Flame Temperature Distribution Research Articles

Study on the Flame Transition Characteristics of a Gas Turbine Combustor

Gas turbines are widely used as important equipment for electricity generation on islands and offshore platforms. During the operation of a gas turbine, the flame shape in the combustion chamber undergoes variations in response to changes in parameters such as gas turbine load, fuel distribution, and burner structure. These alterations in flame shape exert influence on combustion instability, emissions, and load characteristics. This study explores the variations in flame transition, emissions, and operating parameters among three distinct center stage structures: namely, the non-premix center stage (NPCS), premix center stage (PCS), and enhanced premix center stage (PCSE). The investigation is conducted using a heavy-duty gas turbine hybrid burner on a full temperature, full pressure, and full-size single burner experimental bench. Simultaneously, a multi-parameter numerical simulation regarding the influence of the central fuel split on flame shape analysis was conducted using the PCS burner under the design point for a more in-depth understanding of the mechanisms and for influencing factors associated with flame transition. The findings indicate that variations in flame transition loads among different central stage structures: for the NPCS burner, the transition occurs between 45% and 50% load; for the PCS burners, it takes place between 60% and 65% load; for the PCSE burners, it shifts between 55% and 60% load. Additionally, a reduction in NOx emissions is observed during the flame transition process. Furthermore, it was found that decreasing the central stage fuel results in a decline in flame angle for the same burner structure. As the central stage fuel diminishes to a specific value, the flame shape undergoes a sudden change. Further reduction in central stage fuel does not significantly affect the flame shape and temperature distribution.

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.

Development of thermally assisted OH PLIF temperature measurement method based on a single femtosecond laser

Recently, OH planar laser-induced fluorescence (PLIF) using the broadband, ultrashort femtosecond-duration (fs-duration) and the thermally assisted vibrational transfer in excited state has been investigated in flames. In this present work, we first measured temperature by thermally assisted OH laser-induced fluorescence (TALF) method with a single ultrashort broadband fs laser. In the experiment, the fs excitation of OH at ultraviolet wavelength is followed by fluorescence detection from two different vibrational bands. The ratio of two measured (1–0) and (0–0) band fluorescence is calibrated with calculated temperature using Chemkin PRO PRIMIX. The calibrated results are used in measuring temperature distributions in different laminar flames. It is found that TALF method using the fs laser can detect 2D temperature distribution in the burnt area with high OH fluorescence signal. However, OH chemiluminescence brings inevitable noise at the flame front that the TALF method does not perform well. And because (1–0) band fluorescence is so weak, the noise from the camera sensor and imaging intensifier (I.I.) remains at the measured temperature imaging. In conclusion, quantitative temperature measurement based on OH TALF based on a single broadband, ultrashort fs laser can be applied in laminar flames with high frequency by a simple experiment setup.

Experimental investigation on hydrogen jet flame behavior and temperature distribution with different shapes of outlet

Hydrogen's wide flammability range causes its high-pressure jet flames to exhibit large-scale, high-temperature characteristics, posing risks of casualties and property damage. This study investigates the impact of different nozzle shapes and release pressures on flame behavior and temperature distribution through high-pressure hydrogen jet flame experiments. Circular outlets (0.5–4 mm diameter) and rectangular outlets (aspect ratios 1 to 8) are used, covering release pressures from 20 to 220 bar. High-pressure hydrogen is released through a nozzle into ambient air, igniting to form a flame. Flame length, width, and axial temperature are measured. Findings indicate that visible flame size increases with release pressure. The models for dimensionless visible flame length and width, considering the dimensionless heat release rate, are proposed for different nozzle shapes. Additionally, the dimensionless temperature rise along the flame axis is observed to be a function of the dimensionless distance and dimensionless heat release rate.

The Study of Hydrogen Volume Fraction Effects on the Flame Temperature of Turbulence Diffusion Propane Jet Flames

This paper studies the influence of hydrogen volume fraction effects on the temperature distribution of diffusion turbulent propane jet flames. Numbers of experimental scenarios have been carried out to investigate the evolution of temperature distribution under different hydrogen volume fractions. In the continuous region, these experimental results show that the temperature distribution and the maximum temperature of diffusion of turbulent jet flames are proportional to the hydrogen volume fraction under the same heat release rate of propane. Considering the model of virtual point source and the three-stage model, the theoretical model between the hydrogen volume fraction and flame temperature has been analyzed. The relationship among the temperature distribution, hydrogen volume fraction, and heat release rate has been modified. It can provide some important references for the fire risk assessment of turbulent diffusion jet flames.

Study on flame height and temperature distribution of double-deck bridge fire based on large-scale fire experiments

Vehicle fire is one of the important causes of bridge fires. This study conducted large-scale actual fire experiments by simulating heat release rates (HRR) of oil tank truck fires with 50 MW, 100 MW, and 200 MW in rectangular oil pans of varying sizes. The flame shape and spatial temperature distribution at different HRRs were studied bycontrollingvariables such as wind speed,firesource location, andlayer spacing. The results indicated that the actual HRR of the large-scale fire exceeded the anticipated value. In large-scale fire experiments, flame splitting into two main peaks was observed along the long side of the rectangular oil pan due to the coupling effect of ambient wind, long side, and sidewall effect of the diagonal web member. The average flame height was determined through image processing, and subsequently, a formula for predicting flame height during bridge fires under varying heat release rates was developed through the use of dimensionless analysis and feature length analysis. The spatial temperature distribution in the vertical direction of the axis of the center of the fire source, the temperature distribution of the diagonal web member and the bottom of the dense crossbeams, which are critical components of the bridge, were also analyzed. Furthermore, the conclusion that the flame in the lower bridge space which split into two main peaks is validated by the results. The results of this study can provide important theoretical support for investigating bridge fire resistance strategies.

Imaging of flame propagation and temperature distribution in an all-metal gasoline engine with endoscopic access via anisole fluorescence

Laser-based optical diagnostic tools are widely used to investigate in-cylinder processes in internal combustion engines. For laser-induced fluorescence (LIF), many tracers have been used in the past. Recently, anisole has been characterized spectroscopically for engine-relevant pressures and temperatures and emerged as a potentially advantageous alternative to more commonly used tracers in the past due to its photo-physical properties. Its high fluorescence quantum yield and large absorption cross section result in high signal intensity. This is particularly beneficial for endoscopic imaging systems, which typically have worse light collection efficiency than traditional imaging systems in fully optically accessible engines with transparent liners. In this work, we exploited the strong anisole LIF signal in two single-shot experiments: to image flame propagation, and the instantaneous gas-phase temperature during compression stroke and gas exchange process. Measurements were performed in a production gasoline engine modified for endoscopic optical access via an advanced UV endoscope system. First, LIF of anisole was compared to that of toluene during compression stroke. Anisole LIF yields a much higher signal-to-noise ratio and better image quality with lower tracer concentrations. Due to the higher signal of anisole LIF, small structures of the turbulent flame burning into the anisole/isooctane mixture were well visible after ignition. Second, the red-shift of the anisole fluorescence spectrum with increasing temperature and oxygen partial pressure was exploited for ratiometric temperature measurements based on single-shot images. The available spectroscopic data were used to develop several signal ratio models, which were calibrated in situ using a heated tracer/bath gas mixture introduced inside the combustion chamber. The calibrated signal ratio models were then extrapolated to the engine-relevant ranges. Models with two-step exponential interpolation show better agreement with the adiabatic temperature than linear or 3D surface exponential interpolation. The gas-phase temperature images based on single shots were obtained using one selected model, showing a near uniform and a stratified temperature distribution during the compression stroke and gas exchange process, respectively.

Effect of distance of vertical barrier wall and release temperature on the hydrogen jet flame width and temperature distribution induced by impingement of ignited release of cryogenic hydrogen

Cryogenic storage option is one of the important ways of storing hydrogen, but under-expanded ignited releases of cryogenic hydrogen could easily lead to jet fires, causing serious damage to people and properties. Barrier walls are important means to reduce the severity of cryogenic hydrogen jet flames, however, its effect on the cryogenic hydrogen jet flame and related temperature distribution are still unclear. In this work, the effect of the distance of barrier wall (0.20, 0.25, 0.30, 0.35 and 0.40 m) and release temperature (140, 180, 220, 260 and 300 K) on the hydrogen jet flame width and temperature distribution is investigated experimentally. It is found that the flame width in the horizontal and vertical direction and the temperature on the vertical barrier wall increase with the decrease of the distance to the nozzle and release temperature. The normalized flame width and inverse excess maximum temperature on the barrier wall increases linearly with the scaled distance considering nozzle diameter and release temperature. The temperature distribution is normalized as Gaussian distribution both in the horizontal and vertical direction, while the excess temperature is higher upward than that of downward. The results can provide a theoretical basis and data support for the blocking of jet fires formed by cryogenic hydrogen ignited releases.

Numerical and Experimental Reconstruction of Temperature Distribution and Soot Concentration Field for Thin-Slice Flames Using a Charge Coupled Device Camera

This work proposed a novel model to simultaneously reconstruct temperature distribution and soot volume fraction field for two-dimensional thin-slice flames using the knowledge of monochromatic radiation intensities at two wavelengths using a CCD camera. The deduction process and numerical analysis of the model were described. Effects of wavelength combinations and measurement errors on reconstruction accuracy were considered in detail. Numerical results have proven the model’s accuracy and showed that the temperature and soot volume fraction fields can be reconstructed well even with noisy input data from flame radiation. In addition, a series of experiments were conducted on a mesoscale combustor to obtain the real thin-slice flames for further experimental reconstruction via the model. The experimental results indicated that the proposed model can successfully reconstruct the flame temperature distribution and soot volume fraction field and the main features of thin-slice flames also can be reasonably reproduced.

Experimental investigation on the behaviors and temperature distribution of cryogenic hydrogen jet flames

The jet flame resulting from the ignition of released cryogenic hydrogen is a threat to the surrounding people and facilities. However, the behaviors and temperature distribution of cryogenic hydrogen jet flame are still unclear. In this study, experiments are conducted at different release temperatures and release pressures. It has been found that the length and width of the jet flame increase as the release pressure increases and the release temperature decreases. The prediction model of cryogenic hydrogen jet flame length and width considering release pressure and temperature is proposed. The temperature of the cryogenic hydrogen jet flame increases with the increase of the release pressure and decrease of the release temperature as well. The temperature on the centerline can be expressed as a function in flame calibers, and the critical separation distance can be calculated based on three criteria. The dimensionless jet flame temperature distribution presents a three-stage distribution.

Flame behavior and temperature distribution of coupled fire induced by the interaction of hydrogen jet flame and pool flame

Once fires occur unexpectedly at the oil-hydrogen integrated refueling stations, there is a high likelihood that they will escalate into a coupled fire, resulting in unpredictable casualties and property losses. In this work, experiments on coupled fire induced by hydrogen jet flame and a heptane pool flame were conducted with different nozzle diameters and release pressures. It has been found that there is a critical diameter above which the hydrogen jet can be ignited instantly. This critical diameter is determined by the release pressure and the location of the pool flame. The heat release rate is greater than that of the single pool flame, and it reaches its highest point at 0.2 MPa. Compared to a single fire, the height of the flame decreases while the length of the flame increases, a prediction model is proposed for the dimensionless flame length and width, taking into account the ratio of the heat release rate of the hydrogen jet flame to the heat release rate of the pool flame. The temperature of the coupled fire reaches its highest point at 0.2 MPa and increases as the nozzle diameter. And it decreases with the increase in the distance when Y= 0 m. However, it increases with the increase of the distance when Y= 0.05 m due to the inclination of the flame.

Improving the biodiesel combustion and emission characteristics in the lean pre-vaporized premixed system using diethyl ether as a fuel additive

This paper is a lab-scale experimental study of the impact of employing diethyl ether (DEE) as an additive to waste cooking oil biodiesel with Jet A-1 on the combustion as well as emission features of a swirl-stabilized premixed flame. First, waste cooking oil biodiesel with a volume fraction of 20% was blended with Jet A-1 and symbolized as W20. Then, diethyl ether with a volume fraction of 20% was blended with 20% biodiesel and 60% Jet A-1, symbolized as W20D20. The three test fuels (W20, W20D20 blend, and pure Jet A-1) were premixed with preheated air and pre-vaporized before being admitted to the vertical cylindrical combustor having an inner diameter of 150 mm and a length of 500 mm via a swirl burner (radial type) of 0.55 swirl number and 8 straight vanes with an angle of 45°. Local flame temperatures and emissions were measured and recorded at 350 °C of preheated air with a constant equivalence ratio (φ) of 0.85. According to the findings, a relatively wide range of flame temperatures was observed in the flame of the W20 blend, while the W20D20 blend had a flame temperature distribution very close to that of the Jet A-1. The W20D20 blend reduced UHC emissions by 69.6%, CO emissions by 61.4%, and NOx emissions by 12.5% relative to Jet A-1 at the combustion chamber outlet. Overall, adding DEE to biodiesel significantly impacts both combustion and emission profiles.

