Performance and Emission Characteristics of Second-Generation Biodiesel with Oxygenated Additives

Abstract

Biofuels are environmental friendly renewable fuels, that can be directly used in a diesel engine. However, a few shortcomings like a higher density, viscosity, a lower calorific value and increase in NOx emissions, has caused researchers to look for fuel additives to improve the physiochemical properties of these fuels and to enhance their performance and reduce harmful emissions. It is for this reason that modern research is focused on blending oxygenated additives such as alcohols and ethers with different generations of biodiesel. Since most studies have covered the effect of alcohol on biodiesel, there are few studies which have investigated the effect of oxygenated additives such as alcohols and ethers, especially related to second-generation biodiesel. Moreover, the details of their composition and molecular structure are still lacking. Hence, this study focuses on the performance and emission characteristics of biodiesel with the inclusion of oxygenated additives (alcohols and ethers) of non-edible-oil-based second-generation blends. The reviewed results showed that Neem biodiesel with methanol or diethyl ether reduced brake-specific fuel consumption by 10%, increased brake thermal efficiency by 25% and reduced CO and HC emissions due to a higher oxygen content. Diethyl ether reduced NOx emissions as well by producing a cooling effect, i.e., a reduced in-cylinder temperature. The addition of heptane, butanol and di ethyl ether to Jatropha biodiesel showed an improved brake thermal efficiency and an increment in brake-specific fuel consumption (5–20%), with reduced HC and CO2 (3–12%) emissions. Calophyllum inophyllum biodiesel also showed impressive results in terms of improving efficiency and reducing emissions with addition of butanol, pentanol, decanol and hexanol. Other factors that influenced emissions are the cetane number, viscosity, density and the latent heat of evaporation of tested biodiesel blends. This review would help the research community and the relevant industries to consider an efficient biodiesel blend for future study or its implementation as an alternate fuel in diesel engines.