| Summary: | Due to skyrocketing fuel price and demand, engine manufacturers and researchers have been thriving to find alternative sources of fuel for internal combustion engines. Biodiesel and vegetable-based fuels are prospective substitutes for petro-diesel fuel for compressions ignition (CI) or diesel engines, and favourable over petro-diesel fuel in terms of sustainability and environmental friendliness. It is found from the literatures that higher viscous fuels (HVFs) and biodiesel fuels have substandard engine performance and emissions especially in the case of brake specific fuel consumption (BSFC), torque and NOX emissions compared to those of the engines using petro-diesel. This is mainly due to their higher viscosity and density as well as lower volatility and calorific value and thus, they are termed as higher viscous fuels. Furthermore, the higher viscosity and density of HVFs retard the combustion efficiency since HVFs are less prone to evaporate, diffuse and mix properly with the in-cylinder air. Based on these findings, researchers have put effort into improving the performance of CI engines running with HVFs. Generally, three techniques are very popular by the researchers, namely, blending the HVFs with petro-diesel (known as fuel blend), preheating the HVFs, and altering the injection strategy from the original engine-settings for petro-diesel operation. In this paper, a comprehensive review is presented on these techniques to improve the performance of CI engines run on HVFs.
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