Combustor Operating Conditions Research Articles

Flame soot absorption coefficient and temperature reconstruction through line-of-sight attenuation and light field imaging

The accuracy and efficiency of 3-D flame temperature field reconstruction using the light field imaging technique heavily depend on soot radiation characteristics. In this study, we employ the line-of-sight attenuation method to reconstruct the soot absorption coefficient distribution in a pure absorbing flame. Utilizing these soot absorption coefficients, the radiative transfer equation is effectively transformed within the framework of the light field imaging technique into a linear inverse problem and also outlines the flame boundary. This proposed strategy reduces the unwanted detection rays significantly, thus eliminating the extensive computational processing. Consequently, the proposed approach substantially enhances the accuracy and efficiency of flame temperature reconstruction. Numerical simulations were carried out on a bimodal asymmetric flame to validate the noise tolerance capabilities, investigate the effects of varying voxel numbers on flame division and carry out a comparative study. Experimental studies were also conducted to reconstruct flame temperature and soot absorption coefficient distributions under different combustion operating conditions. Thermocouple measurements were performed and compared with the reconstructed temperatures. Outcomes achieved from both numerical simulations and experimental studies demonstrate the feasibility, accuracy and robustness of the proposed method.

Theoretical Evaluation of YSZ and Alumina-YSZ Thermal Barrier Coatings in a Hydrogen Enriched Combustion Environment

Abstract Yttria-stabilized zirconia (YSZ) ((ZrO2)0.93(Y2O3)0.07) and alumina-yttria-stabilized zirconia ((Al2O3)0.853 + (ZrO2)0.93(Y2O3)0.07) thermal barrier coatings (TBCs) were modeled in the presence of hydrogen-enriched combustion product gases to evaluate phase composition and thermal expansivity (coefficient of thermal expansion). Thermal equilibrium simulations for various equivalence ratios (0.5–0.75) and hydrogen enrichment percentages (0−50%) were conducted to determine the product gas composition for various combustor operating conditions. The obtained product gases were then used in a second thermal equilibrium simulation to demonstrate their effect on the defined thermal barrier coatings. The modeling predictions showed that hydrogen enrichment percentage and equivalence ratio were positively correlated to thermal expansivity for both the thermal barrier coatings examined. The alumina-YSZ composite coating exhibited a higher CTE, more closely matching the CTE of a metallic bond coat, for the studied conditions. This closer match of thermal expansivity results in less significant thermal stresses than the YSZ thermal barrier coating. An increase in hydrogen enrichment percentage and equivalence ratio yielded increased percentages of phase transitions from tetragonal zirconia (t-ZrO2) to cubic zirconia (c-ZrO2). The YSZ thermal barrier coating had a larger percentage of phase transitions throughout the operating range examined, which renders concerns for potential failure from thermal cycling and creep. Theoretical examination of the phase composition and thermal expansivity provided further insights into the fate and behavior of the thermal barrier coatings.

Performance assessment and optimization of three-dimensional hybrid slot–effusion jet cooling configuration of an annular combustor liner

In this study, the film cooling performance of a three-dimensional (3D) hybrid slot–effusion configuration and its advantages over a baseline pure 3D slot cooling are investigated in detail using both experimental and numerical investigations. The numerical model is validated by in-house experiments conducted on a hybrid cooling configuration with a 3D slot and staggered effusion array. Infrared thermography and hot wire anemometry are used in this study to analyze the thermal and flow fields. The cooling performance of pure 3D slot and hybrid configurations is compared under identical coolant consumption. The coolant mass flow ratio (MFR) determines the cooling behavior in hybrid cooling. At low MFRs, hybrid cooling is less effective than pure 3D slot cooling. In addition, it is observed that there exists an optimal MFR where hybrid cooling outperforms 3D slot cooling. Subsequently, the effect of key design variables on the cooling performance of the hybrid configuration is studied, and they are optimized at typical combustor operating conditions using a genetic algorithm coupled to a Kriging surrogate model. The optimal configuration is experimentally tested at laboratory conditions and compared with the baseline 3D slot configuration, and it is noted that there is a significant improvement in the cooling effectiveness. Additionally, the film cooling performance of the optimized configuration at combustor representative operating conditions of maximum BR of 2 shows an enhancement of 16% in area-averaged adiabatic effectiveness and a 60% reduction in the standard deviation of local adiabatic effectiveness as compared to the baseline 3D slot cooling.

