Steady Combustion Research Articles

Effect of aluminum nanoparticles size and concentration on the combustion characteristics of nanofluid fuel: Experiments and modeling

Nanofluid fuel has garnered significant attention due to its potential to enhance combustion characteristics, energy density, and ignition properties. The study comprehensively examined the effects of aluminum nanoparticles with diverse sizes (50 nm, 100 nm, 200 nm, 500 nm, 1 μm) and concentrations (2.5 wt%, 5.0 wt%, 7.5 wt%) on the ignition and combustion characteristics of nanofluid fuel droplets, utilizing a mechanically mixed aluminum-based nanofluid fuel solution that incorporated kerosene, aluminum particles, and the surfactant oleic acid. The combustion process of the nanofluid fuel droplets encompasses phases of ignition, steady combustion, micro-explosion, and agglomerate reaction. The surface temperature of the nanofluid fuel droplets consistently exceeded that of a pure kerosene droplet, with temperature elevations correlating positively with particle concentration but not with the particle size. The surface temperature of nanofluid fuel droplets containing 7.5 wt% aluminum particles is approximately 205°C. The incorporation of oleic acid into pure kerosene prolongs the ignition delay from 0.317 s to 0.333 s. The combustion rate of the nanofluid fuel droplets escalates upon the addition of aluminum particles, with the rate escalating in tandem with the diameter and concentration of the aluminum particles. Nanofluid fuel droplets containing 5.0 wt% aluminum and 5.0 wt% oleic acid particles exhibit a combustion rate akin to that of pure kerosene droplets, with rates of 0.596 and 0.604 mm2 s−1, respectively. Concurrently, the ignition delay for nanofluid fuel droplets is longer than that of pure kerosene, yet it exhibits insensitivity to particle size. The ignition delay for nanofluid fuel droplets with the addition of 7.5 wt% aluminum particles is approximately 1.5 times that of kerosene. Nanofluid fuel droplets devoid of oleic acid yield divergent results due to particle agglomeration effects. Subsequently, as particle size increased, the surface of combustion residue develops more pronounced bulges, becoming more prone to rupture. Ultimately, a kinetic prediction model is proposed, accounting for the inhomogeneous properties within the droplet. The root mean squared errors for ignition delay time, combustion rate, and steady surface temperature are all below 8 %, indicating a strong correlation between model predictions and experimental data. This research could help accelerate the adoption of aluminum-based nanofluid fuel.

Experimental Study on the Combustion Characteristics of Ultralow-Concentration Methane in Divergent Porous Media Burner

ABSTRACT To improve the stable combustion characteristics of ultralow-concentration methane (Concentration of 3.5%-5.0%), a series of combustion experiments were carried out by filling alumina spheres with different particle sizes (i.e. 5 mm, 10 mm and 15 mm) in a divergent burner, and the effects of divergent angle (i.e. 10°, 20° and 30°) and pore distribution on the flame propagation and stable combustion characteristics of ultralow-concentration methane were revealed. The results show that larger particle sizes and methane flow rates lead to the double flame surface phenomenon, and increasing angle and decreasing particle size can help to improve the preheating efficiency of the burner. Moreover, the inlet flow rates corresponding to the steady combustion of ultra-low concentrations methane are between 0.225 m/s and 0.308 m/s, the increase in inlet velocity, particle size, and angle will reduce the stability of the flame and make the shape of the flame surface developed in the order of “V→W→∧.” The burner with 10 mm particles and 30° angle has a wider stable combustion range, and the burner filled with smaller pore distribution help to improve the utilization of the lower concentration methane premixed.

