Search

Biodiesel is composed of various types of methyl ester compounds with different concentrations. The role of unsaturation degree was observed through single-molecule droplet combustion from three fatty acid methyl ester compounds. This research was conducted under normal gravity at ambient temperature and atmospheric pressure. Analysis of droplet combustion characteristics was observed along the heating, evaporation, ignition, and combustion stages. The cis configuration and allyl groups in unsaturated molecules related to different unsaturation degrees affect the droplet combustion process. Allyl and bis-allyl groups play an important role in accelerating hydrogen atom abstraction due to the weaker bond dissociation energy of the CH bond adjacent to the carbon double bond. The lower energy gap in unsaturated molecules is prone to electron excitation. Increasing the unsaturation degree resulted in shorter ignition delay and burning duration but higher droplet temperature, burning rate constant, specific power output, and flame dimensions. Soot particles formed above the flame tip on the unsaturated molecules gave a higher flame dimension. A high concentration of linoleic methyl ester in biodiesel fuel is recommended due to of high power output. However, the soot formation at a higher level of unsaturation degree should be considered.

This study aimed to investigate the effect of the different carbon chain lengths and the degree of unsaturation of six fatty acids as the constituent of vegetable oils. The droplet combustion was carried out at an ambient temperature and atmospheric pressure. The variation in the carbon chain length and the degree of unsaturation resulted in different physical and chemical properties of the fuel, which affect the droplet combustion characteristics. The increase of the carbon chain length results in longer ignition delay times and shorter burning durations, as well as higher droplet temperatures, burning rate constant, and specific power output. Conversely, an increase in the degree of unsaturation with the presence of double bond results in shorter ignition delay and longer burning duration, as well as higher droplet temperatures, but lower burning rate constant and specific power output. The droplet diameter evolution divides the combustion period into unsteady burning zones and quasi-linear burning zones. The flame dimension of unsaturated fatty acid is higher due to the soot formation at the top of the flame. A bluish flame related to the higher oxygen content in the molecule can be observed in saturated fatty acids. The short-chain saturated fatty acid has a large non-luminous zone because they are rich in oxygen. In contrast, the long-chain saturated fatty acid has a narrow non-luminous zone with high flame radiation.

• Unsaturation degree influences the burning rate, energy density, and power output. • The droplet temperature of FAME during combustion is related to the energy density. • Unsaturated FAME produces high flame luminosity with soot particle formation. • Unsaturated FAME requires less energy to dissociate their molecules. • The C=C bond related to the HOMO-LUMO energy gap is prone to electron excitation. Biodiesel is composed of various types of methyl ester compounds with different concentrations. The role of unsaturation degree was observed through single-molecule droplet combustion from three fatty acid methyl ester compounds. This research was conducted under normal gravity at ambient temperature and atmospheric pressure. Analysis of droplet combustion characteristics was observed along the heating, evaporation, ignition, and combustion stages. The cis configuration and allyl groups in unsaturated molecules related to different unsaturation degrees affect the droplet combustion process. Allyl and bis-allyl groups play an important role in accelerating hydrogen atom abstraction due to the weaker bond dissociation energy of the C H bond adjacent to the carbon double bond. The lower energy gap in unsaturated molecules is prone to electron excitation. Increasing the unsaturation degree resulted in shorter ignition delay and burning duration but higher droplet temperature, burning rate constant, specific power output, and flame dimensions. Soot particles formed above the flame tip on the unsaturated molecules gave a higher flame dimension. A high concentration of linoleic methyl ester in biodiesel fuel is recommended due to of high power output. However, the soot formation at a higher level of unsaturation degree should be considered. [ABSTRACT FROM AUTHOR]

The objective of this research is to investigate the droplet combustion characteristics of gasoline-ethanol fuel blended. The combustion characteristics included ignition delay time, burning lifetime, burning rate constant, flame height, flame temperature, and microexplosion. Testing was conducted using fuel blended with ethanol percentage of 0%(E0), 10%(E10), 20% (E20), 30% (E30) and 100% (E100). The fuel was dripped on the tip of the thermocouple junction and ignited using a torch of a butane-air mixture on a cylindrical burner. The results showed that the ignition delay time increase with the increase of ethanol percentage due to its high latent heat of evaporation and flash point temperature. However, flame temperature decrease with the increase of ethanol percentage due to the lower heat release rate of the mixture, related to the lower heating value of ethanol, and the burning rate constant of the fuels were not different significantly. The droplet diameter of the E100 (pure ethanol) decrease according to the d2–law, but the droplet diameters of the E0, E10, E20, and E30 changed drastically, exhibiting expansion and shrinkage. The Combustion of E20 fuel droplet has the highest burning rate constant, and flame height due to the oxygen content in ethanol can accelerate the combustion reaction and the fastest fuel droplet evaporates and diffuses into the air. Besides, the combustion of the E20 fuel droplet has the lowest burning lifetime due to the intensity of the microexplosion often makes the fuel droplet break into small droplets, which helps accelerate the process of evaporation and mixing of fuel with air, so that the combustion reaction occurs faster. Microexplosionphenomenon also identified due to the difference between the boiling point temperature gasoline and ethanol.