Atomizing Air Flow Rate Research Articles

Quality by design – Spray drying of ciprofloxacin-quercetin fixed-dose combination intended for inhalation

Spray drying is a well-suited technique for producing fixed-dose drug combinations. There has been a growing interest in utilizing spray drying to engineer carrier-free inhalable drug particles. The aim of this study was to understand and optimise the spray drying process of a ciprofloxacin-quercetin fixed dose combination intended for pulmonary administration. A 24-1 fractional factorial design and multivariate data analysis was used to identify important process parameters and investigate correlations with particle characteristics. The independent variables were solute concentration along with the processing parameters: solution flow rate, atomizing air flow rate and inlet temperature. The dependent variables included particle size distribution, yield and residual moisture content (RMC). Correlations between dependent and independent variables were further investigated via principal component analysis. Overall, solution flow rate, atomizing air flow rate and inlet temperature were found to affect the particle size D(v,50) and D(v,90) while the solute concentration and the atomizing air flow rate mainly affected the span. The inlet temperature was the most important parameter affecting the RMC and the yield. The formulation with optimized independent variables had a D(v,50) and span values of 2.42 µm and 1.81 with excellent process yield >70% and low RMC i.e. 3.4%. The optimized formulation was further investigated for its in vitro aerosolization performance using next generation impactor (NGI); it exhibited high emitted dose (ED > 80%) and fine particle fractions (FPF > 70%) for both drugs.

The effect of preheating of a viscous and non-Newtonian bioliquid on its internally mixed twin-fluid atomization

The present study investigates the influence of preheating temperature on the internally mixed twin-fluid atomization of a high-viscosity fluid, known as fast pyrolysis bio-oil (FPBO), motivated by the recent surge in the deployment of bioliquid sprays in sustainable energy systems. The bulk and interfacial rheological properties of FPBO were determined at three different temperatures, up to 80 °C, and used to elucidate its resulting flow structures and spray characteristics at two liquid flow rates, 30 and 40 mL/min, and five atomizing airflow rates between 6.5 and 16 L/min and between 8.5 and 21 L/min, respectively. The preheated FPBO exhibited a shear-thinning behaviour characterized by a power-law model. An internal impingement of gas-liquid flows was used to generate small droplets at the immediate vicinity of the nozzle exit. However, the near-field flow visualizations of FPBO sprays revealed the coexistence of long undulating ligaments adhered to the nozzle inner wall along with the presence of dispersed droplets connected by thin threads in regions far from the nozzle. The FPBO preheated at a higher temperature exhibited a narrower size distribution and a smaller mean diameter of spray droplets. A general model was developed through energy balance considerations to predict the mean diameter of spray droplets for both Newtonian and non-Newtonian fluids within ±10% of error.

Interrelationships Between Coating Uniformity and Efficiency in Pan Coating Processes.

The relationships between coating uniformity and efficiency were explored for tablet coating processes in pan coaters. The factors affecting the size of the spray zone were modeled using one-dimensional deposition analysis of spray droplets. This model was incorporated into the analytical model developed for coating uniformity by Choi et al. (AAPS PharmSciTech 22(7), 2021) that farther elucidated the effects of tablet shape and bed porosity. The results were compared with literature data on coating efficiency. The variables examined included tablet shape and size, coating time, pan speed, atomizing and pattern air flow rates, bed porosity, spray rate, batch size, coating solution concentration, spray gun-to-bed distance, and pan diameter. It is shown that, except for pan diameter and atomizing air flow rate, variables that improve coating efficiency adversely affected coating uniformity and vice versa. Implications of these relationships are discussed to improve formulation, process, and equipment designs.