Experimental and numerical investigation on oscillatory combustion characteristics of an integrated flameholder

Integrated flameholders are widely used in advanced afterburner. Oscillatory combustion can be easily caused by the complex flow field and non-uniform fuel distribution in advanced afterburner with integrated flameholders. Therefore, the oscillatory combustion characteristics under uniform and non-uniform fuel distribution downstream of integrated flameholder is investigated by using an experimental method with numerical simulation. The results show that oscillatory combustion is more likely to occur under the condition of non-uniform fuel distribution. When oscillatory combustion occurs, the main frequency is approximately 33.99 Hz and the flame variations can be divided into three phases: re-ignition phase, instability pre-transmission phase and extinction phase. Furthermore, three combustion states are observed at equivalence ratio Φ varied between 0.2 and 0.85: steady combustion, quasi-periodic oscillatory combustion and limit-cycle oscillatory combustion. Limit-cycle oscillatory combustion exhibits a relatively simple proper orthogonal decomposition structure and a longer axial motion wavelength than quasi-periodic oscillatory combustion. Notably, during oscillatory combustion, the pressure and heat release rate pulsations are roughly in the same frequency and phase, which shows that the oscillatory combustion is mainly caused by thermoacoustic interaction. These results provide guidance for further investigations of oscillatory combustion in advanced afterburner with integrated flameholders and development measures for its suppression.

Design and experimental study of a 300 We class combustion-driven high frequency free-piston Stirling electric generator

Portable electric power generator with a power level of several hundred Watts plays an important role in outdoor activities, emergency relief and tactical power supply. As an external-combustion heat engine with outstanding heat source adaptability, free-piston Stirling generator (FPSG) owns attractive advantages of quietness, high thermal efficiency, and high reliability. This paper proposes a novel ultra-high frequency (UHF) FPSG-based portable power supply system driven by a diesel porous media evaporative combustor (PMEC). An experimental setup was designed and built based on the quasi-one-dimension thermoacoustic impedance matching of the FPSG and three-dimension thermal coupling of steady combustion and alternating flow between FPSG and combustor. The fundamental operating characteristics of the system were investigated in terms of combustion powers and electric loads. Preliminary experimental results show that a maximum output electric power of 350 We at a heating temperature of 875 K and a maximum fuel-to-electric efficiency of 11.98 % were obtained. Computational fluid dynamics (CFD) simulations were employed to delve into the intricate combustion and heat transfer processes, unveiling the formation of carbon deposits and confirming the efficacy of cyclone holes in reducing carbon deposition. This pioneering exploration of 130 Hz UHF and evaporative-combustion coupled heat transfer successfully showcases the feasibility of constructing a high-specific-power FPSG-based portable power system.

Numerical Analysis of Postcombustion Effects on the Supersonic Jet Behavior

During the top blowing process of the basic oxygen furnace, the oxygen jet may react with CO before it reaches the surface of the molten bath. This combustion reaction affects the dynamic characteristics of the jet, which, in turn, affects its interaction with the bath. In this study, a numerical model is developed to investigate the transient and steady combustion characteristics of the supersonic jet emitted from the top lance. The transient combustion simulation shows that the CO ratio gradually decreases while the CO2 mole fraction increases at the interaction boundary region between jet and ambient due to the chemical reactions. In addition, the jet profile is changed when the postcombustion is introduced. Due to the flame formation and turbulence change at the jet combustion interface, the axial velocity at height of 2 m (x = 73 re) is 89% higher than that of the noncombustion reaction jet flow. In the results, it is demonstrated that the combustion interface is favorable to reduce the jet decay, resulting a higher dynamic pressure before the jet reaches the bath surface. Furthermore, a higher core temperature and lower density are obtained for the combustion jet compared to that of without combustion reaction.

Influence of buoyancy on the mixing, flame structure, and production of NO in hydrogen diffusion flames

This study investigates the impact of buoyancy on the mixing and flame structure of hydrogen jet diffusion flames. A validated Computational Fluid Dynamics (CFD) model for hydrogen diffusion flames is developed, employing the k−ω turbulence model and a steady flamelet combustion model. By accounting for the buoyancy term, the model accurately predicts the stoichiometric hydrogen flame length within a mere 0.2% deviation from the experimental value. In contrast, excluding the buoyancy term leads to a prediction divergence of around 5%.Deeper analysis of the mixture fraction field indicates that buoyancy enhances mixing in the flame’s far-field region, facilitating a more rapid dilution of the fuel stream within the air. This, in turn, results in a shorter flame. The scope of the modelling is expanded to encompass buoyancy effects onhydrogen flames with jet Reynolds numbers (ReJ) up to 15,000. While the buoyancy’s influence on flame control weakens as ReJ increases, a noticeable ∼4% variation in stoichiometric flame length persists between scenarios with and without buoyancy.

