Spray Development Research Articles

Experimental investigation of the combined impact of backpressure with the pintle dynamic on the hydrogen spray exiting a medium pressure DI outward-opening injector

A vast scientific literature has shed light on hydrogen as a promising vector for carbon-free mobility. Within this scope, over the last few decades several efforts were directed towards the characterization of hydrogen spray, given its significant influence on the combustion efficiency. Nevertheless, several aspects underlying the hydrogen spray development are still far from being fully understood. This framework prompted the authors to undertake a robust experimental campaign, performing hydrogen injections over a wide range of injection settings. In this study, the schlieren method was utilized to capture the image of jets performed at injection pressure of 3.6 MPa and exiting an outward-opening injector. Afterwards, the spray images were processed by means of an in-home developed Matlab script. In order to assess the spray characteristics, such as the penetration length, area and volume, the analysis of the results was focused on the combined impact of backpressure, ranging from 0.12 to 1.5 MPa, with current profile determining the pintle dynamic. Besides, a qualitative analysis of the injection setting impact on the shock wave position was carried out. In the light of emerged findings, the research serves as a further baseline for forthcoming research activities dealing with hydrogen spray.

Design, development, and evaluation of spray dried flurbiprofen loaded sustained release polymeric nanoparticles using QBD approach to manage inflammation

Spray-dried Flurbiprofen (FLB) loaded polymeric nanoformulation using Eudragit L 100 and Ethylcellulose. They were optimized and evaluated. This study determined drug release (%) and encapsulation efficiency (%) by developing a nanoparticulate system using the design of experiment (DoE) approach. FLB is slightly soluble in water; it dissolves slowly and has a low oral bioavailability. FLB-loaded polymeric nanoparticles were produced by solvent evaporation and Spray drying technology. In this research, nanoparticle formulation was prepared by screening and optimization by approaching two different statistical methods (Plackett-Burman and Central composite Designs). The polymeric nanoparticles were evaluated for various characteristics, including drug release, percentage of encapsulation efficiency, X-ray diffraction (X-RD), surface morphology, and Fourier transform infrared (FTIR) spectroscopy. Based on the X-RD analysis, it was found that the drug was successfully incorporated into the polymeric nanoparticles. As a result of nanoparticles containing FLB, % Drug release values were found to be nearly 85-90% increased while % EE was observed in the range of 79-89%. An excellent sustained release, i.e., 14 h, is possible by combining Ethylcellulose (EC) and Eudragit L 100 (ED-100) polymers. The results are beneficial in identifying the ideal formulation parameters for effective encapsulation. Abbreviations: FLB: Flurbiprofen; API: Active pharmaceutical ingredient; DR: Drug release; EE: Encapsulation efficiency; DoE: Design of experiment; X-RD: X-ray diffraction; FTIR: Fourier transform infrared spectroscopy.; PVA: Polyvinyl alcohol; EC: Ethylcellulose; EUGD: Eudragit L 100; NPs: Nanoparticles; PBD: Placket- Burman Design; CCD: Central Composite Design; CMV: Critical method variables; GIT: Gastrointestinal track; SLN: Solid lipid nanoparticles; NLC: Nanostructured lipid carriers; NSAID: Nonsteroidal anti-inflammatory drug; BCS: Biopharmaceutical classification system; PS: Particle size; PDI: Polydispersity Index; ZP: Zeta potential; FE-SEM: Field emission scanning electron microscopy; 2D: 2 Dimensional; 3D: 3 Dimensional

Simulation Analysis of the Effect of Slit/Slot Pintle Geometry on Atomization of Bipropellant Engine

In order to optimize the slit/slot geometry design of a bipropellant pintle injector, the impinging spray development of a pintle injector was numerically investigated. The VOF (volume of fluid) and LES (large eddy simulation) methods were employed for an analysis to capture the gas–liquid interface by means of the AMR (adaptive mesh refinement) method. In those simulation cases, different flowrates, slot numbers, pintle diameters, slot thicknesses and slot shapes were compared for an analysis. In a comparison of visualization and quantification, a high flowrate and large pintle diameter were shown to be more positive features for improving the atomization quality and mixing effect. As for the slot parameters and shape, the spray development was mainly determined by the flow proportion between the slit jet and slot jet. The simulation results indicated that dominant slot jets cause a more dispersed spatial distribution, which is more conducive to the subsequent improvement of combustion efficiency in a limited space. However, an excessive increase in the number of slot jets can weaken the overall atomization quality and mixing effect, so it is suggested to ensure a balance for geometry design optimization.

