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► We measure the temperature of water/oil emulsion droplets during micro-explosion. ► The emulsion droplets were heated by using the Leidenfrost regime. ► The size of the dispersed ...water droplets affects the temperature of micro-explosion. ► Temperature of m-e and size of water droplets are not monotonically correlated. ► Very high metastable temperature of the water were reached before micro-explosion.
The burning of water in oil emulsions is considered as an effective alternative to bring out waste oil because of a significant reduction in carbon monoxide, nitrogen oxides and particulates in the exhaust. These advantages have different origins, an important contribution is provided by the phenomenon of micro-explosion. In this work, the influence of the size of the dispersed water droplets in the micro-explosion phenomenon is studied by the hot plate technique. The variation of the temperature and the evolution of the phenomenon have been investigated using a synchronized thermocouple/high speed imaging system. Three emulsions with the same amount of water (30%mass) but with different distribution of the size of the dispersed water droplets have been tested.
The results show that the size distribution of the dispersed water droplets plays an important role in the phenomenon of micro-explosion. Moreover, some internal phenomenon as the separation process between water and oil seems to affect significantly the phenomenon.
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•An experimental study of micro-explosion by means two different approaches has been carried out.•Temperature of micro-explosion and fall in temperature after micro-explosion are ...evaluated.•Separation of the continuous and dispersed compounds has been observed.•The influence of the thermocouple and the heat transfer are discussed.
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.
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•The microchannels emulsifier is able to form a rather stable water–oil emulsion.•WiDE resulted stable after 2 h running into the high pressure common rail system.•WiDE emulsion was ...successfully used in an optical diesel engine.•WiDE implied a reduction in PM and NOx compared to that resulting from diesel oil.•The 2D chemiluminescence technique highlights a reduction in soot formation.
The paper reports the results of an experimental investigation carried out on a prototype optically accessible compression ignition engine fueled with water in diesel emulsion (WiDE) and Diesel only. The effect of WiDE on combustion process evolution and exhaust emissions was investigated through standard engine benchmark and optical diagnostics. 2D chemiluminescent emission measurements centered at 690 nm were carried out during the whole combustion process to discriminate the soot emission from other excited chemical species. The emulsion was produced through a prototype designed microchannels emulsifier that can also work inline. The water concentration was 9.1%v with a small amount (0.2%v) of nonionic surfactant (SPAN80) used to stabilize the emulsion. Tests were performed comparing combustion and exhaust emissions of the reference commercial diesel fuel to the WiDE. For any investigated fuel and operating point, engine tests were carried out changing the injection interval to achieve the same chemical energy as the reference diesel (935 J/str). Compared to Diesel, the WiDE induced an increase in ignition time, enhancing the air/fuel mixing with a simultaneous reduction in both PM and NOx. The digital imaging and 2D chemiluminescence techniques highlighted a reduction in soot formation without significant changes on the soot oxidation rate. The results suggest the use of WiDE as a reliable method to improve NOx-soot trade-off of CI engines.
This work aims on the efficient use of animal fat in a diesel engine by making its stable emulsions with ethanol and water. A single cylinder direct injection diesel engine is tested using neat ...diesel, neat animal fat and animal fat emulsion (optimal emulsion) as fuels under variable load operating conditions. Results show increased peak pressure and ignition delay with ethanol animal fat emulsion as compared to neat fat. Heat release pattern shows improvement in the premixed combustion phase with animal fat emulsion as compared to neat animal fat. Drastic reduction in smoke, nitric oxide, hydrocarbon and carbon monoxide emissions are observed with the emulsion as compared to neat fat and neat diesel mainly at high power outputs. Only, hydrocarbon and carbon monoxide emissions are found as high with the emulsion at light loads. In general, animal fat emulsion shows considerable reduction in all emissions and improvement in engine performance as compared to neat fat.
Burning a water-in-oil emulsion enables reduction in solid and gaseous pollutants in comparison with neat oil. In the emulsion, Heavy Fuel-Oil and water lie in distinct phases, having a high ...difference in boiling point (up to 200 K). In an emulsion droplet injected and subsequently heated inside a flame, the internal water droplets are enclosed inside the emulsion and do not systematically vaporise at boiling point. They are known to reach a metastable state, breaking up at a temperature below the spinodal limit of water. From this moment, the surrounding Fuel-Oil is fragmented into numerous faster and smaller droplets by the suddenly expanding steam. This physical phenomenon is called “micro-explosion”. This work demonstrates a numerical modelisation of unsteady heat and mass transfer at the surface and inside of the emulsion droplet, and provides a prediction of its micro-explosion delay, using homogeneous nucleation hypothesis. This assumption of homogeneous nucleation for internal water droplets matches the use of a “drop tower” experimental facility. Finally, comparisons between predicted ranges for micro-explosion delays and experimental delays from literature are discussed, along with combustion parameters (ambient temperature, relative velocity) and combustible emulsion parameters. As a result, the experimental and numerical micro-explosion delays decrease with liquid or ambient temperature and relative velocity, and increase with water content and radius of emulsion droplet. Their low average deviation reveals the accuracy of the assumption of homogeneous nucleation in the considered situations.