Identification of Stability Constraints in the Particle Engineering of an Inhaled Monoclonal Antibody Dried Powder

Monoclonal antibody (mAb) based therapies may provide a valuable new treatment modality for acute and chronic lung diseases, including asthma, respiratory infections, and lung cancer. Currently mAbs are delivered via systemic administration routes, but direct delivery to the lungs via the inhaled route could provide higher concentrations at the site of disease and reduced off-target effects. Though lyophilized mAbs may be reconstituted and delivered to the lungs using nebulizers, dry powder inhalers provide a more patient-friendly delivery method based upon their fast administration time and portability. However, particle engineering processes required to prepare respirable dried powders for DPI delivery involve multiple potential stressors for mAbs, which have not been fully explored. In this study, a systematic examination of various aspects of the particle engineering process (atomization, freezing, drying, and storage) was performed to further understand their impact on mAb structure and aggregation. Using anti-streptavidin IgG1 as a model mAb, atomization settings were optimized using a design of experiments approach to elucidate the relationship between feed flow rate, formulation solid content, and atomization airflow rate and protein structural changes and aggregation. The optimized atomization conditions were then applied to spray drying and spray freezing drying particle engineering processes to determine the effects of freezing and drying on IgG1 stability and aerosol performance of the powders. IgG1 was found to be particularly susceptible to degradation induced by the expansive air-ice interface generated by spray freeze drying and this process also produced powders that exhibited decreased storage stability. This study further delineates the design space for manufacturing of respirable biologic therapies and is intended to serve as a roadmap for future development work.

Effect of spray drying process parameters on Uncaria tomentosa (Willd. ex Schult.) DC. dried extracts

Uncaria tomentosa (Willd. ex Schult.) DC. (Cat's claw) is a plant member of the Rubiaceae family, from the Amazon region, and used in traditional medicine as raw material for phytomedicines indicated for arthritis and osteoarthritis. This study aimed to evaluate the spray drying process parameters on the properties of different extracts obtained from Uncaria tomentosa. A reduced 24-1 multifactorial design was applied to evaluate the importance of the equipment variables (pump speed, spray nozzle diameter, air inlet temperature, and atomization airflow rate) in the process. Maltodextrin and acacia gum were used as carriers in a 1:1 (m/m) ratio, considering the solid residue content of the liquid plant extract. Process yield, moisture, and hygroscopicity were evaluated as dependent variables. Higher atomization airflow rate led to higher process yield for powdered dried extracts with maltodextrin. Higher temperature led to lower moisture contents regarding powdered dried extracts with acacia gum. No variable, for any carrier, was considered significant for hygroscopicity. The best spray drying configuration for the desired characteristics (i.e. lower hygroscopicity and moisture) used the larger spray nozzle with a diameter of 1.2 mm and the higher temperature of 150 °C, with both carriers.

Breakup mechanisms in air-assisted atomization of highly viscous pyrolysis oils

Air-assisted atomization of the sprays produced by injecting different types of highly viscous pyrolysis oils are studied. Different breakup and atomization regimes are characterized using the long distance microscopic imaging technique. The high resolution imaging reveals detailed underlying two-phase interactions in pyrolysis oil injection that are found unlike other conventional liquid fuels. Several cases of droplet size characterization are carried out using the Malvern’s laser diffraction measurements under variable liquid flow rates, atomizing air flow rates and oil preheating temperatures. The time-averaged and high resolution instantaneous images reveal that the highly viscous nature of pyrolysis oils prevent the instability mechanisms from efficiently atomizing the liquid. The present broad set of measured data suggest that the atomization quality of pyrolysis oils can be optimized by applying a combination of liquid preheating and air-assisted atomization. The flow visualizations reveal the transition from ligament-dominated two-phase flow field into fully atomized sprays when proper oil preheating temperatures and sufficient atomizing air flow rates are provided. Visualized observations are quantitatively verified using the droplet size distribution measurements as well as the Sauter mean diameter (SMD) values for several measurement conditions.

