Micro-explosion Phenomenon Research Articles

The decarbonization of coal tar via microwave-initiated catalytic deep dehydrogenation

Coal tar, a major by-product of the coal industry, presents considerable difficulties in its refining and conversion into fuels due to its complex chemical composition and physical properties, such as high viscosity, corrosiveness, thermal instability, etc. Here we report a new route for producing hydrogen-rich gases together with carbonaceous materials, including carbon nanotubes, through the microwave-initiated catalytic deep dehydrogenation of coal tar using inexpensive iron catalysts. The resulting carbonaceous materials generated over the catalyst were investigated using a variety of techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature programmed oxidation (TPO) and Raman spectroscopy. Importantly, we have found that an aqueous emulsion feed of the coal tar enables considerably easier handling and an enhanced hydrogen production whilst also significantly reducing the extent of catalyst deactivation. This behaviour is shown to be assisted by the phenomenon of micro-explosion that enhances mass and heat transfer during the catalytic reactions.

Abating environmental pollutants of a diesel engine by using emulsified fuel

The present work primarily focused on the impact of emulsified fuel in a diesel engine on environmental pollutant reduction. In this investigation, Water in Diesel Emulsion10 (WiDE10) was used as a fuel. It was injected at three different injection timings (IT). The first one was at a normal injection timing of 23° Before Top Dead Centre (BTDC), the second one was advanced injection timing of 26° BTDC and the third one was the retarded injection timing of 20° BTDC. The higher water content emulsified fuel showed the maximum diminishing of oxides of nitrogen (NO X ) emissions. This is due to the effect of lower combustion temperature. The brake specific fuel consumption (BSFC) increased with an increase in water quantity. This is due to the decrease in the overall heating value of the fuel mixture. The combustion efficiency got improved for WiDE when compared with the pure diesel. This effect can be attributed to a micro-explosion phenomenon.

Effective power and effective power density analysis for water in diesel emulsion as fuel in diesel engine performance

In the present theoretical study, a comparative performance analysis of a single cylinder compression ignition engine with diesel, 5% and 10% water in diesel emulsion as fuels have been investigated. Effect of variation in engine operating parameters like inlet pressure, friction coefficient compression ratio, equivalence ratio, and a residual gas fraction on engine performance parameters, i.e., effective power, effective power density, and total heat loss have been analyzed. Analysis has been carried out on the basis of isobaric heat addition and isochoric heat rejection assumptions with temperature variable specific heats and composition of alternative fuels. Microexplosion phenomenon for secondary atomization in water in diesel emulsion fuels improves the fuel combustion efficiency for better performance.The theoretical analysis revealed that the effective power and effective power density for diesel fuel are found to be increased by 14.4% and 28.6% respectively, compared to 5% and 10% water in diesel emulsion fuels in compression ignition engine at 1 bar inlet pressure. Highest effective power and effective power density are obtained with an equivalence ratio of 1.2 for all mentioned fuels. Increase in inlet pressure results in increase effective power, effective power density, and total heat loss performances. Highest effective efficiency has been found with an equivalence ratio of 0.89 for diesel, 5% and 10% water in diesel emulsion fuels and is highly affected by inlet pressure for all mention fuel type. Also, an increase in friction coefficient and residual gas fraction decreases effective power, effective power density and effective efficiency for diesel, 5% and 10% water in diesel emulsion fuels. Obtained results are an essential tool for compression ignition engine designer and also provoked to use the water in diesel emulsion fuels as an alternative fuel in place of neat diesel fuel.