Unconventional gasoline spray injection events: Compared evolution of experimental data and numerical simulations

The current homologation standards in the automotive field impose the manufacturers to develop very efficient and clean engines. Low-Temperature Combustion engines have the potential to simultaneously reduce all the pollutants released while maintaining high efficiency. Among them, in Gasoline Compression Ignition (GCI) combustion technology, multiple injections allow to generate a tailored stratified charge which can auto ignite limiting the rough Pressure Rise Rate (PRR) and heat release rate typical of GCI. Therefore, the three-dimensional local distribution of the mixture becomes the key-point which the engine performance depends on. Due to emphasis on the multi-dimensional and local nature of the mixture formation phenomenon, three-dimensional CFD simulations are a promising and attractive method aiming at the design of the injection event features (timing, pattern, etc.). This paper deals with both experimental and CFD campaign on the evolution of a gasoline spray at ultra high-pressure multiple injection as well as high backpressure, typical of Gasoline Compression Ignition engines. The experimental tests have been conducted on a reference Diesel Common-Rail injector which shots in a constant-volume chamber. The hydraulic behaviour of the injector was characterized by means of the Bosch Tube principle whilst the Mie-scattering technique was used to capture the spray images. The numerical methodology is required to predict the Liquid Length Penetration and the jet morphology features (shape, area). Both experiments and simulations were conducted at different values of injection pressure (350, 500, 700 bar), back pressure (1–8 bar), energizing time (350, 600 µs), according to the operations of a real reference GCI test engine. Furthermore, a dedicated sub-model which takes into consideration the effect of the spray dynamics during the injection transient opening stage has been validated. The importance of this approach when dealing with short energizing time (e.g. 350 μs) is shown.Comparing both the experimental and numerical results, the model has proven to efficiently reproduce the spray penetration and morphology features, also under the hypothesis of injector ballistic phase operations, whose determination is crucial in the early development and sustainability of such combustion concept.

Formulation & Development of Transdermal Spray of Turmeric Lemongrass as Antifungal

The study aims to find out the effectiveness of the combination of citral and curcumin as antifungal compounds. Lemongrass (Cymbopogon citratus) is a valuable family of grass known due to its flavoring, medicinal, and fragrance application. Haldi (Turmeric) scientifically known as Curcuma longa belongs to familthey Zingiberaceae. Its polyphenolic compound curcumin has been showing a variety of antifungal investigations due to extensive traditional uses and very low side effects.Turmeric has beenutilized in traditional medicine for various diseases counting diabetes, hepatitis, hemorrhoids, hysteria, indigestion, skin disease, inflammation, anorexia, hepatic disorders, cough, and sinusitis. In this formulation substudy combination of two bioactive oils is considered to form an effective antifungal spray preparation. The spray preparation is helpful to achieve fast absorption of the drugs through the transdermal way of drug administration. The effectiveness and activity rate of spray preparation is more beneficial. Lemongrass oil and curcumin are dissolved in ethanol to form a stable, safe, and effective spray formulation.

