Experimental study of evaporation of palm biodiesel with multi-walled carbon nanotubes additives at elevated temperatures

Abstract

Evaporation characteristics of palm biodiesel blended with multi-walled carbon nanotubes (MWCNTs) with different concentrations and outer diameters at ambient temperatures between 473 and 673 K have been investigated. Nano-additives were dispersed in concentration doses of 100 ppm and 200 ppm and outer diameters of 10-20 nm and 30-50 nm. Results showed that droplets underwent an initial heating period and a steady evaporation period without the occurrence of micro-explosions or puffing. In the steady evaporation period, the D 2 -law could be applied for all mixtures. Then droplets completely vaporised at the end of their lifetime. MWCNTs with smaller outer diameters (10-20 nm) exhibited a significantly greater enhancement of the evaporation constant across all temperatures, while larger outer diameters (30-50 mm) only provided improvement at higher ambient temperatures (> 600 K). A high degree of temperature dependence with the concentration of larger MWCNTs (30-50 nm) was observed with retardation of evaporation at lower ambient temperatures (< 523 K) and significant enhancement at higher ambient temperatures (> 600 K). The results suggested an internal aggregation mechanism of MWCNTs contributing to heat transfer to be responsible for this behaviour. Smaller MWCNTs (10-20 nm) with lower concentration (100 ppm) were found to provide the maximum enhancement of evaporation in the temperature domain of interest.

Numerical Simulation of Palm Biodiesel Droplet Evaporation at Various Temperatures and Pressures

“…Figure 1 shows the domain's model geometry, boundary conditions, and mesh refinements. A droplet diameter of 1.1 mm is chosen to model the experimental setup used in [14]. Due to its axisymmetric geometry, only a fourth of the droplet is modelled in a domain of 50 mm diameter.…”

“…Therefore, this study is aimed at filling that knowledge gap by developing a numerical approach to model and observe the fundamental evaporation process of a single palm biodiesel droplet, considering three variables: temperature, pressure, and oxygen composition. The numerical results generated by this approach are then compared with the experimental results of Hashimoto et al [10], Manjunath et al [11,12], and our previous study [14].…”

“…The turbulence induced by the injection process is more significant than the environmental composition in influencing the evaporation process under high pressure and temperature conditions. Amsal et al [14] observed a small difference in the evaporation rate between inert and oxidizing environments. In engine operation, the fuel evaporation process often fluctuates with changes in pressure and oxidant concentration, as is the case when exhaust gas recirculation (EGR) is reused in an engine cycle [24].…”

“…Manjunath et al [11,12] monitored PME evaporation in a weakly convective flow at ambient temperatures of 423-573 K. The long-chain saturation factor is found to influence the vaporisation constants with larger-chain hydrocarbons exhibiting lower evaporation rates. Additive studies with ceria [13] and carbon nanotubes [14] further elucidated the influence of the multicomponent nature of PME with variance both in additive concentration and temperature. These studies revealed that a droplet experienced a significant expansion period during the initial preheating period, followed by a steady, linear evaporation period prior to extinction.…”

“…Most of the literature reviewed in this study investigated the evaporation behaviours of droplets in an inert environment, except for the works by Manjunath et al [11,12] and Amsal et al [14], as these studies investigated droplet behaviours at temperature ranges below the ignition temperature of biodiesel. The turbulence induced by the injection process is more significant than the environmental composition in influencing the evaporation process under high pressure and temperature conditions.…”