Laboratory-scale Combustor Research Articles

Linear stability analysis of a combustor model with a delayed feedback tube

We conducted a linear stability analysis of a laboratory-scale combustor to develop a delayed feedback method for mitigating combustion oscillations. We employed linearized hydrodynamic equations and a flame transfer function in the frequency domain to assess the stability under various feedback tube configurations, including changes in the length, radius, and connection position. The results of the stability analysis demonstrated a significant improvement in stability when the length of the feedback tube was 0.56 times the wavelength of the unstable mode. Furthermore, the tube radius had an optimal value for stabilizing the system. The connection position also played a crucial role in stability. The effective feedback tube conditions determined in the analysis were applied to a real combustor to demonstrate the successful suppression of oscillations experimentally. The suppression mechanism is discussed using the acoustic power based on the calculation results. The acoustic power profile of the system revealed that the oscillation suppression was not simply an addition of acoustic dissipation, but importantly, a reduction in acoustic power generation at the flame.

Experimental Investigation of Sulfur and Nitrogen Oxide Emissions and Corrosion Propensity During the Combustion of Coals and Biomass Fuels

ABSTRACT The increasing use of biomass in Indonesian coal-fired power plants, mainly through co-firing, presents challenges due to different fuel characteristics, which can affect gas emissions, ash deposition, and combustion efficiency. This study assesses flue gas emissions (SO2 and NOx) and corrosion tendencies of various biomass types and coal. The study begins with characteristic testing and ash analysis of coal and biomass samples, including proximate, ultimate, and calorific value analyses, to determine their suitability as fuels. Preliminary calculations predict flue gas emissions and ash deposit formation, followed by laboratory-scale combustion experiments using a DTF to assess flue gas and ash deposit characteristics. The results show that sulfur in biomass is converted to the gas phase up to 99%, while in coal, it is converted up to 95% at high temperatures. NOx levels are primarily affected by the nitrogen contents of the fuels; for instance, Coal-B at 0.88 wt% produces less NOx than solid recovered fuel (SRF) and refused derived fuel (RDF) with 1.73 wt% and 1.51 wt%, respectively, yet still generates higher emissions than the other three biomass types. In general, wood chips (WC), rise husk (RH), and palm kernel shell (PKS) emit 30–80% less flue gas compared to coal. However, ash deposition results indicate that PKS, SRF, and RDF exhibit corrosion tendencies due to the dominance of albite (NaAlSi3O8) in the mineral phase. Additionally, the high chlorine content in SRF (0.544 wt%) and RDF (0.224 wt%) leads to the formation of sticky ash deposits, which potentially impact heat transfer surfaces. These findings contribute to identifying suitable biomass types for both co-firing or dedicated combustion in coal-fired power plants.

Two-Photon Planar Laser-Induced Fluorescence Of Near-Wall CO During The Interaction Between A Flame And A Cooling Air Film

Reducing the anthropogenic pollutant emissions is a major concern in the aeronautical community. Implementing high-power density core engines made of lighter materials would undoubtedly increase the thermal efficiency and reduce CO 2 emissions. Nevertheless, near-wall combustion processes will become significant, raising concerns regarding thermal management. As a result, walls in aero-engine combustors are commonly cooled, but it also introduces more complex physical phenomena associated to pollutant formation during flame-cooling air interaction (FCAI). This experimental study aims at elucidating the role of the cooling air film on CO emissions during FCAI. The experiments are conducted in an atmospheric pressure and optically-accessible lab-scale combustion test rig dedicated to near-wall combustion. It generates a lean premixed turbulent methane/air V-shaped flame, with one branch of the flame that interacts with an oil-cooled stainless-steel wall. A splash-cooling plate system enables to generate a momentum-controlled parietal cooling air film. The novelty of this study is to develop and implement planar laser-induced fluorescence of the CO molecule (CO-PLIF), complemented by planar laser-induced fluorescence of the OH radical (OH-PLIF) as well as global CO emissions in the exhaust gases. Results show that the excitation of the Hopfield-Birge system enables to detect the AN ngström bands and the third positive system. However, significant interferences with C 2 and CN emissions are highlighted, being more pronounced in rich combustion conditions, and originating from the incomplete fuel oxidation as well as the high energy density of the two-photon excitation process. A broadband collection strategy of the AN ngström bands is selected, since these interferences are limited in lean combustion regimes. The analysis of the flame dynamics indicates that the increase of the cooling air film momentum shifts the reactive flow away from the wall, but also controls the flame wrinkling through modified aerodynamics. As a result, the flame is not influenced anymore by thermal quenching processes, and can effectively burn further away from the wall. Global emission measurements indicate an increase in CO when the cooling air film momentum increases. While thermal quenching favors a faster oxidation downstream of the flame, the establishment of the cooling air film leads to a longer flame with more production areas. CO-PLIF imaging concurs this phenomenon, with a CO distribution all along the wall when the cooling air film is well established.

Effects of molten silicate reactivity on high temperature erosion behavior of plasma sprayed Yb2Si2O7-based EBCs

Particulate/debris damage caused by ingestion of calcium magnesium aluminosilicates (CMAS) hinders the durability of environmental barrier coatings (EBCs) used to protect SiC-based ceramic matrix composite components in next generation gas turbine engines. Similarly, ingestion of any debris in the engine can lead to mechanical damage and recession of coatings due to particulate erosion. Investigating particulate interactions at relevant engine conditions is crucial for determining limiting mechanisms in the operating lifetime of EBCs. This study assessed the effects of extrinsic phase formation and microstructural changes due to CMAS interactions on the erosion durability of Yb2Si2O7-based EBCs in a laboratory-scale combustion facility. CMAS exposures and erosion testing were carried out at 1316°C. Using 60 μm Al2O3 particles as the erodent material, the effects of CMAS loading on erosion durability at various impingement angles were evaluated.

Combustion regimes stability based on liftoff and blow-off measurements of oxy-fuel flames in an internal recirculation combustion chamber

The effect of dilution on the static stability of turbulent oxy-methane flames was evaluated in an equivalence ratio range of 0.6 to 1.0 with CO2 mole fraction ranging from 0% to 71.8%. A set of experiments was carried out in a lab scale combustor with internal recirculation. The anchored flame, lifted flame, and MILD regimes were established keeping the bulk velocity of the O2/CO2 mixture stable at 30 m/s. Measurements of the reaction zone were carried out by OH∗ chemiluminescence. The anchored flame presented a jet flame macrostructure stabilized at the burner’s nozzle with CO2 mole fraction varying from 0% to 42.9% at stoichiometric conditions. The lifted flame exhibited oscillations in terms of the topology and of the liftoff height in the range of 42.9% to 60% CO2 mole fraction. The MILD regime occurred from 60% to blow-off occurred at 71.9% CO2 mole fraction. In the MILD regime, the chemical reactions were uniformly distributed inside the combustion chamber, in addition to a considerable reduction in OH∗ intensity. The maximum OH∗ intensity in the MILD regime decreased by 89% when compared to the anchored flame case. Liftoff and blow-off were assessed in the equivalence ratio range of 0.6 to 1.0. Regardless of the equivalence ratio, both phenomena exhibited a correlation with the laminar flame speed rather than the adiabatic flame temperature. Such a correlation suggests that laminar flame speed is a representative parameter of changes in species transport and chemical kinetics caused by dilution.

