The impact of fuel injection pressure on the exhaust emissions of a direct injection diesel engine fueled with biodiesel–diesel fuel blends Metin Gumus a , Cenk Sayin a , Mustafa Canakci b,c,⇑ a Department of Mechanical Engineering, Faculty of Technology, Marmara University, 34722 Istanbul, Turkey b Department of Automotive Engineering, Faculty of Technology, Kocaeli University, 41380 Izmit, Turkey c Alternative Fuels R&D Center, Kocaeli University, 41275 Izmit, Turkey article info Article history: Received 17 August 2011 Received in revised form 10 October 2011 Accepted 7 November 2011 Available online 19 November 2011 Keywords: Biodiesel Injection pressure Direct injection diesel engine Exhaust emissions abstract In this study, the effects of fuel injection pressure on the exhaust emissions and brake specific fuel con- sumption (BSFC) of a direct injection (DI) diesel engine have been discussed. The engine was fueled with biodiesel–diesel blends when running the engine at four different fuel injection pressures (18, 20, 22, and 24 MPa) and four different engine loads in terms of mean effective pressure (12.5, 25, 37.5, and 50 kPa). The results confirmed that the BSFC, carbon dioxide (CO 2 ), nitrogen oxides (NO x ) and oxygen (O 2 ) emis- sion increased, smoke opacity, unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions decreased due to the fuel properties and combustion characteristics of biodiesel. On the other hand, the increased injection pressure caused to decrease in BSFC of high percentage biodiesel–diesel blends (such as B20, B50, and B100), smoke opacity, the emissions of CO, UHC and increased the emissions of CO 2 ,O 2 and NO x . The increased or decreased injection pressure caused to increase in BSFC values com- pared to original (ORG) injection pressure for diesel fuel and low percentage biodiesel–diesel blends (B5). Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Exhaust emissions from diesel engines fueled with petroleum– diesel fuel have caused environmental pollution and global prob- lems. The European Commission has published the some directives (2005/55/EC for Euro 4/5, etc.) to reduce the exhaust emissions from light- and heavy-duty diesel engines. Hence, the vehicle man- ufacturers and academic researchers have directed searching the commercial diesel engines with high performance and low emis- sions. For this purpose, the research projects have generally focused on the highest injection pressure, multipoint injection, dif- ferent catalyst type (oxidation catalyst, NO x absorber, etc.), exhaust gas recirculation, particulate traps, and controlling the timing of the start of injection [1]. For many years, the ready availability of inexpensive middle- distillate petroleum fuels has provided little incentive for experi- menting with alternative renewable fuels for diesel engines. US Department of Energy states that the world’s oil supply will reach its maximum production and midpoint of depletion sometime around the year 2020. The depleting reserves and environmental issues in addition to the ozone depletion concerns have pushed the countries towards searching for the alternative energy sources with particular emphasis on those renewable natures. Future pro- jections indicate that the only feasible option is the production of alternative fuels derived from non-petroleum sources [2,3]. For substituting the petroleum fuels used in internal combus- tion engines, fuels of bio-origin provide a feasible solution to the twin crises of ‘fossil fuel depletion’ and ‘environmental degrada- tion’. The fuels of bio-origin may be alcohols, biodiesel, and biogas. Some of these fuels can be used directly while others need to be formulated to bring the relevant properties close to conventional fuels [4]. The fuel characteristics of biodiesel are approximately the same as those of fossil diesel fuel. Therefore, it may be directly used as a fuel for diesel engines without any modification of the design or equipment. The properties of biodiesel can very depending upon processing technology and feedstock, but generally it has high cetane number, oxygen content, and very low aromatic content when compared to the conventional diesel fuel. The molecular structure of biodiesel is similar to diesel fuel, and it contains addi- tional oxygen, which is useful to reduce CO, UHC and smoke opac- ity in the exhaust. In addition, biodiesel is bio-degradable, it can be mixed with diesel fuel at any ratio and it is sulfur-free. Though it has many advantages over diesel fuel, there are several problems that need to be addressed such as its lower heating value, higher viscosity, poor cold flow properties and oxidative stability, and sometimes its higher nitrogen oxides (NO x ) emission [4–7]. 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.11.020 ⇑ Corresponding author at: Department of Automotive Engineering, Faculty of Technology, Kocaeli University, 41380 Izmit, Turkey. Tel.: +90 262 3032285; fax: +90 262 3032203. E-mail address: mustafacanakci@hotmail.com (M. Canakci). Fuel 95 (2012) 486–494 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel