Flame Photographs Research Articles

Experimental Investigation of Non-Premixed Combustion Process in a Swirl Burner with LPG and Hydrogen Mixture

In the modern world, issues related to the use of alternative fuels are becoming increasingly pressing. These fuels offer the potential to achieve significantly improved environmental and technological performance. Currently, among such fuels, biodiesel, ammonia, LPG, and hydrogen are considered the most promising options. LPG and hydrogen exhibit a high Lower Heating Value (LHV) and have a relatively low environmental impact. This article investigates the combustion of hydrogen-LPG mixtures in a diffusion burner. The main parameters under study include the proportion of hydrogen in the fuel, equivalence ratio, and vane angle. The analyzed parameters encompass NOx and CO concentrations. The studies have demonstrated that the addition of hydrogen can reduce greenhouse gas emissions, as the combustion product is clean water. The primary focus of this research is the examination of combustion processes involving flow swirl systems and alternative fuels and their mixtures. The studies indicate that flame stabilization is significantly influenced by several factors. The first factor is the amount of hydrogen added to the fuel mixture. The second factor is the degree of mixing between the fuel and oxidizer, along with hydrogen. Lastly, the equivalence ratio plays a crucial role. As the studies have shown, the maximum stabilization for a speed of 5 m/s is achieved at an angle of 60° and a hydrogen fraction of 40%, resulting in φLBO = 0.9. This represents an 8.0% improvement in stabilization compared to the baseline mode, primarily due to the substantial proportion of hydrogen. An analysis of flame photographs reveals that as the twist angle increases, a recirculation zone becomes more apparent. Increasing the blade angle and incorporating hydrogen leads to a reduction in CO concentrations in the exhaust gases. The analysis indicates that increasing the hydrogen proportion to 50%, compared to the absence of hydrogen, results in a 30% decrease in CO concentration. In our case, for the option φ = 0.3 and blade angles of 60°, the reduction in CO concentration was 28.5%. From the authors’ perspective, the most optimal vane angle is 45°, along with a hydrogen fraction of 30–40%. With these parameters, it was possible to achieve concentrations of NOx = 17–25 ppm, φLBO = 0.66, and CO = 130–122 ppm.

Spray Flame Characterization of a Dual Injector for Compact Combustion Systems

ABSTRACT The scalability of liquid fuel operated jet stabilized combustion system toward scales and mixing timescales relevant for corresponding micro gas turbine systems is impeded by the lack of suitable injection concepts. The high momentum of the combustion air jet can deteriorate the spray quality of conventional injection systems. In combustors with reduced mixing timescales (e.g. MGT and compact aero-engines) this results in elevated emissions and a prompt primary atomization is essential. For this purpose, a canonical confined jet spray burner is developed and equipped with a novel in-house dual-pressure swirl/airblast injection concept. An extensive parameter variation on the jet bulk velocity (80 , equivalence ratio (0.6 , combustion air preheat temperature (500 (K) 800) and premixing length (0.0 (mm) ≤ 48) is conducted to delineate the operational range. The spray process originating a partially premixed and a direct injection case is characterized by means of phase Doppler interferometry and shadowgraphy. The combustion process is described via OH*-chemiluminescence, flame photographs and exhaust gas measurements. The results show that the developed injection system yields Sauter mean diameters predominantly below 25 μm over the entire parameter range due to robust and prompt primary atomization. Moreover, the primary atomization process of the dual injector is sufficient under all conditions to confine secondary atomization close-to the combustor nozzle exit. The flame stabilization and reaction progress are more sensitive to the air preheat temperature than the bulk jet velocity variation as the mixture homogenization is limited by the vaporization process. Moreover, with decreasing reactivity (i.e. equivalence ratio and preheat temperature) the flame stabilization is increasingly dominated by the recirculated hot exhaust gas, indicating a transition from conventional turbulent flame propagation to auto-ignition influenced reaction progress. The resulting NOx and CO emissions approximate the values measured previously in related methane powered combustion systems. Consequently, the developed injection system is promising to expand the flexibility of compact gas turbines to liquid fuels while maintaining low emissions.

