Fuel Droplets Research Articles

Effects of Initial Droplet Diameter on Interference between Flame Propagating in Combustible Mixtures and a Single Fuel Droplet

Effects of Initial Droplet Diameter on Interference between Flame Propagating in Combustible Mixtures and a Single Fuel Droplet

Submicron aerosols of liquid fuels: Method of production, experimental characterization and a semi-empirical model

For combustion processes involving the atomization of liquid fuels, the minimization of droplet size is important for enhancing fuel vaporization, increasing the efficiency of air-fuel mixtures, and reducing soot and NOx emissions. In this paper, a methodology for producing aerosols of submicron-sized droplets for liquid fuels is presented. The method of droplet formation is based on disintegration, by gas jets, of thin liquid films formed as bubbles on a liquid surface. Using compressed air and CO2, we atomized and studied droplet aerosols of gasoline, diesel, and 0.1–2 wt% aqueous solutions of sodium alginate, with dynamic viscosities up to 210 mPa s, as models of a highly viscous alternative fuel. The produced droplet volume distributions were bi-modal with two peaks between the droplet diameters 0.1–1 µm and 1–10 µm; the respective volume and Sauter mean droplet diameters were substantially smaller than typically produced by other atomization methods, reaching minima between 0.4 and 0.7 μm. The liquid flow rates of a few hundreds of mg/min for 2 wt% sodium alginate solution and ∼20 g/min for gasoline were measured. The minima of the observed air-to-liquid mass ratios were smaller than the respective stoichiometric air-fuel ratios. Dimensional analysis allowed identifying a dimensionless parameter not previously described in the literature, which plays a primary role in the aerosol production process. This analysis and the experimental data enabled establishment of a semi-empirical model describing the droplet aerosol production by the liquid atomization method used here. The potential advantages demonstrated in this study over the existing fuel atomization techniques include the small size of the generated droplets, simplicity of the method and the device design, low-cost of manufacturing, easy operation and scale-up. Submicron fuel droplets are expected to decrease environmental impact in combustion applications, which suggests further investigations and development of the presented fuel atomization technique.

Effect of Diffusion of Coal Pyrolysis Products on the Ignition Characteristics and Conditions of Coal–Water Fuel Droplets

This paper presents a theoretical study of the thermal preparation and ignition of a coal–water fuel droplet under intense radiative-convective heating with diffusion of gaseous pyrolysis products of the solid fuel into the ambient gaseous medium. It has been found that gaseous pyrolysis products are ignited at a distance from the heating surface approximately equal to the radius of the droplet, after which the coke of the main fuel layer is ignited. The time between the ignition of volatiles and the coke residue is less than 0.5 s. Comparison of the ignition delays obtained by mathematical modeling and experimentally has shown satisfactory agreement between theoretical and experimental values.

Flow field and combustion characteristics of integrated combustion mode using cavity with low flow resistance for gas turbine engines

Structural weight and flow resistance of the combustor were important parameters affecting the overall performance of gas turbine. The integrated combustion mode and trapped-vortex combustion mode were the means to fulfill these requirements. Components integration of combustor was an important trend in the development of the combustion technology. In this paper, the trapped-vortex combustion mode was combined with integrated combustion mode, and a new type of integrated combustor with various cavities was proposed. By integrating the flameholder with the structural strut, light weight of the structure could be achieved. By adopting trapped vortex combustion mode, high combustion efficiency could be obtained in wide range of inlet velocity and fuel-air ratio. Using the particle image velocimetry and experimental system, the flow field and combustion characteristics, including ignition, combustion efficiency, outlet temperature distribution and wall cooling characteristics, were thoroughly analyzed. Fuel droplets injected by simple nozzles could be evaporated and mixed with mainstream air in a short distance. The feasibility of the novel combustion mode was completely verified. Low flow resistance and high combustion efficiency was achieved, which was difficult for the integrated combustion mode. The results were beneficial to the research of high performance gas turbines with compact structure.

