Micro-explosion Phenomenon Research Articles

Microexplosion of aluminum slurry droplets

The microexplosion of a slurry droplet is experimentally and theoretically investigated. The microexplosion was considered to be caused by the shell formation and the following pressure build-up in the shell which would be promoted by the suppression of evaporation, subsequent superheating and heterogeneous nucleation of a liquid carrier. Experimentally, the microexplosion phenomena was examined for various surfactant concentrations and particle loading under different ambient temperature ranges (500–900 K). To closely investigate the pressure build-up and the heterogeneous nucleation, a numerical model was introduced by considering the three stages such as the shell formation, suppression of evaporation and pressure build-up inside. The microexplosion time was estimated by postulating the limit of superheat for heterogeneous nucleation. The simulation yielded a reasonably good agreement with experimental results for Al/ n-heptane slurry droplets under various solid loadings (10–40 wt.%).

Influences of vanadium compound on burning characteristics of emulsified marine fuel oil C

Vanadium is one of the most significant trace elements in heavy fuel oils. While most previous studies emphasize its effects on the high-temperature corrosion of power-plant materials, the understanding of the basic combustion characteristics influenced by the vanadium content in fuel oils is still rather limited. The influences of the controlling factors, such as water-to-oil ratio, amount of emulsifying agent, and content of vanadium pentoxide on the burning characteristics of marine heavy No.6 fuel oil are thus investigated in this experimental study by using a suspended droplet approach. It is shown that the ignition delay, degree of micro-explosion, burning time, and flame length are affected by those factors to various extents. Increase of the water-to-oil ratio might enhance the micro-explosion phenomenon while the addition of an appropriate amount of the emulsifying agent Span-80 promotes the homogeneity of micro-water-droplets over their oil base, leading to alterations of the heated droplet characteristics of the emulsions. However, the existence of V 2O 5 in a fuel oil would result in deterioration of burning quality.

Study on Behavior of Birchley-Riley's Fuel Droplet Heated in the Electric Furnace.

As a Birchley-Riley's fuel droplet consisted of an aqueous core embedded within a liquid fuel shell was heated in the electric furnace, the puffing and the microexplosion were observed. The waiting time for microexplosion was dominated by water content, droplet volume, fuel type and ambient temperature. When the waiting time data plot was fitted by Weibull distribution, its shape parameter was equal to 2 and the microexplosion phenomenon was classified as wear out failure type.

Behavior of Ignition and Combustion for Asphalt/Water-Emulsified Fuels.

The ignition and combustion behavior of single droplets of asphalt/water emulsified fuel (As/W) were observed in an electric furnace in order to obtain fundamental data for practical use. The ignition delay and the burnout time of single droplets of asphalt. C-heavy oil and As/W emulsions were investigated under specified furnace temperatures. Each fuel showed peculiar ignition and combustion behavior, and especially As/W emulsified fuel-J (As/W J) had a very strong microexplosion. The values of the ignition delay and the burnout time of As/W emulsified fuels were smaller than those of asphalt and C heavy oil. The reason can be explained by the occurrence of the microexplosion phenomena. Thus, the mechanism was discussed for some factors related to the phenomena.

Nonideal vaporization of dilating binary droplets with radiation absorption

A recently developed liquid vaporization model for multicomponent droplets has been enhanced in order to study the effect of thermal radiation absorption in binary droplet vaporization. The possible coupling between radiation absorption and droplet microexplosion is also investigated. The results show that radiation absorption can influence droplet vaporization in combustion environments. In addition to this, the results serve to explain some experimental findings on microexplosion phenomena, such as the radial location of the onset of bubble formation. The vaporization model including radiation absorption also predicts the experimentally observed sparkle at the end of droplet combustion (flash vaporization).

An Experimental Investigation of Burning Droplets of Emulsified Marine Fuel Oils with Water

An experimental investigation is presented of the influences of emulsification of marine fuel oils A and C with water on the micro-explosion phenomenon and combustion characteristics of a burning droplet. The amount of surfactant and water-to-oil ratio by volume in the emulsion are varied to observe the variations of ignition delay, flame length, time required to attain the maximum flame length, duration as well as intensity of micro-explosion, flame appearance, and overall burning time. The measurements show that the emulsification effects on the combustion of marine fuel oils A and C are different. A droplet of C-oil emulsion is shown to be influenced by the addition of water and surfactant more significantly. The micro-explosion phenomena of droplets of A-and C-oil emulsions are seen to occur after and before their ignition, respectively. In addition, separate combinations of water and surfactant content exist for these fuel oils to achieve better emulsification effects on combustion. Droplets of emulsions with W/O = 15/85, E% = 2% for fuel oil A and W/O = 25/75, E% = 1% for fuel oil C are found to have the most violent droplet-disruption phenomenon and the longest flame length.

