REVIEW ARTICLE A comprehensive review on water-emulsified diesel fuel: chemistry, engine performance and exhaust emissions Amit Jhalani 1 & Dilip Sharma 1 & Shyam Lal Soni 2 & Pushpendra Kumar Sharma 1 & Sumit Sharma 1 Received: 31 August 2018 /Accepted: 7 December 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Increasing environmental concern, human health and the continuous upgradation in the stringent standards of vehicular emissions have shown much interest in cleaner diesel fuels. Out of various strategies to mitigate the diesel engine emissions, use of water blended diesel in the form of emulsion has grabbed sufficient attention of the fuel research community. Various researches have shown that water-emulsified diesel has sufficient potential to improve the engine performance simultaneously with a significant reduction in the levels of nitrogen oxides (NO x ) and particulate matter (PM) emissions. Micro-explosion phenomenon of combustion in emulsion fuel helps to provide efficient and complete combustion which in turn improves brake thermal efficiency. The current study presents a comprehensive review of the usage of water-emulsified diesel fuel in CI engines. Focusing on the performance, combustion, and emission analysis, it also talks in detail about the principle and the chemistry involved in making of a stable and homogeneous water–diesel emulsion compatible for CI engine. The literature survey concludes two crucial points. First, the water-blended diesel emulsion serves as an economical, fuel efficient, and cleaner combustion technology. Second, the optimum blend ratio, emulsifier quantity, and proper process differs in almost all the research papers and hence needed to be standardized. Keywords Emulsion . Water . Diesel engine . Exhaust emission . Surfactant . HLB value Introduction It is a well-known fact that the world is suffering from an energy crisis along with the ill effects of the uncontrolled and unplanned exploitation of the available energy re- sources. If we talk only about the petroleum, there is a continuous increase in the use of diesel engine not only in conventional automobile sector but also in applications like power generation and agriculture. It is leading to diminution of fossil fuel resources and degradation in the environment and human health which are the pressing issues being addressed in the recent times. Along with it, stringent emission regulations and policies have spurred the search for improved diesel engine performance and cleaner combustion (Fig. 1). India is going to implement the BS-VI standards directly from BS-IV which is equiv- alent to Euro VI standards by the year 2020 surpassing BS-V which would be quite challengeable (UITP India 2018). These stringent regulations on pollution control promote the fuel scientists to think of alternative fuels and work upon emission control strategies via fuel mod- ification. However, after treatment, technologies like cat- alytic converters and diesel particulate filter (DPF) help to reduce particulate matter emissions and NO x but it results in higher consumption of fuel and poorer economy (Simon et al 2013; Mingrui et al. 2016). Various other emission con- trol techniques are also being used to combat the issues of diesel pollution, out of which water emulsification has been found to be a prominent and most economical solution. However, water can be introduced into the cylinder via three different methods, i.e., direct injection into the cyl- inder (Bedford et al. 2000; Mingrui et al. 2017; Zhang et al. 2017), injection into the intake manifold with air (Ma et al. 2014; Nour et al. 2016; Khalife et al. 2017), and in the emulsion form. In direct water injection, it is easier to change the water to fuel ratio while varying Responsible editor: Philippe Garrigues * Amit Jhalani jhalaniamit@gmail.com; 2015rme9521@mnit.ac.in 1 Department of Mechanical Engineering, Malaviya National Institute of Technology Jaipur, JLN Marg, Malaviya Nagar, Jaipur, Rajasthan 302017, India 2 National Institute of Technology Uttarakhand, Srinagar, India Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-3958-y