Development of a Carrier-Free Dry Powder Ofloxacin Formulation With Enhanced Aerosolization Properties

Tuberculosis (TB) is a serious infectious disease that affects more than new 10 million patients each year. Many of these cases are resistant to first-line drugs so second-line ones, like fluoroquinolones, need to be incorporated into the therapeutic. Ofloxacin (OF) is a fluoroquinolone which demonstrates high antibiotic activity against the bacteria that causes TB (M. tuberculosis). In this work, ionic complexes, composed by hyaluronic acid (HA) and OF, with different neutralization degrees, were prepared and processed by spray drying (SD) to obtain powders for inhalatory administration. Combining a formulation with high neutralization degree, high SD atomization air flowrate and the use of a high-performance collection cyclone, very good process yields were obtained. Carrier-free formulations with a loading of 0.39–0.46 gOF/gpowder showed excellent emitted, fine particle, and respirable fractions for capsule loadings of 25 and 100 mg. The ionic complexes demonstrated higher mucoadhesion than pure OF and HA. The best formulation did not affect CALU-3 cell viability up to a dose 6.5 times higher than the MIC90 reported to treat multi-drug resistant TB.

Pulmonary delivery of Nanocomposite Microparticles (NCMPs) incorporating miR-146a for treatment of COPD.

The treatment and management of COPD by inhalation to the lungs has emerged as an attractive alternative route to oral dosing due to higher concentrations of the drug being administered to site of action. In this study, Nanocomposite Microparticles (NCMPs) of microRNA (miR-146a) containing PGA-co-PDL nanoparticles (NPs) for dry powder inhalation were formulated using l-leucine and mannitol. The spray-drying (Buchi B290) process was optimised and used to incorporate NPs into NCMPs using mix of l-leucine and mannitol excipients in different ratios (F1; 100:0% w/w, F2; 75:25% w/w, F3; 50:50% w/w, F4; 25:75% w/w, F5; 0:100% w/w) to investigate yield %, moisture content, aerosolisation performance and miR-146a biological activity. The optimum condition was performed at feed rate 0.5 ml/min, aspirator rate 28 m3/h, atomizing air flow rate 480 L/h, and inlet drying temperature 70 °C which produced highest yield percentage and closest recovered NPs size to original prior spray-drying. The optimum formulation (F4) had a high yield (86.0 ± 15.01%), recovered NPs size after spray-drying 409.7 ± 10.05 nm (initial NPs size 244.8 ± 4.40 nm) and low moisture content (2.02 ± 0.03%). The aerosolisation performance showed high Fine Particle Fraction (FPF) 51.33 ± 2.9%, Emitted Dose (ED) of 81.81 ± 3.0%, and the mass median aerodynamic diameter (MMAD) was ≤5 µm suggesting a deposition in the respirable region of the lungs. The biological activity of miR-146a was preserved after spray-drying process and miR-146a loaded NCMPs produced target genes IRAK1 and TRAF6 silencing. These results indicate the optimal process parameters for the preparation of NCMPs of miR-146a-containing PGA-co-PDL NPs suitable for inhalation in the treatment and management of COPD.

회전 분무장치에서 작동조건의 변화가 미립화 성능에 미치는 영향

In order to apply rotary atomizer to agricultural spraying system, the motor direct coupled rotary atomizer was proposed. The effect of operating conditions such as atomizing air flow rate, working fluid flow rate, and rotation speed of spinning cup on the atomization performance was investigated for the proposed direct coupled rotary atomizer. The motor speed was controlled in the range of 6,000 to 12,000 rpm using an alternating current transformer, and the atomizing air was supplied by the compressor. In this study, LDPA was used to analyze the spray characteristics of the rotary atomizer. The representative particle diameters of D10, SMD, MMD, D90, and DMax tended to decrease as the atomizing air flow rate and the motor speed increased, but increased as the working fluid flow rate increased. Also, SMD was found to be influenced by order of atomizing air flow rate> motor speed> working fluid flow rate, and DMax was influenced by order of operating fluid supply> motor speed> atomizing air flow rate.

DRY POWDER FORMULATION FROM PHYSALIS PERUVIANA L. FRUITS EXTRACT WITH ANTIDIABETIC ACTIVITY FORMULATED VIA CO-SPRAY DRYING

Objective: To establish the drying conditions of an extract of fruits of Physalis peruviana using spray drying (SD) technique by applying a statistical experimental design (SED), to obtain powders for direct compression, retaining the antidiabetic activity.
 Methods: A 2[6-2] fractional factorial SED was used to get a suitable SD operating conditions to produce powder extract of P. peruviana with high process yield, acceptable moisture content, good flowability, low hygroscopicity and satisfactory morphological and particle size. Operating variables studied were air inlet temperature, atomization air flow rate, feed-rate pump, aspiration rate, extract concentration and coadjuvant proportion. P. peruviana powder obtained under the operating conditions selected was evaluated by X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC) and by in vitro α-amylase inhibition assay, to prove that the antidiabetic activity was remained after the SD.
 Results: Injection temperature (120 °C), atomization air flow rate (600 l/h), pump setting (5 %), aspirator setting (100 %), extract concentration (7.5 % p/p) and extract: coadjuvant ratio (1:0.75), were the operational conditions selected. Dry extract showed an amorphous state by XRPD and a probable protective effect of coadjutant on the extract, characterized by DSC and the antidiabetic in vitro assay. Antidiabetic activity of the extract remained after its transformation to a solid state by SD in the chosen conditions.
 Conclusion: The results suggest that coprocessed extract could be used for the production of compressed solids or employed as an intermediate herbal product for the treatment of diabetes.

Computational Fluid Dynamics-Discrete Element Method Modeling of an Industrial-Scale Wurster Coater

Large-scale fluid bed coating operations using Wurster coaters are common in the pharmaceutical industry. Experimental measurements of the coating thickness are usually analyzed for just few particles. To better predict the coating uniformity of the entire batch, computational techniques can be applied for process understanding of the key process parameters that influence the quality attributes. Recent advances in computational hardware, such as graphics processing unit, have enabled simulations of large industrial-scale systems. In this work, we perform coupled computational fluid dynamics-discrete element method simulations of a large-scale coater that model the actual particle sizes. The influence of process parameters, inlet air flow rate, atomizing air flow rate, bead size distribution, and Wurster gap height is studied. The focus of this study is to characterize the flow inside the coater; eventually, this information will be used to predict the coating uniformity of the beads. We report the residence time distribution of the beads inside the Wurster column, that is, the active coating zone, which serves as a proxy for the amount of coating received by the beads per pass. The residence time provides qualitative and quantitative measurements of the particle-coating uniformity. We find that inlet air flow rate has the largest impact on the flow behavior and, hence, the coating uniformity.

Optimization of Ciprofloxacin Hydrochloride Spray-Dried Microparticles for Pulmonary Delivery Using Design of Experiments.

Ciprofloxacin is a broad-spectrum antibiotic for treatment of pulmonary diseases such as chronic obstructive pulmonary disease and cystic fibrosis. The purpose of this work was to rationally study the spray drying of ciprofloxacin in order to identify the formulation and operating conditions that lead to a product with aerodynamic properties appropriate for dry powder inhalation. A 24 - 1 fractional factorial design was applied to investigate the effect of selected variables (i.e., ciprofloxacin hydrochloride (CIP) concentration, drying air inlet temperature, feed flow rate, and atomization air flow rate) on several product and process parameters (i.e., particle size, aerodynamic diameter, moisture content, densities, porosity, powder flowability, outlet temperature, and process yield) and to determine an optimal condition. The studied factors had a significant effect on the evaluated responses (higher p value 0.0017), except for the moisture content (p value > 0.05). The optimal formulation and operating conditions were as follows: CIP concentration 10mg/mL, drying air inlet temperature 110°C, feed volumetric flow rate 3.0mL/min, and atomization air volumetric flow rate 473L/h. The product obtained under this set had a particle size that guarantees access to the lung, a moisture content acceptable for dry powder inhalation, fair flowability, and high process yield. The PDRX and SEM analysis of the optimal product showed a crystalline structure and round and dimpled particles. Moreover, the product was obtained by a simple and green spray drying method.