Assessment of gasoline direct injector fouling effects on fuel injection, engine performance and emissions

The current optical and thermal experimental tests were mainly focused on obtaining a comprehensive understanding of the effects of gasoline direct injector fouling on mass flow rates, spray characteristics, engine emissions and engine performance. A robust injector fouling cycle was employed to produce coked injectors in a multi-cylinder thermal engine. Deposit build-up in the coked injectors and fouling cycle repeatability was first examined by measurements of fuel flow rate. Macroscopic spray characteristics of the clean and the coked injectors were carried out using high-speed imaging and Planar Laser Induced Fluorescence (PLIF) of sprays foot-print. Fuel droplets size and velocity were characterised with a two-dimensional Phase Doppler Particle Analyser (PDPA). It was observed that the deposit build-up inside injector nozzles and on injector tips reduced the plume cone angle while increased plume penetration length, plume separation angles, mean droplet velocity and size for the coked injector. Impact of injector fouling was further investigated by PLIF measurements of in-cylinder charge inhomogeneity and repeatability in mixture preparation. The coked injectors showed higher degree of inhomogeneity and poorer repeatability in mixture preparation. These were in agreement with combustion analysis results where the coked injectors showed lower load and lower combustion stability compared with the clean injector under same operating conditions. Significantly higher unburned hydrocarbon emissions and particulate number concentration were also observed for the coked injectors. This work was carried out to obtain a broad picture of injector cooking effects in GDI engines.

The Combustion of Emulsified Glycerol-Heavy Oil Fuel Droplet

In this work the evaporation of the emulsified glycerol- heavy fuel oil (CG-HFO) droplets with different activator is modeled. The influence of activator gas bubbles volume developments on the evaporation of fuel droplets in the high temperature combustion chamber is studied. The crude glycerol as the secondary product of biodiesel production is used as the first component of the emulsion while the second component is heavy fuel oil. The crude glycerol contains methanol, aromatics, minerals, a little bit biodiesel and water. These materials were pressurized and injected in the chamber with three inputs: the first one is for the CG-HFO, the second one is for activator while the third one is for air for forming the emulsion and then passing to the combustion chamber. The applied pressure is determined according to contents which lead to flame stability of the primary formed emulation. A comparison of calculated results, basing on semi-empirical method, with experimental ones demonstrates the modeling acceptable accuracy.

Model for Fuel Droplet Evaporation in Combustion Chamber of Liquid Propellant Rocket Engines

Complete burning of liquid propellants droplets is very important to avoid combustion instability and to get higher specific impulse from liquid rocket engines. Combustion takes place in gaseous phase and reaction is fast. So, the time consumed by a droplet for complete burning is the time taken by a droplet to get evaporated. An analytical mono component fuel droplet evaporation model is developed and proposed for droplet evaporation in liquid rocket engine based on heat and mass transfer. Effect of the fuel droplet curvature on vapor pressure is incorporated in the model. The model is applied on a small-scale combustion chamber of bi-propellant liquid rocket engine where fuel concentration away from droplet is not zero. A code is generated and applied. The results of the model show that fuel droplet diameter, combustion chamber pressure, chamber diameter, mass flow rate and droplet relative velocity with hot gas has significant effects on the life of droplet and characteristic length. Effects of chamber pressure and diameter are more significant for larger droplet size.

高温壁面上におけるO/WおよびW/Oエマルション燃料液滴の微粒化挙動の比較

高温壁面上におけるO/WおよびW/Oエマルション燃料液滴の微粒化挙動の比較

Ignition of liquid droplets fuels under conditions of radiation-conductive heating in air

The results of an experimental investigation of ignition liquid fuel (kerosene, diesel fuel) by the single drops under conditions of radiation-conducting heating in air are presented. The dependences of the ignition delay time of the typical fuels droplets on the initial temperature of the heated oxidant in a limited space are established. The parameters of stable ignition of liquid fuel droplets are set.

Effect of Diffusion of Coal Pyrolysis Products on the Ignition Characteristics and conditions of Coal-Water Fuel Droplets

Effect of Diffusion of Coal Pyrolysis Products on the Ignition Characteristics and conditions of Coal-Water Fuel Droplets

Ignition of a Droplet of Composite Liquid Fuel in a Vortex Combustion Chamber

Experimental study results of a droplet ignition and combustion were obtained for coal-water slurry containing petrochemicals (CWSP) prepared from coal processing waste, low-grade coal and waste petroleum products. A comparative analysis of process characteristics were carried out in different conditions of fuel droplet interaction with heated air flow: droplet soars in air flow in a vortex combustion chamber, droplet soars in ascending air flow in a cone-shaped combustion chamber, and droplet is placed in a thermocouple junction and motionless in air flow. The size (initial radii) of CWSP droplet was varied in the range of 0.5–1.5 mm. The ignition delay time of fuel was determined by the intensity of the visible glow in the vicinity of the droplet during CWSP combustion. It was established (under similar conditions) that ignition delay time of CWSP droplets in the combustion chamber is lower in 2–3.5 times than similar characteristic in conditions of motionless droplet placed in a thermocouple junction. The average value of ignition delay time of CWSP droplet is 3–12 s in conditions of oxidizer temperature is 600–850 K. Obtained experimental results were explained by the influence of heat and mass transfer processes in the droplet vicinity on ignition characteristics in different conditions of CWSP droplet interaction with heated air flow. Experimental results are of interest for the development of combustion technology of promising fuel for thermal power engineering.

Ignition of coal-water fuels made of coal processing wastes and different oils

The paper presents results of a comparison of integral characteristics for ignition and combustion of droplets of organic coal-water fuels (OCWF) made using processing wastes (filter cakes) of coals of different grade and typical liquid combustibles: waste engine, turbine oil, and fuel oil. In experiments, sizes (radii) of fuel droplets are from 0.4mm to 1.5mm; a temperature of oxidizer varies from 600K to 1200K; oxidizer flow rate is in a range from 0.5m/s to 5m/s. We consider the two hydrodynamic regimes of a relative motion of the droplets and oxidizer flow: a steady-state regime with droplet position on a junction of a low-inertia thermocouple and a regime of droplet soaring in oxidizer flow. Minimal ignition temperatures (significantly less than 1000K) of filter-cake-based OCWF are reported. Study presents dependences of the integral characteristics of OCWF ignition on properties of liquid fuel components, such as, primarily, the flash point and ignition temperature. Based on experimental results, recommendations for choosing an optimal regime of combustion and a method of slag removal depending on used components of OCWF are given. Experimental data and formulated conclusions can be considered asa significant contribution to a development of OCWF technologies, which can help to solve global problems of humanity, i.e. reduction of an atmospheric pollution, global warming and dimming.

Experimental Study of Evaporation Characteristics of Low Ignitibility Fuel Droplet at High Temperatures and Pressures

Experimental Study of Evaporation Characteristics of Low Ignitibility Fuel Droplet at High Temperatures and Pressures

An Investigation on the Ignition Characteristics of Lubricant Component Containing Fuel Droplets Using Rapid Compression and Expansion Machine

An Investigation on the Ignition Characteristics of Lubricant Component Containing Fuel Droplets Using Rapid Compression and Expansion Machine

Modeling of droplet/wall interaction based on SPH method

Fuel droplet impingement on different wall conditions have been studied using Smoothed Particle Hydrodynamics (SPH) method, and a new splashing sub-model is proposed based on numerical results to calculate the splashing mass fraction of the incident droplet and compared with experimental results. Temporal evolution of the droplet shape after impingement is studied with various initial and boundary conditions. It is found that few splashes take place when the drop hits a relatively smoothed dry surface. Wall film plays a great role on droplet splashing. On one hand, the film slows down the droplet spreading process and transmits the energy to the crown part, making it easier to splash; on the other hand, the incident energy is dissipated when the drop moves through the film. The result shows that when non-dimensional wall film (hnd) is less than 0.5, the splashing mass fraction is relatively high and secondary droplets are easier to form. Further increase hnd, the fraction goes down and more film part splashes. The splashing sub-model is fitted and modified using numerical data and experimental data in a wet wall case. The result shows that the splashing mass and secondary droplets can be predicted as a function of We using the proposed sub-model.