The Viscosity and Combustion Characteristics of Single-Droplet Water-Diesel Emulsion

Diesel fuel exhibits excellent combustion characteristics and stability. However, diesel use is becoming restricted because of its associated environmental problems. Fuel emulsification, which increases efficiency and reduces pollution, became the solution of environmental problem. In this study, five water:diesel emulsions with mass ratios (0.3, 0.6, 1.0, 1.2, and 1.5) via ultrasonication were synthesized with and without surfactant. The optimal water:diesel ratio (=1:1) of an emulsion containing the surfactant was found by analyzing fuel concentration, mixing time, and viscosity. The combustion characteristics of single-droplet optimal emulsions were studied through ignition delay, burning rate, and total droplet lifetime at high temperature (400–700 °C) and pressure (1–15 bar), and micro-explosion phenomenon was observed. Although the ignition delay of emulsion increased, the total lifetime of the emulsion droplet was lower than that of diesel under 5 bar, 600 °C condition.

Evolution of Microexplosion Phenomenon in Parent–Child Droplets of Water in Biodiesel Emulsions Enhanced by Different Surfactant Dosages and Hydrophilic–Lipophilic Balance Values

This experimental study endeavors to investigate the evolution of microexplosion phenomenon of water in biodiesel emulsion droplets with the base fuel (B5) containing 95% diesel and 5% of palm oil methyl ester (POME). Parameters such as water content varied from 9%, 12%, and 15%, surfactant dosages of 5%, 10%, and 15% and the hydrophilic–lipophilic balance (HLB) values of 6, 7, 8, and 9 were varied to study its impact on microexplosion phenomenon. Three different sizes of emulsion droplets of approximately Ø2.8 mm, Ø2.2 mm, and Ø0.3 mm were visualized for the evolution of microexplosion phenomenon under the Leidenfrost effect using hot plate as a heat source. The evolution of microexplosion phenomenon of parent droplets, puffing behavior, and waiting time was visualized with high-resolution images. It was observed that the coalescence process was the dominating factor in inducing the microexplosion, and the coalescence process can either be advanced or be delayed by the surfactant dosage. The waiting time for the microexplosion was found to be influenced by the surfactant dosage and the droplet size. The rate of phase change of emulsions and puffing was found to be influenced by the surfactant dosage. By analyzing the postbehavior of the child droplets formed after the microexplosion of the parent droplet, it was observed that the child droplets undergo a series of puffing process and eventually microexplosion phenomenon also. The size of the parent droplets has a significant influence on the size of the child droplet.

The Influence of Formulation Ratio and Emulsifying Settings on Tri-Fuel (Diesel–Ethanol–Biodiesel) Emulsion Properties

In this study, an alternative fuel for compression ignition (CI) engines called tri-fuel emulsion was prepared using an ultrasonic emulsifier. The objective of the study is to investigate the effect of emulsifying settings and formulation ratio on the physicochemical properties of tri-fuel emulsions. Design of experiment (DOE) with the two-level factorial design was employed to analyze the effect of emulsifying settings such as time, amplitude, and cycle along with the variation ratio of tri-fuel emulsion components as control factors. Numbers of responses identified were important parameters that may contribute to microexplosion phenomenon in CI engine. Analysis of variance (ANOVA) was carried out for each response, and the results indicated that density, dynamic viscosity, surface tension, and average droplet size were influenced by specific preparation control factors. Furthermore, interaction among the control factors was found to affect the responses as well. Interaction means the effect of two factors together is different than what would be expected from each factor separately. Besides, the stability of the tri-fuel emulsion was observed for three months. Furthermore, a qualitative approach with a multiobjective lens digital microscope revealed the geometry of freshly made dispersed tri-fuel emulsion droplets. Microscopic examination on tri-fuel emulsion droplets has shown that the dispersed ethanol capsulated within diesel with the help of biodiesel is similar to a water in diesel emulsion and is dissimilar to commercial diesel mixed with fatty acid methyl esters found in the market.

A comprehensive review on water-emulsified diesel fuel: chemistry, engine performance and exhaust emissions.