Clean co-combustion of glycerol and methanol blends using a novel fuel-flexible injector

This study explores combustion of highly oxygenated fuel blends (glycerol/methanol, G/M) to mitigate carbon footprint using a novel fuel injector, called Swirl Burst (SB) injector. The recently developed SB injector yields fine droplets immediately rather than a breaking jet/film of conventional injectors. The advanced atomization resulted in ultra-clean combustion with high fuel flexibility even for viscous oils without fuel preheating. The present work investigates the effects of fuel composition and the atomizing air to liquid mass ratio (ALR) across the injector on the global combustion characteristics of G/M blends without fuel preheating in an uninsulated lab-scale combustor. Results show that the SB injection resulted in mainly clean lean-premixed and near complete combustion for the G/M mixes of 50/50, 60/40 and 70/30 by power with near-zero emissions of CO and NOx. Increase in ALR resulted in more radially distributed flames with slightly reduced flame lift-off height, with ultra-clean and near complete combustion for all the ALRs for the 50/50 and 70/30 blends. Clean and efficient G/M combustion without fuel preheating achieved by the fuel-flexible SB injection signifies the potential to combust crude glycerol − the largest oxygenated byproduct of biodiesel production − to enable biofuel cost effectiveness with near-zero emissions.

CO2, Ar, and He dilution effects on combustion dynamics and characteristics in a laboratory-scale combustor

This study aimed to investigate the impact of CO2, Ar, and He addition on combustion instability under varying acoustic frequencies, dynamic pressure amplitudes, and light emission intensities. Experiments involved using pure methane as fuel at a 1.0 equivalence ratio, with three distinct acoustic frequencies. The burner operated at 5 kW, and the combustion chamber was excited at frequencies of 90 Hz, 160 Hz, and 320 Hz. It was observed that with dilution, the temperatures decreased more from the burner exit temperature to the exhaust section. As the oxygen concentration in the oxidizer decreases in Ar, He, and CO2 dilution, CO emissions increase, but CO2 emissions decrease. The addition of Ar, He, and CO2 causes an effect that reduces the flame temperature and brightness while causing the flame length to extend due to the diluting effect. While a decrease in instability was observed in He-Ar-CO2 dilution in 20 % oxygen, instability increased again in the three 19 % cases. It is observed that mixtures under the diluent effect approach the blowoff limit due to the increase in ignition delay. It has been determined that the addition of diluent increases the tendency for the flame to go out, especially due to the thermal effect. The methane fuel with an 18 % oxygen concentration in the oxidizer of Ar remained below lean extinction limits, undergoing blowoff. The temperature was measured as 1156 K at 21 % oxygen concentration, 584 K at 19 % oxygen concentration for carbon dioxide, 877 K for Helium, and finally 777 K for argon. In the case of pure air for the combustion of methane, CO emissions were measured at 140 ppm. Average CO levels at 20 % oxygen concentration in the oxidizer are 1254 ppm, 356 ppm, and 308 ppm with carbon dioxide, argon, and helium, respectively. The study also shows that an increase in O2 in oxidizing air leads to a decrease in CO emissions, while an increase in He/Ar/CO2 gases leads to an increase in CO emissions. Regarding NOX emissions, undiluted conditions measured a value of 14 ppm. NOX emission levels approached 0 ppm in all dilution cases and achieved its goal.

Novel Combustion Instability Diagnosis Method With Upstream Pulsation of Repetitive Laser-Induced Plasmas

Abstract In this experimental study, we are presenting the ability of laser-induced plasmas with successive pulsation to identify combustion instabilities (CI) of a premixed lab-scale combustor. An acoustic disturbance equivalent to a shockwave perturbation is generated in the main air supply line of a swirled injector prior to the fuel addition by focusing nanosecond laser pulses of 1.6 W average power at 10 Hz. The shockwaves are attenuated to be strong pressure waves when reaching the combustor and impact the pressure field for short periods. After plasma breakdowns, the system returns back to its original state after 4 ms once the added acoustic energy has been fully dissipated. Given a set geometry, it is observed that the laser-induced breakdown amplifies the characteristic frequency peaks of the combustor system when actuated in cold flow. Furthermore, when applied to reacting flows, the pulsating acoustic perturbations impact the pressure fluctuation in the combustor, e.g., reducing the amplitude of the primary characteristic frequency peak at certain conditions. The identification of the main instability modes thanks to the plasma shockwave provides proof of the potential use of this novel diagnosis strategy in various and complex combustion systems.