Effect of water-in-heavy fuel oil emulsion on the non-reacting spray characteristics under dierent ambient conditions and injection pressures: A CFD study

Emulsi ed fuel is one of the main strategies to substitute the conventional fossil fuel for the purpose of emission control and enhancement of fuel eciency. Accordingly, non-reacting spray characteristics of water-in-Heavy Fuel Oil (HFO) emulsion are numerically investigated in the present study via CFD analysis. Three di erent volumetric percentages of water in HFO are investigated and compared with pure HFO. E ects of four di erent injection pressures on injected fuel spray characteristics are studied. Moreover, in fluences of three di erent ambient back pressures and two ambient temperatures are considered. For these purposes, the characteristics of spray penetration, cone angle, volume, and SMD are evaluated through the analyses of non-dimensional numbers. For modeling the interaction of the fuel discrete phase and the gaseous continuous phase, Eulerian- Lagrangian multiphase formulation in OpenFOAM CFD toolbox is implemented. Fuel droplet tracking in Lagrangian scheme is applied by Lagrangian Particle Tracking method. Also, KH-RT as a hybrid breakup model for liquid fuel core breakup and standard model of k ???? in RANS for turbulence modeling are utilized. Numerical results are validated against existing experimental data with suitable accordance. Longer spray penetration length, larger cone angle, and greater spray volume are achieved for the emulsi ed fuels.

Simulation of the primary breakup of a high-viscosity liquid jet by a coaxial annular gas flow

The conversion of low-grade fossil and biogenic energy resources (petcoke, biomass) to a synthesis gas in a high pressure entrained flow gasification process opens a wide spectrum for high efficient energy conversion processes. The synthesis gas can be used for production of methane (SNG), liquid fuels (BtL, CtL) or as fuel for operation of a gas turbine in a combined cycle power plant (IGCC). The production of a tar free high quality syngas is a challenging objective especially due to the fact that typical liquid or suspension fuels for entrained flow gasifiers feature viscosities up to 1000 mPas. Fuel droplet conversion at typical entrained flow gasification conditions is characterized by heat up, evaporation and subsequent degradation of the vapour phase. To guarantee a high fuel conversion rate in the gasifier an efficient atomization of the fuel is required. Mainly twin-fluid burner nozzles are used for atomization of those typically high viscous fuels. The present study is focused on the assessment of the accuracy of CFD computations for the primary breakup of high-viscosity liquids using an external mixing twin fluid nozzle. In a first step experiments were performed with a Newtonian glycerol-water-mixture featuring a liquid viscosity of 400 mPas. Jet breakup was investigated using a high speed camera as well as PIV and LDA-System for a detailed investigation of the flow field. In a second step the experimental results serve as reference data to assess the accuracy of CFD computations. Compressible large eddy simulations (LES) were performed to capture the morphology of the primary breakup as well as the important flow field characteristics. A Volume of Fluid (VOF) approach was used to track the unsteady evolution and breakup of the liquid jet. Comparison of experimental and numerical results showed good agreement with respect to breakup frequency, velocity fields and morphology.

Acoustically Coupled Combustion of Liquid Fuel Droplets

The dynamics of oscillatory flames is relevant to acoustically coupled combustion instabilities arising in many practical engineering systems. This paper reviews fundamental studies that pertain to the combustion of single liquid fuel droplets in an acoustically resonant environment. This flow field is not only an idealized model for the study of the fundamental interaction of reactive, evaporative, acoustic, and other transport-based timescales, but it may also be used to identify relevant phenomena in more complex or practical geometries that require a focus for future combustion control efforts. The nature of these phenomena is discussed in detail, in addition to their implications for broader issues associated with combustion instabilities.

Interaction between a Fuel Droplet and Premixed Gas in Spontaneous Ignition Process

Interaction between a Fuel Droplet and Premixed Gas in Spontaneous Ignition Process

GS0605 微小重力環境・加圧雰囲気において液滴間隔の広い燃料液滴列を燃え広がる火炎の観察

High pressure microgravity experiments on flame spread along a fuel droplet array was investigated to establish a spray combustion model for a practical numerical simulation of spray combustion. n-decane was employed as a fuel. Fuel droplets were suspended at the midpoint of a SiC fiber of 14μm in diameter. To simulate flame spread through a 3D fuel-droplet-matrix, a fuel droplet array was placed in a spindly optical cell. The fuel droplet array was ignited from the open end of the optical cell. Experiments were conducted in wide droplet spacing range. The flame spread speed decreased as the ambient pressure increased. Normalized flame spread speed was the largest at the nondimensional droplet spacing of 3.75 in the ambient pressure range of 0.10 - 0.30 MPa.