Increasing environmental concern, human health and the continuous upgradation in the stringent standards of vehicular emissions have shown much interest in cleaner diesel fuels. Out of various strategies to mitigate the diesel engine emissions, use of water blended diesel in the form of emulsion has grabbed sufficient attention of the fuel research community. Various researches have shown that water-emulsified diesel has sufficient potential to improve the engine performance simultaneously with a significant reduction in the levels of nitrogen oxides (NOx) and particulate matter (PM) emissions. Micro-explosion phenomenon of combustion in emulsion fuel helps to provide efficient and complete combustion which in turn improves brake thermal efficiency. The current study presents a comprehensive review of the usage of water-emulsified diesel fuel in CI engines. Focusing on the performance, combustion, and emission analysis, it also talks in detail about the principle and the chemistry involved in making of a stable and homogeneous water-diesel emulsion compatible for CI engine. The literature survey concludes two crucial points. First, the water-blended diesel emulsion serves as an economical, fuel efficient, and cleaner combustion technology. Second, the optimum blend ratio, emulsifier quantity, and proper process differs in almost all the research papers and hence needed to be standardized.

Experimental understanding on the dynamics of micro-explosion and puffing in ternary emulsion droplets

Dynamics of puffing and micro-explosion phenomena occurring in ternary fuel emulsion droplets under high temperature environment were explored using high speed backlight imaging technique. A single droplet composed of diesel-biodiesel-ethanol emulsion was placed at the tip of a 75 µm gauge thermocouple and introduced rapidly into a furnace maintained at 500 °C. Several interesting features such as oscillation of suspended droplets, physical transformations occurring within the droplet, vapour expulsion, puffing, micro-explosion, sheet formation, perforations, growth of perforations, sheet disintegration and rotation of secondary droplets were observed. High resolution image analysis revealed separation of emulsion components within the core of the suspended droplet, which appeared either as a single nucleus or multiple nuclei. Two distinct types of micro-explosion were identified. For droplets encountering a single nucleus at the core resulted in a stronger vapour expulsion followed by intense micro-explosion. For droplets having multiple nuclei at the core resulted in a weaker vapour expulsion and slower growth of droplet prior to micro-explosion. Both types of micro-explosion process resulted in a number of child droplets. For the case of strong vapour expulsion nearly 80% of its child droplets have their sizes distributed within 150 μm compared to 60% for weaker vapour expulsion. The child droplets that were generated from the primary events of both puffing and micro-explosion cascaded further into secondary and tertiary events of puffing and micro-explosion in freely suspended environment.

Hydrogen production from crude oil with fine iron particles through microwave-initiated catalytic dehydrogenation promoted by emulsified feed

With increasing concerns about climate change caused by carbon dioxide emissions, decarbonization is rapidly becoming an important and attractive challenge for continuing fossil fuel utilization. This paper reports an entirely new route of producing hydrogen directly from crude oil through microwave-initiated, iron-catalyzed deep dehydrogenation. Importantly, there is very little carbon dioxide emission in this process, a key element towards stabilising global mean temperature. The analytical techniques of Scanning Electron Microscope, Transmission Electron Microscopy, Temperature Programmed Oxidation and Raman spectroscopy were employed to interrogate the catalytic process and the nature of carbon deposition over the catalyst which was brought about by the dehydrogenation process. The presence of emulsified feed significantly promotes hydrogen production, owing to its presence depressing carbonaceous deposition on the catalyst together with the occurrence of the micro-explosion phenomenon.