Carrier free indomethacin microparticles for dry powder inhalation

The present studies were designed to evaluate inhalatory microparticles carrying indomethacin (IN) for potential local (specific and non-specific bronchial inflammatory asthma responses) and systemic treatments (joint inflammation, rheumatoid arthritis and osteoarthritis pain) by optimizing microparticle properties, characterizing their lung deposition, drug release, evaluating cytotoxicity and also pharmacological effect in vitro. The acidic groups of IN were complexed with the cationic groups of the polyelectrolyte polylysine in order to increase the drug water compatibility. The polylysine/indomethacin ratio was fixed and the pH was adjusted in different formulations. Microparticles were obtained by spray drying using a relatively high atomization air flowrate (742 L/min) and a high-performance cyclone in order to optimize the production of microparticles with adequate attributes for inhalatory delivery. The produced microparticles exhibited high process yield and IN loading, volumetric mean diameters smaller than 5 μm and narrow particle size distributions. According to demonstrated aerosolization performance, the powders were suitable for inhalatory indomethacin local and systemic treatments. Emitted fraction was higher than 90%, the MMAD was around 3 μm and the GSD lower than 3. The respirable fraction for particles with aerodynamic diameters smaller than 5 μm was around 29% while for particles with aerodynamic diameters smaller than 3 μm the value was around 17%. The addition of lactose as carrier worsened the aerodynamic performance of the microparticles. The developed powdered systems got wet and dissolved quickly and presented higher release rates respect to pure IN in simulated lung physiological conditions. Furthermore, the assays performed in RAW 264.7 cell line showed that the microparticles exhibited the same anti-inflammatory capability as the pure drug. The developed particles did not affect the RAW 264.7 cell viability. In conclusion, a promising powder formulation for DPIs has been developed to treat, locally and systemically, inflammatory diseases.

The effect of binder concentration in fluidized-bed granulation: Transition between wet and melt granulation

According to the binder nature, fluidized-bed granulation (FBG) is usually classified as wet or melt granulation. In particular, the industrial urea granulation performed in fluidized beds, is often called “melt granulation” because a highly concentrated urea solution is used as binder (between 95–97wt%) (Cotabarren et al., 2012). However, plant disturbances can cause changes in binder urea concentration and thus granulation can shift from melt to wet granulation and vice versa.In a previous investigation, the granulation system urea (seeds)–urea (binder) was extensively studied in a pilot-scale batch fluidized-bed granulator (Veliz Moraga et al., 2015). Besides, the effect of seed size, bed temperature, binder flowrate and fluidization and atomization air flowrates on process variables as well as on product properties were studied. The aim of this work is to analyze the effect of the binder urea concentration on the urea granulation performance and product properties. This concentration was varied from 87.5wt% to 98wt%, while the fluidization air velocity, urea melt flowrate, bed temperature set-point and atomization air flowrate were kept constant. The product properties (percentage of agglomerates and coated particles, crushing strength and moisture content) and granulation efficiency are discussed in terms of the transition from wet to melt granulation. The critical urea content was experimentally found; indeed, urea concentrations lower than the critical one dramatically affect the product quality. Finally, the criterion proposed by Villa et al. (2016) for predicting agglomerates formation is used to determine the minimum allowable binder urea concentration. The prediction is consistent with the trends experimentally observed, indicating the good capacity of the criterion to identify the boundary for agglomeration occurrence.

