Droplet Combustion Research Articles

Effect of micro-explosion and puffing on combustion interactions of multi-component fuel droplet array during flame spread

Micro-explosion is a potential scheme to increase the combustion rate of engine spray and reduce emissions. The present study investigates the effects of micro-explosion and puffing on the combustion interaction of multi-component fuel droplet array using a magnified high-speed backlit illumination technique. The mechanisms of micro-explosion and puffing in droplet array combustion were proposed. The results indicate that droplet array combustion primarily consists of two droplets burning in the same flame, three droplets burning in the same flame, and independent flame combustion. Three droplets burning in the same flame lasts the longest at droplet spacings of 2 and 3, accounting for 97.14 % and 72.06 % of the total combustion time, respectively. The total combustion duration of the droplet array is shortened by 34.1 % and 40.3 % at droplet spacings of 2 and 3 compared to the theoretical combustion time. However, the total combustion duration of the droplet array is 1.9 % and 7.4 % longer than the theoretical value at droplet spacings of 4 and 5. Most importantly, the interaction factor first increases and then decreases with increasing droplet spacing. The third droplet has the smallest interaction factor. This is mainly determined by the combined effects of hypoxia, flame heating, and vapor cooling.

Experimental study on droplet dynamics behavior and combustion characteristics of high performance green propellant in electrical ignition mode

High performance green propellant represented by ammonium dinitramide-based liquid propellant and its new ignition method are the research hotspots of space propulsion in the 21st century. Exploring the complex multi-scale physical properties of multi-component ammonium dinitramide-based liquid propellant droplets in the electrical ignition mode has wide application significance for spray, propulsion system design and combustion control. The droplet dynamics behavior and combustion characteristics of propellant droplets at different ignition voltages were studied experimentally. The droplet dynamics behavior during the evaporation process, including violent volume oscillation, approximate steady-state expansion, contraction, secondary expansion, puffing and micro-explosion, have been determined by the generation, growth, and discharge of vapor bubbles. In the initial evaporation process, the heterogeneous nucleation is dominant. As the droplet is continuously heated, homogenization nucleation gradually dominates. The main physical and chemical mechanisms of bubble evolution driven by temperature involve methanol boiling, water overheating, ammonium dinitramide decomposition and combustion reaction between vapor molecules. Increasing the ignition voltage increases the droplet dynamics behavior and the combustion, but promotes the combustion instability. Increasing the ignition voltage increases the ignition delay time, puffing delay time, droplet lifetime, maximum temperature of droplet, and reduces the ignition critical diameter. It is proposed that the method of suppressing the droplet breakup dynamics at decomposition area and enhancing the droplet breakup dynamics at the combustion area are conducive to the combustion control of the thruster in electrical ignition mode. This research provides novel insight into the study of the electrical ignition mechanism of liquid fuels.

Evaporation and combustion of low asphaltene heavy oil droplets under conditions representative of practical applications

The evaporation and burning characteristics of isolated heavy fuel oil (HFO) droplets are experimentally studied at conditions representative of practical applications, producing novel, detailed results on the effect of oxygen concentration. Also, and for the first time for HFO, the temporal evolution of the flame stand-off ratio (based on CH* emission) and the cenosphere burning size are presented along with the droplet size histories. The effect of ambient oxygen concentration is first analyzed qualitatively, identifying different sub-stages. Later, a quantitative analysis is presented in terms of ignition delay time, micro-explosion regimes, shell swelling ratio, cenosphere size and several time metrics. The results show that, as ambient oxygen changes, the liquid and solid stages show marked differences not only in terms of time scales but also in the transitions of burning regimes. Cenospheres generated in oxygen-free conditions are found to be ∼1.4 times larger than those in droplet combustion. Although similar in size, the solid-to-liquid consumption time ratio in 5% O2 is found to be significantly longer, about twice than for the 10% O2 ambient. The characterization of these differences is thought to be relevant not only for oil flames but also for the promising future of heavy oil gasification applications.