Experimental study of dynamics of flames from discrete methanol fuel wicks in ullages

The paper presents an experimental study of the burning characteristics of discrete methanol wicks in ullages, where the burning occurs at distances much lower than the lip of the burner. Burning configurations consisting of two methanol wicks burning in varying ullages (from zero to 24 cm at intervals of 6 cm) have been considered in the experiments. At zero and 6 cm ullages, flame shapes resemble that of a general buoyant pool flame. As the ullage is increased to 12 cm or higher, a plume-induced instability triggers in the ullage and the flame bends towards one side over the wicks, resembling a boundary layer type of flame. The transition from a pool flame to a boundary layer-type flame has been illustrated with direct flame photographs. At deeper ullages, as the flame leans over the fuel wicks, the mass burning rates are enhanced from 9% to 35% for different ullages. The resulting air flow inside the ullage and flame shape affects the mass burning rate and has been visualized using smoke flow in the ullage. This study opens further research on the coupling effect of burning of heterogeneous materials in ullages with the flow field induced by the buoyant plume.

A Comparative Study of Thermal, Luminous, and Infrared Radiation Characteristics of Natural gas Flame in the Presence of Alkali, Alkali-Earth, and Transition Metallic Solution Additives

Abstract Experiments were performed to find out the effect of alkali, alkali-earth, and transition metallic additives on thermal, luminous, IR, and total radiative properties of natural gas flame. A total of 25 mL of 0.5 M alkali salts of NaNO3 and KNO3, alkali-earth salts of Ca(NO3)2, Ba(NO3)2, and Sr(NO3)2 and transition nitrate salts of Cu(NO3)2 and Mn(NO3)2 (Merck company) were prepared, and flame tests were done on each solution by using a Bunsen burner with the equivalence ratio of 1.05, which is close to the condition of stoichiometric air–fuel mixing. The optical characteristics of flame were measured in visible and infrared radiation (IR) spectrums by a TES-1332A luminance meter, BOMEM FTIR, and IR flame photography technique. Also, the total radiation was gauged by a HFP01 sensor. The results indicated that, in general, due to the increased rate of nucleation of intermediate soot particles, the flame in the presence of alkali metal additives has higher total, luminous, and IR radiation than in the presence of other metal additives. Also, the metallic additives do not significantly change the flame temperature. The results also revealed that although all metallic additives enhance the luminous radiation of flame, which is due to chemiluminescence phenomenon or atomic emission, luminous radiation of metal additives is negligible in comparison with their radiation in IR wavelengths. Furthermore, the results show that the boiling temperature of metallic salt solutions has a greater impact on flame luminosity than their ionization energy does.

Optical diagnostics and multi-point pressure sensing on the knocking combustion with multiple spark ignition

Engine knock is an abnormal combustion phenomenon that limits the thermal efficiency and service life of spark-ignition engines. A better understanding of the knock mechanisms and characteristics is beneficial to knock alleviation and engine efficiency improvement. In this study, a metal liner with four evenly-spaced spark plugs in the periphery of the combustion chamber is designed to initiate knock from different positions. Four spark strategies are applied to the single-cylinder optical research engine and six pressure sensors are utilized to analyze the local pressure oscillations in the cylinder. The knocking combustion is investigated by simultaneous 72 kHz high-speed imaging and 6-point pressure sensing. The experimental results indicate that using multiple spark-ignition could promote knock intensity, advance the start of auto-ignition and introduce more acoustic resonance modes. The center pressure sensor is more sensitive to the first radial resonant mode (0, 1) of the knock pressure oscillation, while the side sensors are more sensitive to the first and second circumferential resonant modes (1, 0) and (2, 0). The knock onset judged by natural flame photography is earlier than that by pressure analysis because the auto-ignition event happens first and induces the subsequent pressure fluctuation. Natural flame luminosity analysis demonstrates that the initial auto-ignition sites only cause weak pressure oscillations, and the instantaneous combustion of the remaining end-gas increases the heat release rate significantly and gives rise to more violent pressure oscillations. Statistically, the maximum amplitude of pressure oscillation follows an exponential relationship with the peak mean flame luminosity. The end-gas resides in the gaps among the flame fronts generated by different spark strategies while the first auto-ignition sites are not evenly distributed in the end-gas zone. This fact gives insights into the local temperature non-uniformity of the end gas zone that affects the spatial distributions of the initial auto-ignition sites in the cylinder.