Deep-learning-based reduced-order modeling to optimize recuperative burner operating conditions

This study analyzed a recuperative burner system that is critical for energy efficiency and pollutant reduction in the firing processes required in the manufacturing industries. We aimed to optimize the operating conditions of a recuperative burner using computational fluid dynamics (CFD) combined with a novel reduced-order deep-learning technique. The Reynolds-averaged Navier–Stokes model and finite-rate/eddy-dissipation models were used to generate reliable CFD simulation results considering four operating conditions (temperature and mass flow rate of air and fuel). We first validated the CFD model with two-dimensional axis-symmetric experimental burner results and created a proper orthogonal decomposition transformer model using large-scale snapshots of the CFD results and various operating conditions. Subsequently, a genetic algorithm was employed to find the optimal conditions for five different objective functions: fuel economy, decrease in carbon monoxide emissions, reduction in nitrogen oxide emissions, decrease in carbon dioxide production, and an all-encompassing view of the four objectives. Finally, by comparing our proposed approach with previous methods, we confirmed that the obtained optimal operating conditions improve the performance of the recuperative burner. This study provides an optimized framework for recuperative burners to reduce environmental pollution, with potential applications in many industries, such as ceramics, steel, and batteries.

Modelling of the Flame Synthesis of Single-walled Carbon Nanotubes in Non-premixed Flames with Aerosol Catalyst

The use of aerosol catalyst in the flame synthesis of carbon nanotube (CNT) is known to yield single-walled CNT (SWCNT) that is useful for various applications. Modelling works are needed to optimize operating conditions for SWCNT growth but are unavailable. Therefore, a baseline model for the aerosol-catalyst system in flames is developed and the effect of oxygen on SWCNT growth is investigated. A baseline flame model for a normal diffusion flame with 24% oxygen concentration at the inlet is established via Computational Fluid Dynamic simulation. A dispersed phase model (DPM) is employed to simulate the entrainment of catalyst particles. The flame model is coupled with a published CNT growth rate model to predict the CNT growth rate at each particle. Inlet oxygen concentration is varied from 19% to 27% to study the effect of oxygen on SWCNT growth. Satisfactory validation of the baseline flame shape and temperature is established. Results show that particle 3 for the baseline case yields the highest CNT length compared to other particles due to the suitable path for the synthesis. The particles are classified based on the shortest time residence, moderate and longest time residence. Increasing oxygen concentration from 19% to 27% results in a 30% decrease in CNT length for particle 3 for each inlet condition due to lower carbon precursor and composition in the flame. Furthermore, the results showed that regardless of burner operating conditions, high SWCNT growth is consistently predicted between 120-140 mm HAB, which indicates the existence of an optimum range of species concentration for SWCNT growth in aerosol-based flame synthesis. Thus, it can be inferred that SWCNT growth in the aerosol–based method is highly dependent on carbon source and moderately dependent on temperature

Experimental study of stability and pollutant emissions of turbulent biogas flames under microsecond pulsed plasma