Captivating Combustion Traits of Bio-Oil Droplets Enriched with Bio-Additives from the Areca Shell Waste

Fuel derived from crude vegetable oil, such as coconut oil, holds promise as an alternative energy source to mitigate the increasing reliance on fossil fuels driven by population growth and industrial activities. The experiment involved suspending a single droplet of crude coconut oil mixed with activated carbon from areca shell waste and placed at the junction on R-type thermocouple (Pt/Pt-Rh13%). The droplets were ignited using a hot wire and subjected to atmospheric pressure and room temperature. Coconut oil comprises a saturated triglyceride carbon chain compound of approximately 91%, and areca shell waste possesses a porous structure that fosters favorable interactions between fuel molecules. The droplet combustion method was selected to streamline the process and enhance the contact area between air and fuel, thereby boosting the reactivity of fuel molecules. The research found that adding activated carbon shortens the carbon chain, making it more reactive and easier for the fuel to ignite. Specifically, activated carbon significantly enhances fuel performance at a concentration of two parts per million (ppm). At this level, the fuel absorbs heat more effectively and ignites faster compared to one ppm and three ppm levels. Moreover, the results show that heat absorption occurs slowly at one ppm, while at three ppm, the increased molecular mass of the fuel can strengthen carbon-bonding forces. These factors contribute to a longer ignition time for the fuel. The findings suggest that the activated carbon from areca shell waste can play a good role as a combustion catalyst, where overall, fuel performance increases.

The impact of carbon quantum dots derived from spent coffee grounds on the droplet combustion of diesel/n-butanol blend

As global concerns surrounding climate change mount and fossil fuel reserves diminish, the application of additives in internal combustion engines is increasingly prevalent. Butanol and carbonaceous nanomaterials, such as carbon quantum dots (CQD), are being employed as additives to increase engine efficiency and mitigate the emission of pollutants. Nevertheless, understanding the impact of these additives on combustion behavior at the droplet scale through combustion assessments before their use in engines is crucial. In this study, our main objective was to assess the impact of incorporating CQD dispersed in n-butanol as additives to conventional diesel fuel on the combustion characteristics at the droplet scale. CQD were obtained from spent coffee grounds (SCGs) using n-butanol as a solvent. The product obtained was mixed with Colombian commercial diesel (10 % vol. palm oil biodiesel), and its combustion was evaluated using the droplet combustion method. Before the CQD synthesis, SCGs were characterized by thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). CQD were characterized via Fourier transform infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), UV–vis, and fluorescence spectroscopy. Results indicated that adding n-butanol and CQD to commercial diesel leads to a 5.4 % and 16.5 % increase in droplet ignition delay, respectively. These additives also cause droplet contraction and expansion cycles, resulting in unstable combustion. However, CQD reduces the frequency of microexplosions caused by boiling n-butanol inside the droplet, which mitigates instabilities during droplet combustion. Including CQD can enhance fuel evaporation by increasing the density of nucleation sites for bubble formation and preventing micro-explosions, thereby leading to stable combustion. These attributes can significantly influence the performance of blends in Compression Ignition (CI) Engines.

Study on Combustion Performances and Droplet Combustion Characteristics of Palm Oil Biodiesel Blends Fuel

Study on Combustion Performances and Droplet Combustion Characteristics of Palm Oil Biodiesel Blends Fuel

Peranan medan magnet dan campuran etanol-biodiesel minyak jelantah pada pembakaran droplet terhadap perilaku api dan emisi gas buang

Petroleum reserves are increasingly depleting, causing a scarcity of petroleum fuel caused by the rapid progress of transportation and the manufacturing industry. This condition forces researchers to search for and develop new renewable energy source. The purpose of research is to understanding and determines role of north-south (U-S) and south-south (S-S) magnetic fields to blend waste cooking oil biodiesel-ethanol on flame evolution, flue gas emissions, and temperature during droplet combustion. Waste cooking oil biodiesel and ethanol were used in this research by adding variations in the direction of repulsive and attractive magnetic fields with an intensity of 11000 gauss. Diameter of droplets tested was 0.3 mm and was placed on a type K thermocouple wire with diameter of 0.1 mm. This research found the role of attractive magnetic field (U-S) in blend waste cooking oil biodiesel-ethanol 20% to produce the shortest flame evolution of 704 ms, lowest CO of 165 ppm, and highest temperature of 828.5 oC. This happens because ethanol has a low flash point and large oxygen content, causing the combustion reaction to occur rapidly. The attractive of magnetic field (U-S) plays a role on attracting oxygen around flame to enter combustion reaction, while the H2O resulting from combustion is pumped out of flame.