In this article, the liquid water eruptive transport occurring during the water breakthrough from the Gas Diffusion Layer (GDL) of a PEMFC into the gas channel is investigated. A dedicated ...experimental set-up is used enabling the simultaneous measurement of pressure inside the water system and visualization of droplet formation. A single-drop capillary model is proposed to explain the eruptive nature of droplet formation. The model is built on four physical equations involving Laplace's law, a water system compressibility law, the pressure losses occurring during droplet formation, and a spherical droplet geometrical function. Two numerical resolution methods are implemented and compared. For this model, three parameters have to be identified from the experimental data. The identification procedure is explained in the paper and the comparison with experimental results shows the ability of the present model to reproduce the eruptive nature of liquid water breakthrough from the GDL.
•Eruptive droplet formation is studied with a dedicated ex situ experimental set-up.•A theoretical model of the eruptive water transport in PEMFC is proposed.•Laplace's law, the system compressibility, and the pressure losses are considered.•The identification procedure for the model parameters is detailed.•The model is validated for various water injection rates and pore sizes.
The use of biofuel emulsions as fuel for diesel engines: A review Kumar, M Senthil; Bellettre, J; Tazerout, M
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy,
11/2009, Letnik:
223, Številka:
7
Book Review, Journal Article
Recenzirano
Abstract
Animal fats/vegetable oils (called biofuels) and their emulsions are quite promising alternative fuels for diesel engines. This article reports a comprehensive study on the use of animal ...fats/vegetable oils and their emulsions as fuel in compression ignition engines. Emulsions preparation method and their effects on engine performance, emission, and combustion characteristics have been studied in detail.
Information indicates that biofuel emulsions in diesel engines enhanced the combustion efficiency with improved performance as compared to neat fuels. The maximum percentage of water addition to biofuel was found as 30 per cent by volume for maximum efficiency. They reduced NO
x
, smoke, and particulate emissions considerably. Emulsions resulted in higher ignition delay as a result of vaporization of water as compared to neat fuels. Peak pressure, rate of pressure rise, and premixed combustion rate in the heat release curve were found to be higher when compared to neat oils because of longer ignition delay. Further improvements could be achieved by adding oxygenated fuels like methanol, dimethyl carbonate, and cetane number improvers like diethyl ether with biofuels in small quantities. It has also been suggested that dual fuel operation can significantly reduce particulate and NO
x
emissions with biofuels. Exhaust gas recirculation can reduce ignition delay considerably with reduced NO
x
emissions. Finally, modelling techniques were presented because they can help in in-depth analysis of the combustion process of biofuel emulsions in diesel engines.
The effect of fuel inlet temperature on performance, emission and combustion characteristics of a diesel engine is evaluated. A single cylinder direct injection diesel engine developing a power ...output of 2.8
kW at 1500
rev/min is tested using preheated animal fat as fuel. Experiments are conducted at the fuel inlet temperatures of 30, 40, 50, 60 and 70
°C. Animal fat at low temperature results in higher ignition delay and combustion duration than diesel. Preheated animal fat shows reduced ignition delay and combustion duration. Peak pressure and rate of pressure rise are found as high with animal fat at high fuel inlet temperatures. Heat release pattern shows reduced premixed combustion phase with animal fat as compared to neat diesel at normal temperature. Preheating improves the premixed combustion rate. At low temperature, animal fat results in lower smoke emissions than diesel. The maximum smoke density is K=6.5
m
−1 with diesel and K=3.6
m
−1 with animal fat at 30
°C. Preheated animal fat further reduces smoke levels at all temperatures. The smoke level is reduced up to K=1.7
m
−1 with preheated animal fat at the temperature of 70
°C. Hydrocarbon and carbon monoxide emissions are higher with animal fat at low temperature as compared to diesel. Fuel Preheating reduces these emissions. NO emission is found as low with animal fat at low temperature. Fuel preheating results in increased NO emission. However, the level is still lower than diesel even at high temperature (i.e. 70
°C). On the whole it is concluded that preheated animal fat can be used in diesel engines with reduced smoke, hydrocarbon and carbon monoxide emissions with no major detoriation in engine performance.
This paper focuses on effective solution to improve the combustion of low quality animal fat by making stable emulsions with water. Animal fat emulsions are prepared by mixing the fat with water, ...surfactant and co-surfactant. Ethanol is chosen as the co-surfactant because of its dilution ability. SPAN 83 also called Sorbitan Sesquiolate is used as the surfactant because it well stabilizes and forms stable animal fat emulsions. Emulsions and micro-emulsions are prepared for different co-surfactant/surfactant (C/S) ratios. A number of formulations are made and the Sauter mean diameter of water droplets are estimated using electron microscope images. Results are presented in pseudo ternary diagrams. Influence of different parameters affecting the emulsion characteristics are studied experimentally. According to the stability, structure, viscosity, fat content and economical aspects, the optimum emulsion is found as the emulsion with 36.4% of ethanol, 3.6% of SPAN 83, 10% of water and 50% of animal fat by volume.
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