Formulation of an Economical Microemulsion of Diesel/Colza Oil Fuel and Investigation of Some Physical Parameters for Its Stability Reza Najjar , a Somaiyeh Heidari, a,b and Mohand Tazerout b a Polymer Research Laboratory, Faculty of Chemistry, University of Tabriz, Tabriz 5166616471, Iran; najjar@tabrizu.ac.ir (for correspondence) b Departement des Systemes Energetiques et Environnement, Ecole des Mines de Nantes, 4 Rue Alfred Kastler, BP 20722, 44307 Nantes, Cedex 03, France Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.12820 The formulation of an economical diesel/colza oil/water microemulsion fuel is reported. The modification of diesel fuel significantly improves its fuel properties as well as envi- ronmental pollution issues. To investigate the possibility of using colza oil with diesel fuel and adding water to reduce emissions of diesel combustion, the phase diagrams of the system were constructed using titration method with co- surfactant. n-Butanol is selected as co-surfactant among the investigated alcohols with different chain lengths as it formed wide single phase area. Using of n-butanol was helped to tune solubilizing of water in diesel/colza oil blend and to reduce its viscosity. Here, a 4:1 blend of diesel:colza oil, 5% water and n-butanol was selected as base system which was then optimized to obtain a reasonably economi- cal formulation with acceptable physical properties. Accord- ing to the measurements of physical properties, such as viscosity, temperature stability, water droplet size and consid- ering an economical point of view, the optimum microemul- sion system was composed of 75% diesel/colza oil (4:1), 5% water, 10% n-butanol, 8% Brij 30 and 2% Tween 80, and was prepared in room temperature (21–25) 8C by stirring with 500 rpm for 5 min. The optimum system was stable up to 458C. V C 2017 American Institute of Chemical Engineers Environ Prog, 00: 000–000, 2017 Keywords: microemulsion, fuel, diesel/colza oil, water droplet size, surfactant, co-surfactant INTRODUCTION The diesel engines are mainly employed in transport, agricultural and industrial applications for systems requiring high power. One of the most pronounced disadvantages of the diesel engines is that they generate high smoke and nitric oxide emissions in atmosphere, causing serious environmen- tal problems [1–3]. The rapid decline of energy resources of the world, rising the fuel prices and high levels of diesel exhaust emissions have led to more attempts to find alterna- tive fuels [4,5]. The main advantages of alternative fuels, including exhaust gas emissions with higher quality, renew- ability, biodegradability and less or non-toxic nature, make them appealing for use as future fuels. Vegetable oils and some of their derivatives have been identified as suitable replacement for diesel fuels [6,7]. Among the vegetable oils, colza oil was chosen here for several reasons including: a biodiesel can be derived from colza oil [8–10], it can be used as mixture with diesel fuel [11] or it can be directly injected into the engine as pure vegetable oil [12]. Several solutions are known to be used to reduce the high viscosity of vegeta- ble oils, such as blending of vegetable oil with diesel, pyrol- ysis, trans-esterification and microemulsification based on vegetable oil [13–15]. Microemulsification method enables to replace the diesel partially by vegetable oil and also it makes possible to add water into the fuel [6]. Adding water into the diesel fuel features some advantages for the engines [16]. The investigations show that, the presence of water in the diesel has an important impact on decreasing in the peak flame temperature which helps in reducing the NOx emis- sions in diesel engine [17,18]. Also, adding water into the diesel helps to improve fuel atomization and significant decrease in particulate emission, which is attributed to micro-explosion phenomenon occurred in emulsion water droplets [6,19]. One of major approaches which has been reported in the literature for introducing water into the com- bustion zone is the use of diesel-water emulsions [20,21]. Microemulsions are clear, thermodynamically stable mixtures of oil, water and surfactant, which sometimes contains a co- surfactant to fine tune the system [22,23]. The three kinds of microemulsions are direct (oil dispersed in water, o/w), reversed (water dispersed in oil, w/o) and bicontinuous [24]. Reverse micelle microemulsions (w/o) is important as they can be used for production of biofuel because this method improves the high viscosity problem of vegetable oil without producing a lot of wastewater [25]. The surfactant decreases water and oil surface tension and surface activity in the microemulsion system [26]. Also, co-surfactant helps the rapid migration of surfactant at oil/water interfaces and enhances the emulsion stability [27]. The choose of n-butanol as co-surfactant among the many available co-surfactants has been because of its high compatibility with diesel oil. This similarity allows that n-butanol can be mixed with diesel and vegetable oil in any ratio [28]. However, the properties such as viscosity and cetane number are among the other features V C 2017 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2017 1