Novel Combustion Instability Diagnosis Method With Upstream Pulsation of Repetitive Laser-Induced Plasmas

Abstract In this experimental study, we are presenting the ability of laser-induced plasmas with successive pulsation to identify combustion instabilities (CI) of a premixed lab-scale combustor. An acoustic disturbance equivalent to a shockwave perturbation is generated in the main air supply line of a swirled injector prior to the fuel addition by focusing nanosecond laser pulses of 1.6 W average power at 10 Hz. The shockwaves are attenuated to be strong pressure waves when reaching the combustor and impact the pressure field for short periods. After plasma breakdowns, the system returns back to its original state after 4 ms once the added acoustic energy has been fully dissipated. Given a set geometry, it is observed that the laser-induced breakdown amplifies the characteristic frequency peaks of the combustor system when actuated in cold flow. Furthermore, when applied to reacting flows, the pulsating acoustic perturbations impact the pressure fluctuation in the combustor, e.g., reducing the amplitude of the primary characteristic frequency peak at certain conditions. The identification of the main instability modes thanks to the plasma shockwave provides proof of the potential use of this novel diagnosis strategy in various and complex combustion systems.

Dynamic Response Mechanism of Ethanol Atomization–Combustion Instability under a Contrary Equivalence Ratio Adjusting Trend

This study experimentally explored the effects of equivalence ratio settings on ethanol fuel combustion oscillations with a laboratory-scale combustor. A contrary flame equivalence ratio adjusting trend was selected to investigate the dynamic characteristics of an ethanol atomization burner. Research findings denote that optimizing the equivalence ratio settings can prevent the occurrence of combustion instability in ethanol burners. In the combustion chamber, the sound pressure amplitude increased from 138 Pa to 171 Pa and eventually dropped to 38 Pa, as the equivalence ratio increased from 0.45 to 0.90. However, the sound pressure amplitude increased from 35 Pa to 199 Pa and eventually dropped to 162 Pa, as the equivalence ratio decreased from 0.90 to 0.45. The oscillation frequency of the ethanol atomization burner presents a migration characteristic; this is mainly due to thermal effects associated with changes in the equivalence ratio that increase/decrease the speed of sound in burnt gases, leading to increased/decreased oscillation frequencies. The trend of the change in flame heat release rate is basically like that of sound pressure, but the time-series signal of the flame heat release rate is different from that of sound pressure. It can be concluded that the reversible change in equivalence ratio will bring significant changes to the amplitude of combustion oscillations. At the same time, the macroscopic morphology of the flame will also undergo significant changes. The flame front length decreased from 25 cm to 18 cm, and the flame frontal angle increased from 23 to 42 degrees when the equivalence ratio increased. A strange phenomenon has been observed, which is that there is also sound pressure fluctuation inside the atomized air pipeline, and it presents a special square waveform. This study explored the equivalence ratio adjusting trends on ethanol combustion instability, which will provide the theoretical basis for the design of ethanol atomization burners.

Chemical reactor network modeling in the context of solid fuel combustion under oxy-fuel atmospheres

A multi-phase chemical reactor network (CRN) is developed and applied to investigate solid fuel combustion under oxy-fuel atmospheres in a laboratory-scale combustion chamber. The development of a novel solid-gas plug flow reactor (sPFR) allows the full coupling of solid and gas phase processes to increase the fidelity in CRN modeling. Together with the recently developed solid-gas perfectly stirred reactor (sPSR), the new sPFR is applied within a multi-phase reactor network to model the complex features of the investigated application. To design an initial reactor network, a hybrid experimental and computational fluid dynamics (CFD)-driven approach is being pursued, taking into account both global and local information on flow and temperature fields. Initially, an in-depth investigation of the physical processes is conducted, covering solid fuel conversion processes such as devolatilization and char conversion, along with the thermochemical characteristics of the flue gas. In particular, the prediction of carbon monoxide (CO) emissions is analyzed in detail by means of sensitivity analyses. Based on the findings of the sensitivity study, the network complexity of the initial reactor network is increased to enable an accurate prediction of the CO formation in comparison to the experiments. Finally, the formation of nitric oxides (NOx), sulfur oxides (SOx), and aromatic pollutants is discussed, highlighting the importance of detailed chemistry in solid fuel combustion at technically relevant scales.

