enables measurement of small temperature variations in the vitiated flow associated with non-perfect mixing of the different streams in the SB.
Effects of the atomization air on the topology of a Jet A-1 spray flame in a turbulent vitiated crossflow
Miniero, Luigi; Pandey, Khushboo; Shcherbanev, Serge; et al. (2021)
The effects of the air-to-liquid ratio on a Jet A-1 spray in a vitiated turbulent crossflow are investigated by means of OH* chemiluminescence and OH-PLIF. The turbulent crossflow is generated with a 4 X 4 matrix of CH4-H2-Air lean technically premixed flames operated at 50 kW, equivalence ratio 0.7 and with a 5% H2 enrichment by mass. A Jet A-1 spray, generated with an air-assisted atomizer and corresponding to 5 kW power is introduced in the crossflow. The current work focuses on the effects of atomization air on the flame topology and heat release. The time-averaged high-speed OH* chemiluminescence images provide an estimate of the flame location and global features. For more insights, OH-PLIF experiments are performed at the central plane of the spray. In addition to the on-resonance OH PLIF signature, the detuning of the laser from the OH excitation wavelengths provides the spatial information about the presence of Jet A-1 droplets/vapour. It is reported that for low ALR the isolated combustion of relatively large droplets creates a localised heat release region on the windward side and closer to the atomizer. Whereas with increase in the ALR, the spray flame manifests higher degree of spatial uniformity.
Thermal Effect and Hydrodynamic Perturbation in a Coplanar Nanosecond Pulse Periodic Surface Dielectric Barrier Discharge
Zhang, Bin; Zhang, Xiaobing; Dharmaputra, Bayu; et al. (2025)
High Voltage
The thermal effect and hydrodynamic perturbation within a high-frequency pulse-periodic nanosecond coplanar surface dielectric barrier discharge (ncSDBD), are studied experimentally and numerically. The discharge is initiated in a coplanar open electrodes arrangement with 10 mm inter-electrode gap for pulse repetition frequencies (PRF) between 10 and 100 kHz. The discharge morphology, heat release, ozone distribution and refractive index perturbation with different repetition frequency are measured by intensified charge-coupled device (ICCD) imaging, spatially resolved emission spectroscopy, optical absorption methods and the background-oriented schlieren technique, respectively. With the increase of frequency and number of pulses, the discharge morphology changes from quasi-uniform structure at 10 kHz to filamentary mode, and a higher gas temperature is observed near the grounded electrode. In turn, the gas heating largely determines the dynamics of ozone. The discharge characteristics and hydrodynamic perturbation are modelled and analysed numerically. The existence of the exposed grounded electrode facilitates the connection between the positive and negative discharges. During the afterglow phase, a large amount of positive charge accumulates near the two exposed electrodes due to charge separation, resulting in a strong body force, which triggers the blowing up of the flow.
Air-blast atomization and ignition of a kerosene spray in hot vitiated crossflow
Miniero, Luigi; Pandey, Khushboo; Fredrich, Daniel; et al. (2023)
Combustion and Flame
Increasingly stringent regulations of pollutant emissions from aviation require rapid implementation of novel combustion technologies. Promising concepts based on moderate or intense low-oxygen dilution (MILD) combustion have been investigated in academia and industry. This MILD regime can be obtained from the recirculation of the hot vitiated combustion products to raise the temperature of the reactants, resulting in distributed reaction regions and lower flame temperatures. In the present work, we consider the air-blast atomization of a kerosene spray in crossflow, which enables efficient mixing between fuel and oxidizer. We investigate experimentally and numerically the effect of the spray air-to-liquid mass-flow ratio (ALR) variation on the reaction front and flame topology of a kerosene spray flame. The spray is injected transversely into a turbulent vitiated crossflow composed of the products of a lean CH4-H2 flame. The spray flame thermal power is varied between 2.5 and 5 kW, along with the atomizer ALR between 2 and 6. The experimental characterization of the reaction zone is performed using OH* chemiluminescence and OH and fuel planar laser-induced fluorescence (PLIF). The Large Eddy Simulations (LES) of the multiphase reactive flow provide good agreement with the experimental observations. Experiments and simulations show that the ALR governs mixing, resulting in different flame stabilization mechanisms and combustion regimes. Low ALR results in a relatively small jet-to-crossflow momentum ratio and a large spray Sauter mean diameter (SMD). A thick windward reaction region is formed due to inefficient shear layer mixing between the fuel spray and the crossflow. Meanwhile, the correspondingly large spray SMD leads to isolated penetration and localized combustion of fuel clusters. At high ALR, the higher penetration and the faster droplet evaporation due to the lower spray SMD result in an efficient entrainment-induced mixing between the two streams, forming more distributed reaction regions.