Determining the global activation energy of methane–air premixed flames

In this work, the determination of the apparent activation energy of a global chemical reaction mechanism of the methane–air flames is revisited. The one-step formulation allows to derive the theoretical background for the method to measure the activation energy within the burner stabilised flame setup. The validity of this approach is demonstrated by using the numerical simulations with the detailed reaction model and direct thin filament pyrometry measurements of the temperature distribution in flame. The combination of numerical and experimental approaches allows us to find the activation energy for various mixture compositions. The prediction of numerical simulations and measured values of the activation energy is found to be in good agreement with each other and the data known from the literature. It is demonstrated that two critical phenomena need to be taken into account to obtain a reliable estimate of the activation energy: the flame blow-off and the onset of the diffusive-thermal instabilities. The effect of these critical events on the accuracy of the measurements is discussed as well as prospects of further investigation.

Modeling of cryogenic compressed hydrogen jet flames

Hydrogen will likely be stored and transported at high densities to have sufficient hydrogen on-site for efficient distribution. Cryogenic compressed hydrogen (CcH2) is a high-density hydrogen storage method combining cryogenic temperatures and high pressures. Hydrogen releases from such high-density sources will result in high-momentum jets and jet flames if the jets ignite. This study modelled CcH2 jet flames for stagnation pressures of 2∼5 bar and stagnation temperatures of 55∼150 K. The numerical models were validated by experimental data from the literature. The results show that the flame length increases with increasing pressure but decreases with increasing temperature. The CcH2 jet flames are longer than their room-temperature counterparts with the same mass flow rate. Then, the CcH2 jet flame lengths were correlated with the mass flow rate and stagnation temperature. Correlations were also developed for predicting trajectory temperatures and the radial temperature distributions in the CcH2 jet flames. The present study provides a scientific basis for developing cryogenic hydrogen safety codes and standards and quantitative risk assessment models.

Numerical investigation of combustion characteristics under oxygen-enriched combustion combined with flue gas recirculation in a cement rotary kiln

A new technology combining oxygen-enriched combustion with flue gas recirculation (OEC-FGR) in the cement rotary kiln is put forward, based on the technical complementarity of these strategies. The effects of the flue gas recirculation rate on the combustion characteristics and NOx formation with a primary air oxygen concentration of 27% in a cement rotary kiln of 5000 t/d capacity are numerically investigated. The introduction of recirculating flue gas has significant influences the flame size, temperature distribution, and NOx formation. As the FGR rate increases, the flame lengthens and the high-temperature region shrinks. At the same time, the position of the temperature peak is delayed and the length of the calcination section is shortened. Furthermore, NOx formation is remarkably reduced, owing to the lengthened low oxygen reduction zone and lower temperature. As the FGR rate increased from 0% to 27%, the maximum NOx concentration on the center line in the kiln and the NOx concentration at the outlet decreased by 392 ppm and 343 ppm, respectively, and both decreased the most when the FGR rate increased from 0% to 10%. Moreover, good burnout is obtained with the new combustion technology, although considerable CO is generated near the burner. Since the length of the clinker calcination zone may be adversely affected by an excessively high FGR rate, the FGR rate should be carefully determined. In this study, a better compromise between calcination performance and NOx reduction could be achieved when the FGR rate was 20% .

Influence of a self-formed three-stage dual-wing-shaped carbon on reduction of soot emission from acetylene diffusion flame

This paper reports the formation of a self-formed three-stage dual-wing-shaped carbon (TSDWSC) from acetylene diffusion flame for the first time. The TSDWSC grows naturally from the protrusion at the outlet of the nozzle, while the emission of soot can be greatly reduced. The evolution of the TSDWSC involves three stages: the first unclosed dual-wing, the second unclosed dual-wing and the unmatured third dual-wing. The effects of protrusion, the flow rate of acetylene and various burner nozzle diameters on the formation of the TSDWSC are investigated. The experimental results show that with the increase of the protrusion height, the time when the first stage begins to appear decreases. With the increase of the acetylene flow rate, the stage number of the final dual-wing-shaped carbon increases. The TSDWSC can only be generated when the nozzle inner diameter is 2 or 3 mm. Using a two-color thermometer, the flame temperature distribution along the flame centerline is measured after the complete growth of the TSDWSC. The results show that the temperature of the TSDWSC area in the lower part is remarkably lower than that of the flame area in the upper part. The efficiency of reducing soot emission increases gradually with the evolution of the TSDWSC and reaches 100%, while the temperature of the flame area in the upper also rises gradually. X-ray diffraction (XRD) result indicates the formation of carbon crystals.