Biogas is a mixture of methane (50–80%.vol), carbon dioxide (20–45%.vol), and in smaller proportions of N2, O2, H2S, and NH3. For a high rate of CO2 in the biogas, the combustion can generate strong instabilities and the flame can be very lifted from the burner and even blown. To overcome these problems of instabilities and flame extinction, the use of a microsecond pulsed plasma is considered for this study. This study aims to characterize the effects of microsecond pulsed discharges on the stabilization and emission characteristics of non-premixed swirling biogas/air flames at different operating conditions of combustion (CO2 rate, power, and equivalence ratio) and plasma (pulse repetition frequency and input electrical voltage). The plasma is performed above a coaxial burner with a swirler of the oxidizer. It is generated by a DC-pulsed power generator with a high voltage (HV) pulse duration of a few microseconds. The burner consists of two concentric tubes and a central metal rod used as a cathode for the plasma. The outer tube contains a swirler and supplies the oxidant flow, and the inner tube delivers the fuel (methane, biogas) around the central metal rod. High voltage pulses are applied on two anode tungsten wires that are symmetrically arranged from either side of the cathode to obtain two plasma zones in the stabilization region of the flame. The burner is placed in a parallelepiped combustion chamber with a volume of 100x48x48 cm3. Mass flow rates of air and fuel are regulated by thermal mass flow controllers (Brooks SLA5851S). OH* chemiluminescence measurements are done to describe the structure and the flame stability throughout the lift-off heights (Hf) variation. Results showed that plasma generated by microsecond HV pulses can improve flame stability by decreasing its Hf especially at low fuel velocities. In this regard, the optical emission spectra (OES) were visualized. The results reveal that the pulsed plasma generates chemically active species such as excited N2*, CH*, OH* molecules, and H* atoms, leading to improved flame stability. Their intensities' dependence on the pulse repetition frequency, the sight position of the OES, the concentration of CO2 in the fuel, and the fuel velocities were investigated in detail. Furthermore, the NOx and CO emissions in the burned gas are investigated over a wide range of repetition pulse frequencies. It is seen that the microsecond pulsed plasma slightly increases the NOx emission and reduces CO concentration in the flue gases.

A numerical study of piston bowl geometry and diesel injection timing in a heavy-duty diesel/syngas RCCI engine

The current numerical study aims to examine the single and combined effects of various piston bowl geometries, diesel main Start of Injection (SOI) timing, and syngas energy ratio on the combustion characteristics, specific emissions (g/kW·h), energy distribution, and exergy of a heavy-duty off-road Reactivity-Controlled Compression Ignition (RCCI) diesel engine. The examined geometries include the stock chamber (baseline combustion chamber), wide-shallow chamber, dual-swirl chamber, stepped-lip chamber. The main SOI timing was varied from −20 to −5 Crank Angle (CA) After Top Dead Center (ATDC) with 5 CA steps. Also, syngas energy ratio including 0% Conventional Diesel Combustion (CDC) mode, 20%, 40%, and 60% of total fuel energy per cycle. To accomplish this goal, the SAGE combustion model coupled with a reduced chemical kinetic mechanism consists of 360 reactions, and 72 species was applied to conduct this investigation. The numerical findings showed that the use of the wide-shallow chamber extended the engine operable range under diesel-syngas combustion operating conditions. In comparison to the baseline CDC case, the application of the dual-swirl chamber under CDC conditions, and main SOI timing of −15 CA ATDC led to reduction of Carbon Monoxide ([Formula: see text]), Hydro-Carbon ([Formula: see text]), Particle Matter ([Formula: see text]), Carbon Dioxide ([Formula: see text]), Indicated Specific Energy Consumption (ISEC), Gross Indicated Efficiency (GIE), and exergy efficiency but with a Nitrogen Oxides ([Formula: see text]) penalty rate. In general, an increase in the bore to bowl diameter ratio caused a shorter ignition delay period and combustion duration. The utilization of the stepped-lip chamber at both CDC and diesel-syngas combustion operating modes resulted in a shorter ignition delay period, but a longer combustion duration. Nonetheless, the stepped-lip combustion chamber reduced the diffusive flame temperature. Also, it is noteworthy that the utilization of the stock chamber along with the main SOI timing at −5 CA ATDC under diesel-syngas 60% combustion mode is a suitable technique to pass EURO-VI [Formula: see text] and [Formula: see text] emissions regulations.

Emission analysis of sugarcane bagasse combustion in a burner pilot

Although biomass is from a renewable source, and its biological development captures CO2, burning emits a mixture of various components, such as particulate materials, CO2, CO, NOx, oxides, VOCs, among others, and may contain F, Hg and As. These gases contribute toward anthropogenic air polluting agents and are emitted for energy sources by various industrial sectors, such as sugarcane bagasse burning, which is a waste product of the sugar and alcohol industry. This study aims to quantify gas emissions, mainly CO2, CO, and NOx, from sugarcane bagasse burning under different burner operating conditions and to evaluate the emission and control of these pollutants using a Venturi scrubber. The sugarcane bagasse combustion process occurred in an experimental burner, comprising a rotary feeder, combustion chamber, exhaust gas chamber, Venturi scrubber, cyclone, blowers, and exhaust ducts. The Venturi scrubber, located between the burner and the cyclone, has a rectangular geometry. The gas velocity was evaluated from 3.4 to 11 m/s and the water flow rates from 2.5 L/min to 6.0 L/min. The results indicate that CO concentrations ranged from 34 to 311 ppm, the NOx concentrations from 8 to 80 ppm, while CO2 reached values from 6000 to 26000 ppm. Investigating and quantifying these emissions are important to understand the global carbon balance, given the considerable magnitude of CO2 emissions from these non-fossil fuels.