LES of a turbulent lifted methanol spray flame using a novel spray flamelet/progress variable model

Turbulent spray flames are complex combustion configurations and are difficult to be accurately simulated. In this paper, we focus on further development and validation of the two-phase spray flamelet/progress variable (TSFPV) model, which is first proposed in our previous work and shows sound performance because it is able to consider the effect of droplet evaporation on the flamelet structure. A spray evaporation source term (SEST) model is improved in the present work to model the evaporation sources and is applied to the calculation of one-dimensional laminar counterflow flames to generate the spray flamelet library. The SEST model is validated on the configuration of two-dimensional counterflow spray flames, and the a priori and a posteriori results show good agreement with the solutions using the Lagrangian particle tracking (LPT) method. The effect of pre-vaporized fuel vapor is further considered in the spray flamelet library, in which both the spray and gaseous flame regimes are covered. The TSFPV model is well validated on the configuration of the laminar mixing layer by comparing the a priori and a posteriori results with detailed chemistry (DC) solutions. Large Eddy Simulation (LES) of the Sydney turbulent lifted methanol spray flame Mt2A is conducted using the TSFPV model. The flame lift-off is correctly captured and the final predicted lift-off height is very close to the experimental value. The predicted mean droplet velocities show good agreement with experimental measurements, and the rms velocities agree well with the experimental data at downstream locations with a late jet breakup. The droplet size increases along the downstream direction and this trend is well reproduced in the current simulation, though the local peak value of droplet size near the upstream shear layer is not well captured. The central jet temperature at upstream locations is also well predicted by the TSFPV model. Overall, the results show good agreement with the experimental measurements, which illustrates the potential of the TSFPV model for spray combustion modeling.

Computational study of the ECN spray C via one-way coupling of internal nozzle flow and ensuing spray

In this study, computational fluid dynamics simulations of the Engine Combustion Network Spray C injector were performed to investigate the effect of the internal nozzle flow on the development of the ensuing spray in automotive fuel injectors. A set of simulation best practices was first developed to achieve an accurate representation of the internal nozzle flow. Detailed, spatiotemporally defined information was extracted at the injector's orifice exit and stored in maps that were subsequently employed to initialize a Lagrangian spray by means of a static, one-way coupling (OWC) approach. To highlight the impact of the in-nozzle flow on the spray, the OWC approach was compared with the conventional rate-of-injection (ROI) approach, for which the spray parcels are commonly initialized using a blob injection model. The results indicated that, using the ROI approach, considerable evaporation was observed within the plume in the near-nozzle region. On the other hand, the OWC approach showed evidence of evaporation farther downstream and at the plume periphery. The different behavior observed with the two approaches was mostly due to substantial differences in fuel mass distribution. The liquid fuel concentration predicted by the OWC approach matched well with X-ray tomography measurements of projected fuel mass per unit volume, in terms of both magnitude and distribution. In contrast, an unphysical distribution of fuel mass characterized by an extremely low liquid concentration was predicted by the ROI approach. In the far-field, the effect of the in-nozzle flow was found to be weaker as the spray penetrated and interacted with the ambient gas. In this region, the OWC and ROI approaches provided similar predictions of vapor penetration, spray morphology, and mixing-related characteristics.

Ecophysiological Responses of Rice (Oryza sativa L.) to Drought and High Temperature

Global rice crop production is being threatened by a frequent rise in high temperatures and drought. Drought and heat stresses adversely affect the morphological, physiological, and biochemical characteristics of rice, resulting in reduced crop productivity. Heat and drought stresses entail physiological changes in rice plants, such as stomata closure, reduced photosynthesis, loss of turgor adjustment, and reduction in crop productivity. These stresses also cause metabolic changes by increasing the activities of antioxidative enzymes, phytohormones, abscisic acid, reactive oxygen species, and reactive stress metabolites. Among the different growth stages of rice, the reproductive stage is the most sensitive stage to high temperature and drought, resulting in low seed setting and grain yield. Genetic improvement and development of drought and heat-stress-tolerant rice varieties increase seed setting and enhance yield production even under stress conditions. Because of the multigenic nature of traits, the development of drought and high-temperature-tolerant varieties through genetic improvement is the best approach. Here, we summarized the effects of heat and drought stresses on the physiological traits of rice. We focused on different approaches to managing high-temperature and drought stresses, such as an adjustment in cultural practices, genetic improvement through molecular breeding, and the development of transgenics and chemical spray from an agricultural practice perspective.

