Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Influence of injection timing and split injection strategies on performance, emissions, and combustion characteristics of diesel engine fueled with biodiesel blended fuels H.G. How a,b, ⁎ , H.H. Masjuki a, ⁎ , M.A. Kalam a , Y.H. Teoh c a Centre for Energy Sciences, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia b Department of Engineering, School of Engineering, Computing and Built Environment, KDU Penang University College, 32, Jalan Anson, 10400 Georgetown, Penang, Malaysia c School of Mechanical Engineering, Universiti Sains Malaysia, Engineering Campus, 14300 Nibong Tebal, Penang, Malaysia ARTICLE INFO Keywords: Diesel engine NO x Injection timing Split injection Biodiesel ABSTRACT Biodiesel can be used as alternative to replace fossil diesel. However, usage of biodiesel in an unmodified diesel engine can cause higher in nitrogen oxides (NOx) emission. In order to reduce the harmful emission, certain injection strategies can be carried out. In this paper, the effects of biodiesel blends, fuel injection timing and split injection schemes on the engine performance, emissions and combustion characteristics of a medium-duty diesel engine are investigated. Parametric studies relating with start of injection timing variation and multiple injection schemes using B20 and B50 biodiesel blends were performed and benchmarked with petroleum diesel fuel as baseline. A remarkably lower NOx level below 100 ppm can be obtained by retard start of injection (SOI) timing for both of the B20 and B50 fuel operations and with triple injection scheme. It was found that with the use of B50, simultaneous NOx and smoke suppression from the levels of petroleum diesel fuel is attainable in parallel with the implementation of late SOI timing and triple injection scheme in a diesel engine. In conclusion, multiple split injections is a practical strategies to simultaneously decrease NOx and smoke emissions when the SOI timing is fine-tuned and is an ideal alternative to operate with biodiesel fuel. 1. Introduction The widespread use of diesel engine has caused air pollution pro- blems. This is due to their higher exhaust discharges of nitrogen oxides (NO x ), particulate matter (PM) and smoke in comparison with that of a gasoline engine [1]. The air pollutants jeopardize human health in different ways, necessitating the needs to curb this problem [2–4]. To minimize this impact, research effort are being focused on injection strategies such as variable injection timing, split injection, variable injection pressure, variable nozzle configuration, and others [5,6]. In- jection timing optimization can be performed in order to produce a suitable ignition delay as well as to reduce the amount of exhaust emission in diesel engine. For instance, advancing the injection timing reduces the amount of carbon monoxide (CO), hydrocarbon (HC) and smoke while increases the amount of NO x emitted [5]. More time is available for oxidation when injection is advanced, thus reducing the amount of CO, HC and smoke, but with higher amount of NO x emitted. In order to reduce amount of NO x emitted, the injection can be carried out later to lessen the air temperature even though at the expense of increasing the amount of CO, HC and smoke emitted due to incomplete combustion. Another strategy can be implemented to diesel engines to attain lower emission limit is by split injection. It can be carried out to reduce engine noise and amount of NO x emitted. Furthermore, accurately performed split injection schemes can be favorable in reducing com- bustion noise, waste emissions and diesel consumption and therefore, they are effective tools [7]. Besides, particulate emissions can be re- duced substantially without a great increase in NO x emissions [8,9]. This is because high heat release rate (HRR) can be prevented at the beginning of combustion, hence decrease the flame temperature and permit better fuel and air mixing to enhance in-cylinder charge homogeneity. Besides, energy demands of the world are increasing nowadays. Depletion of fossil diesel fuel can be slowed by adopting renewable source of energy such as biodiesel. Biodiesel can be made from vegetable oil, animal fat or waste materials such as spent coffee grounds [10]. Also, it is nontoxic, renewable and biodegradable http://dx.doi.org/10.1016/j.fuel.2017.10.102 Received 8 August 2017; Received in revised form 15 October 2017; Accepted 24 October 2017 ⁎ Corresponding authors at: Centre for Energy Sciences, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. E-mail addresses: heoygeok.how@kdupg.edu.my, heoygeok@gmail.com (H.G. How), masjuki@um.edu.my (H.H. Masjuki), kalam@um.edu.my (M.A. Kalam), yewhengteoh@usm.my (Y.H. Teoh). Fuel 213 (2018) 106–114 0016-2361/ © 2017 Elsevier Ltd. All rights reserved. MARK