Tangential Flue Gas Recirculation (TFGR) technique for enhancement of radiation characteristics and reduction of NOx emission in natural gas burners

Experiments were carried out to find out the effect of different TFGR ratios on flame characteristics, pollutant emission, temperature, luminosity, IR radiation and total radiation of natural gas flames. A spiral duct connected tangentially to the furnace inlet linked the furnace to the chimney. A centrifugal fan was installed on the spiral duct to suck the combustion products and a spiral duct back-draft round damper was installed to adjust the FGR volume flow rate. The optical properties of the flame were studied for visible and IR wavelengths by a TES-1332 A digital luminance meter, a BOMEM FTIR and IR flame photography. Also, the total radiation of flame was determined by an SBG01 heat flux sensor. Furthermore, an S type thermocouple was used to measure the flame temperature. The results indicate that TFGR changes the nonluminous natural gas flame to a luminous flame by the dissociation of the recirculated CO2 to CO. TFGR enhances the tangential momentum of flame and generates a voluminous flame, increases the heat transfer area of flame and eliminates the hot-spot region in the core of flame, which decrease the axial flame temperature and thermal corrosion. Furthermore, the concentration and residence time of CO2 and H2O, as the most important radiative species of natural gas flames, increase in the flame reaction zone, which results in the enhancement of the IR emissivity and the radiation heat transfer of natural gas flame. Finally, although the TFGR increases the concentration of CO emission to a level lower than the standard level, it causes natural gas burners to emit significantly less dangerous NOx.

An Experimental Study on Kerosene Spray Combustion Under Conventional and Hot-Diluted Conditions

ABSTRACT The combustion of kerosene spray under hot-diluted conditions and conventional conditions was experimentally investigated. By examining flame photographs, chemiluminescence images, and in-field temperature measurements, the separate effect of different variables including oxygen concentration, temperature and velocity of the co-flowing air, fuel flow rate and injection pressure, and eventually the type of spray nozzle on multiple parameters such as flame stability, structure, luminosity, temperature field, and qualitative CH radical distribution, as well as HCO and NO2 with lower precision, in the reaction region, have been studied. It was observed that an increment in injection pressure and co-flow temperature enhances the spray flame stability, while dilution exacerbates it. Also, a solid cone spray pattern with a lower spray angle has better stability than hollow cone ones with a higher spray angle. Moreover, it was noted that liquid fuels, compared to gaseous fuels, require higher preheating temperatures, for the same dilution level, to engender a stable flame. For combustion of spray in conventional conditions, a double-flame structure was observed consisting of a bluish section at the leading edge emerging into a yellowish sooting trail. An increase in co-flow velocity, as well as injection pressure, strengthens the inner flame front, whereas raising the co-flow temperature or diluting the oxidant, deteriorates the inner flame front. In the case of highly preheated air (without dilution), the flame liftoff height is reduced to as close to the atomizer as a few millimeters, forming a single flame structure similar to gaseous flames. In this case, the peak temperature was considerably higher than the conventional combustion, yet the gain was much lower than the preheating level. Combined effects of preheating and dilution alter the spray flame structure in a way that the flame volume is reduced, the temperature field has become more homogeneous, the peak temperature is limited to less than 1500 K, and temperature fluctuations have significantly decreased, seemingly approaching MILD combustion regime conditions.