Dissociation of methane and carbon dioxide hydrates: Synergistic effects

The dissociation and combustion of methane hydrate samples were studied experimentally in a laboratory-scale combustion chamber with variable thermal conditions. The temperature in the combustion chamber was varied from 800 °C to 1000 °C to reproduce high-potential reactors and combustion chambers. Ignition delays, combustion times, and combustion product compositions were determined for gas hydrates in the form of granules and tablets. Synergistic effects were analyzed from the simultaneous dissociation of methane and carbon dioxide hydrate samples. Critical conditions were determined in which carbon dioxide prevented methane ignition. The definable parameters were determined as functions of the arrangement schemes of two gas hydrates and input experimental parameters, and the corresponding predictive mathematical expressions were obtained. Methane hydrate granules were found to ignite significantly faster than methane hydrate tablets. An increase in the temperature in the combustion chamber was proved advisable in the case of methane hydrate tablets. Granulated hydrate samples ignited consistently in a wide range of temperatures, and the ignition delay times changed negligibly with varying temperature. The methane hydrate combustion stability was analyzed, and a model was developed describing the patterns and predicting the carbon dioxide hydrate flow rate required for fire suppression. Finally, conditions were identified in which the synergistic effects of simultaneously dissociating hydrates with flammable and nonflammable gases would make it possible to effectively manage their safe and sustainable application in the energy industry.

Ammonia/syngas MILD combustion by a novel burner

Ammonia has received increasing attention as one of the most attractive energy carriers because of its carbon-free nature and the established reliable and economic infrastructure for its storage and distribution. However, the low burning velocity and nitrogen-containment of pure NH3 can cause some challenges for its combustion control such as flame instability and large NOx emissions. To overcome these issues, strategies of co-burning NH3 with highly reactive fuels such as CH4 or H2 have been developed and applied. Syngas, which can be produced from biomass pyrolysis, is a promising alternative fuel in the transition from carbon-based fuels to carbon-free fuels. Therefore, comparing to co-firing NH3 with CH4, co-firing NH3 with syngas is a better environmentally friendly option to improve the NH3 combustion property. However, co-firing NH3 with syngas faces severer combustion instability, NOx emissions and NH3 leakage due to the low heating value of syngas. To the best of the authors’ knowledge, the NH3/syngas combustion with low NOx emissions and zero NH3 leakage has not been achieved in a lab-scale combustor. In the present study, NH3/syngas MILD combustion was carried out in a novel burner developed in our previous work. In the novel burner, the high-temperature and diluted air produced by the lean premixed syngas combustion is the key to accomplish the MILD combustion of NH3. The impact of the temperature and O2 mole fraction of the HTDA on the emissions of NO, NO2, N2O, NH3, and CO was experimentally investigated with varying equivalence ratios and NH3 flow rates. The chemical reactor network was employed to analyze the experimental observation from the chemical kinetic aspect.

Flow characteristics of a trapped-vortex pilot cavity under the influence of radial structure

In this study, using a laboratory-scale combustor model, we examined the flow modes in the trapped-vortex cavity under the influence of a radial bluff-body structure by particle image velocimetry (PIV) technology. The tested area included both inside the cavity and the mainstream zone. It is found that, under different inlet parameters, structure width, and circumferential positions, the flow characteristics change significantly for this structure. The number of vortexes, the distribution of vorticity, and the Q-value differ at different circumferential positions; while the increase in radial structure width, incoming flow velocity, and total pressure will all lead to stronger vortex flow. The flow pattern inside the cavity and behind the radial structure are coupled with each other, forming six typical flow modes. Further theoretical analysis summarized the causes of the six flow modes according to two aspects: how the mainstream influences the cavity flow, and the influence degree of the mainstream on the cavity flow. Considering the effect of the radial structure, the mainstream at different positions will have different effects on the cavity, which can be represented by the ratio of the radial position to the width of the structure. The influence degree was related to the inlet parameters and the width of the radial structure, which can be represented by the dynamic pressure of cavity inlet jets.