Tomographic Reconstruction of OH Density Maps for Jet-A1 Spray Flame in a Vitiated Crossflow
Miniero, Luigi; Pandey, Khushboo; Shcherbanev, Serge; et al. (2022)
This paper aims at describing the effects of the variation of air-to-liquid ratio (ALR) on the morphology, reaction zone and combustion regime of a Jet A-1 spray flame in a vitiated turbulent crossflow. The variation of these characteristics as a function of the ALR is a result of the effect of the parameter on both the droplets size and jet-to-crossflow momentum ratio. At low ALR, the spray is characterised by larger droplets and weaker crossflow entrainment. The large-inertia droplets tend not to follow the air jet and penetrate independently in the vitiated crossflow, where they burn in a single droplet combustion regime. On the other hand, the better atomisation and the high fuel-oxidisers mixture obtained through crossflow entrainment favour the formation of a MILD combustion regime. The experimental investigation is performed by means of OH* chemiluminescence and a discrete tomographic reconstruction of the OH- and Jet A-1 Planar laser induced fluorescence of the reaction zone.
Morphology and dynamics of a premixed hydrogen-methane-air jet flame in hot vitiated turbulent crossflow
Solana Pérez, Roberto; Miniero, Luigi; Shcherbanev, Serge; et al. (2020)
Proceedings of ASME Turbo Expo 2020 Turbomachinery Technical Conference and Exposition GT2020 September 21-25, 2020, Virtual, Online
The effect of hydrogen enrichment of a premixed hydrogen-methane-air jet in hot vitiated crossflow was studied at atmospheric condition. The hot turbulent vitiated crossflow is generated by a symmetric array of 4 4 jet flames burning a lean mixture of natural gas and air in fully premixed condition at equivalence ratio phi = 0.7 and total thermal power of 50 kW. This crossflow is then used to ignite the premixed perpendicular jet of hydrogen-methane-air at ambient temperature. Three jet parameters are varied to study the effect of hydrogen addition on the flame morphology and estabilization mechanism: the hydrogen mass fraction of the H2/CH4 fuel blend (x = 0-100%), the jet equivalence ratio (phi = 0.8-2.0) and the jet-to-crossflow momentum ratio (J = 3-12). High-speed hydroxyl (OH) chemiluminescence is used to obtain the time-resolved imaging of the reactive jet and to compute its time averaged morphology. OH planar laser induced fluorescence (OH-PLIF) is used to acquire OH concentration fields at the jet center plane. The jet morphology is analyzed by considering its mean trajectory, extracted from the experimental data and fitted with empirical correlations available from the literature. New correlations are proposed for the flame length, width and center of gravity as function of the hydrogen content. It is shown that with increasing hydrogen fraction, the flame is shortened and more compact, and it stabilises close to the jet root. Another finding of this work is the reattachment of the flame at the base of the windward jet shear layer when hydrogen fraction is increased. Robust flame anchoring is observed for H2 mass fractions of the CH4/H2 fuel blend that exceed 50%. Moreover, it is shown using instantaneous OH-PLIF images that for these conditions of increasing hydrogen concentration, the windward shear layer features larger-scale coherent structures that govern the aerodynamics of the reactive premixed jet in turbulent vitiated crossflow.