Simultaneously retrieving of soot temperature and volume fraction in participating media and laminar diffusion flame using multi-spectral light field imaging

The inner distribution of the flame properties can be retrieved by solving the intractably ill-posed inverse problem from spectral radiation imaging. This study presents a simultaneous retrieving method of the three-dimensional temperature and soot volume fraction distribution in the small-scaled flame by proposing a multi-spectral light field imaging process. The results show that the temperature and soot volume fraction of the participating media and laminar diffusion flame can be reliably retrieved. Specifically, the reconstructed properties of the inner region of lower flame height are moderately affected by the selection of the visible wavelength group. The ray number slightly affects the retrieve, while the deviation is susceptible to measurement error, which is better to be less than 52 dB. The proposed approach can be used for the flame spectral diagnostic and the radiative properties calculation.

Effect of diethyl ether addition to waste cooking oil biodiesel on the combustion and emission characteristics of a swirl-stabilized premixed flame

Waste cooking oil biodiesel is a promising alternative to diesel and jet fuels. However, the challenge of using waste cooking oil biodiesel is its higher viscosity and lower volatility than diesel fuel, which hinder its spray and atomization from achieving diesel levels. These drawbacks can be enhanced by adding a less viscous fuel like diethyl ether. Thus, an experimental approach has been performed to investigate the effect of diethyl ether addition to waste cooking oil biodiesel in the lean pre-vaporized premixed system. Test fuels considered in this study are B20 (20% biodiesel + 80% Jet A-1), B20D10 (20% biodiesel + 10% diethyl ether + 70% Jet A-1), B20D30 (20% biodiesel + 30% diethyl ether + 50% Jet A-1) as well as pure Jet A-1. These blends are applied in the lean pre-vaporized premixed system with preheated air at 350 ℃ at a fixed equivalence ratio of 0.85 (lean condition). Results showed a 68, 38.4, 14.5, and 43.4% decrease in CO, NOx, CO2, and UHC emissions, respectively, for the B20D30 blend, compared with pure Jet A-1 fuel at the combustor exit, while the B20D10 blend indicated a 15.8, 8.9, 6.17, and 51.4% drop in CO, NOx, CO2, and UHC levels, correspondingly. Jet A-1 achieved a higher maximum temperature than those for other blends. The B20 blend revealed a relative variation in flame temperature distribution, while diethyl ether blends shared a similar temperature distribution compared with Jet A-1. Generally, B20D10 and B20D30 blends had the ability to reduce emission levels. Overall, it can be concluded that the recommended diethyl ether blending ratio is 30%, regarding emission levels and flame temperature profile.

Rapid online tomograph in non-uniform complex combustion fields based on laser absorption spectroscopy

Laser absorption spectroscopy tomography is widely applied to measure the two-dimensional distribution information in complex combustion flow fields. Rapid and accurate estimation of the integrated absorption area (IA) is the key to achieving accurate online reconstruction. In this paper, a novel method is introduced with the wavelength modulation spectroscopy (WMS) for obtaining the IA, which is applied in the reconstruction of temperature and species concentrations distributions of non-uniform complex combustion flames. With this method, the traditional time-consuming line-shape fitting process is no longer required, and the IA is obtained through simple algebraic operations instead. This method has been validated via numerical simulations and field experiments on afterburner flames. The experimental results show that the measurement accuracy is comparable to that achieved with the conventional WMS with line-shape fitting (WMS-F), however the computational efficiency is improved significantly by at least two orders of magnitude, demonstrating its potential for real industrial applications, where often rapid reconstructions are desirable or required.

Experimental investigation on the partial oxidation of methane with the effect of shrunk structure

Hydrogen energy is an ideal clean energy to solve the expanding energy demand and environmental problems caused by fossil fuels. In order to produce hydrogen, a double-layer porous media burner with shrunk structure was designed to explore the partial oxidation (POX) of methane. And the combustion temperature, species concentration and reforming efficiency were studied under different shrunk parameters and operating conditions. The results indicated that the shrunk structure greatly influenced the flame position and temperature distribution. The flame moved to the downstream section with the decreasing of the inner shrunk diameter and the increasing of the shrunk height. When the diameter of the filled Al2O3 pellets was 8 mm, the hydrogen yield reached the highest value of 43.8%. With the increasing of equivalence ratio, the reforming efficiency increased first and then decreased, and the maximum value of 53.0% was reached at φ = 1.5. However, the reforming efficiency and axial temperature kept increasing when the inlet velocity increased from 10 to 18 cm/s. The corresponding results provided theoretical reference for the control of flame position and species production by the design of shrunk structure in porous media burner.