Visualization of in-cylinder combustion flame and evaluation of engine characteristics of MPFI engine fueled by lemon peel oil blended gasoline

This paper reports the results of experimental work carried out on a twin-cylinder gasoline Port Fuel Injection (PFI) engine fueled with lemon peel oil blends. Flame visualization photography is used along with combustion diagnostic tools to investigate the effects of non-octane enhancer bio-fuel lemon peel oil (LPO) on the combustion, performance and emission characteristics of the gasoline engine. The captured combustion flame photographs are post-processed using MATLAB code to single out high diffusion flame regions. The oil extracted from lemon grinds is blended with gasoline in the ratios of 10%, 20% and 30% by volume and tested in the engine at different load conditions. The flame images of 20% and 30% LPO blends show higher diffusion flame regions whereas 10% LPO blend shows least. The gasoline at 80% load shows the least diffusion flames. But the same gasoline shows higher diffusion flame at full load. Among the blends, 10% lemon peel blend shows a better heat release rate compared to gasoline. From the performance analysis, it was determined that the brake thermal efficiency of 10% LPO blend increased by 3% over sole gasoline at full load. The CO, HC, and NOx emission were decreased by 5%, 6.3% and 5% for 10% LPO blend compared to gasoline. From the results, it is concluded that the LPO up to a maximum of 10% by volume can be added with gasoline to improve the performance and emission.

Pengaruh Lip Thickness Turncated Nozzle Sudut Luar terhadap Karakteristik Api Difusi Concentric Jet Flow

Diffusion combustion is a daily combustion process where is often used primarily in industrial systems. An optimal burner design is needed to get more efficient combustion results. Then the shape of the burner nozzle greatly affects the turbulence between the fuel and air which forms the flow recirculation zone. The flow recirculation zone functions to produce homogeneous mixing and get a more perfect combustion. Recirculation zones are formed to disrupt flow rates, causing vortices and backflow around the end of nozzle. This research uses burner concentric jet flow. The lip thickness of the outer angles turncated nozzle are used 16 mm, 12 mm, 8 mm, 4 mm, and 0 mm length variation To obtain flame stability, the lift off and blow off limits are used with variations in air velocity. Thermocouples are used to measure the flame temperature distribution. The numerical simulations are used to reinforce this study. The results showed that the characteristics of the concentric jet flow diffusion affected by the use of the lip thickness of the outer angles turncated nozzle. The highest concentric jet flow diffusion stability is at 16 mm nozzle. The highest concentric jet flow diffusion temperature is at 12 mm nozzle. Experimental and numerical simulations show the perfect combustion on the 12 mm lip thickness nozzle. This can be seen by direct photographs of blue-dominated flames and the visualization of the temperature contour distribution which is dominated by red.

Facile Preparation of Micrometer KClO₄/Zr Energetic Composite Particles with Enhanced Light Radiation.

Developing energetic composite materials consisting of fuel and oxidizer is an effective strategy to enhance the energy release property. However, this strategy has rarely been applied in Potassium Perchlorate (KClO4)-containing energetic materials, even though KClO4 is a much stronger oxidizer than most previously reported metal-oxide oxidizer. One of the main obstacles is the lack of simple and in situ ways to introduce KClO4 into the composite. In present work, micrometer KClO4/Zirconium (KClO4/Zr) composite particles were successfully prepared using a facile chemical solution-deposition method. The structure and particle morphologies of as-obtained KClO4/Zr composite were characterized by X-ray diffraction (XRD) and scanning electronic microscope (SEM)-EDS (Energy Dispersive Spectrometer). The evolutionary combustion behavior was evaluated using flame-based light-radiation spectra and successive photography technique. Results showed that the morphology, light-radiation properties and flame-evolution characteristics of KClO4/Zr composite varied with the content of KClO4 and the particle size of Zr. Compared with the mechanical mixture of KClO4/Zr, the KClO4/Zr composite showed much higher light-radiation intensity and longer light-emission duration time after reasonably controlling the preparation parameters. Flame photographs revealed that the enhanced light radiation of KClO4/Zr composite should be ascribed to higher use efficiency of “oxygen” in the oxidizer, which promoted both the solid–solid and solid–gas reaction pathways between KClO4 and Zr.

