• Energy Research

Abstract Airblast atomization is a suitable model platform to understand atomization physics since the atomizer geometry has an insignificant influence on the spray formation. Besides its theoretical relevance, this configuration is used in several practical applications ranging from healthcare to combustion. Presently, a plain-jet airblast atomizer has been investigated experimentally under atmospheric conditions at various atomizing pressures and liquid preheating temperatures. To cover a wide range of liquids by viscosity and surface tension, water, diesel oil, light heating oil, and crude rapeseed oil were atomized to evaluate the droplet size-velocity correlations when the spray is fully developed. Increasing the temperature of high-viscosity liquids prior to atomization improves the spray characteristics until their kinematic viscosity decreases to a certain value that is newly introduced as a limiting viscosity. Further preheating has a marginal effect on droplet size-velocity plots, and the spray becomes more homogeneous. Several SMD-estimating formulae were analyzed and improved to consider the effect of liquid preheating and to extend their range of validity. When the kinematic viscosity exceeded the limiting viscosity, the part containing the Weber number was corrected linearly by the preheating temperature. The coefficient of the Ohnesorge number was corrected by the inverse of the kinematic viscosity, without considering the limiting viscosity. The above results help to correct the SMD of atmospheric measurements to elevated liquid temperatures and to contribute to advanced atomization models for numerical software.

Abstract Airblast atomization is a suitable model platform to understand atomization physics since the atomizer geometry has an insignificant influence on the spray formation. Besides its theoretical relevance, this configuration is used in several practical applications ranging from healthcare to combustion. Presently, a plain-jet airblast atomizer has been investigated experimentally under atmospheric conditions at various atomizing pressures and liquid preheating temperatures. To cover a wide range of liquids by viscosity and surface tension, water, diesel oil, light heating oil, and crude rapeseed oil were atomized to evaluate the droplet size-velocity correlations when the spray is fully developed. Increasing the temperature of high-viscosity liquids prior to atomization improves the spray characteristics until their kinematic viscosity decreases to a certain value that is newly introduced as a limiting viscosity. Further preheating has a marginal effect on droplet size-velocity plots, and the spray becomes more homogeneous. Several SMD-estimating formulae were analyzed and improved to consider the effect of liquid preheating and to extend their range of validity. When the kinematic viscosity exceeded the limiting viscosity, the part containing the Weber number was corrected linearly by the preheating temperature. The coefficient of the Ohnesorge number was corrected by the inverse of the kinematic viscosity, without considering the limiting viscosity. The above results help to correct the SMD of atmospheric measurements to elevated liquid temperatures and to contribute to advanced atomization models for numerical software.

Rotary atomization is used in a wide variety of fields, exploiting the external control option of the spray while no high-pressure fluid is needed. Most papers on rotary atomization deal with liquid jet breakup, while external spray characteristics are rarely evaluated; this is performed currently. The water spray was measured by a two-component phase Doppler anemometer. The optical setup requires a special measurement chamber to avoid spray deposition on the optical components. Therefore, the first goal was to find a proper filter that enables the removal of biased droplets by secondary flows. Since most droplets have a similar radial-to-tangential velocity ratio at each measurement point, i.e., scattering around a line, this was the first component of the best filter. The second component was the need for a positive radial velocity component. This filter efficiently removed droplets originating from alternative processes, increasing the R2 of the line fit. The physical soundness of this filter was checked by evaluating the effect of filtering on the angle of the velocity components of each droplet at a given measurement point. The proposed filter efficiently detected recirculation, a secondary effect of the measurement setup with less regular dataset shapes. Finally, the slope and intercept values of the fitted lines were evaluated and presented. The mean of the former followed the same trend irrespective of the rotational speed and the mass flow rate; it was principally dependent on the radial distance from the atomizer. The intercept showed a regular but less universal behavior.

Rotary atomization is used in a wide variety of fields, exploiting the external control option of the spray while no high-pressure fluid is needed. Most papers on rotary atomization deal with liquid jet breakup, while external spray characteristics are rarely evaluated; this is performed currently. The water spray was measured by a two-component phase Doppler anemometer. The optical setup requires a special measurement chamber to avoid spray deposition on the optical components. Therefore, the first goal was to find a proper filter that enables the removal of biased droplets by secondary flows. Since most droplets have a similar radial-to-tangential velocity ratio at each measurement point, i.e., scattering around a line, this was the first component of the best filter. The second component was the need for a positive radial velocity component. This filter efficiently removed droplets originating from alternative processes, increasing the R2 of the line fit. The physical soundness of this filter was checked by evaluating the effect of filtering on the angle of the velocity components of each droplet at a given measurement point. The proposed filter efficiently detected recirculation, a secondary effect of the measurement setup with less regular dataset shapes. Finally, the slope and intercept values of the fitted lines were evaluated and presented. The mean of the former followed the same trend irrespective of the rotational speed and the mass flow rate; it was principally dependent on the radial distance from the atomizer. The intercept showed a regular but less universal behavior.

