Ignition and Combustion Characteristics of Heptane-Based Nanofluid Fuel Droplets

Abstract

Nanofluid fuels are promising fuels in the fields of spaceflight and aviation. Their stability is a critical constraint for potential applications. Oleic acid can enhance the stability of nanofluid fuels, but it influences the ignition and combustion performance of nanofluid fuels. In this study, the effects of various concentrations of oleic acid and nanoparticles (NPs) on the ignition and combustion performance of the heptane-based nanofluid droplets were studied using a high-temperature tubular resistance furnace system at 600–700 °C. The ignition delay times, ignition temperatures, and combustion processes of all samples were measured. The results show that with the increase of temperature, the ignition delay times and ignition temperatures of the pure heptane, heptane with addition of oleic acid, and heptane-based nanofluid droplets decrease. The addition of oleic acid into the heptane, its ignition delay time and ignition temperature significantly increase with the increase in oleic acid concentration, which are greatly increased by 60 and 40%, respectively, for the heptane droplet with 2% oleic acid compared with the heptane droplet. Oleic acid makes the heptane droplet to undergo microexplosion, surfactant combustion, and secondary extinguishment. With the increase in temperature and concentration of oleic acid, the microexplosion and the number of generated bubbles are more obvious. Al NPs have little influence on the ignition delay time of the heptane droplet with oleic acid at 600 and 650 °C, while the enhancement of nanoparticles is significant at 700 °C. In addition, Al NPs can decrease the ignition temperature of heptane-based nanofluid droplets and the decreased percent reaches 17%, but the promoting effect is weaker than the inhibition effect of oleic acid. With the increase in concentration of Al NPs, microexplosion of the heptane-based nanofluid droplet will be enhanced.

Effect of double‐droplet interaction on ignition and combustion characteristics of heptane‐based nanofluid fuels in a high‐temperature environment

“…The droplet is re‐ignited. This phenomenon is also found in the studies of Gan and Han et al 12,19 Since the oxide film on the surface of the Al‐NPs is destroyed at high temperature when the flame of ricinoleic acid becomes weaker, the oxygen contacts the surface of the Al agglomerates and reacts with them so that the agglomerates emit dazzling white light. Eventually, as the reaction completes, the hot agglomerates gradually cool and the combustion is over.…”

“…The breakup of the droplet is observed after the droplet expands significantly. Gan and Han et al, 12,19 also observed this phenomenon. This is because during the droplet combustion, the concentration of ricinoleic acid on the surface of the droplet will become higher and higher due to its high boiling, and it eventually forms a film region that hinders the release of vapor inside the droplet.…”

“…The relationship between the ignition delay time of nanofluid fuel and ambient temperature is found. Han et al, 19 systematically measured the ignition delay time and ignition temperature of the single droplet of the Al/heptane nanofluid fuel. Thus, it can be seen that the studies on the ignition and combustion characteristics of the double droplets of the Al/n‐heptane‐based nanofluid fuel are very deficient.…”

Review and Perspectives of CO2 Absorption by Water- and Amine-Based Nanofluids

“…Nanofluids are defined as the combination of nanoparticles (1−100 nm) and base fluid, which can be classified according to the type of base liquid. 15 This section divides the base fluids into two categories (water and amine solutions). The difference between the base liquids will directly affect the absorption effect of CO 2 , and the reported base fluids are listed as follows: (1) water, deionized (DI) water; 16 and (2) amine solutions, MEA, 17 methyldiethanolamine (MDEA), 18 diethanoleamine (DEA), 19 piperazine (PZ), 20 4-diethylamino-2-butanol (DEAB), 21 2-amino-2-methyl-1-propanol (AMP), 22 triethylenetetramine (TETA), 23 and MEA−MDEA.…”

Numerical analysis of the autoignition of isolated wet ethanol droplets immersed in a hot and humid air atmosphere

“…The transient behaviour of the autoignition of alkane droplets has been extensively studied due to its technological interest. Both experimental [15][16][17][18][19][20] and numerical studies [21][22][23] of n-heptane, n-dodecane and n-hexadecane have revealed a catalog of exotic ignition behaviours, that includes single-stage ignition, two-stage ignition and cool flames.…”