A multi-step machine learning approach for accelerating QbD-based process development of protein spray drying

This study proposes a new material-efficient multi-step machine learning (ML) approach for the development of a design space (DS) for spray drying proteins. Typically, a DS is developed by performing a design of experiments (DoE) with the spray dryer and the protein of interest, followed by deriving the DoE models via multi-variate regression. This approach was followed as a benchmark to the ML approach. The more complex the process and required accuracy of the final model is, the more experiments are necessary. However, most biologics are expensive and thus experiments should be kept to a minimum. Therefore, the suitability of using a surrogate material and ML for the development of a DS was investigated. To this end, a DoE was performed with the surrogate and the data used for training the ML approach. The ML and DoE model predictions were compared to measurements of three protein-based validation runs. The suitability of using lactose as surrogate was investigated and advantages of the proposed approach were demonstrated. Limitations were identified at protein concentrations >35 mg/ml and particle sizes of x50>6 µm. Within the investigated DS protein secondary structure was preserved, and most process settings, resulted in yields >75% and residual moisture <10 wt%.

Development of spray dried functional milk protein concentrate containing whey proteins as fibrils

Fibrillated milk protein concentrate (MPC) was produced by selective fibrillation of whey proteins and spray dried to extend shelf life. The fibrillated MPC powder was characterized for whey protein fibrils and functionality. Observations from Thioflavin T fluorescence value, transmission electron microscopy, gel electrophoresis, rheology, and turbidity confirmed the presence of fibrils in fibrillated MPC. However, fibrils in reconstituted fibrillated MPC were thinner compared with the fibrils before spray drying. Aggregation of fibrils was also seen in fibrillated MPC dispersions. Further, rheological analysis of reconstituted fibrillated MPC at different total solids levels showed that reconstituted fibrillated MPC has significantly higher viscosity, consistency index, and shear thinning behavior compared with control. Reconstituted fibrillated MPC also showed significantly lower surface tension and interfacial tension, with higher emulsification capacity, foaming capacity, and foam stability. Fibrillated MPC powder can be used as a functional ingredient in dairy and food formulations.

Development of a Cosmetic Spray With Photoprotective Properties Based on Green Tea

Sunburn is the result of the skin’s protective response to damage from ultraviolet (UV) rays. The melanin found in human skin absorbs ultraviolet light, helping to protect it, but some (light-skinned people) have less of it in their skin, which immediately increases the risk of sun damage. Excessive exposure to ultraviolet radiation adversely affects human skin. Active cohesion of basal cells and increased division of corneocytes thickens the stratum corneum of the epidermis, protecting underlying cells and basal keratinocytes from damage. The aim of the work is to search for and analyze natural components that have photoprotective properties that do not pose a danger to humans. One of these components are polyphenols, which form a natural photoprotective defense mechanism in plants. Green tea extract contains polyphenols capable of capturing ultraviolet radiation, therefore it is a promising environmentally friendly analogue of physical and chemical UV filters. Analysis of the developed liquid cosmetic spray based on green tea extract showed a high content of polyphenols, which may indicate the prospect of development in this direction.

Farm Fields as Toxic Sinkhole

Farm Fields as Toxic Sinkhole

An investigation of the effect of chamber temperature on macroscopic spray characteristic under GCI engine conditions