Experimental evidence for microexplosions in water/fuel oil emulsion flames inferred by laser light scattering

Water fuel-oil emulsion flames have been studied on an experimental apparatus, conceived and realised in order to offer optical access all along a semi-industrial confined flame. The main objective of the work was to provide experimental evidence and gather information on the secondary atomisation mechanism, which was previously observed only in single droplet experiments. Laser light scattering diagnostic was applied to confined 600 kW fuel-oil and water/fuel-oil emulsion flames. The coexistence of fuel droplets, soot and cenospheres required a proper interpretation of the experimental results. The analysis of the scattered light intensities, of the polarization ratios and light extinctions enabled to localise, in semi-industrial scale turbulent diffusion flames, microexplosion phenomena, through which the water emulsions reduce solid particulate emissions. Unburned solid conventional sampling confirmed the amount and size reduction of the cenospheres, due to the microexplosions. The beneficial effect of water on soot formation has also been detected, showing a different behaviour between soot and cenosphere emissions by increasing the emulsified water content.

Vaporization behavior of fuel droplets in a hot air stream

Tm GASIFICATION behavior of a liquid droplet provides a fundamental input for the modeling of many spray systems, and has been studied extensively [l-4]. Theoretical analysis for the multicomponent fuel droplet presents several complexities absent in a similar analysis for the single component droplet. First, the phase-change process at the droplet surface and the transport of a fuel vapor mixture in the gas phase need to be properly described. Second, the evaporation process is inherently time varying due to the continuous change in the composition and temperature of the droplet as vaporization proceeds. Another difference between the two cases is due to the phenomenon of microexplosion [2]. The earlier viewpoint [2] of multicomponent droplet vaporization assumes that the composition and temperature within the droplet are spatially uniform but time varying. Such theories predict that the gasification process is similar to batch distillation in that the sequence of gasification is controlled by the volatility differentials among the different components. However, Sirignano [4] showed that even in the limit of high vortex strength, the internal liquid circulation can only reduce the characteristic length scale for diffusion by a factor of three. Landis and Mills [S] investigated the vaporization of a bi-component fuel droplet in a stagnant atmosphere. A quasi-steady gas-phase model was used and the equations governing the unsteady mass and heat diffusion within the droplet were solved numerically. Results when compared with rapid mixing behavior showed significant differences. A unique feature of the diffusion-dominated droplet gasification mechanism is the possible attainment of approximately steady-state temperature and concentration profiles within the droplet, which then leads to a steady-state gasification rate. Based on this concept, Law and Law [6] formulated a d2-law model for multicomponent droplet vaporization and combustion. As indicated above, the literature on the gasification behavior of an isolated droplet is extensive. However, most of these studies deal with droplet combustion or evaporation under high-temperature conditions. Not much information is available on the behavior of evaporating droplets in relatively low-temperature air streams. Under such conditions, the possibility of an envelope flame is precluded and the droplet gasification rate is low. The droplet heat-up time may not be negligibly small compared to its lifetime, although the latter is relatively large and the liquid-phase transient processes may still be important. In this paper, the vaporization behavior of pure and multicomponent fuel droplets flowing in a well-characterized laminar flow is studied. The predictions of three vaporization models are compared with the experimental data.

B108 高速ドラムカメラの試作と気中微小爆発の可視化計測

It is known that the large scale explosion satisfies the similarity law. But it is not clarified that the microexplosion satisfies the similarity law or not. If the microexplosion induced spherical shock wave satisfy the similarity law, large scale explosion can be simulate by a microexplosion in a laboratory.To explore the suitable method for measuring the microexplosion phenomena, we've designed and constructed a high speed drum camera combined with a pulsed Argon-ion laser as a light source. In selecting the appropriate laser pulse interval and the mirror rotating speed, framing speed of 4×10 6 fps and 40 numbers of flame can be obtained. And in case of streak recording, streak speed of 100 ns/mm and 500 mm record length can be obtained. Consequently, it is found that the present microexplosion induced spherical shock wave satisfies the similarity law.

The Vaporizing Behavior of the Fuel Droplet of Water-in-oil Emulsion on the Hot Surface

The experiments were carried out to investigate qualitatively the effects of emulsion internal phase structure such as the size distribution of water droplets on the micro-explosion phenomena of water-in-'A' heavy oil emulsified droplets vaporizing on the hot surface. The results confirm that the size distribution of water droplets in the emulsified fuels plays a very important role in the boiling phenomena, in spite of the same water content included in the fuels. That is, Emulsified fuel 1 with fine- and uniform-size distribution of the internal water droplets has a longer life time than the neat fuel ('A' heavy oil) on account of a distinctive feature such as 'two stage vaporization'. In contrast, Emulsified fuel 2 with some coarse sizes of them has a life time less than a half of vaporization was caused by the destruction of the vapor film due to the 'violent micro explosion' of coarse-coalescent water droplets.

高圧容器内における乳化燃料油滴の燃焼

In relation to the remarkable effect of emulsified diesel oil with water particles on reducing exhaust pollutants (NOx, soot etc.) and also specific fuel consumption of the diesel engines, the micro-explosion phenomena in the flame of a heated fuel droplet on a silica filament in a high pressure chamber investigated experimentally.The experimental results are summarized as follows:With the increase of the initial air pressure in the chamber, (1) The micro-explosion likely becomes weaker, so that the projected flame area on the motion picture of 8-mm wide gets smaller.(2) The difference between the flame shape of the emulsion and that of diesel oil gets less.(3) The burning time of an emulsified fuel droplet increases approaching that of diesel oil droplet.As a result, the authors appraise the effect of the micro-explosion on reducing specific fuel consumption and exhaust smoke of a diesel engine to be small because of the high pressure in the engine cylinder.