Heat and mass transfer at the ignition of single and double gas hydrate powder flow in a reactor

This paper details the heat and mass transfer at the ignition patterns of single (methane) and double (methane-isopropanol) granulated hydrates in a heated air. The experiments were performed in a laboratory-scale combustion chamber in the form of an oblong reactor with free-falling powder of the gas hydrate granules. The air in the combustion chamber was heated by the walls with ceramic plate heaters. The variation ranges of the input parameters were chosen to match the capacities of modern energy generation systems. We established the ignition delay times of the gas hydrate granules, combustion regimes, and sizes of the flame zone behind moving granules. We also analyzed the joint influence of the gas hydrate granules on their ignition behavior. A model was developed to estimate the threshold boundary conditions of gas hydrate ignition in different-sized chambers, with variable hydrate component composition granule size. Gas hydrate dissociation rates were determined in different sections of the laboratory-scale combustion chamber. Thermal conditions were predicted in which gas hydrates consistently ignite in combustion chambers with minimum cooling of the chamber walls and minimum unburnt fuel.

Co-combustion of methane hydrate and conventional fuels

This paper presents the experimental data on the co-combustion of methane hydrate powder with conventional fuels: gasoline, kerosene, Diesel fuel, coal, and coal slime. For the experiments we used a laboratory-scale combustion chamber based on an induction system on the walls and a spark ignition system. Fuel ignition delay times were measured during separate and simultaneous supply of fuel components. It was found that the combustion of slow-burning fuels can be intensified by injecting methane hydrate granules. Liquid fuels with high concentrations of light fractions can be used to intensify the combustion of methane hydrate at relatively low temperatures in the combustion chamber. After recording the concentrations of the main components of combustion products, we rationalized the environmental benefits of gas hydrates used as the primary and secondary fuel components. The relative efficiency coefficients were calculated for fuels in terms of their environmental, economic, and energy performance indicators. We also formulated recommendations on the co-combustion of gas hydrates with conventional fuels in combustion chambers. Finally, we proposed engineering solutions for the effective use of gas hydrates in power plants.

The Lean Blowout Prediction Techniques in Lean Premixed Gas Turbine: An Overview

The lean blowout is the most critical issue in lean premixed gas turbine combustion. Decades of research into LBO prediction methods have yielded promising results. Predictions can be classified into five categories based on methodology: semi-empirical model, numerical simulation, hybrid, experimental, and data-driven model. First is the semi-empirical model, which is the initial model used for LBO limit prediction at the design stages. An example is Lefebvre’s LBO model that could estimate the LBO limit for eight different gas turbine combustors with a ±30% uncertainty. To further develop the prediction of the LBO limit, a second method based on numerical simulation was proposed, which provided deeper information and improved the accuracy of the LBO limit. The numerical prediction method outperformed the semi-empirical model on a specific gas turbine with ±15% uncertainty, but more testing is required on other combustors. Then, scientists proposed a hybrid method to obtain the best out of the earlier models and managed to improve the prediction to ±10% uncertainty. Later, the laboratory-scale combustors were used to study LBO phenomena further and provide more information using the flame characteristics. Because the actual gas turbine is highly complex, all previous methods suffer from simplistic representation. On the other hand, the data-driven prediction methods showed better accuracy and replica using a real dataset from a gas turbine log file. This method has demonstrated 99% accuracy in predicting LBO using artificial intelligence techniques. It could provide critical information for LBO limits prediction at the design stages. However, more research is required on data-driven methods to achieve robust prediction accuracy on various lean premixed combustors.

Size-Based Effects of Anthropogenic Ultrafine Particles on Lysosomal TRPML1 Channel and Autophagy in Motoneuron-like Cells.