Abstract The increase in human consumption of plant and animal oils has led to the rise in waste cooking oil (WCO) production. Instead of disposing the used cooking oil as waste, recent technological advance has enabled the use of WCO as a sustainable feedstock for biofuels production, thereby maximising the value of biowastes via energy recovery while concomitantly solving the disposal issue. The current regulatory frameworks for WCO collection and recycling practices imposed by major WCO producing countries are reviewed, followed by the overview of the progress in biodiesel conversion techniques, along with novel methods to improve the feasibility for upscaling. The factors which influence the efficiency of the reactions such as properties of feedstock, heterogenous catalytic processes, cost effectiveness and selectivity of reaction product are discussed. Ultrasonic-assisted transesterification is found to be the least energy intensive method for producing biodiesel. The production of bio-jet fuels from WCO, while scarce, provide diversity in waste utilisation if problems such as carbon chain length, requirements of bio-jet fuel properties, extreme reaction conditions and effectiveness of selected catalyst-support system can be solved. Technoeconomic studies revealed that WCO biofuels is financially viable with benefit of mitigating carbon emissions, provided that the price gap between the produced fuel and commercial fuels, sufficient supply of WCO and variation in the oil properties are addressed. This review shows that WCO is a biowaste with high potential for advanced transportation fuel production for ground and aviation industries. The advancement in fuel production technology and relevant policies would accelerate the application of sustainable WCO biofuels.

Abstract The increase in human consumption of plant and animal oils has led to the rise in waste cooking oil (WCO) production. Instead of disposing the used cooking oil as waste, recent technological advance has enabled the use of WCO as a sustainable feedstock for biofuels production, thereby maximising the value of biowastes via energy recovery while concomitantly solving the disposal issue. The current regulatory frameworks for WCO collection and recycling practices imposed by major WCO producing countries are reviewed, followed by the overview of the progress in biodiesel conversion techniques, along with novel methods to improve the feasibility for upscaling. The factors which influence the efficiency of the reactions such as properties of feedstock, heterogenous catalytic processes, cost effectiveness and selectivity of reaction product are discussed. Ultrasonic-assisted transesterification is found to be the least energy intensive method for producing biodiesel. The production of bio-jet fuels from WCO, while scarce, provide diversity in waste utilisation if problems such as carbon chain length, requirements of bio-jet fuel properties, extreme reaction conditions and effectiveness of selected catalyst-support system can be solved. Technoeconomic studies revealed that WCO biofuels is financially viable with benefit of mitigating carbon emissions, provided that the price gap between the produced fuel and commercial fuels, sufficient supply of WCO and variation in the oil properties are addressed. This review shows that WCO is a biowaste with high potential for advanced transportation fuel production for ground and aviation industries. The advancement in fuel production technology and relevant policies would accelerate the application of sustainable WCO biofuels.

Abstract Real-time combustion and emission control is an ongoing challenge in combustion technology and science. Hence, the scope of the present paper is the investigation of the relationship between the chemiluminescent signal and the CO and NOX emissions. Flame emission spectrometry measurements were carried out to determine the characteristic free radicals of the spectra. For the experiments, a lean premixed liquid fuel burner equipped with an airblast atomizer was used in a test rig at 15 kW combustion power. The following measurement parameters were modified: combustion air flow rate, atomizing pressure, and the vertical alignment of the spectrometer. Furthermore, various half-cone angle quarls were mounted on the burner lip to extend the lean flame blowout stability limit. The CO and NOX emissions and the chemiluminescence intensity ratios of the strongest peaks of OH*, CH*, C2*, HCO*, and CH2O* were evaluated separately at first. Then a correlation analysis of the intensity ratios and the pollutant emission components was carried out. A notable linear correlation was found between both the HCO*/C2* and OH*/C2* intensity ratios and the CO emission in certain parameter combinations.