Optimization of process parameters for preparing AlN nanopowders by combining carbon-containing droplet combustion and carbothermal reduction methods

In this research, AlN nano-powders were prepared by combining carbon-containing droplet combustion (CCDC) and carbothermal reduction (CR) methods. Firstly, Al2O3+C mixed precursor was synthesized by the CCDC method, and then AlN nano-powder was obtained by the carbothermal reduction of this CCDC precursor. The effects of urea and glucose contents, ignition temperature, and combustion atmosphere on precursors and AlN powders were studied in detail. The results showed that with the molar ratio of urea to aluminum nitrate (U/A) of 3, the atomic ratio of carbon to aluminum (C/Al) of 6, and the ignition temperature at 800 °C under air atmosphere, the prepared precursor was composed of hollow and spherical structure particles exhibiting rough and porous surface morphology with high specific surface area (SSA) (41.4 m2/g). AlN nano-powders obtained by the carbothermal reduction of this precursor were found to be consisted of fine particles with the size of 20–30 nm with high SSA of 39.9 m2/g.

Karakteristik Pembakaran Droplet Campuran Metil Oleat – Etanol dengan Penambahan Multi -Walled Carbon Nanotubes

This research intended to investigate the combustion characteristics of methyl oleic – ethanol blend with OH functionalized multi-walled carbon nanotubes (MWCNT-OH) addition. Methyl oleic is an unsaturated fatty acid methyl ester, which is a constituent of various biodiesels. The observed fuel was a mixture of Methyl oleic with 20% vol of ethanol. MWCNT-OH content was varied by 100 ppm, 200 ppm, 300 ppm, 400 ppm, and 500 ppm (wt based). The presence of ethanol in the droplets is intended to promote the microexplosion phenomenon, generating smaller droplets and a shorter burning time. The experimental results show that the MWCNT-OH addition on the droplet of Methyl oleic – ethanol blend decreased the ignition delay and droplet burning time, while the constant burning rate and droplet temperature (and flame temperature) were increased. Reducing ignition delay time due to the higher thermal conductivity of nanofluid droplets results in more effective heat absorption from the environment and better heat transport inside the droplet. Hence, droplet vaporization, flammable mixture formation and ignition occur in a shorter time. Furthermore, this condition encourages a higher burning rate and a lower droplet burning time. The higher droplet and flame temperatures are related to the higher heating value of the methyl oleic – ethanol – MWCNT-OH mixture and higher droplet burning rate, which results in a higher heat release rate.

The effect of surfactants on boron nanofuel combustion

In this study, the effect of surfactants on the combustion of boron nanofuel was experimentally observed. 1-butanol was chosen as the base fuel, and 70 nm boron nanoparticles were combined with two surfactants, Span 80 and oleic acid, to create the nanofuel. Experiments including single droplet combustion and heating value measurements were conducted, and optical and spectroscopical data were obtained to quantitatively evaluate the effects of the surfactants on boron combustion. The results showed that the addition of surfactants was essential for boron combustion by inducing puffing and atomization. The puffing intensity was stronger with Span 80 than with oleic acid, leading to more active boron combustion and a shorter droplet lifetime overall. An increase in boron concentration enhanced both puffing and boron combustion when surfactants were present. The addition of boron nanoparticles increased the heating value of the nanofuel compared to the base fuel. However, while the inclusion of oleic acid slightly rose the heating value of nanofuel, the addition of Span 80 decreased the heating value of nanofuel.

Defying the D2-law in fuel droplet combustion under gravity

We show both experimentally and theoretically for the first time that the widely used D2-law for describing the shrinking kinetics of a vaporizing droplet is not the true law for single burning droplets under the influence of gravity. Experimentally, the instantaneous diameter D for such a droplet is identified to obey a new kinetic law: Dn decreases linearly with time t, with the exponent n=2.53±0.30−2.69±0.14 for a variety of common liquid fuels such as alkanes and alcohols of low and high boiling hydrocarbons. Theoretically, we develop a phenomenological theory to show n=8/3≈2.67 well capturing the experimental values. The burning rate constant in this new D8/3-law no longer behaves like the thermal diffusivity α of the gas phase but turns into α3ℓ−7/3/g due to the additional inherent fluid-property-determined buoyancy length ℓ under the influence of the gravitational acceleration g. This non-square power law is purely transport determined. It is a consequence of simultaneous momentum, heat, and mass transfer resulted from buoyant convection setup by the blazing flame around the droplet, insensitive to combustion chemistry and detailed reaction kinetics. This study provides not only renewed insights into the multifaceted droplet combustion phenomenon but also possibly new paradigms for a better understanding or characterization of actual fuel droplet combustion processes in normal gravity environments.