A novel Fe2O3/Al2O3 porous media catalyst prepared by ultrasonic-assisted impregnation for low-concentration methane catalytic combustion

Porous media (PM) catalytic combustion offers a potential strategy for stable and efficient combustion of low-concentration methane (LCM). Herein, a porous media catalyst loaded with Fe2O3 as the active component (Fe2O3/Al2O3) was developed by ultrasonic-assisted impregnation for LCM catalytic combustion in a four-layer porous media burner. The influences of the gas flows, velocities, equivalence ratios, and PM arrangement patterns on the temperature distribution, combustion stability, methane conversion, and emissions were investigated in detail. The results indicated that the Fe2O3/Al2O3 catalyst possessed exceptional catalytic activity and thermal stability at medium-to-high temperatures, which broadened the limiting equivalence ratio for CH4 stationary combustion to 0.43 with the CH4 conversion exceeding 99 %. LCM enabled higher combustion stability in the PM burner with a gradually varied configuration, achieving steady combustion for more than 120 min under the lean combustion condition (0.43 equivalence ratio and 50 L/min). The high-quality flue gas from LCM catalytic combustion with an average temperature over 600 ℃, lower CO (< 150 ppm) and NOx emissions (< 10 ppm) could serve for the comprehensive utilization of power generation, heating, and cooling. The catalytic oxidation of LCM on the Fe2O3 surface was primarily divided into four steps with the second-step CH4 dehydrogenation in CH4 dissociation being the dominant rate-limiting step. This work proves that the catalyst fabricated by ultrasonic-assisted impregnation can effectively break through the lean combustion threshold, which provides a valiant reference for the clean and efficient utilization of LCM.

Joint design and simulation of GOX-GCH4 combustion and cooling in an experimental water-cooled subscale rocket engine

This paper presents the authors’ most recent research regarding the feasibility of cooling a 1 kN scaled-down experimental rocket engine, running on gaseous oxygen and gaseous methane, for a ground test. The cooling segment of a rocket engine has always been a delicate problem, increasing the development time and costs of development. Since a series of problems can occur during the first ignition of a rocket engine prototype, removing as many potential issues from the initial test, such as using liquid methane for the cooling system, could result in a more stable experiment. Using water as the cooling agent can contribute to a more accelerated TRL increase of the engine’s subcomponents while reducing the risks taken for a whole assembly test. Thus, the combustion chamber, nozzle, and injector can be tested separately from the final cooling method, which can be added subsequently. In the present work, both a steady and transient CFD combustion simulation of a multicomponent compound, consisting of gaseous oxygen and gaseous methane was conducted in the combustion chamber of a small-scale rocket engine. The simulation is based on PDF-flamelet approach for the oxygen and methane combustion, along with real gas equations for the cooling agent.

Study on synergistic heat transfer enhancement and adaptive control behavior of baffle under sudden change of inlet velocity in a micro combustor

The rapid advancement of micromachining technology has led to the proliferation of micro-combustors in both civilian and military applications, and the actual operation process requires the ability to adapt to complex working conditions. The sudden change of the operating conditions poses a huge threat to the flame stability in micro-combustion, but the flame regulation, especially the adaptive regulation, has proved to be challenging under the sudden change of inlet velocity. In this paper, we report a novel method that significantly improves combustion performance, including heat transfer enhancement under steady-state conditions and adaptive stable flame regulation under velocity sudden increase. We successfully harnessed the synergistic benefits of both the front and rear baffles, investigated the angle matching of the baffles at various inlet velocities, and employed nitinol memory metal as the baffle material to examine its impact on enhancing heat transfer and flame control behavior. According to the results, under the synergic action, the combustion efficiency reaches to 96.92%, and the baffle angle matching 60° + 30° shows good combustion performance at medium-low velocity, and a flame breaking limit of 92 m/s is obtained at 0° + 0° with high-velocity condition. In addition, nitinol alloy is selected as the deformation baffle material, the flame breaking limit is further extended by 6 m/s, and the combustion efficiency can still be maintained at 0.45 ms by a velocity sudden increment of 60 m/s, and the pressure loss is reduced by more than 70%. This study is helpful to provide a reference for the steady combustion under the sudden change of micro-scale conditions, and provides a new idea for the adaptive control of flame.