Spray characteristics play an important role in the application of gasoline compression ignition (GCI) engines because it affects engine performance as well as engine design. In this study, the influence of temperature on the non-vaporizing spray process was evaluated through the experimental process on the constant volume chamber (CVC) with simulated conditions of the GCI engine. The experimental matrix was constructed by varying key factors, including chamber temperature, fuel injection pressure, and chamber gas density. The CVC with built-in heaters allows for temperature variations at 323 K, 398 K, and 423 K. To accommodate low load conditions, the fuel injection pressure is varied between 50 MPa and 110 MPa. Simultaneously, chosen variations of gas density, including two levels of chamber density are selected at 15 kg/m3 and 30 kg/m3 respectively. In addition, the injector angles are arranged at 90° (vertical) and 180° (horizontal) to create an overview of the spray characteristics for the case study of GCI engine conditions, viable for future studies using a constant-volume combustion chamber (CVCC), or even rapid compression engine machine (RCEM) in which the injector is commonly set horizontally. The gasoline blended with biodiesel by volume percentage consisting of 80% gasoline and 20% biodiesel was used as the main fuel in this study, namely the GB20 blend. The results of the spray characteristics collected through the images of the spray process based on the Schlieren optical method and the highspeed camera, consisting of the spray evolution and penetration length, spray penetration rate, spray area, as well as the spray cone angle are investigated. The difference in the spray process is denoted as the chamber temperature is increased. The spray penetrates to the chamber wall limit more quickly at elevated temperatures. The results were recorded as a decrease in impingement time by 12% and 9.5%, respectively, at the injection pressure of 50 MPa together with an ambient gas density value of 15 kg/m3. The cone angle of the spray tends to reduce by approximately around 3° to 10° in all experimental cases when the chamber temperature is high. However, when entering the post-phase at 450–600 μs, cone angle differences are negligible during the injection reaching the stable phase.

A computational study of droplet-spray formation from pressurized metered dose inhalers with applications to drug deposition in a human lung-airway model

Orally administered drugs using portable devices, such as pressurized metered dose inhalers (pMDIs), can alleviate the symptoms of various respiratory diseases. The basic non-isothermal fluid-particle dynamics of pMDIs have been simulated, including computer model validations and different inhalation techniques, using the Ventolin HFA from GlaxoSmithKline (UK) as a representative application. Specifically, the evolution of thermal droplet sprays has been realistically simulated and experimentally validated, employing the open-source computational fluid dynamics (CFD) toolbox OpenFOAM. The segmental droplet temperature results show elevated temperatures for higher inhalation flow rates because of stronger convective flow around the evaporating droplets. The general problems of high, wasteful oropharyngeal deposition and cold impacting droplets were tackled by devising a new ‘pulsed injection’ strategy in which the spray was broken into pulses with a time delay between them. This new methodology indicated up to a 20% increase in useful lung deposition beyond the oropharynx over conventional drug administration methods. In addition, compared to the conventional single injection approach, the segmental variations in temperature of the deposited aerosols show an increase in temperature of around 10% and 7% for the 30 LPM and 60 LPM cases up to segment 4 for pulsed injection. An increase of 23% and 13% for the 30 LPM and 60 LPM cases were observed for segments 5–7 for pulsed injection. Also, a reduction in inertia of the droplets at 30 LPM, where the spray was broken into eight pulses with 100 ms delay between them, resulted in higher residence times and an increase in temperature of over 35°C.Copyright © 2023 American Association for Aerosol Research

Limitations of cetane number to predict transient combustion phenomena in high-pressure fuel sprays

Fundamental understanding of in-cylinder processes in diesel engines is important to screen emerging biofuels and advanced combustion modes that can reduce greenhouse gas emissions and regulated pollutants including soot. In this study, the role of fuel properties on spray development and combustion is investigated by systematically isolating chemical and thermophysical effects. Three different fuels are considered, two with similar chemical properties and two with similar thermophysical properties with one fuel common to both groups. Experiments are performed in a constant-pressure flow chamber designed to provide stable test conditions and facilitate acquisition of at least 150 injections in quick succession for each fuel under reacting high-pressure, high-temperature ambient conditions using a modified conventional diesel engine injector. High speed optical diagnostics including rainbow schlieren deflectometry, OH* chemiluminescence, and a two-color pyrometry system are employed to simultaneously image the transient spray and reacting jets. Image analysis is performed to determine liquid length, vapor penetration length, timing and location of first stage and main ignition events, lift-off location, total soot mass, and more. Results show that fuels with similar chemical properties or cetane number (CN) exhibit similar delay times for first stage and main ignition events as may be expected, but very different liquid length, first stage and main ignition locations, lift-off length, apparent turbulent flame speed, and soot formation. As such, the ability to characterize candidate biofuels with CN or other parameters derived from simple flame configurations is called into question. In this study, thermophysical properties controlling the liquid length are identified as the main contributing factor for the observed differences.