Fire behaviors study on 18650 batteries pack using a cone-calorimeter

To investigate the effects of different state of charges (SOCs), external heating powers and charging/discharging treatment on the fire behaviors of 18650 batteries pack, three groups of abuse experiments were conducted with the help of a cone-calorimeter. The fire hazards of batteries pack were characterized by measuring the flame photographs, battery surface temperature, ignition time, thermal runaway time, heat release rate and radiative heat flux. According to the results, it is found that the fire behaviors of batteries pack will appear in advance and behave more violent with the increase in SOC. Additionally, the higher heating power will exacerbate the fire hazards of batteries pack by increasing the surface temperature rise rate, the total heat released and the total heat flux of pack leading to an earlier thermal runaway and more rigorous consequence. Finally, the pack with discharging/charging treatment has a much lower heat released compared to the pack without any treatment due to the incomplete burning and incomplete release of energy. Besides, their fire behaviors also exhibit earlier and severer.

A study on the fire behaviors of 18650 battery and batteries pack under discharge

In order to have a better understanding of the fire behaviors of lithium-ion battery (LIB) and batteries pack under discharge, a series of fire tests were conducted. The fire behaviors of LIB were characterized by parameters including the flame photographs, surface temperature, mass loss, radiative heat flux and hydrogen fluoride (HF) mass flow. The results indicate that the number of batteries will affect the fire behaviors of LIB. Pack with larger number of LIB possesses a faster temperature rise, a higher peak heat flux and total radiative heat, leading to a quicker thermal runaway. Additionally, the discharging treatment also has a significant impact on LIB. It can accelerate the warming-up process, increase the fire risks of LIB, decrease the combustion efficiency of LIB and reduce the radiative heat. This is the result of the heat generation during discharge and the more reactive materials inside the battery under discharge. Besides, the HF generated during tests is discussed in the paper to note the toxicity of the released gases in LIB fire.

Low Cost Image Processing of Bunsen Flame Photography for Estimation of Flame Speeds

ABSTRACTThe need for measuring laminar flame speeds for various fuels and blends is crucial for determining flame stabilization characteristics and design parameters for practical burner configurations. Various methodologies have been used over the years to estimate laminar flame speeds with axisymmetric Bunsen flames being one of the oldest and “simplest” techniques. Nonetheless, the cost of the instrumentation to measure laminar flame speeds with minimum experimental uncertainties remains noticeably high. The present work describes a low-cost flame speed estimation methodology and investigates its efficacy for methane and propane-air mixtures at different equivalence ratios. Flame propagation speeds with respect to the unburned gas were evaluated using both the cone angle and the surface area measurement methods. The experimental approach involves an automated image processing procedure that numerically processes plain photographic images of the flames and estimates the Bunsen cone borders, the cone angle, and the surface area in a straightforward manner. Those values are then used to extract the flame speed. Thus, it can be considered as an integrated experimental and numerical processing methodology that affords flame speed estimation, with reasonable accuracy, for a variety of gaseous fuel-oxidizer mixtures, relevant to industrial burner applications.

Emulsified jet fuel flame characterization with image processing

This work describes a RGB digital image processing approach of emulsified jet fuel flame, which allows the characterization of the combustion phenomenon in the case of new fuels through color chemiluminiscence measurements. By applying RGB techniques, the image processing of the flame reveals useful parameters in an effective and cost-efficient technique for the determination of relevant chemical species, such as CH* and C2*, equivalence ratio, and temperature estimation.Second generation emulsified aviation fuels containing water-jet fuel have been a challenge for simultaneous thrust augmentation and pollution diminution, with subsequent cost reduction and fossil fuel dependence. Testing new fuels would normally require expensive equipment and reliable investigation techniques, while image processing proved to be a reliable method for the estimation of combustion chemical species and temperature in the case of classic fuels.For the combustion behavior of emulsified jet fuel, a co-annular spray burner was used, allowing the complex investigation with UV-VIS spectrometer and flame photography. RGB image processing techniques showed good agreement with more complicated diagnosis tools, such as spectrometers.