Experiment Study and Industrial Application of Slotted Bluff-Body Burner Applied to Deep Peak Regulation

During the deep peak shaving period, the boiler needs to operate at a lower load, so higher requirements were set for the boiler's stable combustion. In order to better evaluate and compare the stable ignition capacity of bluff-body burners and slotted bluff-body burners, guidance and calculation support for the design of boiler deep peak shaving were needed. This study adopted the reflux heating chain ignition analysis method to study the differences in the steady combustion mechanism between the bluff-body burner and the slotted bluff-body burner. A thermal combustion experiment was conducted in employing the single angle coal powder combustion furnace. The experimental results were compared against the theoretical analysis results. In addition, a study was conducted on the application of slotted bluff-body burners in the deep peak shaving of a 330MW unit power plant boiler. The results showed that as long as the small slot flow can catch fire, the mixed temperature of the reflux fluid of the slotted bluff-body burner will be higher than that of the bluff body burner. This will enhance its steady combustion ability. The combustion test results were found to be consistent with the analysis results, indicating that when the slotted bluff-body burner is used on the 330MW unit, the boiler combustion is in good condition. In this case, it has a stable combustion capacity of 66MW (20% economic continuous rating) without oil injection at low loads. This study revealed the advantages of the slotted bluff-body burner in terms of its steady combustion mechanism compared to traditional bluff-body burners. It verified the feasibility for boiler deep peak shaving in practical applications. This is of great significance for improving the flexibility of coal-fired power generation units, enhancing the flexibility of the power system, and promoting carbon reduction.

Effects of temperature ratio on combustion instability in a non-premixed hydrogen-rich ram combustor

The effects of the burnt-to-unburnt temperature ratio (Tb/Tu) (reciprocal density ratio) on thermoacoustic combustion instability were investigated in a hydrogen-rich ram combustor by controlling the inlet air temperature under cruising conditions. Steady and unsteady combustion dynamics were investigated with the simultaneous measurement of combustion pressure and near-infrared (NIR) emissions. Time-resolved NIR images were analyzed using dynamic mode decomposition (DMD) to extract modes of the combustion instability, which show two oscillation modes: longitudinal (500 Hz) and flame-vortex interaction modes (2000 Hz) with a Strouhal number of approximately 0.5. The thermoacoustic combustion instability was not excited at Tb/Tu = 3.3, but was excited at Tb/Tu= 2.6 and 2.9. The DMD modes show that the structure of the vortex mode is similar to that of the fourth longitudinal mode at Tb/Tu = 2.6 and 2.9, indicating that the coupling of the vortex and the fourth longitudinal modes excited the thermoacoustic combustion instability.

Comparative analysis of combustion stability and flow performance in micro combustor based on the synergistic action of slotted blunt body and front-baffle