An emerging body of evidence indicates an association between anthropogenic particulate matter (PM) and neurodegeneration. Although the historical focus of PM toxicity has been on the cardiopulmonary system, ultrafine PM particles can also exert detrimental effects in the brain. However, only a few studies are available on the harmful interaction between PM and CNS and on the putative pathomechanisms. Ultrafine PM particles with a diameter < 0.1 μm (PM0.1) and nanoparticles < 20 nm (NP20) were sampled in a lab-scale combustion system. Their effect on cell tracking in the space was studied by time-lapse and high-content microscopy in NSC-34 motor neurons while pHrodo™ Green conjugates were used to detect PM endocytosis. Western blotting analysis was used to quantify protein expression of lysosomal channels (i.e., TRPML1 and TPC2) and autophagy markers. Current-clamp electrophysiology and Fura2-video imaging techniques were used to measure membrane potential, intracellular Ca2+ homeostasis and TRPML1 activity in NSC-34 cells exposed to PM0.1 and NP20. NP20, but not PM0.1, reduced NSC-34 motor neuron movement in the space. Furthermore, NP20 was able to shift membrane potential of motor neurons toward more depolarizing values. PM0.1 and NP20 were able to enter into the cells by endocytosis and exerted mitochondrial toxicity with the consequent stimulation of ROS production. This latter event was sufficient to determine the hyperactivation of the lysosomal channel TRPML1. Consequently, both LC3-II and p62 protein expression increased after 48 h of exposure together with AMPK activation, suggesting an engulfment of autophagy. The antioxidant molecule Trolox restored TRPML1 function and autophagy. Restoring TRPML1 function by an antioxidant agent may be considered a protective mechanism able to reestablish autophagy flux in motor neurons exposed to nanoparticles.

Evaluation of flue gas emission factor and toxicity of the PM-bounded PAH from lab-scale waste combustion

Atmospheric particulate matter (PM) has a significant threat not only to human health but also to our environment. In Hungary, 54% of PM10 comes from residential combustion, which also includes the practice of household waste burning. Therefore, this work aims to investigate the quality of combustion through the flue gas concentrations (CO, CO2, O2) and to identify and evaluate the negative impacts of PM and PAHs generated during controlled lab-scale combustion of different mixed wastes (cardboard and glossy paper, polypropylene and polyethylene terephthalate, polyester and cotton). Mixed wastes were burnt in a lab-scale tubular furnace at different temperatures with 180 dm3/h air flow rate. Chemical analyses were coupled with ecotoxicological tests using the bioluminescent bacterium Vibrio fischeri. Ecotoxicity was expressed as toxic unit (TU) values, toxic equivalent factors (TEF) were also presented. During the combustion same amount of O2 enters the reaction, but a different amount CO2 is generated due to the C content of the sample. The waste with highest C-content related to the highest CO2 emission. Increasing the combustion temperature produces more PM-bound PAHs, which remains the same composition in the case of plastic and textile groups. The TU of solid contaminants decreases with increasing combustion temperature and increases with the minerals which are left behind in the water from the solid contaminants.

Effect of Counter- and Co-Swirl on Low-Frequency Combustion Instabilities of Jet A-1 Spray Flames

Abstract The present article experimentally investigates the influence of pilot swirling directions on low-frequency combustion instabilities of pilot diffusion flames in a laboratory-scale combustor with jet A-1 fuel and air at atmospheric pressure. Airblast atomization nozzles with either counter-rotating (CTR) or corotating (COR) pilot swirl flows were examined using nonlinear time-series analyses and high-speed flame imaging measurements under idle and subidle operating conditions. We show that while the amplitude and frequency of limit cycle oscillations are observed to be similar for both cases, detailed examinations of measured experimental data reveal marked differences in stabilization mechanisms and pressure-heat release coupling processes. The spray flame dynamics subjected to counter-rotating swirl flows are governed by large-amplitude pressure oscillations, even under the influence of destructive pressure-heat release rate interference. The mechanism of destructive interference is closely related to the interactions between a spiral diffusion flame and a periodically detached reaction zone. Nonpremixed liquid-fueled flames involving corotating swirl, on the other hand, feature a more compact and intense reaction zone.