Stabilisation of swirling dual-fuel flames

C7H16-CH4-air flames stabilised in a bluff body swirl burner have been examined with flame photographs, OH∗ chemiluminescence, and simultaneous 5 kHz OH-PLIF and Mie scattering with a focus on local an global extinction characteristics. The aim of this study is to investigate flame structure when more than one fuel is present and provide both insight and data for dual-fuel modellers. Flame imaging shows that the presence of an additional fuel affects the stabilisation characteristics of one fuel, whether it be liquid or premixed gaseous. With the addition of more CH4 in the oxidiser channel, dual-fuel flames with C7H16 spray became more premixed in appearance, evidenced by flame photographs, mean OH∗ chemiluminescence images, and instantaneous and mean OH-PLIF images. Addition of CH4 to such systems also forces the flame to stabilise on the outside of the swirled channel, similar to premixed CH4-air flames far from blow-off. However, the flame branch in the region of the shear layer directly above the bluff body edge moves further from the base of the burner with the addition of CH4, suggesting that typical spray flame behaviour is lost even with a small addition of CH4 to the system. This observation is supported by global extinction curves, which show that C7H16-CH4-air flames appear to behave more similarly to premixed flames than spray flames, but remain of fundamental interest due to their unique stabilisation behaviour and relative insensitivity to bulk velocity changes compared to spray-only flames at similar equivalence ratios.

Experimental study of flame characteristics and stability regimes of biogas – Air cross flow non-premixed flames

Biogas is an alternative fuel that typically contains around 45% carbon-dioxide by volume, besides methane. Due to the inherent content of carbon-dioxide, it is necessary to study the flame characteristics and stability limits in cross-flow non-premixed burners. In this study, cross-flow non-premixed flames, where biogas is injected through a horizontal porous plate and air is blown parallel to the fuel injector, are studied systematically. In order to increase the stable operating regime, devices such as backward facing steps and cylindrical bluff-bodies are commonly employed. Different step-heights and locations from leading edge of the fuel injector are considered for the cases with backward facing steps. A rectangular cylindrical bluff-body is also used as a flame stabilizing obstacle. Baseline cases are studied without any backward facing step or cylindrical bluff-body. Volume flow rate of biogas is varied from 36 liter per hour to 360 liter per hour. Air velocity is varied in the range of 0.2 m/s to 3.0 m/s. For a given fuel velocity, air velocity is gradually increased in order to record the transition of flame from one regime to another. Flame stabilization is carefully assessed by monitoring the high definition direct flame photographs captured from front and top views, for all the cases. The cases are repeated at least three times to ensure repeatability. Stability maps are plotted as a function of fuel velocity and air velocity for all the cases. For cases with backward facing steps, both step height and its location play an important role in delineating the boundaries of the flame regimes. Parametric variations show interesting features. Bluff-body flames become quite oscillatory and three dimensional at higher air velocities. For this case, stability maps of flames from biogas and pure methane are compared.

Experimental Investigation of Flame Speed of Gasoline Fuel-Air Mixture

Flame speed is an important aspect of fuel combustion characteristics. It affects combustion system design and performance. In this study, a laboratory experimental rig has been built to investigate the effect of equivalence ratio of gasoline-air mixture in a centrally ignited constant volume combustion chamber on flame speed at an initial pressure of 1bar and an initial temperature of 483 K using high speed flame photography technique. The results of the outwardly expanding spherical flame showed that the flame speed depends on both equivalence ratio and flame radius. It decreases slightly with the increase of flame radius and increases with the equivalence ratio until slightly larger than stiochiometric and then decreases. The flame speed reached 1.45 m/s at Φ= 0.8, (1.6) m/s at Φ= 1 and 1.27 m/s at Φ= 1.5