Effect of plasma-flow coupling on the ignition enhancement with non-equilibrium plasma in a sequential combustor
Shcherbanev, Serge; Malé, Quentin; Dharmaputra, Bayu; et al. (2022)
Journal of Physics D: Applied Physics
The effect of the regime of nanosecond repetitively pulsed discharges (NRPDs) on ignition and stabilization of a natural-gas/hydrogen/air flame in the sequential stage of a lab-scale atmospheric pressure sequential combustor is investigated experimentally. Electrical parameters of the NRPDs are characterized by measuring voltage, current, and deposited energy. Fast gas heating (FGH) of the nanosecond discharges is measured in a single pulse regime and validated by means of 0D kinetic modelling. It was found that the conventional scheme for energy release from internal degrees of freedom adequately describes the dynamics of FGH in vitiated hot environment diluted with air. Short-gated ICCD imaging and spatially-resolved emission spectroscopy are used to identify the coupling between the NRPDs and the vitiated hot flow. The effectiveness of the NRPDs actuation is assessed through the OH* chemiluminescence images of the sequential flame. The distance of the center of gravity of the sequential flame to the outlet of the mixing channel is evaluated, with and without plasma actuation. The effect of fuel reactivity on plasma effectiveness is also studied by varying the fraction of hydrogen in the fuel blend of the second stage of the combustor. The results show that the glow NRPDs regime allows strengthening the flame anchoring for the most reactive blends considered in this work, while the spark NRPDs is required for the ignition and prevention of lean blow-out of the flame for the least reactive fuel blends which exhibit low fractions of hydrogen.
Nonlinear dynamics and thermoacoustic intermittency of a hydrogen-powered sequential combustor
Impagnatiello, Matteo; Shcherbanev, Serge; Dharmaputra, Bayu; et al. (2025)
Combustion and Flame
This study experimentally investigates the coupling between thermoacoustic instabilities and autoignition kernel formation in Constant Pressure Sequential Combustors (CPSCs). Two fuel types are examined: a less reactive methane–hydrogen blend (FCH4) and pure hydrogen (FH2). By increasing the thermal power of the first stage, thermoacoustic instabilities arise in both configurations, albeit with distinct behaviors. FCH4 exhibits a gradual onset of instability, whereas FH2 undergoes a subcritical Hopf bifurcation, characterized by abrupt, intermittent transitions between a linearly stable state and limit cycles at intermediate first-stage power. Distinct acoustic pressure spectra are observed during instability: FCH4 features a single dominant peak around 290 Hz, while FH2 displays multiple high-amplitude peaks corresponding to harmonics of the fundamental frequency near 400 Hz. Analysis of acoustic pressure and OH* chemiluminescence during instability reveals a strong coupling between acoustic fluctuations and autoignition kernel formation. With FCH4, the temporal evolution of the OH* chemiluminescence associated with these kernels follows a quasi-sinusoidal profile at the instability frequency, whereas with FH2, it consists of sharp pulses synchronized with the fundamental acoustic mode. Although existing Low-Order Models (LOMs) successfully capture the experimental behavior in FCH4, they fail to replicate the complex dynamics of FH2. To address this, a novel LOM incorporating a strongly nonlinear Heat Release Rate (HRR) feedback term is developed, specifically tailored for configurations with significant coupling between autoignition and thermoacoustics. This model successfully replicates the key spectral features of FH2, underscoring the need for advanced models to accurately reproduce the complex thermoacoustic behavior of sequential combustors. The findings of this study provide a deeper understanding of the challenges associated with sequential combustors operating under autoignition conditions, particularly in the context of decarbonization through 100% hydrogen operation. Novelty and Significance Statement This study presents, for the first time, experimental results from a lab-scale constant-pressure sequential combustor fired with pure hydrogen in both stages. The behavior under pure hydrogen fueling is compared with that of a methane–hydrogen blend. In both cases, a strong coupling is observed between autoignition kernel formation and thermoacoustic instabilities. However, the acoustic pressure spectra under pure hydrogen fueling exhibit distinct and atypical features compared to those obtained with the methane–hydrogen blend. The critical role of autoignition kernels in triggering and sustaining these instabilities is highlighted. Additionally, a novel Low-Order Model is proposed, accurately replicating the key spectral features observed in the pure hydrogen case. These findings provide valuable insights for the community, supporting the transition to pure hydrogen fueling in sequential combustors under autoigniting conditions.

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Serge Shcherbanev

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