Possibilities of steam boiler process optimization in the TPP Ugljevik

The paper presents a technical solution for modernization with the aim of increasing the efficiency of the steam boiler of TPP Ugljevik, which implies the reorganization of the combustion system. More efficient operation of the furnace can be achieved by replacing the existing burners, reducing the number of burner levels as well as the organization of tangential combustion. The flame formed in the shape of a tube around the two central combustion vortices provides a larger amount of heat transferred to the combustion furnace, less fouling of its screen walls and thus a lower average temperature of the combustion products at its outlet. As the chosen reorganization affects the increase of the temperature of the superheated steam and the decrease of the temperature of the reheated steam, it has been proposed to reduce the area of the semi-irradiated superheater and increase the area of the second reheater. Taking into consideration that the reorganization of the combustion system may lead to the change of the thermal load of the evaporator located in the furnace, the paper presents the work of the steam boiler operation under new operating conditions. Used calculation system enables reliable prediction of operating characteristics of the steam boiler in new operating conditions of combustion, and its application helps assess the quality of the boiler in terms of how effective, efficient, safe and environmentally friendly its operating mode is. In this way, it is possible to form a comprehensive description of the operating mode of the steam boiler.

Fundamental Study of CH4-Air Combustion Under an Axisymmetric Small-scale Rectangular Combustor Using Computational Modeling

The optimization of the design and operating conditions of industrial combustors depends on the fundamental study of combustion dynamics and flow behaviors. Complete combustion increases the thermal efficiency as well as reduces the emission significantly. A study of this kind also allows exploring alternative fuels that would increase the combustion efficiency thus the life cycle of the systems. To develop a highly-performed combustion system for rocket engines or power plants, fundamental research under an axisymmetric small-scale combustor is considered in this study. The k-Ɛ (2 Eqn.) and species transport model (STM) are used to study the flow turbulence and combustion behavior, respectively. A Parallel flow injection configuration of fuel and air is considered. In this study, combustion behavior is investigated at a wide range of fuel and air flowrate conditions while keeping the air slot dimension (240 mm) and fuel injection slot diameter (10 mm) constant. The fuel velocity (FV) and air velocity (AV) are changed from 2 m/s to 30 m/s so that a better test matrix could be proposed. At each run, turbulence, the flame temperature, reaction heat release rate, mass fraction of CO2, etc are studied. It is seen that the combustion temperature increases with the increase in fuel injection velocity. The static flame temperature reaches its maximum (2177 K-2287 K) and falls within the standard limits of CH4-Air combustion. The mass fraction of CO2 is found to be within the acceptable limit (0.121-0.153). The heat of the reaction is found to be high at variable Reair and ReCH4 conditions. It is observed that the computational models used in this study are capable of predicting the flow and combustion behaviors accurately.

Influence of alternative fuel properties and combustor operating conditions on the nvPM and gaseous emissions produced by a small-scale RQL combustor

