Fuel Droplet Diameter Research Articles

Investigation of combustion characteristics on triethyl borate, trimethyl borate, diesel, and gasoline droplets

In this study, the evolution of fuel droplet diameter, flame structure, and maximum flame temperature over time was observed using a high-speed camera and a thermal camera at the same time. Traditional fuels (diesel and gasoline) and new generation fuels (triethyl borate and trimethyl borate) fuels were investigated within the droplet experiments. It has been shown that the flame structure of diesel and gasoline fuel droplets has a large non-luminous region that is seen during the combustion process, unlike triethyl borate and trimethyl borate fuels. The curves of the time-dependent variation of the dimensionless square of the droplet diameter (D/D0)2 of the fuel droplets considered in the study generally exhibited curve properties conforming to the D2-law. In the flame formed by the trimethyl borate droplet, the highest flame temperature was observed by the thermal camera, while the shortest burning time was detected. According to the experimental conditions in the study, the shortest ignition delay was measured for trimethyl borate, while the longest ignition delay time was observed for diesel fuel droplet. Also, it was determined that the lowest burn rate constant was detected for the gasoline droplet, while the highest burn rate constant was seen for diesel fuel.

Combustion characteristics of trimethyl borate, diesel, and trimethyl borate-diesel blend droplets

In this study, droplet tests were carried out for pure and blended forms of diesel fuel, which is the traditional fuel, and trimethyl borate fuel, which is new generation fuels. In this context, the evolution of fuel droplet diameter, flame structure, and flame temperature over time was observed using a high-speed camera and a thermal camera simultaneously. Measurements were made for the addition of 20%, 40%, 60%, and 80% trimethyl borate fuel to diesel fuel in fuel blends. The curves of the time-dependent change of the dimensionless square of the droplet diameter (D/D0)2 of the fuel droplets considered in the study, in general, have been determined to comply with the D2-law. Also, as the amount of diesel rose, there were high changes in droplet distortion and high deviations from the hemispherical geometry, and also elongation in the dominant shape droplet shape changed times. While the highest flame temperature was monitored by the thermal camera in the flame formed by the trimethyl borate droplet, as the amount of diesel fuel in the mixture increased, the maximum flame temperature decreased, but the burning time of the droplet was prolonged. On the other hand, the shortest ignition delay was measured for trimethyl borate, while the longest ignition delay time was detected for diesel fuel droplet. In general, it has been observed that the addition of trimethyl borate reduces the ignition delay, shortens the extinction time, and increases the temperature during combustion compared to diesel.

Autoignition of isolated n-heptane droplets in air and hot combustion products at microturbine conditions

Spontaneous ignition of isolated n-heptane droplets with initial diameters of 20–100 is simulated using air at 4 atm and 700–1200 K, which includes the typical operating conditions of recuperated microturbines. Because some fuel droplets in a combustor may be sprayed or carried to near the recirculation zone, the simulations use a mixture of pure air and hot combustion products as the oxidiser. The flame structures, evaporation times, and autoignition times in both physical and mixture fraction spaces for the different conditions are presented and compared. The variables examined include the air preheat temperature, amount of dilution with hot products, initial fuel droplet diameter, oxidiser temperature, and oxygen concentration. The results show that droplets in pure air at microturbine conditions fully evaporate before ignition, suggesting that a prevaporised concept is suitable for microturbines. The dilution with hot combustion products decreases the ignition delay time mainly by raising the oxidiser temperature. Low-temperature chemistry does not have a significant effect on droplet ignition because adding even a small amount of hot combustion products can increase the oxidiser temperature to higher than the temperatures favourable for low-temperature kinetics. The cool flame is only observed for 100 droplets at low temperatures, but two-stage ignition is not observed.

Design and Numerical Analysis of a Micro Gas Turbine Combustion Chamber

The interest in micro gas turbines has been steadily increasing. As a result, attention has been focused on obtaining optimal configurations for micro gas turbines depending on the applications in which they are used. This paper presents the CFD modeling results regarding an annular type combustion chamber, part of an 800N micro gas turbine, predestined to equip a small scale multifunctional airplane. Two configurations have been taken into consideration and 3D RANS numerical simulations have been conducted with the use of the commercial software ANSYS CFX. The liquid fuel droplets were modeled by the particle transport model, which tracks the particles in a Lagrangian way. An initial fuel droplet diameter of 500µm has been imposed. The numerical results obtained are encouraging. The flame was developed in the central area of the fire tube, its walls thus not being subjected to high temperatures. Also, the maximum temperatures were obtained in the primary zone of the fire tube. The temperature then decreased in the fire tube's secondary zone and dilution zone. The numerical results will be validated by conducting combustion tests on a testing rig which will be developed inside the institute's Combustion Chamber Laboratory.

Influences of liquid fuel atomization and flow rate fluctuations on spray combustion instabilities in a backward-facing step combustor

Combustion instabilities occurring in spray combustion fields inside a backward facing step combustor have been investigated by performing large-eddy simulations (LES). In this study, the influence of fluctuations in the incoming oxidizer air velocity (caused by drastic pressure oscillations in the combustor during combustion instability) on the droplet diameter distribution (due to atomization) of the injected liquid fuel spray, as well as the influence of pressure oscillations on the fuel flow rate have been taken into consideration using appropriate models. For the temporal fluctuations in fuel droplet diameter distribution, a model for the Sauter Mean Diamter (SMD) of atomized droplets, obtained as a function of spray injection parameters and gas/liquid properties, is incorporated in the LES. Additionally, to consider the temporal fluctuations in fuel flow rate along with its phase difference with the pressure oscillations, a model derived from Bernoullis principle is proposed and employed in the LES. The objective is to examine in detail, the impacts of the fluctuations in fuel droplet diameter distribution and the fluctuations in fuel injection rate individually, as well as the impact of the mutual interaction of these two fluctuations, on the spray combustion instability characteristics. Results of the LES reveal that the temporal fluctuations in fuel droplet diameter distribution resulting from combustion instability, lead to a reduction in the intensity of pressure oscillations and hence the combustion instability’s strength. Additionally, the temporal fluctuations in liquid fuel flow rate strongly influence the intensity of spray combustion instability, and it is observed that the combustion instability intensity increases with the increase in phase difference between the fuel flow rate fluctuations and pressure oscillations. Furthermore, the effect of the temporal fluctuations in fuel droplet diameter distribution resulting in the reduction of combustion instability intensity, becomes more pronounced as the phase shift between the fuel flow rate fluctuations and pressure oscillations becomes larger. It is clarified that the above-mentioned behavior of spray combustion instability, results from the change in the correlation between heat release rate fluctuations and pressure oscillations near the combustor’s dump plane, which is caused by the change in the local residence time of fuel droplets and the local fuel droplet evaporation rate.

Factors Affecting Characteristic Length of the Combustion Chamber of Liquid Propellant Rocket Engines

Optimum characteristic length of the combustion chamber of liquid rocket engine is very important to get higher energy from the liquid propellants. Characteristic length is defined by the time required for complete burning of fuel. Combustion reactions are very fast and combustion is evaporation dependent. This paper proposes fuel droplet evaporation model for liquid propellant rocket engine and discusses the factors which can affect the required size of characteristic length of the combustion chamber based on proposed model. The analysis is performed for low temperature combustion chamber. A computer code based on proposed model is generated, which solve analytical equations to calculate combustion chamber characteristic length under various input conditions. The analysis shows that characteristic length is affected by combustion chamber temperature, pressure, fuel droplet diameter, chamber diameter, mass flow rate of propellants and relative velocity of the droplet in the combustion chamber.

A simplified model for a diesel spray

This paper describes a computer simulation and measurements of the liquid phase of Diesel spray formation.The spray is divided into small elementary volumes in which the amounts of liquid and gaseous fuel, air, mean, maximum and minimum fuel droplet diameter are calculated, as well as their number. The total air–fuel and air–fuel vapour ratios are calculated for each elementary volume. The mathematical model of the Diesel spray is based on continuity and momentum equations in Eulerian-Lagrangian formulation.The measurements of the sprays were carried out in the combustion chamber at the LTT, which is equipped with a high pressure 250 MPa fuel injection system. During the experiments, ambient pressure varied from 3 MPa to 7 MPa, temperature from 673 K to 973 K, injection pressure from 40 MPa to 200 MPa and nozzle temperature from 243 K to 363 K. The injection quantity was 13.5 mm3 per cycle in all cases. The combustion chamber was filled with pure nitrogen instead of air. Thermodynamic properties of nitrogen are similar to those of air. That way, self-ignition was prevented. We measured only the liquid phase of the fuel in the spray, and to this end, Mie scattering measuring technique was applied.The comparison between the simulated and actual liquid spray penetration depth and spray cone angle showed good matching.

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.

Improvement of fuel oil spray combustion inside a 7 MW industrial furnace: A numerical study

This paper presents a numerical analysis of fuel oil spray combustion inside an industrial furnace. The industrial furnace is a 7MW cylindrical furnace which supplies heat to an oil refinery. The commercial CFD software Fluent is used for modeling transport and reaction processes in the furnace. The chosen combustion model is validated against measurement data available in the literature and good agreement is achieved. Fuel oil spray combustion is improved by varying fuel and burner parameters such as relative air-fuel ratio, fuel droplet diameter, fuel spray half-angle and burner swirl number. These parameters affect the flame shape and stability, on which depends the performance of the industrial furnace, particularly the heating output and gas species emissions. The numerical analysis revealed that complete combustion and minimum fractions of unburnt species are obtained by lean air-fuel mixtures, highly swirling flows, wide fuel spray angles and small fuel droplets. On the other side, the highest furnace heating outputs are achieved for near-stoichiometric air-fuel mixtures, narrow fuel spray angles, swirl numbers between 0.6 and 1.0 and small fuel droplets.

Influence of fuel injection frequency on droplet dispersion in ethanol pulsed spray flames

The optimized use of ethanol in current and new vehicles requires detailed information on atomization, evaporation, mixing and combustion processes of this fuel. In this work, laser diagnostic tools are applied to analyze ethanol combustion in pulsed spray flames. Fuel droplet diameter and velocity distributions are measured by Phase Doppler Interferometry (PDI) across the flame. The evolution of droplets dispersion at early stages of the injection event is visualized in a diametral plane at exit of the injector by high repetition rate Mie scattering. The burner is formed by a swirler mixer and an automotive port fuel injector both positioned at the top exit of a vertical cylinder. Three injection frequencies (100 Hz, 250 Hz, and 400 Hz) are analyzed in depth. The increase in the injection frequency induced a transition from higher to lower density spray patterns impacting the combustion process of the droplets. The higher density spray presented droplet dispersion similar to a cloud in group combustion mode, promoting a mono-modal droplet diameter distribution across the flame centerline and produced an elongated flame with a visible reaction zone down to the injection plane of the burner. The lower density spray suggests droplets in the internal group combustion mode, being highly susceptible to swirling flow structures and promoting a bi-modal diameter distribution at the centerline, mainly produced by residual droplets with high axial velocity and preferential evaporation of small droplets. Furthermore, the lowest density spray led to a shorter flame presenting similarities to a lifted flame.

Model-predicted effects of fuel droplet diameter and [formula omitted] addition in strained, opposed-flow, non-premixed, multicomponent, hydrocarbon flames

As the use of alternative fuels increases, it is increasingly important to understand the influence of chemical and physical properties on flame behavior. The objective of this paper is to explore the impact of adding O2 to the fuel side of opposed-flow diffusion flames, where the multicomponent fuel is delivered as liquid droplets of varying diameter. The approach is based on the computational simulation of ideal opposed-flow stagnation flames with a separation distance of 5mm between the fuel and air inlets. The fuel composition is a mixture of n-heptane, n-dodecane, and n-hexadecane, which is selected to represent a Fischer–Tropsch fuel. Gas-phase chemical kinetics is modeled using a reduced, but detailed, reaction mechanism containing 196 species. The influence of the finite vaporization rate is evaluated by comparing predictions with pre-vaporized fuel to those with monodispersed initial fuel droplet diameters of 20 and 30μm. The effects of O2 in the fuel stream are assessed using simulations with 0%, 5% or 10% O2 incorporated into the N2 carrier gas. In all cases the pressure is 10atm, the inlet gases are at 950K, the droplets are initially at room temperature, and the inlet velocities of the fuel droplets and carrier gas is 1ms−1. The fuel loading is adjusted to achieve an overall equivalence ratio of unity. The predictions illustrate substantially different behavior under different conditions; these differences can be related to the time available for fuel vapor to react with the premixed O2.