Effect of water–kerosene emulsified fuel on radiation, NOx emission and thermal characteristics of a liquid burner flame in lean combustion regime

A homogeneous stable emulsified fuel containing 5% water, 93% kerosene and 2% surfactant (1.68% span 80 and 0.32% tween 80) was prepared. Then, the effects of the fuel on the flame structure, radiation heat flux, thermal characteristics and NOx pollutant emission of a liquid burner were investigated in lean combustion regime. Light microscopy imaging of the stable water–kerosene emulsified fuel was used to analyze the micro-explosion phenomenon of the fuel droplets. Also, based on chemiluminescence technique, a TES-1332A digital luminance meter with spectral sensitivity close to CIE photopic curve was used to determine the effect of intermediate soot and carbonaceous particles on flame emissivity coefficient. The results indicate that the micro-explosion phenomenon of emulsified fuel droplets produces a large number of small-scale droplets which, compared with neat kerosene, enhance the mixing rate and decrease the flame reaction zone. Also, although the heat absorbed by the water content of emulsified fuel decreases the flame temperature, emulsified fuel enhances the average emissivity coefficient and radiation heat flux as much as 58% and 25%, respectively. The results also demonstrate that emulsified fuel increases the yellow luminous radiation of flame, which means the concentrations of intermediate soot and carbonaceous particles in the flame have been enhanced. Furthermore, in the case of emulsified fuel, in comparison with neat kerosene, decrease in flame temperature along with increase in OH radicals by water dissociation lead to decrease in the NOx pollutant emission as much as 34%.

Ignition and combustion of a single aluminum particle in hot gas flow

For simulating the aggregated aluminum bulks on the burning surface of solid propellants, large aluminum particles (40–160 µm) are used in this work. The isolated aluminum particles are ignited in hot oxidizing gas. Based on the bright-spot diameter profiles and the known respective reaction mechanisms, the total ignition and combustion process of aluminum particle can be divided into three stages, namely, pre-heating, ignition and combustion. The initial and bright-spot diameters of the aluminum particle are measured directly from the images by using the in-house automated data processing routines. Ignition delay time, ti, and combustion time, tc, are also obtained by post-processing the sequential images and can be associated with the particle diameters, D, in the form of ti = aD + b and tc = αD, respectively. The changing trends of ignition delay time and combustion time with the effective oxidizer mole fraction in the range of 22.8%–49.1% are distinctly different. The oxidizing environments with a high effective oxidizer mole fraction can result in short combustion time but long ignition delay time. For small particles (40–110 µm), the environmental effective oxidizer mole fraction exerts a limited effect on the sum of ignition delay time and combustion time, which indicates total time. By considering the effects of particle sizes and effective oxidizer mole fractions of environments, the percentages of ignition delay time in the total time are analyzed. These results suggest that with the goal of decreasing the total time, suitable methods can be employed for different conditions. Furthermore, we observe and discuss the phenomenon of aluminum particle microexplosion in an environment with high effective oxidizer mole fraction, which decreases particle combustion time by a large margin.

Experimental investigation of emulsified fuels produced with a micro-channel emulsifier: Puffing and micro-explosion analyses

In this investigation, puffing and micro-explosion occurrence in emulsified fuels are studied. The emulsified fuels are formulated using a micro-channel emulsifier, a blend of rapeseed oil in diesel fuel as continuous phase, water as dispersed phase and Sorbitan Sesquioleate as surfactant. Several stable dispersed systems are obtained, classified as emulsions based on their optical appearance and dispersed droplet size. The dynamic viscosity measured as a function of shear rate indicated non-Newtonian behavior with a shear-thinning response for all emulsions. An increase of water percentage led to emulsified fuels with higher viscosity levels. Finally, puffing and micro-explosion occurrence was studied by placing emulsified fuel droplets on a heated plate leading to the Leidenfrost effect. The puffing occurrence is reported for all emulsified fuels tested. A sudden puffing is noted when the water ratio is increased. Conversely, the micro-explosion phenomenon only occurred in emulsions formulated without surfactant. However, an analysis conducted on a smaller emulsion droplet showed several ejected child droplets and micro-explosion. This fact denotes a strong relationship between the emulsion droplet size, water ratio and water droplet size with the occurrence of the puffing and micro-explosion phenomena.