Composition changes and micro explosion characteristics of burning droplets formed by combustion of micrometer iron wires

To analyze the composition changes during the combustion process of iron droplets using the energy balance equation, iron wires with diameters of tens of micrometers were burned to form temperature-stable iron droplets with diameters of hundreds of micrometers. High-speed two-color imaging pyrometry was employed to measure the spatially resolved surface temperature and volume changes of the droplets under varying oxygen concentrations. Experimental results showed that the droplet's temperature stabilized between the melting points of wüstite and iron. Quantitative analysis revealed the presence of bubbles within the droplets, primarily sourced from the oxidation of carbon in the iron to carbon dioxide. Simulation results of the droplet combustion process revealed that at the experimental combustion temperatures, the transport of oxygen in molten iron oxides was the rate-limiting step. The gas responsible for micro-explosions originates from the release of dissolved excess oxygen before the solidification of molten iron oxides, with rough estimates indicating that the mass of the released gas is only 0.02% to 0.03% of the droplet mass. The impact of reaction kinetics parameters on the simulation results, as well as the role of the micro-explosion mechanism in the self-sustained combustion of iron wires, were also discussed.

Effect of Microwave Antenna Material and Diameter on the Ignition and Combustion Characteristics of ADN-Based Liquid Propellant Droplets

Microwave-assisted ignition is an emerging high-performance ignition method with promising future applications in aerospace. In this work, based on a rectangular waveguide resonant cavity test bed, the effects of two parameters (material and diameter) of the microwave antenna on the ignition and combustion characteristics of ADN-based liquid propellant droplets were investigated using experimental methods. A high-speed camera was used to record the droplet combustion process in the combustion chamber, the effect of the microwave antenna on the propellant combustion response was analyzed based on the emission spectroscopy method, and finally, the loss of the microwave antenna was evaluated using a scanning electron microscope. The experimental results show that the droplet has the lowest critical ignition power (179 W) when the material of the microwave antenna is tungsten, but the ignition delay time is higher than that of copper. A finer diameter of microwave antenna is more favorable for plasma generation. At a microwave power of 260 W, the ignition delay time of the droplet with a microwave antenna diameter of 0.3 mm is 100 ms lower than that of 0.8 mm, which is about 37.5%. In addition, this study points out the mechanism of microwave discharge in the droplet combustion process. The metallic microwave antenna not only collects the electrons escaping from the gas discharge, but also generates a large amount of metallic vapor, which provides charged particles to the plasma. This study provides the possibility for the application of microwave-assisted liquid fuel ignition.

Study on the combustion characteristics and reaction mechanism of aluminum/alcohol-based nanofluid fuel

Enhancing the volumetric energy density of fuels is a crucial approach in the exploration of efficient energy sources. As a commonly used high-energy additive, Aluminum nanoparticles (Al NPs) holds broad application prospects. This study delves into the effects of Al NPs on the combustion characteristics of methanol and ethanol fuels through in-depth analysis of single droplet combustion and spray combustion experiments involving alcohol-based nanofluid fuels. The experiments revealed that adding Al NPs significantly enhances fuel combustion efficiency, shortening both the combustion life and ignition delay time. Spray combustion tests demonstrated that adding 2 wt% Al NPs increased the maximum and average flame propagation speeds of ethanol fuel spray by 48.93 % and 47.94 %, respectively, while the maximum explosion pressure rose from 0.66MPa to 0.83MPa, with a reduced time to reach peak explosion pressure by 106ms. Based on the SEM and XRD characterization results of the combustion residues and the analysis of flame morphology, a physical model of the alcohol-based nanofluid fuel spray combustion flame was established. Numerical simulations of the gas-phase kinetics model showed that the generation rates of radicals such as H, O, and OH were significantly increased with the addition of Al NPs, intensifying the combustion reaction. The findings provide a theoretical basis for future fuel design and combustion performance optimization.

