Fuel Drops Research Articles

Microexplosive Atomization of Heterogeneous Fuel Drops for Intensifying Their Ignition

Models of microexplosive atomization of two-liquid unmixed drops under high-temperature heating are developed. Two most common mechanisms, namely, superheating of interphase boundary and critical bubble size, are chosen as atomization criteria. Two mathematical models, one based on solution of heat conduction equation and the other on VOF, are presented. The studied drops contain rapeseed oil and aqueous suspension of graphite. Experiments were conducted to determine the time lag of atomization of moving two-liquid unmixed drops under high-temperature heating. The theoretical and experimental atomization time lag values are found to be in satisfactory agreement. The results can be used to develop existing and create new gas-vapor-droplet technologies in chemical and petroleum engineering fields because they help predict the conditions of intense secondary atomization of heterogeneous drops by microexplosive dispersion.

Fuel drop impact on heated solid surface in film evaporation regime

This study reports an experimental investigation on the dynamics of impacting hydrocarbon fuel drops on a heated stainless steel surface in the film evaporation regime. The analysis is focused on the description of maximum spreading diameter of the impacting fuel drops on the heated surface kept at different temperatures below the boiling point of the fuel. By considering four different fuels of varying physical properties and fuel drops with impact velocity in the range 0.6 – 3.5 m/sec, the study explores a wide range of Weber number (30 – 902), Reynolds number (372 – 13457) and Ohnesorge number (0.0022 – 0.0151). The drop morphology and spreading dynamics on the heated surface are quantified by studying high speed videos of drop impact captured during experiments. Data analysis suggests that, in addition to Weber number and surface temperature, dynamic viscosity of the fuel also plays a role in determining the quantified trends of maximum spreading diameter. Existing theoretical models for the prediction of maximum diameter on unheated flat surfaces can be extended for drop impact on heated surfaces in the film evaporation regime by using surface temperature dependent fuel viscosity. With the support of the present experimental data, an empirical model involving an explicit surface temperature term is proposed for the prediction of maximum diameter on a heated surface in the film evaporation regime.

Conditions of the Water–Coal Fuel Drop Dispersion at Their Ignition in the Conditions of High-Temperature Heating

ABSTRACTThe results of a numerical analysis of the conditions and characteristics of the dispersion of the water–coal particles during ignition under the conditions of an intense radiation-convective heating have been presented in the article. A comparative analysis of the theoretical and experimental values of ignition delay times of the fuel particles has showed their good correlation. Also, a comparative analysis of the characteristic dispersion times, obtained theoretically and established in the experiments, has showed a good correlation between them. According to the results of the numerical simulation, it has been established that dispersion of the water–coal particles during their heating before their ignition can occur as a result of the occurrence of the filtration stresses in the porous structure of the fuel. It has been found that the dispersion of the particles occurs before a complete evaporation within the pore moisture.The theoretical analysis has shown that the permeability of a dry coal structure has a significant effect on the characteristics and dispersion conditions. The influence of the values of the dimensionless Darcy criterion (Da) on the dispersion conditions has also been analyzed. It has been established that as the value of Da increases, the dispersion time decreases substantially. This is due to a decrease in the permeability of the porous structure of the fuel.

Post-spreading behavior of impacting fuel drops on stainless steel surface

Hydrocarbon fuel drops impacting on metallic solid surfaces kept at room temperature exhibit no receding after the completion of early inertia-driven primary spreading. The experimental data of impacting drops of different fuels on a smooth stainless steel surface reveal a sluggish spreading, referred to as post-spreading, after reaching the maximum spreading diameter at the end of primary spreading. A systematic analysis involving maximum spreading factor, final spreading factor and temporal variation of post-spreading diameter of impacting fuel drops of varying Weber number is reported to describe the behavior of the post-spreading process. It is found that the dynamics of post-spreading of impacting fuel drops is different from Tanner’s spreading as the exponent n in the power law describing the temporal spreading behavior (β ∝ τn) varies with Weber number and is significantly less than 0.1. The extent of post-spreading is found to be as high as 20% of the maximum spread factor for the impact of low Weber number fuel drops. Due to the presence of post-spreading, the final spread factor of impacting fuel drops is always higher than the maximum spread factor.

Theoretical Estimation of the Impact Velocity during the PWR Spent Fuel Drop in Water Condition

The spent fuel stored in the pool is vulnerable to external impacts, since the severe reactor conditions degrade the structural integrity of the fuel. Therefore an accident during shipping and handling should be considered. In an extreme case, the fuel assembly drop can be happened accidentally during handling the nuclear fuel in the spent fuel pool. The rod failure during such drop accident can be evaluated by calculating the impact force acting on the fuel assembly at the bottom of the spent fuel pool. The impact force can be evaluated with the impact velocity at the bottom of the spent fuel pool. Since fuel rods occupies most of weight and volume of a nuclear fuel assembly, the information of the rods are important to estimate the hydraulic resistance force. In this study, the hydraulic force acting on the short rod bundle model during the drop accident is calculated, and the result is verified by comparing the numerical simulations. The methodology suggested by this study is expected to be useful for evaluating the integrity of the spent fuel.

On Combustion of Diesel Fuel Drops at LPG Fuelling by Diesel Gas Method

The Liquid Petroleum Gas can be use at diesel engine with significant reductions in nitrous oxides and smoke emissions and affects the in-cylinder mixture forming and combustion process. The paper presents the results of a thermodynamic model developed for vaporization and combustion processes simulation for an automotive diesel engine fuelled with LPG by diesel gas method. The mass flow of vaporized substance at the particle area, drops combustion time and flame position are determinate, showing a significant influence of LPG cycle dose on their characteristic parameters. The drops combustion duration decreases for dual fuelling and the flame radius increases.

Erratum to: Influence of Biofuel Additions on the Ignition Delay of Single Diesel Fuel Drops

Erratum to: Influence of Biofuel Additions on the Ignition Delay of Single Diesel Fuel Drops

Influence of Biofuel Additions on the Ignition Delay of Single Diesel Fuel Drops

The behavior of single drops of two- and three-component mineral diesel fuel blends with ethanol and rapeseed oil methyl ester in a heated atmosphere has been investigated. With the use of the known quasi-stationary approach, the influence of the thermal properties of fuel blend components and their composition on the ignition delay time of the drop has been investigated. It has been established that under inert heating conditions of the drop, additions of low-boiling ethanol to diesel fuel should shorten the duration of the preignition period, and additions of rapeseed oil methyl ester should, on the contrary, prolong it. Analysis of the obtained data has made it possible to determine the optimal composition of the fuel blend for the most economical operation of the diesel. The prognostic estimates made are confirmed by laboratory experiments and bench tests of fuel blends.

Wake of a Shattering Fuel Drop

This article presents a mathematical model that describes the evaporation aerodynamics of a mist in the wake of a shattering drop behind a detonation front. The model is based on a previously obtained distribution function for stripped droplets by size. Stripped droplets are considered as a multivelocity continuum, and a system of differential equations describing two-phase polydisperse spray dynamics is proposed. The mathematical problem is formulated at a one-dimensional spatial approximation of flowfield and is solved in closed form in dynamic 3D space. This study includes a detailed calculation of the ballistics of an evaporating spray generated in the wake of a kerosene drop fragmented by an air stream. The following issues are also investigated: the internal structure of the spray as it relates to the dynamic process of spray formation; the evolution of the dispersive characteristics of the liquid-phase jet of spray; the stabilization and range of a jet; and the structure and processes of jet and vapor cloud formation. By rough estimations, the intensification of liquid transfer into the vapor phase due to shattering leads to over-riching and cooling of the air-vapor combustible mixture in a wake, essentially increasing the induction period of ignition.

Fuel Drop Size Measurement in a Carburetted Induction System with Two Throttling Methods

A new throttling system far SI engines is examined. The SMD of the fuel droplets in the induction system is measured to evaluate the performance of the new device with respect to the conventional throttle plate arrangement. The measurements are conducted at steady now conditions. A forward angular scattering technique with a He-Ne laser beam is used for droplet size measurement. The experiments are carried out with different mixture strength, stream velocity and throttle positions. It is observed that A/F ratio has no effect on SMD. However, stream velocity and throttle position have a significant influence on SMD. The new throttling method is found to be more effective in reducing the SMD, particularly at low throttle opening and high stream velocity compared to the conventional throttle plate.

Evaporation and Combustion of a Fuel Drop in Supercritical Environments. 3rd Report, Observation from the Lateral Side of a Drop on a Hot Wall.

Evaporation and combustion processes of a single fuel drop in ambient gas pressurized and heated beyond the critical point of the fuel (a supercritical environment) were observed from the lateral side of the drop on a flat hot wall settled in a high-pressure bomb. The ambient gas temperature near the wall was controlled to be the same as the wall temperature. The fuel drop showed different evaporation lifetimes in air and in nitrogen. The difference in the evaporation lifetime was larger under higher ambient pressure. Drop volume decreased gradually in a subcritical environment, but in a supercritical environment the drop maintained close to the initial volume during evaporation and showed a sudden decrease just before extinction. In an ambient temperature range around the critical tempreature of the fuel, longer duration of combustion and smaller flame width were found for the drop in the supercritical ambient pressure than for that in the subcritical ambient pressure.

Evaporation and Combustion of a Single Fuel Drop in Supercritical Environments. 1st Report, Observation of Evaporation and Combustion Processes on a Hot Wall.

An experimental study was conducted on the evaporation and combustion phenomena of a single n-dodecane drop in ambient gas pressurized and heated beyond the critical point of fuel, that is, supercritical environments produced on a hot wall. The evaporation lifetime in air at the wall temperature below the ignition temperature was found to be shorter than that in nitrogen at the same wall temperature. The end of combustion time in air at ambient pressure below the critical pressure of the fuel was correlated with the evaporation lifetime, and it was maximum in the wall temperature range where the drop showed spheroidal evaporation. As the ambient pressure increased beyond the critical pressure of the fuel, the end of combustion time increased in the wall temperature range around the critical temperature of the fuel, and in other wall temperature ranges, it decreased.

Evaporation and Combustion of a Single Fuel Drop in Supercritical Environments 2nd Report, Effect of Euel Property.

An experimental study was conducted on the evaporation and combustion phenomena of a single fuel drop in ambient gas pressurized and heated beyond the critical point of fuel, that is, supercritical environments on a hot wall. Several kinds of liquid paraffin such as n-heptane, n-decane, n-dodecane and n-tetradecane were used as the test fuel. The evaporation lifetime in air was found to be shorter than that in nitrogen at the same wall temperature. The difference in the evaporation lifetimes in air and nitrogen environments was greater under higher ambient pressure for the same fuel ; for the same ambient pressure, it was greater under a larger ratio of ambient pressure to critical pressure of the fuel. As ambient pressure increased from subcritical to supercritical pressure, the end of combustion time increased in the wall temperature range around the critical temperature of the fuel, whereas in a wall temperature range higher than the critical temperature of the fuel, it decreased.

The Role of the Heat-up Period in Fuel Drop Evaporation

The Role of the Heat-up Period in Fuel Drop Evaporation

Ignition of fuel droplets behind a shock wave front

An experimental investigation of the ignition process of drops of hydrocarbon fuels (kerosene, decane and hexadecane) in incident shock waves, over a wide range of Mach numbers, has been conducted. An analysis was carried out of the ignition and a physical model of the phenomenon was proposed. In the ignition of a fuel drop in an incident shock wave, the characteristic time of occurrence of the physical processes responsible for preparation of the system for combustion correlates with the start of stripping-off of a layer of liquid from the drop. In weak shock waves (M<3.5), the ignition delay of the fuel drop is determined mainly by the induction period of the chemical reactions, and in strong shock waves by the time of occurrence of the preparatory processes; ignition of the drop in strong shock waves can take place at the start of ''stripping-off'' (or earlier) at the surface of the drop. Depending on the intensity of the shock wave, cases of explosive and nonexplosive ignition of the fuel are observed.

