Effect of multi-walled carbon nanotubes on pre-vaporized palm oil biodiesel/air premixed flames

Abstract

In regard to the current state of global energy, the high demand for traditional fossil fuels and their negative environmental impact have led to an increase of interest in the development of renewable clean fuels. Recently, nano-additives such as carbon nanotubes (CNTs) have been considered as a potential additive to increase fuel combustion performance. Thus, we experimentally studied the combustion characteristics of multi-walled carbon nanotubes (MWCNTs) blended palm-oil biodiesel/air mixtures at a wide range of equivalence ratios, 0.7–1.6. Experiments were conducted at atmospheric pressure and a temperature of 550 K to ensure full vaporization of the liquid biodiesel fuel. Concentrations of the MWCNTs in the mixture were varied from 25 to 200 ppm for two different groups of nanotubes having outer diameter ranges of 10–20 nm and 30–50 nm. The results showed that both laminar burning velocity and blowoff velocity were increased with the additions of MWCNTs. Besides, the flammability limits of MWCNTs blended biodiesel/air premixed flames were also extended at both fuel-lean and fuel-rich conditions. It was also observed that the MWCNTs of 10–20 nm experienced more noticeable improvements in the combustion characteristics compared to the MWCNTs of 30–50 nm. After reaching the highest enhancement, a further increase in the concentration of MWCNTs generally caused less improvement in the laminar burning velocities of the premixed flames. Besides, the addition of MWCNTs increased nitrogen oxides and decreased carbon monoxide concentrations in the combustion products.