Numerical analysis of injector flow and spray characteristics from diesel injectors using fossil and biodiesel fuels Michele Battistoni ⇑ , Carlo Nazareno Grimaldi University of Perugia, Department of Industrial Engineering, Via Goffredo Duranti, 67, 06125 Perugia, Italy article info Article history: Received 20 July 2011 Received in revised form 27 November 2011 Accepted 29 November 2011 Available online 27 December 2011 Keywords: Biodiesel spray Cavitation Nozzle flow Eulerian multiphase flow Primary breakup Coupled simulations abstract The aim of the paper is the comparison of the injection process with two fuels, a standard diesel fuel and a pure biodiesel, methyl ester of soybean oil. Multiphase cavitating flows inside injector nozzles are calcu- lated by means of unsteady CFD simulations on moving grids from needle opening to closure, using an Eulerian–Eulerian two-fluid approach which takes into account bubble dynamics. Afterward, spray evo- lutions are also evaluated in a Lagrangian framework using results of the first computing step, mapped onto the hole exit area, for the initialization of the primary breakup model. Two nozzles with cylindrical and conical holes are studied and their behaviors are discussed in relation to fuel properties. Nozzle flow simulations highlighted that the extent of cavitation regions is not much affected by the fuel type, whereas it is strongly dependent on the nozzle shape. Biodiesel provides a slightly higher mass flow in highly cavitating nozzles. On the contrary using hole shaped nozzles (to reduce cavitation) diesel provides similar or slightly higher mass flow. Comparing the two fuels, the effects of different viscosities and densities play main role which explains these behaviors. Simulations of the spray evolution are also discussed highlighting the differences between the use of fossil and biodiesel fuels in terms of spray penetration, atomization and cone-angle. Usage of diesel fuel in the conical convergent nozzle gives higher liquid penetration. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Biofuels for transportation and for small power generation plants are becoming increasingly popular and also worldwide na- tional legislations are promoting their usage. These types of fuels are renewable energy sources which have properties similar to petroleum diesel fuel, so their advantages in terms of fuel economy and environmental impact are well acknowledged. Most of actual diesel engines can operate using up to 10% of biodiesel blended with standard diesel. Usage of pure oils, even if largely blended, re- quires instead much more attention due to operational and dura- bility issues. Biodiesel can be produced by a variety of biomasses, mainly through trans-esterification. Being oxygenated fuels, bio- diesels contribute to the reduction of particulate matter and un- burnt hydrocarbons. Increased NO x emissions however can be an issue. Also, as a bio-derived product, it contributes to the reduction of net carbon dioxide emission [1–7]. Aiming at increasing the usage of biodiesel as pure fuel or as an important blend with actual diesel, several R&D key areas have been identified, ranging from fuel system to combustion character- istics up to exhaust gas after-treatment. Injection process plays a significant role in this framework, since performances of DI diesel engine are strongly affected by the fuel spray quality. Atomization process and spray development largely depends on nozzle design. Also injection strategies and engine calibration are of primary importance in determining the final output. Biodiesel has usually higher density and viscosity than petro- leum diesel. Also it is a mixture of few organic molecules charac- terized by high molecular mass, thus evaporation and cavitation properties are quite different compared to diesel: distillation oc- curs practically at constant temperature and saturation pressure is extremely low, at ambient temperature. Many investigations have been conducted on combustion and emissions using biodiesel in compression ignition engines, mainly by the experimental standpoint. On the contrary, detailed studies of injection and spray atomization characteristics are less frequent in literature for biofuels, despite their fundamental importance is recognized. Payri et al. [8] found that the injection system is significantly af- fected by higher density and viscosity of biofuel, since both needle motion and flow characteristics are altered. Their tests showed that biodiesel spray is characterized by higher penetration and lower angle, especially for long injection. For short injections, or low temperature cases, they noticed a reduction on the injected 0306-2619/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2011.11.080 ⇑ Corresponding author. E-mail address: michele.battistoni@unipg.it (M. Battistoni). Applied Energy 97 (2012) 656–666 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy