Fuel Droplet Evaporation Research Articles

Analysis on Evaporation Characteristics of Palm Oil Biodiesel using a HSDT Method

The purpose of this study is to investigate the evaporation characteristics of different types of fuels by applying the hot surface deposition test (HSDT). Generally, HSDT method is a simplified method to simulate fuel deposition in diesel engines. In this study, diesel fuel (DF) and palm oil biodiesel with different blend ratios (B10-B50) were used to evaluate the fuel droplet evaporation behavior on a heated aluminum alloy plate surface. Single fuel droplet was impinged on the heated plate at various surface temperatures (Ts). Important data from the evaporation characteristics was the maximum evaporation point (MEP), which is the temperature point where a droplet evaporates in the shortest lifetime (tlife). MEP is referred to identify the surface temperature range in which fewer deposits will be produced by the test fuel. Furthermore, MEP is also used to determine the appropriate droplet interval to create wet and dry conditions in the fuel deposition test. The obtained MEP was 360°C (DF), 365°C (B10, B50), 375°C (B20, B40), and 385°C (B30).

Experimental investigation of multi-burner array with lean lifted spray flames in inline and inclined configurations

Lean combustion in gas turbines garners attention for emissions reduction, yet it faces stability challenges demanding careful design considerations. In this study, a novel CHAIRLIFT combustor concept, which integrates low swirl lean lifted spray flames known for substantial nitrogen oxides emissions reduction, into a Short Helical Combustors (SHC) arrangement, is investigated. A comprehensive experimental test campaign explores key parameters, including staggered arrangement offset, equivalence ratios, and air inlet temperature, to evaluate its performance. The results reveal exceptional stability in low swirl, lifted flames compared to moderate swirl flames with larger inner recirculation zones. The unwanted flow deflection of highly swirled flames in the SHC arrangement is effectively avoided with the investigated low swirl, lifted flames. The study emphasizes the significant influence of fuel droplet evaporation time on flame stability near the flame root under low air inlet temperatures. Furthermore, at high air inlet temperatures, the complex flame stability mechanism in inclined configurations is controlled by various parameters, including outer recirculation zone size, air inlet temperature, and additional vortices generated by pressure differences near the wall. OH∗ chemiluminescence results corroborate these stability mechanisms, showing that at lower temperatures, the flame stabilizes closer to the nozzle exit due to local rich pockets near the shear layer. Conversely, at the same tilt angle, higher air inlet temperatures lead to an increased flame lift-off height due to faster evaporation and enhanced mixing. Exhaust gas analyses confirm the potential of the investigated lean lifted spray flames in a multi-burner arrangement to achieve very low NOx emissions over a wide range of operating conditions for all investigated burner inclinations. These findings may facilitate the future development and optimization of lean combustion technology for aircraft engines.

Experimental Study of Evaporation Characteristics of Acoustically Levitated Fuel Droplets at High Temperatures

Examining fuel droplet evaporation is crucial for enhancing fuel engine efficiency, conserving energy, and reducing emissions. This study utilizes experimental methods involving ultrasonic standing wave levitation and high-speed cameras to investigate the impact of temperatures and droplet properties, including initial diameter and composition, on the evaporation process. The evaporation behaviors of fuel droplets, like hexadecane and diesel, are documented across a temperature spectrum spanning 150 °C to 550 °C, with an initial droplet equivalent diameter ranging from 0.10 to 0.30 mm. The evaporation rate positively correlates with temperature and may vary by 15% to 71% between hexadecane and diesel droplets.

A Numerical Study on Droplet Evaporation using Mass and Heat Transfer Approach

Liquid fuel is injected into many combustion devices like engines, boilers, and gas turbines where it evaporates, mixes with air, and finally burns. The combustion process influences by evaporation and corresponding air-fuel mixing. Hence, the evaporation study of the fuel droplets is important in different thermodynamic conditions. In the present paper, fuel droplet evaporation has been numerically studied by two different approaches i.e., mass transfer and heat transfer. Multiple case studies have been conducted by varying the droplet surface temperature, its initial diameter, and the temperature of ambiance to understand the influence of each parameter on the evaporation process by the two different concepts. Transfer numbers (B), evaporation constants (K), and droplet lifetime are obtained through both heat and mass transfer models. These observations are highly helpful to understand the droplet evaporation process and comparing the two different approaches to droplet evaporation modeling.

Environmental and energy valuation of waste-derived Cymbopogon Martinii Methyl Ester combined with multi-walled carbon (MWCNTs) additives in hydrogen-enriched dual fuel engine

This study uses a Capparis Spinosa Methyl Ester or Cymbopogon Martinii Methyl Ester (CMME25) and hydrogen dual fuel engine using multi-walled multi-additive nanotubes (MWCNT). In this experiment, a single-cylinder diesel engine was used. Through the intake manifold, hydrogen is introduced at predetermined flow rates of 5 and 10 lpm. The enriched hydrogen MWCNT of 50 and 100 ppm is combined with the CMME25 fuel. Results from the first round of experiments showed that combustion characteristics and performance were improved by hydrogen enrichment. The addition of hydrogen in the CMME25 fuel blend exhibited better performance (BTE (2.52% higher at 5 lpm and 4.52% higher at 10 lpm), BSFC (1.8% lower at 5 lpm and 2.2% lower at 10 lpm), and increased combustion parameters with lower ignition delay and combustion duration and lower emission gases (CO (8.3% at 5 lpm and 13.4% at 10 lpm), HC (7.2% at 5 lpm and 13.1% at 10 lpm), smoke (4.27% at 5 lpm and 9.06% at 10 lpm)) except NOx emission (4.82% at 5 lpm and 8.16% at 10 lpm) when compared with CMME25 without hydrogen addition. The second phase discussed the effect of multi-walled nanotubes (MWCNTs) blended with CMME25 fuel enriched with hydrogen of 10 lpm. The addition of multi-walled nanotubes in the CMME25 fuel blend revealed that higher BTE and lower BSFC were observed. MWCNT nanoparticles operate as catalysts to accelerate combustion. Minimising ignition delay and HRR advances peak HRR. Hydrogen increased the hydrogen-carbon ratio, improved air/fuel mixing, and shortened combustion, reducing CO emissions. MWCNTs decreased HC emissions by catalysing fuel oxidation and combustion. NOx emission was 6.3 and 12.8% lower for MWCNT 50 and 100 ppm, respectively. Smoke emissions decreased by 8.1 and 14.22% for MWCNT 50 and 100 ppm. Nanoparticles improved fuel droplet evaporation, thermal conductivity, and smoke emission.

A Pseudocomponent-Based Approach for the Formulation of Evaporation Surrogates of Practical Liquid Fuels

ABSTRACT This study proposes and demonstrates a systematic methodology to formulate surrogates that can efficiently mimic the evaporation behaviors of real fuel droplets at elevated temperatures. The surrogates were designed by employing a discrete component evaporation model, which considers finite conductivity and mass diffusivity effects in the liquid phase. In the first place, a sensitivity analysis (SA) method was applied to rigorously assess the impact of each physical property on the fuel droplet evaporation behaviors. Then, the pseudo-component approach was employed to characterize the target fuel and estimate its physical properties based on hypothetical components. Comparing each pseudo-component (PC) with alkane hydrocarbons based on the most relevant properties (as identified from the SA) led to finding the most similar alkanes to those PCs. Thus, the proposed methodology allows to choose the optimal palette in a systematic manner. The final step is to optimize the mass fractions of the different constituents to emulate the evaporation characteristics of the target fuel by means of a multi-objective genetic algorithm. The fuel droplet evaporation was modeled for those selected compositions, and the results were validated against high-temperature experimental data obtained at a single falling-droplet facility for the target fuels. The method was applied on three different practical fuels, namely diesel, Jet A and heating oil, covering therefore a broad range of real applications. In all cases, the evaporation characteristics of the surrogates designed following the systematic methodology proposed here showed remarkable similarity to the target fuels.

Analysis on roles of thermal radiation to evaporation and combustion of fuel droplets

Thermal radiation is a significant mode of energy transmission besides conduction and convection in most combustion systems. Accurate treatment of thermal radiation is a crucial element for predicting the flame structure and pollutant formation. However, thermal radiation to fuel droplet evaporation is often neglected in the numerical simulations of two-phase spray combustion systems. In this paper, computational analysis on the thermal radiation to evaporation and combustion of fuel droplets in two-phase spray combustion is conducted. The influence of flame radiation on droplet evaporation and combustion is studied by adding radiation source term to the energy equation describing droplet evaporation process. Radiation transfer equation is solved, in which the radiation of CO2, H2O and soot is imposed to consider radiation effect of the flame. The partially premixed combustion model is employed, in which radiation heat transfer between droplet and ambient gases is taken into account. A reduced chemical reaction mechanism for n-heptane consisting of 76 species and 349 reactions is used. Four different numerical setups have been used and compared, and the simulation results coincide with the experiment data in terms of spray statistics and flame shapes. The peak flame temperature increases by 28 K when the radiative heat source term in the evaporation process is considered. The droplet evaporation is significantly enhanced by thermal radiation, leading to a promotion of 34.8% in C7H16 concentration in the center region of combustor. The concentration of combustion products, such as H2O and CO2, increases by 13.2% in the reaction region.

Effect of the Reynolds and Lewis number to the fuel droplet vaporization

In this work we present the effect of Reynolds and Lewis numbers on the fuel droplet vaporization of n-heptane. This study allows us to fully understand the vaporization phenomenon of fine fuel droplets (spray) in energy systems in order to improve combustion efficiency, reduce the formation of pollutants and unburned materials such as CO and NOx. The study is based on an analytical solution of the governing equations of the vaporization process by calculating the droplet diameter evolution, the temperature at the surface of the droplet, the mass fraction of fuel vapor and the mass-flow rate. The analytical results obtained by the theoretical model are compared to the experimental data in order to validate our results.

State of the Art of Fuel Droplet Evaporation

The process of fuel droplet evaporating is one of the most important factors that directly affect the efficiency of the combustion process. Therefore, the current study reviews previous studies that focused on the process of evaporation of a drop of fuel. The review is divided into points. The first part is concerned with modeling of the evaporation process under different initial condition and temperature of the droplet. The second part present the experimental studies concerned with measuring the evaporation time of the droplet, as well as the shape of the droplet during the evaporation process. Most of the studies related to this subject can be divided into three categories: The first category is the studies that are concerned with the process of heating the droplet and studying the evaporation time for different types of fuels or by adding nanomaterials to the fuel and studying their effect on the evaporation process. The second category is the studies concerned with the mechanics of droplet evaporation and the study of droplet shape. The third category is the studies that focus on studying the effect of initial conditions, such as temperature and pressure, as well as the concentration of gasses surrounding the drop and their types. There are other studies concerned with projecting the electric field onto the drop during the evaporation process and studying its effect.

Evaporation and micro-explosion performances of nano-fuel droplets

To investigate the effect of nanoparticles on the evaporation evolution of nano-fuels and reveal the mechanism of heterogeneous heat and mass transfer induced by the dispersion of nanoparticles, carbon nanotubes and CeO2 nano-fuels with different mass concentrations and particle sizes were prepared based on the two-step method and inspected using a laser particle size analyzer. An evaporation visualization apparatus for a single suspended droplet and an image processing technology were utilized to study the evaporation of diesel and nano-fuels at 400 and 700 °C. At 400 °C, the evaporation of diesel and nano-fuel droplets accorded with the D2-law and can be categorized as constant-volume and quasi-steady evaporation stages. The addition of nanoparticles suppressed the evaporation of fuel droplet and increasing the mass concentration or particle size can intensify the extent of suppression. At 700 °C, however, the micro-explosion of droplets occurred, and the variation in the droplet diameter did not conform with the D2-law. Evaporation can be categorized into the constant-volume and fluctuating evaporation stages. Nanoparticles, as heterogeneous nucleation sites, enhanced the expansion and micro-explosion intensities, thereby promoting the fuel droplet evaporation. An increase in the mass concentration or a decrease in the particle size can promote evaporation significantly.

Impacts of preferential vaporization on flashback behaviors of multi-component liquid fuels

Liquid transportation fuels are composed of a wide range of molecular structures and weights, therefore exhibiting a relatively large distillation temperature range. When fuel chemical properties change along with the distillation temperature curve, preferential vaporization effects could play a role in near-limit combustion behaviors. The objective of this study is to experimentally evaluate the role of preferential vaporization on flame flashback behaviors. A unique spray burner is developed to control the extent of fuel spray vaporization by adjusting flow rates and/or the spray injection location from the burner exit. Spray characteristics are comprehensively determined using Phase Doppler Particle Analyzer. Two binary component mixtures are formulated (n-octane/iso-cetane and iso-octane/n-hexadecane) to exhibit common combustion behaviors in the fully vaporized condition but have considerably different preferential vaporization characteristics. Identical flashback behaviors of two mixtures are observed for fully pre-vaporized conditions by setting the burner temperature at 700 K, including both propagation- and ignition-driven flashback behaviors. Partially vaporized conditions are investigated at two global equivalence ratios (1.0 and 1.4) by setting the burner temperature at 450 K. The flashback behaviors for both global equivalence ratio conditions are found to be affected by the preferential vaporization characteristics represented by laminar flame speeds of the vaporized fuel mixture composition. The relative significance of local flow perturbation induced by instantaneous fuel droplet evaporation near the flame surface has been also investigated by analyzing planar laser-induced fluorescence images, as well as considering the changes of Markstein length with the extent of fuel vaporization. Finally, the relative contributions of local laminar flame speed representing local fuel vapor deposit, local flow perturbation, and preferential vaporization are evaluated through feature sensitivity analyses.

Evaporation of a 1-Butanol Gel Fuel Droplet under Elevated Pressure Conditions.

In this study, the evaporation characteristics of a gel fuel droplet under elevated temperatures and pressures were studied. 1-Butanol was selected as the base fuel because it is eco-friendly and has a calorific value similar to that of hydrocarbon-based fuels. In the experiment, 2.5 and 3 wt % hydroxypropyl methylcellulose (HPMC) was added as a gellant to generate the gel fuel. The viscosity of the gel fuel significantly increased compared to that of the 1-butanol fuel, and it decreased as the shear rate increased, which is referred to as the shear-thinning behavior. The evaporation of the 1-butanol gel fuel was divided into three periods, which were categorized as droplet heating, puffing, and crust formation. The behavior of each period changed as the ambient conditions changed. The elevation of the ambient temperature and gellant concentration boosted the intensity of puffing, whereas puffing was suppressed under higher-ambient-pressure conditions. When the ambient temperature increased from 600 to 700 °C, the evaporation rate of the gel fuels increased due to the increase in heat supply from the ambient temperature. Nevertheless, an increase in the ambient pressure and mass concentration of the gellant did not significantly affect the evaporation rate of the gel fuel.

Effect of micro-explosion of biodiesel and ethanol droplets on evaporation: A three-stage mixed fuel droplet evaporation model

The ejection and micro-explosion of a mixed fuel droplet group affected the evaporation and combustion rate of fuel. In order to explore the evaporation, micro-explosion, and interaction rules of the biodiesel and ethanol droplet group with different component proportions and volumes during heating, a set of multiparameter tubular furnace experimental equipment was designed. By setting the experimental parameters of the tubular furnace, the heating sequence pictures of the biodiesel and ethanol droplet group were obtained by high-speed photography, and the droplet parameters were analyzed and processed by Image-Proplus. In the experiment, not only the phenomena of ejection, micro-explosion, and white fog but also the interactions of collision, interweaving, and fusion of droplets were observed, which affected the micro-explosion and evaporation of individual droplets in the droplet group. When the ratio of biodiesel to ethanol was 40:60 (40% biodiesel and 60% ethanol), the micro-explosion intensity was the highest. For the same type of droplet, the higher the micro-explosion intensity, the higher the evaporation rate, and the super micro-explosion made the droplet evaporate almost instantaneously. The modified equation for calculating the micro-explosion intensity was established, and the micro-explosion intensity of the mixed droplet was calculated. By integrating the droplet micro-explosion intensity equation and evaporation equation, a three-stage evaporation model of the mixed droplet was established, and the average evaporation rate of the second-stage BD30E70 (30% biodiesel and 70% ethanol) droplet was nearly 28 times the first stage, which was nearly 32 times the third stage.

Comparison of evaporation rate constants of a single fuel droplet entering subcritical and supercritical environments

This work compares the evaporation rate constants of a single fuel droplet under subcritical and supercritical environments by experimental visualizations (in millimeter scale) and molecular dynamics simulations (in nanometer scale). The objection is to understand the differences of fuel droplet evaporation rate constant variations under the subcritical and supercritical environments. Firstly, an experimental apparatus is designed to study the diesel droplet evaporation under subcritical and supercritical environments. The results show that the droplet evaporation obeys the D2 law in subcritical environments, while the D2 law is no longer strictly applicable in supercritical environments and the evaporation rate constant isn’t a constant but a variable that increases with the evaporation time. Secondly, the molecular dynamics simulations are applied to investigate the evaporation of diesel surrogate n-dodecane under subcritical and supercritical environments. The results show that the droplet temperature keeps at the equilibrium temperature in subcritical environments, but keeps increasing in supercritical environments. In supercritical environments, the reason for the evaporation rate constant keeps increasing is that the droplet density keeps decreasing with the increase of droplet temperature. The droplet surface tension will rapidly vanish in supercritical environments, which implies that the formation of fuel–air mixture is no longer dominated by the surface tension, but is the turbulent diffusion in diesel trans/supercritical injection conditions. It can deduce that the evaporation rate constants of a fuel droplet in micrometer scale (that is commonly generated in engines) will follow the same trend and within the same variation scale at the same ambient pressures and temperatures.

On the evolution of fuel droplet evaporation zone and its interaction with flame front in ignition of spray flames

Evolution of fuel droplet evaporation zone and its interaction with propagating flame front are studied in this work. A general theory is developed to describe the evolutions of flame propagation speed, flame temperature, droplet evaporation onset and completion locations in ignition and propagation of spherical flames. The influences of liquid droplet mass loading, heat exchange coefficient (or evaporation rate) and Lewis number on spherical spray flame ignition are studied. Two flame regimes are considered, that is, heterogeneous and homogeneous flames, based on the mixture condition near the flame front. The results indicate that the spray flame trajectories are considerably affected by the ignition energy addition. The critical condition for successful ignition for the fuel-rich mixture is a coincidence of inner and outer flame balls from igniting kernel and propagating flame. The flame balls always exist in homogeneous mixtures, indicating that ignition failure and critical successful events occur only in purely gaseous mixture. The fuel droplets have limited effects on minimum ignition energy, which, however, increases monotonically with the Lewis number. Moreover, flame kernel originates from heterogeneous mixtures due to the initially dispersed droplets near the spark. The evaporative heat loss in the burned and unburned zones of homogeneous and heterogeneous spray flames is also evaluated, and the results show that for the failed flame kernels, evaporative heat loss behind and before the flame front first increases and then decreases. The evaporative heat loss before the flame front generally increases, although non-monotonicity exists, when the flame is successfully ignited and propagate outwardly. For heterogeneous flames, the ratio of the heat loss from the burned zone to the total one decreases as the flame expands. Moreover, droplet mass loading and heat exchange coefficient considerably affect the evaporating heat loss from burned and unburned zones.

Experimental Study on Evaporation Characteristics of Light Cycle Oil Droplet under Various Ambient Conditions

The authors conducted droplet evaporation experiments of light cycle oil (LCO) at various ambient temperatures and pressures. Five kinds of LCO and three kinds of arranged fuels were used. We investigated the evaporation characteristics of LCO and the relationships between the evaporation characteristics and the cetane index. In addition to that, a surrogate fuel composed of four chemical species, which can simulate the droplet evaporation characteristics of LCO, was suggested. Experimental results show that the differences in droplet lifetime between fuel species become larger with decreasing ambient temperature. This is because the low volatile component made the evaporation rate outstandingly slow at a low ambient temperature. It was found that the relationship between droplet lifetime and the late-stage distillation temperature becomes stronger at low ambient temperature and high ambient pressure. By an analysis employing the properties of chemical species in LCO surrogate fuel, it is clarified that the mass evaporation rate becomes smaller than the internal diffusion, which is the condition similar to that in the distillation test. Finally, the relationship between the droplet lifetime and the cetane index was investigated. It can be concluded that the droplet lifetime is independent of the cetane index under all conditions tested in this study. The experimental data obtained by this research can be utilized for the validation of multicomponent fuel droplet evaporation models in the future.

Numerical and experimental study of the effects of fuel injection and equivalence ratio in a can micro-combustor at atmospheric condition

The present paper aims to examine experimentally and numerically the effect of equivalence ratio and injection pressure on combustion in a can combustor. The results show the combustor temperature rises with an increase in the overall equivalence ratio. With an increase in the injection pressure at a constant equivalence ratio, the flame is extended to the combustor downstream. The IRZ (Inner Recirculation Zone) region in the primary zone has high turbulence kinetic energy increasing the fuel droplet evaporation rate. This zone provides a region of appropriate mixing of fuel-air, leading to a zone of flame-holding. In the intermediate zone, the mixture fraction near liner walls reaches its stoichiometric value, and a flame is formed near the liner walls. With an increase in the equivalence ratio or injection pressure at constant equivalence ratio, the incomplete combustion species is reduced and the pattern factor and combustion efficiency are improved.

Theoretical and numerical analysis of the evaporation of mono- and multicomponent single fuel droplets

Abstract

Effect of Micro-Explosion of Biodiesel and Ethanol Droplets on Evaporation: A Three-Stage Mixed Fuel Droplet Evaporation Model

Effect of Micro-Explosion of Biodiesel and Ethanol Droplets on Evaporation: A Three-Stage Mixed Fuel Droplet Evaporation Model

An experimental assessment of the enhancement of fuel droplet vaporization in a very high turbulence intensity environment

A zero-mean flow fan-stirred chamber is used to gather data on suspended fuel droplet evaporation at turbulence intensities, q1/2, approaching 4.30 m/s. This research is driven by the oft-cited but unconfirmed belief that the droplet evaporation rate, K, eventually plateaus with increasing turbulence kinetic energy. Further motivation comes from numerous real-world examples, including combustion systems, where droplets are exposed to turbulence intensities far beyond the experimental capabilities reported in the literature to date. Decane, ethanol, and heptane fuels are selected and grouped into two categories based on the similarity of their vapor pressures, Pv, and mass diffusivity coefficients, DAB, in an effort to discern which thermophysical properties are important to vaporization enhancement, or lack thereof, in high turbulence. Individual droplets with constant initial diameters, d0, of 500 µm are placed in the central region of a highly homogeneous and isotropic turbulent flow field using a novel multi-fiber intersection technique. Neither alkane fuel exhibits any sign of reduced effect of turbulence, as K/K0 remains a strongly linear function of turbulence intensity throughout the test conditions. Conversely, the normalized evaporation rate of ethanol begins to plateau at the higher levels of intensity. Although equalizing the vapor pressures of ethanol and heptane was sufficient to match K/K0 values at low intensity, their divergence as q1/2 increases implies that the thermodynamically-predicted vapor quantity at the droplet surface does not enforce an upper limit on turbulence effectiveness at moderately elevated temperatures. This is confirmed by decane, which has the lowest volatility and yet experiences the greatest improvement in evaporation rate at the highest levels of turbulence.