Using response surface methodology to optimize the operating parameters in a top-spray fluidized bed coating system

The fluidized bed coating system is a conventional process of particles coating in various industries. In this work, an experimental investigation was conducted using Response Surface Methodology (RSM) to optimize the coating mass of particles in a top-spray fluidized bed coating. The design of experiments (DOEs) is a useful tool for controlling and optimization of products in industry. Thus, DOE was conducted using MINITAB software, version 16. This process used a sodium silicate solution for coating the sodium percarbonate particles. The effect of the fluidization air flow rate, atomization air flow rate and liquid flow rate on the coating mass in the top-spray fluidized bed coating was investigated. The experimental results indicated that the coating mass of particles is directly proportional to the liquid flow rate of the coating solution and inversely proportional to the air flow rate. It was demonstrated that the flow rate of the coating solution had the greatest influence on the coating efficiency.

Process analysis and global optimization for the microencapsulation of phytosterols by spray drying

The response surface methodology (RSM) was used to optimize the microencapsulation of phytosterols by spray drying. The independent variables were drying air inlet temperature, atomization air flowrate, feed flowrate, phytosterols and total solids contents and the mass ratio between wall materials (Arabic gum and maltodextrin). The analyzed responses were process yield, mean volume particle size of product microparticles, phytosterols retention and encapsulation efficiency. Statistical analysis revealed that the selected independent variables, especially the atomization air flowrate and feed phytosterols content, significantly affect the studied responses. Taking into account the observed results and the analysis of variance, all the responses were successfully adjusted to second order models with interactions, showing good R2 values and correlating the experimental data properly. The product microparticles were also obtained by using the predicted optimal operating and formulation variables to test the validity of the quadratic models. The experimental responses were found to be in agreement with the predicted values and were within the acceptable limits, indicating the suitability of the model for predicting key parameters related to process performance and product quality. The recommended optimal formulation and operating conditions for microencapsulation of phytosterols by spray drying are: drying air temperature of 160°C, atomization air and feed flowrates of 498L/h and 2.5mL/min (equivalent to 42mm of height of rotameter and 7% pump scale, respectively), phytosterols and total solids concentrations of 2 and 15g/100mL, respectively, and mass ratio between Arabic gum and maltodextrin of 2.06. The process yield, encapsulation efficiency and phytosterols retention obtained under the optimum conditions were 84, 72 and 76%, respectively. The product microparticles had a mean volume particle size of about 5μm, well below the more restricted upper size limit of 25μm required to guarantee the incorporation of PS into the intestine micellar phase.

Spray atomization of bio-oil/ethanol blends with externally mixed nozzles

Experiments were conducted to investigate the properties of sprays of pyrolysis oil (bio-oil) blends with ethanol using an air assisted atomization nozzle operated without combustion. This was done in order to explore the potential for pyrolysis oil combustion in industrial and residential furnaces. The liquid samples investigated were bio-oil blends with ethanol (EtOH), neat ethanol and diesel. The bio-oil:EtOH blends were prepared in concentrations of 20:80 and 40:60vol%. Twin-fluid externally mixed nozzles SU2, SU4, and SU5 with liquid orifice areas of 0.40, 1.82 and 5.07mm2, respectively, were used in the spray experiments. The liquid and atomizing air flow rates as well as temperature were controlled to maintain constant liquid flow rates (cc/s) equivalent to 30 and 50kW energy input. Images of atomized spray droplets were measured to determine their size and velocity. Results show that it is possible to spray bio-oil/ethanol mixtures containing up to 40% bio-oil that has a low water content (12.60%). High viscosity and a tendency to coagulate were the main drawbacks; however, the 20:80 bio-oil:EtOH blend and neat ethanol in all three nozzles exhibited spray characteristics similar to that of diesel over atomization air flow rates of 15–30SLPM.