Non-volatile Particulate Matter (nvPM) from aircraft gas turbine engines are harmful to both human health and the environment, but can be significantly reduced by using low aromatic Sustainable Aviation Fuel (SAF). As part of the Horizon 2020 funded JETSCREEN (JET fuel SCREENing and optimisation platform for alternative fuels) project, nvPM and gaseous emissions were characterised using regulatory compliant sampling and measurement methodologies for a small-scale (<250kW) non-proprietary RQL combustion rig, at pressures ranging from 1.0 to 2.4 bara. The impact of flow conditions, air to fuel ratio and fuel composition was investigated for a selection of conventional aviation Jet-A1 fuels, SAFs, and blended fuels. Measured concentrations were corrected for particle-size-dependant system losses using particle size measurements, to be representative of combustor exit concentrations.Across the range of fuels (hydrogen contents 13.51%-15:31%), system-loss-corrected nvPM mass, number, and size were shown to decrease with increasing fuel hydrogen content, in agreement with previous studies. Inverse power law correlations are proposed as the best descriptors of these trends. Average reductions in nvPM mass, number, and sizes of 73%, 54% and 17% respectively, were observed for a near-zero aromatic ATJ fuel compared to a reference Jet A1 fuel, with minimal changes to measured gaseous pollutants. It is noted that without size-dependant system loss corrections, nvPM number reductions were overreported (∼6% for the ATJ fuel) due to the smaller particle sizes with increasing fuel hydrogen content. It was hypothesised that observed nvPM deviations from the fuel hydrogen content trends were due to fuel physical properties affecting atomisation, however no correlations were found greater than the measurement uncertainty and combustor rig variability.This study provides a unique dataset intended to facilitate combustion model validation, providing full details of combustor geometry, flow conditions and rig conditions, along with the representative combustor exit nvPM and gaseous data.

Simultaneous multiple laser beam intensity profile correction and its application to a vitiated bluff body combustor field.

Simultaneous high-speed stereo-particle image velocimetry, OH planar-laser-induced fluorescence (PLIF), and CH2O PLIF measurements in a vitiated bluff body combustor are considered. An ex situ, simultaneous, time-resolved laser sheet intensity profile correction procedure is introduced. This procedure is easily implemented experimentally and is capable of correcting multiple sheets at the same time. As a proof of concept, the procedure is applied to perform correction of the CH2O PLIF images in vitiated and unvitiated conditions. The challenges associated with CH2O PLIF under these combustor operating conditions are also discussed.

Thermoacoustics of multi-burner combustors with plenum and chamber cross-talk

This paper presents a thermoacoustic model in the frequency domain for multi-burner combustors composed of multiple plenum-nozzle-chamber modules with cross-talk at both plenums and chambers. The thermoacoustic model is given as a multi-input-multi-output transfer function matrix from heat fluctuation input vector to velocity fluctuation output vector. The discrete rotational symmetry of a multi-burner combustor is exploited to obtain a simple, diagonal transfer function matrix. The resonance equation, whose roots are resonances, is given as a set of scalar equations. The explicit form of the resonance equation reveals how combustor and operating parameters influence the resonances, and which parameters are significant for the longitudinal-azimuthal coupling and the plenum-chamber coupling. The diagonalization also allows us to show constructively that every mode shape is a Bloch wave and those mode shapes can characterize all resonances in terms of longitudinal and azimuthal mode numbers. At a low frequency, the resonance equation can be approximated as biquadratic and quadratic equations for a typical combustor geometry and operating conditions. A bunch of low-frequency resonances, peculiar to multi-burner combustors with cross-talk, are interpreted as azimuthal Helmholtz modes in which plenums/chambers and cross-talk ducts serve as the cavities and necks, respectively. Our combustor model is combined with a diagonal flame transfer function matrix for combustion instability analysis and we develop a set of scalar stability equations whose roots determine combustion instability. This stability equation reveals how combustion instability depends on the combustor geometry and operating parameters. Several numerical examples are presented to validate our thermoacoustic model and theoretical findings.

Combustion operating conditions for municipal Waste-to-Energy facilities in the U.S.

This paper reports the first known comprehensive survey of combustion operating conditions across the wide range of municipal waste-to-energy facilities in the U.S. The survey was conducted in a step-wise fashion. Once the population of 188 units operating at over 70 facilities was defined, this population was stratified by distinguishing characteristics of combustion technology. Stratum-level estimates for operating conditions were determined from data collected in the survey. These stratum-level values were weighted by corresponding design capacity share and combined to infer national-level operating parameter estimates representative of the overall population. Survey results show that typical municipal waste-to-energy combustion operating conditions in the U.S. are (1) furnace temperature above 1160°C, (2) gas residence time above 2.4s, (3) exit gas concentrations of nearly 10% for oxygen (dry basis), and (4) over 16% for moisture. These operating parameter values can serve as benchmarks for laboratory-scale studies representative of municipal waste-to-energy combustion as typically practiced in the U.S.

