Technical feasibility analysis of carbon nanotubes in diesel engines: Effects on stability, combustion properties and emissions

Several studies have reported benefits when using various nanomaterials dispersed in conventional diesel fuel. However, important constraints related to nanomaterial sedimentation, fuel filter blockage and a possible increase in particles emission because of unburnt nanofuels, have not been yet properly addressed. In this study, carbon nanotubes (CNTs) were dispersed in diesel fuel at 50, 100, and 150 mg/L concentrations, and stabilized with sodium dodecylbenzene sulfonate (SDBS). The dispersion stability results indicate that a concentration of 100 mg/L of CNTs presented the lowest sedimentation. However, even with such appropriate content, the concentration of CNTs decreased by 96 % after the engine fuel filter because of nanomaterial retention. Then, in order to assess the impact of nanofuel on diesel engine emissions, the fuel filter was removed for the engine tests. These tests were conducted using the Worldwide Harmonized Light Vehicle Test Cycle (WLTC), with measurements taken for carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), and particulate matter. The emission of HC and NOx when using nanofuel were found to be comparable to those of diesel fuel. However, a notable increase of approximately 34 % in CO emissions was observed. Furthermore, there was an increase in particulate matter, likely attributed to the unreacted nanotubes as well as to the adherence of CNTs to pre-existing PM particles, leading to the formation of larger particles or serving as nucleation sites. These findings give rise to significant concerns and present considerable challenges for the incorporation of SDBS-stabilized CNTs in diesel engine applications.