Flame instability is a key problem that needs to be solved, and the existing improvement methods are still insufficient. Different from the traditional single structure improvement, a novel synergistic combustion stabilization method is proposed. In this paper, the conventional blunt body is slotted to achieve “graded combustion”, and the front baffle is embedded on the slotted blunt body to guide fuel flow, thus strengthening the combustion and improving the flame stability. With the help of simulation software Fluent, the combustion characteristics of conventional blunt body micro combustor (CMC), conventional slotted blunt body micro combustor (MCESB) and front-baffle slotted blunt body micro combustor (MCESB-FA) are compared, and further researched the flow characteristics and inlet velocity. According to the findings, the synergistic action of slotted blunt body and baffle is beneficial to improve combustion performance and flame stability, MCESB-FA demonstrates the highest combustion efficiency, the flame breaking limits of the MCESB-FA up to 80 m/s. Besides, the turbulent kinetic energy behind the blunt body is significantly increased, which is conducive to the heat transfer for the central combustion zone and the cold fuel on both sides, so as to achieve strengthening combustion. Interestingly, the backflow area disappears due to the slotting, but the front-baffle embedding breaks the original fuel flow balance and re-forms the backflow area to achieve steady combustion. Finally, as inlet velocity increase, the MCESB-FA and MCESB have better combustion performance and flow distribution, especially under the combination of slotted blunt body and front-baffle.

Coherent Structures Analysis of Methanol and Hydrogen Flames Using the Scale-Adaptive Simulation Model

Computational fluid dynamics techniques were applied to reproduce the characteristics of the liquid methanol burner described in a previous paper by Guevara et al. In this work, the unstable Reynolds-averaged Navier–Stokes (U-RANS) approach known as the Scale-Adaptive Simulation (SAS) model was employed, together with the steady nonadiabatic flamelets combustion model, to characterize and compare methanol and hydrogen flames. These flames were compared to determine whether this model can reproduce the coherent dynamic structures previously obtained using the LES model in other investigations. The LES turbulence model still entails a very high computational cost for many research centers. Conversely, the SAS model allows for local activation and amplification, promoting the transitions of momentum equations from the stationary to the transient mode and leading to a dramatic reduction in computational time. It was found that the global temperature contour of the hydrogen flame was higher than that of methanol. The air velocity profile peaks in the methanol flame were higher than those in hydrogen due to the coherent structures formed in the near field of atomization. Both flames presented coherent structures in the form of PVC; however, in the case of hydrogen, a ring-type vortex surrounding the flame was also developed. The axial, tangential, and radial velocity profiles of the coherent structures along the axial axis of the combustion chamber were analyzed at a criterion of Q = 0.003. The investigation revealed that the radial and tangential components had similar behaviors, while the axial velocity components differed. Finally, it was found that, using the SAS model, the coherent dynamic structures of the methanol flame were different from those obtained in previous works using the LES model.

An advanced vortex-tube technology for pure ammonia combustion with clean and steady peculiarity

The present study investigates the combustion performance of pure ammonia in a stratified vortex-tube reactive flow (SVRF) concerning stability limits, flame topology, pressure fluctuations, and emissions. The results demonstrate that the SVRF enables efficient and stable combustion of ammonia, characterized by uniform flame topology, low NO emissions, and high combustion efficiency. The lean φg stability limits consistently remain below 0.32 within the qf range of 5.0–30.0 l/min. Moreover, the flame topology remains consistently smooth and uniform throughout the process while maintaining a peak heat release above 5.0 × 107 W/m3. Additionally, pressure fluctuation amplitude generally stays within 100 Pa, indicating a remarkably steady combustion process for ammonia burning in the SVRF. The investigation focuses on the multi-field cooperative coupling, which enhances species and enthalpy transport to increase combustion strength, thereby contributing to a larger stability limit. Various criterion numbers are calculated to quantify the aero-/thermo/flame- dynamic stability. It is found that excellent flame-dynamic/thermo-acoustic stability plays a crucial role in achieving steady combustion of pure ammonia, which can be measured by Ra(x) and the “Gain” of the flame transfer function. The degree of synergy between flame disturbance and fluid disturbance, as well as the response of flame disturbance to fluid disturbance in SVRF, is identified as the primary factor influencing different levels of combustion stability performance. Furthermore, a relationship between aero-/thermo-dynamic stability and flame stability has also been discovered. Favorable aero-/thermo-dynamic stability promotes excellent flame-dynamic behavior by suppressing normal direction fluid fluctuation and resulting in more stable intensity and spatial location fluctuations of the flame. Additionally, momentum flux decreases within the interior region, enhancing good flame-dynamic stability when using pure ammonia as fuel.