Study on the feasibility of the micromix combustion principle in low NOx H2 burners for domestic and industrial boilers: A numerical approach

The purpose of the present investigation is to explore the feasibility of applying the micromix combustion principle (MCP) to design low NOx burners using 100% H2 as fuel for domestic and industrial boilers. Previous investigations studying the MCP on stationary and aero gas turbine applications, showed low NOx emissions without flashback risk, which represent the two main issues when burning 100% H2. Since boiler burner operating conditions differ from gas turbine combustors, the present paper studies the MCP through CFD calculations under re-defined conditions for domestic and industrial burners, adapting the energy densities, air-fuel equivalence ratios and pre-heated air temperatures. A reference geometry was built to validate the selected numerical models with experimental results from literature. Afterwards, burners were re-dimensioned following an existing geometry-scaling methodology. The obtained results evidenced that MCP characteristics were still maintained for the defined cases, keeping low NOx values between 4 and 14 ppm. The numerical results were also validated through experimental NOx measurements in a laboratory scale micromix burner prototype. In order to assess the benefits of using hydrogen micromix burners in domestic and industrial boilers, the present work includes a final discussion with practical design considerations. The present study lays the groundwork for complementary experimental research work, which is being carried out in laboratory-scale prototypes.

Dynamics of ignition kernel in a liquid-fueled gas turbine model combustor studied via time-resolved 3D measurements

This work aims to study the ignition kernel dynamics with spatial-temporal resolved experimental measurements in spark-ignition processes of a liquid-fueled gas turbine model combustor. For this purpose, tomographic chemiluminescence combined with fiber endoscopes are used to measure the time-varying, volumetric CH* distribution of the ignition kernel in different combustor operating conditions at 10 kHz. Based on the time-varying 3D measurements, key properties of ignition kernels, including the 3D size, structure, orientation, growth direction, 3D and 3C (three-component) movement velocity, flame propagation speed, and their temporal evolutions are extracted to provide important insights into the kernel dynamics in such a highly localized transient process. Results show that the growth of the kernel is very sensitive to its motion trajectory. Generally, the kernels move following the flow rotation in the tangential direction, but are oriented along the radial direction and temporally evolve toward the radial direction as the ignition event progresses. Splitting and moving inward are also observed in the radial direction, which is not beneficial to the kernel growth. The evolution of flame propagation speed (ST) during the ignition process shows two distinct stages. In the first stage, ST increases following the power-law of ST=αAtα−1. The rapid growing kernels are with the higher A and lower α. While in the second stage, ST oscillates around a mean value. The transition between the two stages is associated with the corrugation levels of the kernel.

Flow parameter estimation using laser absorption spectroscopy and approximate Bayesian computation

Given spatially sparse or lower dimensional experimental measurements, approximate Bayesian computation (ABC) and numerical simulations can be used to estimate unknown characteristics of complex multi-physics engineering systems. Here, we describe the ABC approach and use it to estimate the speed of high-temperature gases exiting an industrially relevant catalytic burner, as well as to estimate the completeness of combustion within the burner. Using vertical profiles of absorption-weighted average temperature from laser absorption spectroscopy (LAS) at three different burner operating conditions, we combine ABC and large eddy simulations (LES) to generate posterior distributions of inflow speeds and heat addition characteristics above the burner. We show that the ABC method correctly estimates trends in the inflow speed for different conditions, and we find that there is a strong likelihood of incomplete combustion for higher equivalence ratios. We evaluate the predictive capability of the approach using an observing system experiment, indicating that the ABC method, when combined with LES, is able to accurately predict LAS measurements. We thus demonstrate that ABC is an effective tool for obtaining additional insights from available experimental measurements, thereby improving understanding of real-world engineering systems.