Experiments and simulations of NOx formation in the combustion of hydroxylated fuels

This work investigates the influence of molecular structure in hydroxylated fuels (i.e. fuels with one or more hydroxyl groups), such as alcohols and polyols, on NOx formation. The fuels studied are three lower alcohols (methanol, ethanol, and n-propanol), two diols (1,2-ethanediol and 1,2-propanediol), and one triol (1,2,3-propanetriol); all of which are liquids at room temperature and span a wide range of thermophysical properties. Experimental stack emissions measurements of NO/NO2, CO, and CO2 and flame temperature profiles utilizing a rake of thermocouples were obtained in globally lean, swirling, liquid atomized spray flames inside a refractory-lined combustion chamber as a function of the atomizing air flow rate and swirl number. These experiments show significantly lower NOx formation with increasing fuel oxygen content despite similarities in the flame temperature profiles. By controlling the temperature profiles, the contribution to NOx formation through the thermal mechanism were matched, and variations in the contribution through non-thermal NOx formation pathways are observed. Simulations in a perfectly stirred reactor, at conditions representative of those measured within the combustion region, were conducted as a function of temperature and equivalence ratio. The simulations employed a detailed high temperature chemical kinetic model for NOx formation from hydroxylated fuels developed based on recent alcohol combustion models and extended to include polyol combustion chemistry. These simulations provide a qualitative comparison to the range of temperatures and equivalence ratios observed in complex swirling flows and provide insight into the influence of variations in the fuel decomposition pathways on NOx formation. It is observed that increasing the fuel bound oxygen concentration ultimately reduces the formation of NOx by increasing the proportion of fuel oxidized through formaldehyde, as opposed to acetylene or acetaldehyde. The subsequent oxidation of formaldehyde contributes little to the formation of hydrocarbon (HC) radicals. Ultimately, by reducing the contributions to the HC radical pool, NOx can be effectively reduced in these fuels through suppression of non-thermal NOx formation pathways.

EFFECT OF ATOMIZING AIR FLOW ON SPRAY ATOMIZATION OF AN INTERNAL-MIX TWIN-FLUID ATOMIZER

The effect of the atomization air flow rate on the spray characteristics of a swirling twin-fluid atomizer operating on Diesel fuel is investigated. The mean droplet axial velocity and size distributions were simultaneously measured using a phase Doppler anemometer (PDA). The mean droplet diameter is found to increase with radial distance from the spray centreline, while its axial velocity decreases from a peak at the centreline. Increasing the atomizing air-liquid fuel mass ratio (ALR) reduces the fuel droplet size due to the increased shear and increases the spray penetration length as a result of increased momentum. Comparison of the drop size-ALR relations to previous independently developed correlations shows good agreement. A comparison was made between the observable boundaries obtained with Mie scattering and the droplet number density. It is found that the Mie images correspond to 95%-99% edge of the cumulative droplet mass distribution through the spray.

Combustion of straight glycerol with/without methane using a fuel-flexible, low-emissions burner

In this study, we present a fuel-flexible dual-fuel combustor to simultaneously burn methane and/or straight glycerol without preheating either glycerol or air by utilizing a novel flow-blurring (FB) liquid fuel injector. Product gas temperature, NOX and CO emissions at multiple locations inside the combustor are measured to quantitatively assess the flame structure, related to liquid atomization, droplet evaporation, and fuel–air mixing in the near field. For fixed total heat release rate, the impact of fuel mix on combustion performance is investigated by varying the methane gas and glycerol flow rates. For the same fuel mix, air to liquid mass ratio effect is evaluated by varying the atomizing air flow rate. Pure glycerol flame is also investigated to demonstrate the fuel flexibility and ease of switching between gas and liquid fuels in the present system. Results show that the methane combustion can assist glycerol vaporization to results in its rapid oxidation. In spite of the differences in the flame structure, profiles of product gas temperature and emissions at the combustor exit reveal that complete and mainly lean premixed combustion with low emissions is achieved for all of the test cases indicating excellent fuel flexibility of the present combustor using the FB injector.