Critical insights into the effects of bio-based additives on biodiesels properties

Highlights: • The effects of plants extract, bio-oils, cashew nut shell liquid, some cellulosic derivatives and transesterification products on biodiesels and CI engine performance have been discussed. • The mechanisms responsible for the antioxidation effects and cold flow properties improvement of the bio-based additives have been explained. • Future perfective in the area of biodiesel bio-additives has been suggested. -- Abstract: Over the years, efforts have been made by researchers to come up with sustainable, non-toxic, cheap and biodegradable biodiesel additives in order to address the fuel quality challenges faced when using biodiesels. Substantial achievements have been recorded on improving the oxidation stability and cold flow properties (cloud point, pour point and cold filter plugging point) of the biodiesel with respect to the standard specifications, with the bio-based additives in most cases performing similar to the synthetic additives. Herein, a critical review of the status quo has been made and some intriguing issues are raised for further investigations. Maximum induction period of up to 23.99 h and maximum reduction of 4–5 °C in cold flow properties have been documented. Some of the bio-based additives were found to negatively affect other fuel properties of biodiesels, although the values were still within the acceptable limits. Also, of all the reported additives, Pongamia pinnata leaves extract was found to significantly increase the brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), carbon monoxide (CO) emission and hydrocarbon (HC) emission and remarkably decreased oxides of nitrogen (NO_X). Generally, this review summarizes and highlights some basic information for hopeful synthesis of effective biodiesel additives that will ensure cheap, non-toxic and sustainable solution to biodiesel fuel challenges. Strikingly, bio-oils from non-edible sources and ethyl levulinate appear as the most suitable additives for improving the oxidative stability and low temperature properties of biodiesels respectively.