Characteristics of NH3/H2/air flames in a combustor fired by a swirl and bluff-body stabilized burner

Combustion of ammonia (NH3) presents a number of challenges due to its low reactivity, poor flame stability, very low flame speed and high NOx emissions in a range of burning conditions. Therefore, its application in combustion systems requires device modifications, either by adapting existing systems or developing new ones. In this work, a novel combustor fired by a swirl and bluff-body stabilized burner was designed and tested. Initially, flame stability diagrams were established for NH3/H2 fuel mixtures. Then, emissions of NOx and unburnt NH3 were measured for a range of equivalence ratios and NH3 mole fractions in the fuel mixture. In addition, in-flame data for O2 and NOx concentrations and gas temperature were measured for five combustor operating conditions. A parallel mathematical modelling exercise was performed to obtain a qualitative knowledge of the burner aerodynamics and assist the interpretation of the experimental results. The predicted aerodynamic pattern suggests the establishment of an extended central recirculation zone that allows long residence times in the near burner region (NBR) that are critical to ensure stable combustion of the NH3/H2/air mixtures. The measurements revealed that the burner presents a wide range of stable flames for xNH3 between 0.6 and 0.8, showing the positive effects of adding relatively small amounts of H2 to the fuel mixture. The in-flame data show that the flame initiates close to the burner inlet and presents two main reaction zones. NOx is formed in the NBR and is consumed afterwards, through selective non-catalytic reduction reactions. Overall, the present laboratory combustor performs well in terms of flame stability and both NOx and NH3 emissions, and it is foreseen that industrial combustors based on the present design would be able to ensure flame stability and NOx and NH3 emissions control with simple complementary systems.

Combustion regime identification from machine learning trained by Raman/Rayleigh line measurements

A combustion regime identification based on convolutional neural networks (CNNs) is developed using the recently proposed gradient-free regime identification (GFRI) approach applied to two turbulent CH4/air jet flames featuring multi-regime characteristics. The training and the subsequent application of the CNN rely on the processing of one-dimensional Raman/Rayleigh line measurements of species mass fractions and temperature (CNN input). The combustion regime index is then readily predicted at every point along the measured line (CNN output). For training the neural network, the combustion regime index is first determined using the GFRI method (Hartl et al., 2018) based on the chemical explosive mode analysis (CEMA). Six classes of combustion regimes, including premixed (P), dominantly premixed (DP), multi-regime (MR), dominantly non-premixed (DNP), non-premixed (NP), and lean back-supported (LBS), are well detected by the trained CNN, with a pixel-wise accuracy of more than 85% for burner operating conditions unseen during training (different free-stream equivalence ratios). The quasi instantaneous neural network response provides a perspective towards real-time global combustion regime identification for pollutants emission control. From the results, it is also concluded that introducing physical insight, by combining advanced experimental (Raman/Rayleigh line measurements) and numerical analysis (GFRI), allows for reducing the amount of data needed to train neural networks.

Research of the Influence of Temperature Factor on Express Control of Natural Gas Combustion Heat

The article is devoted to the study of the influence of the qualitative and quantitative composition of gas environments on the flame temperature of the combusted gas at different values of gas flow rate and changes volume ratio gas-air in its combustion. The functional scheme of the developed labo­ratory stand (Fig. 1), which provides temperature measurement during combustion of natural gas or propane-butane mixture, is considered. The design of the developed burner is described and the expe­rimental researches are carried out when measuring the flame temperature of the combusted gas during the operation of the laboratory stand. The opera­ting conditions of different thermocouples in measuring the temperature of the flared gas are investigated (Fig. 2). The temperature instability in the lower and upper flames was experimentally determined (Fig. 3) and its difference from the reference data [12, 13]. The measurement of the flame temperature with&#x0D; a uncased thermocouple and two thermocouples of different types with protective housings is reali­zed. Methodical error of temperature measurement by different thermocouples was estimated (Fig. 5). An algorithm for the implementation of measurement control in determining the heat of combustion of natural gas according to the patented method is outlined [11]. Experimental studies of temperature changes of combusted gas mixtures at different gas flow rates and different ratios with air, which is additionally supplied for gas combustion, were carried out (Figs. 4, 7). The computer simulation (Figs. 6, 8) of the change in the flame temperature was performed on the basis of the experimental data, which allowed to obtain approximate equations of the functional dependence of the flame temperature on the gas flow rate and the ratio of the additional air and gas consumption. The possibility of realization of the device of express control of the heating value of natural gas by measuring the combustion temperature of the investigated gases, which is based on the expe­rimentally confirmed increase in the flame temperature of the investigated gases with increasing their calorific value, is substantiated (Fig. 9). The necessity of further investigation of the optimization design characteristics of the burner and the operating conditions of combustion of the gases under rapid cont­rol of their combustion heat was established (Fig. 9).