The effect of minor scandium addition on microstructure evolution and mechanical properties of spray formed Al-Zn-Mg-Cu alloy

In this investigation, both Scandium (Sc)-added and Sc-free Al-Zn-Mg-Cu aluminum alloys were prepared by spray forming. The as-deposited alloys were hot extruded and then subjected to solid solution and aging treatment at different temperatures. The effect of minor scandium addition on microstructure evolution and mechanical properties were studied. The results revealed that, with Sc added spray formed alloy (7055Sc alloy), Sc element was mainly observed in the primary Al3(Sc,Zr) phase, the secondary Al3(Sc,Zr) phase and the W(AlCuSc) phase in the alloy. Compared to the alloy without Sc addition (7055 alloy), the effects of fine grain strengthening, dislocation strengthening and precipitation strengthening of Al3(Sc,Zr) phase were enhanced. At low aging temperature, the precipitation of MgZn2 phase was inhibited and the size of this phase was found large in the 7055Sc alloy. Therefore, after 120 °C for 24 h aging, the yield strength of 7055Sc alloy was tested as 603.4 MPa, which was 46.9 MPa lower than that of 7055 alloy at the same aging temperature. After 160 °C for 24 h aging, in the 7055Sc alloy the quantity and density of MgZn2 phase increased and the size of the phase was smaller. As a result, the yield strength of the 7055Sc alloy was 576.9 MPa, which was 31.6 MPa higher than that of the 7055 alloy. The effects of Sc on the aging precipitation of spray formed 7055Sc alloy at different aging temperatures were explained by the vacancy mechanism of diffusion.

Analysis of performance and emission patterns of novel biofuel feedstock neat coconut fatty acid distillate (CFAD) fuelled single‐cylinder diesel engine

AbstractThis study examined the potential of using coconut fatty acid distillate (CFAD), a by‐product of the processing of edible oils, as a diesel engine fuel. The major novelty of this study is to assess the CFAD as a viable feedstock of biodiesel to address global energy demands. CFAD has not been specifically researched as a feedstock for producing biodiesel or as a fuel for diesel engines, despite the fact that numerous studies on the production and performance of biodiesel have already been conducted. Fourier transform infrared (FTIR) spectroscopy, gas chromatography (GC), and FTIR were used to analyze the fuel. According to the results of the GC test, CFAD oil contains 91.53% saturated fatty acids, compared with only 8.47% unsaturated fatty acids. High saturation values can be seen in myristic acid (16.92%) and lactic acid (45.33%). Longer hydrocarbon chain lengths indicate higher energy density and boiling point, which also indicate lesser volatility. At a frequency of 1708.54 cm−1, C─H stretching vibrations have been identified through FTIR investigation. The vibrations of C─C stretching at 1465.47 cm−1 indicate the presence of alkenes/fingerprint phase. The blends used for this investigation include 90% diesel with 10% CFAD (CFAD10), 80% diesel with 20% CFAD (CFAD20), 70% diesel with 30% CFAD (CFAD30), and 100% CFAD. The CFAD 10%, 20%, and 30% blends as well as the CFAD100 had brake thermal efficiency values of 27.24%, 26.23%, 24.88%, and 21.52%, correspondingly, at full load. The average increment in brake‐specific energy consumption for CFAD10, CFAD20, CFAD30, and CFAD100 over diesel fuel was 8.23%, 10.88%, 13.77%, and 25.90%, respectively. The behavior of CFAD exhibits reduced cylinder pressure because of the large content of moderate saturated fatty acids in this substance. The net heat release rate (NHRR) and cylinder pressure have a similar relationship in that the NHRR increases with increasing diesel volume. In comparison to diesel, the CO emissions from the CFAD20, CFAD30, and CFAD100 blends increased by 10.79%, 16.66%, and 35.89% at maximum load, respectively. It has been reported that NOx is reduced more significantly the more CFAD is present in the mixture. The blend CFAD10 had the least amount of smoke. The high viscosity of the CFAD and its blends influences the fuel droplets range and the development of spray in the cylinder, which results in delayed combustion and higher unburned hydrocarbon emissions.