Effect of H2 and CO in syngas on oxy-MILD combustion

This paper investigates the effect of adding H2 and CO to a syngas on oxy-MILD combustion. This work employs a Perfectly Stirred Reactor (PSR) model to calculate the autoignition temperature and the critical oxygen concentration for different component fuels under oxy-MILD conditions. Our investigation obtains the critical O2 concentration for oxy-MILD combustion of various H2/CO/CH4 component fuels. The results indicate that adding H2 to CH4 significantly reduces the minimum O2 concentration required for achieving the MILD state while adding CO has little effect. Furthermore, using the novel PCA method, we analyze characteristic chemical time scales for oxy-MILD combustion for different fuel ratios. We conclude that the mixture containing H2 and CO can be used as fuel for oxy-MILD combustion, as its characteristic chemical time scale is comparable to the turbulent time scale, resulting in Da number close to unity. However, achieving a steady MILD combustion state is more challenging than methane due to reduced ignition delay times. Moreover, syngas with various ratios of H2/CO presents the potential for controlling the MILD combustion process.

Effect of Acoustic Pressure Oscillations on Burning Rate Augmentation of Composite Solid Propellants at Different Initial Grain Temperatures

ABSTRACT The effect of acoustic pressure oscillations, besides initial grain temperature on the burning rate of composite solid propellants (AP/HTPB/RDX/Al), is experimentally investigated using a T-burner. Mean burning rate is a by-product of the T-burner experiment while screening different propellants for its stability behavior by evaluating its combustion response. Experiments at different frequencies ranging from 200 to 400 Hz and at different pressures of 2–8 MPa and at different initial grain temperatures (room temperature (303 K), hot (343 K), and cold (243 K)) by soaking the propellant samples by a novel method for two industrial-grade propellants (propellant-A and propellant-B) were conducted. Many of the tests were self-excited for propellant-A, whereas propellant-B needed to be pulsed in most of the tests. Various levels of acoustic amplitudes were imposed up to 300 kPa, which is not otherwise possible to impose it externally using any other acoustic drivers, for example, a rotary valve (up to 20 kPa max. is possible). The test results revealed that the acoustic pressure oscillations augment the burning rate tremendously. It was found that the burning rate augmentation factor of propellant-B is lower than propellant-A in most of the cases. The investigations revealed the following new findings: (a) Increasing the initial grain temperature in the presence of acoustic pressure oscillations tends to decrease the augmentation; (b) Many of the results of the augmentation showed a rising and falling trend with acoustic amplitude; (c) The burning rate augmentation factor from self-excited and pulsed tests surprisingly form a continuous trend and shown together. The positive and negative augmentation compels us to further investigate toward a better understanding about the steady combustion behavior of solid propellants since there is no model available as on today to predict the burning rate augmentation precisely due to the combined effect of acoustic pressure oscillations and initial grain temperature.

Preparation, characterization, and thermal decomposition kinetics of high test peroxide gel

High test peroxide gel was prepared by low temperature freezing under the action of calcium ion compound with sodium alginate as a gelling agent. The High test peroxide gel was characterized by ultra depth of field microscope, Fourier infrared spectrometer, rheometer, synchronous thermal analyzer, and electron microscope scanner. The thermal decomposition behavior and reaction kinetics of the gel were investigated. The effective content of H2O2 in the gel before and after aging was also analyzed by KMnO4 titration. The results show that the content of sodium alginate and the concentration of calcium ion compound directly affect the gelling and rheological properties of high test peroxide gel, and the gel with low sodium alginate content had a more uniform tissue structure. The Eα and lg(A/s−1) of the high test peroxide gel decomposition reaction are 69.10 kJ mol−1 and 9.13, respectively. Na2O, CaO, CaCl2 and CaSO4 are the main components of the high test peroxide gel thermal decomposition condensate products. After ignition, a boron-based high test peroxide gel propellant can produce a steady combustion. After being stored at 263 K for 20 days, the effective content of H2O2 in the gel is 96.50%, and the decomposition rate is only 0.63%.