Laser ignition on single droplet characteristics of aviation kerosene at different pressures and initial diameters: ignition, combustion and micro-explosion

In this study, an experimental system for single-droplet ignition by laser under different pressures is established, and the laser ignition is used to examine how pressure and initial diameter influence ignition properties of RP-3 aviation kerosene single-droplet. The findings reveal that depending on the extent of the impact of bubble rupture on the droplet's shape, The droplet's morphological alterations can be classified into three types: micro-expansion, puffing, and micro-explosion. The ignition and combustion of droplets is segmented into four distinct phases: heating, ignition, intense combustion, boiling combustion. The flame width diminishes with rising pressure. Single droplet ignition delay time is strongly influenced by the pressure, which is reduced by 92.7 %, 94.1 % and 94.3 % for the three droplets from small to large diameters with the pressure increases from 1 bar to 4 bar. The change trends of droplet diameters are first increasing and then decreasing. The whole burning rate of RP-3 droplets goes up with the rise of pressure. A droplet laser ignition model is proposed, the minimum ignition energy of RP-3 droplets with an initial diameter of 1.42 mm at pressures of 1–4 bar are obtained to be 0.88 J, 0.80 J, 0.68 J, and 0.59 J, respectively.

Impact of Aluminium and Titanium Additives on Ignition and Combustion in Boron-Loaded Gelled Jet A-1 Fuel

ABSTRACT A high-energy metal has been identified as a possible supplementary energy source for liquid fuel, which can be used to fuel volume-limited propulsive devices. However, the stability of metal particles in liquid fuel is a significant disadvantage, which can be overcome by suspending the particles in the gel fuel network. Boron’s (B) high energy density makes it a potential choice as fuel or energetic fuel additive for propulsion systems. However, the combustion of boron particles is challenging due to a native oxide layer on the boron particle surface that acts as an inhibitor. The influences of aluminum and titanium addition into the gel fuel containing boron particles have been investigated in the present study to understand whether Al or Ti positively enhances the ignition and combustion of boron particles. A droplet combustion study was conducted for gel fuel samples containing boron, boron-aluminum, and boron-titanium combinations. The key analyses include the feature of droplet diameter regression, the effect of Al/Ti additive on the ignition delay of boron particles through spectroscopic analysis, combustion of boron particles through chemiluminescence measurement of intermediate species of boron combustion (BO2) and flame imaging, and analysis of combustion residues. The obtained results and corresponding analyses suggest that the addition of Al particles improves the ignition of boron. In contrast, Ti particles significantly enhance the combustion of boron particles loaded in gel fuel.

Ignition and combustion characteristics of magnesium-based nanofluid fuel

Mg-based nanofluid fuel is a promising fuel for propulsion system in Mars exploration. In this study, Mg-based nanofluid fuel were prepared by one-step method, and the effect of Mg(magnesium) content, Mg size(68 μm,110 μm,175 μm), and oleic acid (OA) on droplet ignition and combustion under the atmosphere of 90 % CO2 and 10 % O2 were investigated. According to the TG-DSC results, 68 m Mg particles under CO2 had the highest exothermic efficiency of 4472 J/g. The combustion of Mg/OA/kerosene droplets consists of five stages: ignition, d2-law combustion, micro-explosion, vapor flame extinguishment, and agglomerate explosion. The ignition delay time of Mg (68 μm, 5 %)/kerosene is 0.045s, which is half that of kerosene (0.0890s). The agglomerates explode violently and emit a brilliant white light at the end of the Mg-based nanofluid fuel combustion. The explosive effect of Mg agglomerates diminishes as the Mg content increases. The rate of combustion decreases with increasing particle size. In the sample with added oleic acid, Mg (68 μm, 5 %)/OA/kerosene shows the best combustion rate of 0.6320 mm2/s. Finally, a numerical model for the combustion of Mg-based nanofluid fuel droplets is proposed. The predictions are within 2 % of the experimental results. The findings are expected to explore future in-situ utilization of CO2 on the Mars surface.