A comprehensive review on the atomization and spray characteristics of renewable biofuels

Due to sustainability, rising energy demands, environmental concerns and energy security issues, scientists and researchers around the world are studying renewable biofuels as an alternative to fossil fuels. Biofuels or alternative fuels such as biodiesel, pure plant oil, DME (dimethyl ether) and alcohols which are derived from different renewable biomass sources were investigated by the scientific community as a substitute fuel for diesel engines. The spray process plays the main role in the proper combustion of fuel in engines, leading to a decrease in tailpipe emissions and an increase in engine efficiency. Development in the understanding of biofuel spray characteristics results in low emissions compared to fossil fuels and thus making biofuels a sustainable option for the future. Since, fuel properties have a significant impact on spray development, hence numerous experimental and computational studies were conducted. This article critically examines the atomization and spray characteristics of various alternative fuels utilized for diesel engines. In addition, recent advances and progress in numerical modeling and simulation of the biodiesel spray process are also discussed. To meet renewable fuels viability in CI (compression ignition) engines as a substitute to diesel fuel, various associated challenges and their probable solutions are also discussed.

An ammonia flash break-up model based on bubble dynamics with force and energy analysis on droplet

Ammonia flash break-up model was developed using bubble dynamics based on force analysis of surface tension and pressure forces in this study. The initial bubble radius was calculated by modifying bubble number density equation considering the superheat degree with assuming a single bubble in the droplet. The Rayleigh–Plesset equation with compressibility factor was employed to calculate bubble growth in the liquid ammonia droplet. Droplet disintegration was predicted by force analysis. The velocity change by flash break-up was assumed to be a product of the surplus energy between the surface-energy change and the pressure work, and the bubble growth rate. The simulation results were compared to results in a previous experimental study of ammonia spray behavior. The time constant of the thermodynamic breakup model was added to simulate the flash boiling condition that induces rapid spray changes. In this study, the time constant 12 is used through the verification process. Compared with previous experimental results of ammonia flash boiling spray, the proposed flash breakup model was superior in predicting radial spray development by the flash boiling compared to the conventional aerodynamic breakup model.

Experimental investigation on effect of gas/spray interactions on transient diesel spray behaviors

The ever-increasing rail pressure in diesel engines may cause the injection induced shock waves. In the present study, different gases (N2 and CO2) were used as the ambient mediums in order to understand the effect of shock waves induced by the high-speed jets on the near-field spray penetration. The tests were carried out in an optically-accessible constant volume vessel and a single-hole diesel injector was used. The injection pressure ( Pinj) ranged from 80 to 150 MPa and the ambient density ( ρambient) are 11.25, 22.52, and 33.81 kg/m3, respectively. Schlieren imaging was used to capture the shock waves ahead of the sprays with a frame speed of 100,000 fps and high-speed imaging was used to capture the spray penetration evolution with a frame speed of 300,000 fps in order to provide sufficient high temporal and spatial resolutions of the spray development. Shock waves can be observed under CO2 atmosphere over all the tested conditions and almost invisible under N2 atmosphere. The timings of occurrence and detachment of the shock waves are advanced with the increase in ρambient, but less sensitivity to Pinj. The difference in penetration lengths for N2 and CO2 atmosphere are not consistent as Pinj and ρambient varied, indicating the complicated role of shock waves in influencing the spray behaviors. Several mechanisms for the generation of shock waves were discussed, as well the physical meaning of the timing to the peak velocity of the spray tip with breakup time.