Influence of Central Air on Flow and Combustion Characteristics and Low-Load Stabilization Performance of a Babcock Burner

On a cold single-phase test stand, the effect of central air on the exit flow field of Babcock, Germany, burner was investigated. Industrial measurements were taken for a 700 MW wall-fired pulverized-coal utility boiler with above burners. Gas temperature, gas composition and concentration in the burner area were measured at 444 MW, 522 MW and 645 MW loads, respectively. Only when the central air mass flow was zero did a center reflux zone exist in the burner outlet area. The steady combustion of faulty coal was aided by early mixing of primary and secondary air, which was made possible by the decreased central air mass flow. At all different loads, the pulverized coal in center region took a long distance to ignite. The temperature in center steadily dropped as central air mass flow decreased, while the temperature in secondary air region gradually rose. Within 1.5 m from the primary air duct outlet, the highest CO concentration was 25 ppm and the highest O2 concentration was close to 21% under all loads. The gas concentration near sidewall was more influenced by load. With all valves opening of burner center air at 30%, the boiler was able to operate safely and stably without oil at a load of 262 MW. The furnace chamber temperature in burner area reached 1056.1 °C.

Numerical and Experimental Investigation of the Decoupling Combustion Characteristics of a Burner with Flame Stabilizer

In order to integrate renewable electricity into the power grid, it is crucial for coal-fired power plant boilers to operate stably across a wide load range. Achieving steady combustion with low nitrogen oxide (NOx) emissions poses a significant challenge for boilers burning low-volatile coal in coal-fired power plants. This study focuses on developing a decoupling combustion technology for low-volatile coal-fired boilers operating at low loads. A three-dimensional numerical simulation is employed to analyze and optimize the geometrical parameters of a burner applied in a real 300 MW pulverized coal fired boiler. Detailed analysis of the burner’s decoupling combustion characteristics, including stable combustion ability and NOx reduction principles, is conducted. The results indicate that this burner showed three stages of coal/air separation, and the flame holder facilitates the stepwise spontaneous ignition and combustion of low-volatile coal. By extending the time between coal pyrolysis and carbon combustion, the burner enhances decoupling combustion and achieves low nitrogen oxide emissions. Based on optimization, a flat partition plate without inclination demonstrates excellent performance in terms of velocity vector field distribution, coal air flow rich/lean separation, combustion, and nitrogen oxide generation. Compared with the initial structural design, the average nitrogen oxide concentration at the outlet is reduced by 59%.

Single droplet combustion of iron nitrate-based precursor solutions: Investigation of time- and size scales of isolated burning FSP-droplets

Flame spray pyrolysis (FSP) is a powerful and versatile technique for the rapid and scalable synthesis of functional nanoparticles. The route of nanoparticle formation depends on the mass transfer of liquid precursor droplets into the gas phase, significantly deciding the quality of generated nanoparticles. Therefore, the study of time- and size scales of isolated burning FSP-droplets plays an important role in better understanding and promoting the use of this technique. Hereby, we have used a low-cost iron nitrate-based precursor-solvent system to investigate the disruptive burning process of single droplets with initial droplet diameters ranging from 48 µm to 125 µm. Different timescales at the level of steady droplet combustion and µ-explosions were correlated to droplet sizes. It has been observed that the total lifetime of a droplet converges towards the duration of the µ-explosion process for small droplet sizes causing the µ-explosion to occur immediately after ignition. In order to study the effect of the solvent composition of ethanol and 2-ethylhexanoic acid (2-EHA), the volumetric fraction of 2-EHA was varied from 20% up to 80%. An increasing fraction of 2-EHA causes the onset of the disruption to occur later and the droplet to become more concentrated with precursor. The results of this work provide fundamental insights into single droplet combustion and contribute to a better understanding of the use of low-cost precursor-solvent systems in FSP.