Calculation and Measurements of Self-Ignition Nuclei in Diesel Combustion

This paper describes a computer simulation of diesel spray formation and the locations of self-ignition nuclei. The spray is divided into small elementary volumes, in which the amounts of fuel, fuel vapors, and air and mean, maximum, and minimum fuel droplet diameters are calculated, as well as their number. The total air/fuel and air/fuel-vapor ratios are calculated for each elementary volume. The paper introduces a new criterion for determining self-ignition nuclei based on assumptions that the strongest self-ignition probability lies in those elementary volumes containing the stoichiometric air ratio, where the fuel is evaporated or the fuel droplet diameter is equal to or lower than 0.0065 mm. The most efficient combustion with regard to consumption and emission will be in those elementary volumes containing the stoichiometric air ratio and fuel droplets with the lowest mean diameters. Measurements of injection and combustion were carried out in a transparent research engine. This engine is a single-c...

Measurements of Characteristics of Evaporating Sprays. Quantitative Analysis of Fuel Droplet Diameter.

An experimental study was carried out to verify the feasibility of a quantitative analysis of fuel droplet diameter at high pressures and temperatures in combustion systems. A fueling system was developed to atomize fuel into droplets of the same diameter. Using this system, fueling was made into a visualized device where high pressure and temperature nitrogen flowed under steady-state conditions. The laser induced fluorescence method was utilized to determine n-dodecane fuel and iso-octanefuel droplet behavior and the phase Doppler particle analyzer was used to measure the diameter and velocity of the droplets. As a result, it was confirmed that a quantitative analysis of fuel droplets is possible. The results indicate that due to its lower boiling point, iso-octane droplets tend to evaporate much faster the n-dodecane droplets.

Measurement on Characteristics of Evaporating Sprays. 1st Report. Quantitative Analysis of Fuel Droplet Diameter.

An experimental study was carried out to make a quantitative analysis of fuel droplet diameter at a high pressure and temperature occurring in combustion systems. A fueling system was developed to atomize fuel into droplets having a single small diameter. By using this system, fueling was made into a visualized device where high pressure and temperature nitrogen flew under steady-state conditions. The laser induced fluorescence method was utilized to determine the n-dodecane fuel and iso-octane fuel droplet behavior and the phase doppler particle analyzer to measure the diameter and velocity of the droplets. As a result, quantitative analysis of a fuel droplet got possible. The results indicate that due to its lower boiling point, iso-octane droplets tend to evaporate much faster then dodecane droplerts.

The Characteristics of Swirl Spray Combustion in Gas Turbine Combustor

The present study conducted experimental study of spray combustion to investigate the effect of the inlet conditions of fuel and air on the flame structure, the flame stability and the characteristics of emission in the can-type model of a gas turbine combustor. In the experiment, the diameter of fuel droplet was measured using Malvern particle size analyser and temperatures in the combustion chamber were measured with R-type shielded thermocouple. In addition, flame structure was taken picture with camera and analysed. Gas analyser was also used to analyse the concentration of each components of exhausting gas. The experimental results showed that the flame condition was optimal with swirl number, 0.63 and equivalence ratio, 0.5 for controlling the flame stability, the combustion temperature and the NOx concentration. The present study concluded that both the flame structure and the emission formation were strongly affected by the swirl intensity, which selection was found as an important parameter for either stabilizing flame or lowering the quantity of NOx.

Diesel odor studies in a laboratory spray burner

An air aspirated burner facility has been modified and instrumented for studying diesel odor formation. Odor sampling and analysis techniques, based on the Diesel Odor Analysis System (DOAS), have been developed and refined. Burner stoichiometry, combustion aerodynamics, swirl, wall quenching and fuel composition were investigated for their effect on odor formation. Fuel composition had a negligible influence and swirl had only a small effect except at very high swirl levels. The most significant factor was overall burner stoichiometry. This pronounced stoichiometry effect appears to be the result of the aerodynamic turbulence and wall quenching at lean operating conditions. Fuel droplet diameter, while having no direct effect on odor production, probably has an indirect effect through its influence on both aerodynamics and quenching. The effect of stoichiometry was to increase odor from very low or undetectable levels at equivalence ratios near 0.5 to moderate to strong levels as burner operation becomes very lean and to very strong levels at rich operating conditions. Increasing aerodynamic turbulence caused odor levels to drop by increasing the size and intensity of the recirculation pattern, thereby allowing more complete combustion. Conversely, increased wall quenching removed energy from the reaction zone, resulting in incomplete combustion and higher odor levels. Very high swirl appeared to cause faster reaction rates and lower odor levels.