Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Comprehensive overview on diesel additives to reduce emissions, enhance fuel properties and improve engine performance Ahmad Fayyazbakhsh, Vahid Pirouzfar ⁎ Young Researchers and Elite Club, Central Tehran Branch, Islamic Azad University, Tehran, Iran ARTICLE INFO Keywords: Diesel fuel Engine performance Fuel properties Oxygenated additives Reduced emissions ABSTRACT The present review investigates modification of diesel fuel formulation and development of a new model to enhance engine performance, improve fuel properties and reduce exhaust emissions. Emissions arising from the fuel can be controlled by blending an oxygenated fuel (renewable fuel) with the diesel fuel. The blending oxygenated fuels namely Methanol, Ethanol, and n-Butanol are examined in addition to their effects. This review paper studies the implication of different torques and various engine speeds. In some conditions, it can even cause an increase in the content of carbon monoxides (CO), carbon dioxide (CO 2 ) and nitrogen oxides. This review showed that the engine speed has a negative effect on all of the air pollutants, so that increasing of the engine speed leads to reduction of the air pollutants. However, the engine load gives rise to most exhaust emissions. Adding the oxygenate fuels increases brake specific fuel consumption (BSFC), while brake thermal efficiency (BTE) decreases. In some researches, a nano-metal additive has been used in the fuel for improving the engine performance. In case of using the nano-metal additives to the diesel fuel (a nano-metal with small thermal conductivity coefficient), the engine performance is seen increased. 1. Introduction There is a growing demand for energy due to the increasing population which can lead to greater air pollution. On the other hand, it is clear that there are limited sources of fossil-based fuels as a sustainable energy. As a result of world industrialization, the demand for oil-based fuels (fossil fuels) has increased dramatically [1–3]. Apart from the economic matters, the widespread use of fossil fuels is responsible for a long-term environmental problem in the form of climate changes and the global warming. The main source of energy in different forms originates from the combustion. Recently, depletion of the fossil fuels due to their continuous use has become the first priority concern for all people in the world whose lives depend on this source of energy for all their activities. Diesel engines have a considerable share of transportation. At the same time, along with the large-scale use of the diesel fuels, lung diseases and cancer invasion have been increased dramatically [4–6], such that a comprehensive study on this issue seems necessary. Today, the fossil fuels constitute about 80% of the total needed energy with almost 50% of it being related to the local transportation [7]. The diesel fuel mainly contains aliphatic hydro- carbons of C 8 – 28 with boiling temperatures varying from 130 to 370 °C [8]. The exhaust emissions from the diesel engines contain various types of air pollutants such as total hydrocarbon content (THC), oxides of nitrogen (NOx), particulate matter (PM), carbon monoxide (CO). The oxides of nitrogen and sulfur which are emitted by internal combustion engines can result in acid rains [6,7]. The main source of greenhouse gas emissions are the fossil fuels [9–11]. The worldwide concern of the environmental pollutants has triggered intensified researches for new alternative sources of energy. Widespread applica- tions of the fossil fuels and the environmental issues associated with their use have directed us to replace them with reasonable price, high efficiency and renewable sources [10–13]. To find a proper convincing answer to this question how to select, distribute and use the data, one needs to focus on both engine technology and fuel efficiency [14–19]. However, the blended renewable bio fuels or the oxygenated fuels with the capability of reduction of the exhaust emissions are among the most important topics in the literature [20–25]. Alcoholic fuels are of potential capability for being used as oxygenated fuel additives with fossil-based fuels (such as gasoline to improve the octane number and to reduce the air pollutant emissions, as well as diesel fuels to control the soot emissions) for the diesel engines. They can be an alternative source of environment friendly fuels to reduce the exhaust gas emissions using the renewable energy in different countries of the world. Previous researches and studies were just focused on addition of vegetable oil, cooking oil, bio diesel, methanol and ethanol to the oil- based fuels. The vegetable oil, cooking oil and biodiesel were all useable http://dx.doi.org/10.1016/j.rser.2017.03.046 Received 16 October 2016; Received in revised form 2 January 2017; Accepted 8 March 2017 ⁎ Corresponding author. E-mail address: v.pirouzfar@iauctb.ac.ir (V. Pirouzfar). Renewable and Sustainable Energy Reviews 74 (2017) 891–901 1364-0321/ © 2017 Elsevier Ltd. All rights reserved. MARK