Micro-explosion and burning characteristics of a single droplet of pyrolytic oil from castor seeds

In the study, castor pyrolytic oil is produced from castor seeds by thermal pyrolysis and its pyrolysis reaction and oxidation reactions are investigated using thermogravimetric analysis. The results are also used to evaluate the characteristic combustion properties, such as the ignition temperature, burnout temperature and combustion characteristics index. The suspended droplet experimental system is also used to explore the micro-explosion phenomena and combustion modes of castor pyrolytic oil under different ambient temperatures. The castor pyrolytic oil is a multi-component fuel and has a complex process during the heating process and micro-explosion occurs, causing the droplet surface distortion. According to the timing and strength of the micro-explosion, there are three different stages: low intensity micro-explosion in the first stage, high intensity micro-explosion in the second stage and medium intensity micro-explosion in the final stage. After high-intensity micro-explosion occurred at 550°C, more volatile vapors were released and the flammable mixture will formed a flame wrapping around droplets after ignition. During the droplet combustion process, the micro-explosion occurred continuously, but the droplet still maintained a sphere-like appearance. The variation of droplet size generally followed d2-law and the combustion rate constant is approximately 1.483mm2/s.

Combustion of aluminum nanoparticle agglomerates: From mild oxidation to microexplosion

While the nano-sized energetic materials are featured with ultra-high energy density, the ubiquitous agglomeration in their combustion is still unexplored. In this paper, the combustion characteristics of aluminum nanoparticle agglomerates in the size range of 4–20µm are investigated on a modified Hencken burner with different temperature (800–1800K) and oxygen concentration (0.5–5.5mol/m3). Due to the heat accumulation effect of the designed porous structures, the nanoparticle agglomerates even maintain the advantages of combustion process of single nanoparticle in terms of a low ignition temperature (∼800K) and a fast energy release rate. Further, the combustion of agglomerates is numerically studied by a newly-developed model, which accurately predicts both burn time and temperature of agglomerate of the mild combustion process. The microexplosion phenomenon occurs when the oxygen concentration exceeds 3.5mol/m3. Measurements of particle temperature, burn time, emission spectra and morphologies indicate that this explosion is driven by the vaporization of unreacted aluminum core, which results in huge stresses to tear the Al/Al2O3 particle into many smaller, dispersed clusters. Thus a melt/vapor dispersion mechanism (MVDM) based on melt dispersion mechanism is proposed to cover the microexplosion and subsequent accelerated oxidation reactions.

Puffing and micro-explosion of diesel–biodiesel–ethanol blends

The puffing and micro-explosion of a single burning droplet comprised of neat diesel, rapeseed methyl ester (RME); binary fuel mixtures of diesel–ethanol, diesel–RME, RME–ethanol; and ternary microemulsion of these fuel blends at various compositions have been studied using high speed backlight imaging method. Fuel droplet was suspended on the tip of a 130μm gauge thermocouple and it was ignited using a glow plug heater. Based on the temporal variation of droplet projected area, the characteristics of fuel droplets studied were classified into smooth burning, puffing and explosion. A ternary plot has been proposed to identify the mixture composition of the blends that can result in smooth burning, puffing and explosion. Micro-explosion phenomenon was observed in the ternary blends with ethanol percentages between 10% and 40%. Secondary droplets resulted from the puffing and explosion of suspended parent droplet were observed to undergo further explosion. The time scales associated with complete disintegration of secondary droplets are found to be comparable to the mixing and the chemical reaction time scales of sprays in diesel engines.

Effect of emulsion fuel on engine emissions–A review

Emulsion fuel is an unconventional fuel for diesel engines, which can be used without modifications in the engine. The benefits of an emulsion fuel include lowering the emissions of nitrogen oxides (NOx) and particulate matter (PM) which are harmful to health and cause diesel engines to suffer. This paper explains in detail the effect of water in the emulsion fuel on the emissions of NOx, PM, carbon monoxide (CO), hydrocarbon (HC), smoke and exhaust temperature. Experimental results from various researchers show a decrease in the NOx and PM emissions simultaneously. However, the results with the increasing water percentage in emulsion fuel are not consistent for HC and CO emissions. The water content in emulsion fuel affects the combustion and reduces the peak temperature in the combustion chamber. On the other hand, microexplosion phenomenon occurs and causes an increase in the volatility of diesel fuel which improves the combustion efficiency.

Experimental Investigation of Microexplosion Occurrence in Water in Diesel Emulsion Droplets during the Leidenfrost Effect

Microexplosion phenomenon is attributed for achieving simultaneous reduction of particulate matter and nitrogen oxides in diesel engine exhaust when water in diesel emulsion is used as fuel. In this work, an emulsion droplet suspended on a wire-type thermocouple on a hot plate as the heat source was used to study the evolution of microexplosion phenomenon of emulsions prepared by two different methods. Microexplosion behavior of emulsions produced by a homogenizer and mechanical stirrer with 5, 10, and 20% water by volume was visualized. A high-speed camera synchronized with a data-logging system was used to capture the events. The results show that the waiting time, puffing frequency, initial temperature drop, and microexplosion temperature were affected by the size and distribution of the dispersed water droplets. No microexplosion was observed for all of the homogenized emulsions, while all of the mechanically stirred emulsions developed microexplosions.

Distribution of thermal energy of child-droplets issued from an optimal micro-explosion

The micro-explosion phenomenon is involved in emulsified fuel droplets placed in a hot atmosphere, such as spray combustion. Droplets of water-in-sunflower oil emulsion are used, since they are representative of a class of emulsions used in practical applications of biofuels. Once the micro-explosion is triggered after a short delay, the rapid (⩽1ms) vaporization of the inside water droplets and the subsequent disintegration of the emulsion droplet blow the fragmented droplets away. These fragmented droplets are called “child-droplets”, and they are too small and fast for an on-the-fly infra-red imaging thermal characterization. The present study focuses on the thermal reaction of a thin plate when impacted by them. Thorough and detailed tests are carried out, to make sure that the plate and the acquisition system are collecting a data that is actually representative of the child-droplets thermal energy. A quantitative post-processing is applied to the transient temperature field on the plate. It leads to the thermal energy of the whole plate, and of representative samples of individual child-droplets. The results show that their thermal energy is governed by a log-normal distribution.

Current Trends in Water-in-Diesel Emulsion as a Fuel

Water-in-diesel emulsion (WiDE) is an alternative fuel for CI engines that can be employed with the existing engine setup with no additional engine retrofitting. It has benefits of simultaneous reduction of both NOx and particulate matters in addition to its impact in the combustion efficiency improvement, although this needs further investigation. This review paper addresses the type of emulsion, the microexplosion phenomenon, emulsion stability and physiochemical improvement, and effect of water content on the combustion and emissions of WiDE fuel. The review also covers the recent experimental methodologies used in the investigation of WiDE for both transport and stationary engine applications. In this review, the fuel injection pump and spray nozzle arrangement has been found to be the most critical components as far as the secondary atomization is concerned and further investigation of the effect of these components in the microexplosion of the emulsion is suggested to be center of focus.

Emulsion droplet micro-explosion: Analysis of two experimental approaches

Combustion of water in oil μ-emulsions is still considered as a useful technology for the energy conversion of waste oil. One of the most relevant advantages is related to the phenomenon of micro-explosion (μ–e) that produces the secondary atomization of the oil. Several experimental approaches have been proposed in the last years with the aim to characterize the μ–e effect under different conditions. In this paper, an experimental comparison between the two useful approaches is presented. The results obtained with the technique of the Suspended droplet will be related to data present in the literature, obtained through the Leidenfrost technique. Quantitative thermal results such as the μ–e temperature and the fall temperature after μ–e show the most important differences. The important role played by the separation process as coalescence and creaming in both approaches is also discussed.