Pengaruh Penambahan Butanol Pada Bahan Bakar Solar Terhadap Karakteristik Pembakaran Single Droplet

Dependence on fossil fuels is one of the most serious threats to the global environment. In addition, petroleum reserves are also decreasing. Meanwhile, the level of oil consumption is always increasing to meet the demand for fuel. Economical and sustainable alternative energy solutions are essential to meet the growing global energy demand without compromising environmental sustainability. One type of alternative fuel that shows very promising potential is biofuel, especially biodiesel. Biodiesel has potential as a more environmentally friendly alternative to diesel fuel, but its low combustion rate and higher viscosity compared to conventional diesel fuel present technical challenges that need to be overcome. The different chemical properties of butanol from biodiesel allow it to have a positive impact on combustion characteristics, such as viscosity, flash point, heating value, and combustion rate. The combustion characteristics that will be studied in this research using single droplet combustion testing include droplet visualization to measure the dimensions of the flame, temperature during the combustion process recorded by a thermocouple, data logger, and video recording during the combustion process to obtain information regarding the ignition delay value. The test steps were repeated five times for each fuel variation and then averaged. In this study, the samples tested included pure diesel, diesel blend with 10% butanol, diesel blend with 20% butanol, diesel blend with 30% butanol, diesel blend with 40% butanol and diesel blend with 50% butanol. From this study, the visualization of the flame is obtained, where the combustion of pure diesel oil droplets has a higher and wider flame, while the flame of the butanol diesel mixture produces a flame whose maximum height is lower than pure diesel oil. The ignition delay time of pure diesel oil is greater than the ignition delay time of the diesel butanol blend. In addition, the maximum combustion temperature produced by each blend is different

SIMULATION OF LIQUID FUEL SPRAY FORMATION AND DISTRIBUTION IN A REACTING TURBULENT FLOW

The paper presentsthe computational experiments of the liquid fuels spray and its droplets distribution in a turbulent reacting flow. Primary and secondary atomization of two types of liquid fuel droplets (isooctane and dodecane) in the presence of combustion was described by the equations of continuity, momentum, internal energy, concentration of components of reacting substances and a two-parameter model for calculating turbulent flow. The study results of the spray, dispersion and combustion of droplets of hydrocarbon liquid fuels in a model combustion chamber when changing the injector injection angle were obtained. The injection angle values varied from 2 to 10 degrees. Based on the computational experiment temperature profiles and concentration characteristics of combustion products and gas in the combustion chamber at various times were obtained. Numerical calculations of the droplets’ Sauter mean diameter distributions have the same dispersion pattern for dodecane. This suggests that the accuracy and adequacy of developed complex model of the formation and distribution of spray in a reacting flow has been confirmed by its strong correlation and good agreement of the modeling results with experimental data from other researchers. This kind of modeling methods and the obtained computational experiments results from them are widely used not only in traditional thermal power engineering, but also in the study of technological processes in the new generation engines chambers, combustion of alternative types of fuels and optimization of their combustion.

Enhancing Droplet Combustion Dynamics in Trimethyl Borate-Based Blends: Exploring Energetic Phenomena

ABSTRACT Trimethyl borate (TMB) is an excellent alternative to alter the combustion of conventional fuels due to the combination of boron, stable methyl groups, and oxygen, which can improve the combustion behavior in many ways compared to alcohols and etheric hydrocarbon structures. In this research, the combustion and energetic phenomena trends of trimethyl borate blends was investigated on a droplet scale. The camera systems were used at the combustion characteristics look at how the size of the droplets, the structure of the flame, and the flame temperature changed over time. The additions of 20%, 40%, 60%, and 80% trimethyl borate fuel to gasoline were tested for their ability to burn. As the amount of TMB increased, high variations in droplet deformation and high breakups from the hemispheric geometry occurred. At this point, changes were observed in droplet shape change independent of mixing ratio. TMB droplet had the highest flame temperature of 600 K and the lowest extinction time of ~ 1270 ms. As the gasoline content of the droplets increased, the droplet flame temperature tended to decrease. Also, the shortest ignition delay time was observed for pure TMB and fuel droplets containing 40%, 60% and 80% TMB (~0.714 ms).