Ignition of Partially Shattered Liquid Fuel Drops in a Reflected Shock Wave Environment

An experimental investigation of the ignition of individual fuel drops after their interaction with an incident and a reflected shock wave near the end wall of a shock tube has been carried out. The influence of the aerodynamic shattering of the fuel drop by the convective flow on the ignition characteristics has been examined by varying the drop-end wall separation distance. Data are presented which show the ignition delay times to be a function of the various experimental conditions encountered in this study. A comparison is made with previous investigations concerning the ignition of a liquid fuel drop due only to the interaction with an incident shock wave.

Multi-component heavy fuel drop histories in a high-temperature flow field

This study is the latest in a series, conducted at The University of Wisconsin, to elucidate the behaviour of combustible fuel drops. Concurrent analytical and experimental studies of temperature and mass histories during the vaporization, combustion and thermal decomposition of a multi-component liquid-fuel drop in a high-temperature flow field have been performed. The fuel investigated is of residual type, a mixture of heavy liquid hydrocarbons. Irregular burning of drops of these fuels has been attributed mainly to asphaltenes and partly to unstable resin components. In the analytical work, temperature-dependent mean properties of both the liquid drop and the boundary layer of air/ fuel vapour mixture have been employed. Assumptions have been adopted to simplify the analytical model. Four governing differential equations in combination with three boundary conditions are reduced by the Zeldovich method to two simultaneous ordinary differential equations for drop mass and drop temperature histories. These are solved numerically by the Runge-Kutta method on a CDC 3600 computer. A simple extension gives a breakdown of the heat balance. The analytical predictions improve on previous predictions using constant properties 1 . It is found that the heat of decomposition and the total heat input to the drop per unit initial drop mass during the liquid phase are unaffected by airstream temperature and initial drop size in the range studied.

The Interaction of an Incident Shock Wave with Liquid Fuel Drops

Liquid hydrocarbon fuel drop interaction with incident shock wave in oxidizing and inert atmospheres, investigating aerodynamic shattering and combustion

Study on the Burning of a Fuel Drop in Heated and Pressurized Air Stream : 1st Report, Experiment

As a clue to elucidating the combustion process in diesel engines, the burning characteristics of a fuel drop in heated and pressurized air stream was studied experimentally. Its pressure was varied from 0.4 to 16 ata, its temperature, from the room temperature to 600°C, and its velocity, up to the transition velocity where the flame shape changes from envelope type to wake type. The fuel drops were simulated by porous spheres transpired liquid fuel. As the fuel, methanol, n-butanol and kerosene were used. Under these conditions, the flame shape, the burning rate m, and the flame transition air velocity Uc were measured. Among the results of measurement, main ones concerning the influence of temperature and pressure are as follows. When the temperature is raised, Uc rapidly icnraeses, but m scarcely changes. When the pressure is raised with the velocity, m increases remarkably. And when the temperature and the pressure are raised, flame becomes long and the soot formation increases.

Study on the Burning of a Fuel Drop in Heated and Pressurized Air Stream : 3rd Report, Empirical Formula for the Flame Transition Air Velocity

When the relative velocity between air stream and burning fuel droplet is raised, the flame shape changes suddenly from an envelope type to a wake type and the burning rate decreases remarkably at a specified velocity Uc. In this report, the experimental data on this flame transition air velocity, which were shown in the 1st Report, are summarized into a formula under the theoretical consideration. Although a few interpretations on the mechanism of flame transition have been proposed, they do not explain the experimental results so well. So the authors assume that the transition occurs when the rate of heat lost to the surroundings exceeds the rate of heat generated by chemical reaction in a region of frontal surface of flame. Under this assumption, the critical condition for transition is described quantitatively. Combining the governing factors, which are found from this condition, the empirical formula for Uc is set up such as to satisfy the experimental results.