Experimental and numerical investigation of an ultra-low NOx methane reactor

This work investigates a patented novel methane reactor, the Lean Azimuthal Flame (LEAF) Combustor. The combustor operates with non-premixed combustion where both the air and methane enter the combustor volume through small, high momentum jets. The air jets, located at the top of the combustor, are angled to create a swirling flow that mixes with the fuel entering from the bottom of the combustor. The resulting toroidal flow is intended to increase mixing and hot product recirculation within the burner to reduce operating temperatures, increase residence time, and limit the formation of NOx with preliminary emissions levels measured at sub-20 ppm. The main objectives of this paper are to: (i) experimentally characterize the combustor behaviour; and (ii) improve the physical understanding of the combustion process in the system under investigation through the use of numerical simulations. Experiments were performed at various air and fuel flow rates to determine the stability range of the combustor. Direct visualization of the combustion process indicates the formation of a low luminosity stable flame with a toroidal shape. Flame photographs and OH* chemiluminescence images are presented to provide a qualitative comparison of flame structure and reaction zone, as well as to analyse the effect of varying air and fuel flow rate on combustor operation. Numerical simulations were performed using the Large Eddy Simulation (LES) approach with the Conditional Moment Closure (CMC) sub-grid combustion model to analyse the flame behaviour within the combustion chamber. The regions around the fuel jet flow in particular were investigated to explore the phenomena of flame lift-off and local extinction in the bottom of the combustor.

A novel configuration of natural gas diffusion burners to enhance optical, thermal and radiative characteristics of flame and reduce NOx emission

A novel, simple and feasible method was proposed for increasing intermediate soot concentration and enhancing thermal and radiative characteristics of natural gas flame. In the method, based on pyrolysis technique, a portion of natural gas, as the secondary gas injection rate, was directly injected into the flame to create high temperature and emissive intermediate soot particles. The portion of the fuel dedicated to secondary injection rate varied in the range of 20–55%. The flame structure, axial temperature, soot concentration and radiation flux were examined and compared with those resulted from a prevalent burner. Also, the optical properties of intermediate soot particles were studied by BOMEM FTIR, IR flame photography and TES-1332A digital luminance meter. The results indicated that natural gas molecules injected into the flame were dominantly pyrolyzed into soot particles. These highly luminous emissive particles enhance the total flame emissivity and radiation. Moreover, considering exhaust emission limits, there was an optimum secondary injection rate (40%), which, besides enhancing the radiation of flame, maintained the emission of CO pollutant and UHC lower than the standard values. Furthermore, in the pyrolysis process absorption of heat from flame reduces maximum flame temperature and consequently NOx emission by 35% in the optimum case.

The impact of C/H on the radiative and thermal behavior of liquid fuel flames and pollutant emissions

The present experimental study is performed to document the effects of carbon-to-hydrogen mass ratio (C/H) in liquid hydrocarbon fuels, on the luminosity, thermal radiation rate, and temperature of flame. Furthermore, extraction of the thermal and radiative characteristics of flame, and measurement of exhaust gases including CO, CO2, and NO x have been carried out. The CHNS elemental analyzer system was employed to ascertain fuel composition. The thermopile sensor and the lux meter were utilized to measure the flame thermal radiation and luminosity. The measured flame radiation spectrum included all possible wavelengths (i.e., flame thermal radiation) and visible wavelengths (i.e., luminosity). The flame photography technique, as a non-intrusive method, depicted the flame visible radiation, IR spectral emittance, and high temperature zone. The results revealed that the luminosity and thermal radiation of the flame increased as we increase C/H. A rise in C/H made the temperature along the flame axis more uniform. The NO x emissions were within standard levels (i.e., under 200 ppm). It was also shown that the C/H variation has a greater effect on luminosity than thermal radiation of the flame. The flame luminosity was increased by 66% when the C/H was increased from 5.47 to 5.68, whereas the flame thermal radiation increased by 26%. In addition, a new correlation is proposed to predict the linear relation of the increase in the thermal radiation and the increase in the luminosity of the flame as a function of C/H.