Born in 1989 BSc in Mechanical Engineering, Budapest University of Technology and Economics, 2011 MSc in Mechanical Engineering, Budapest University of Technology and Economics, 2013 PhD in Mechanical Engineering, Budapest University of Technology and Economics, 2016 Assistant lecturer in Budapest University of Technology and Economics, Department of Energy Engineering, 2016 Assistant Professor in Budapest University of Technology and Economics, Department of Energy Engineering, 2017-
Original scientific paper https://doi.org/10.2298/TSCI150616062J Control and online monitoring of... more Original scientific paper https://doi.org/10.2298/TSCI150616062J Control and online monitoring of combustion have become critical to meet the increasingly strict pollutant emission standards. For such a purpose, optical sensing methods, like flame emission spectrometry, seem to be the most feasible technique. Spectrometry is capable to provide information about the local equivalence ratio inside the flame through the chemiluminescence intensity ratio measurement of various radicals. In the present study, a 15 kW atmospheric burner was analyzed utilizing standard diesel fuel. Its plain jet type atomizer was operated with both air and steam atomizing mediums. Up to now, injection of steam into the reaction zone has attracted less scientific attention contrary to its practical importance. Spatial plots of OH*, CH*, and C 2 * excited radicals were analyzed at 0.35, 0.7, and 1 bar atomization gauge pressures, utilizing both at-omizing mediums. The C 2 * was found to decrease strongly with increasing steam addition. The OH*/CH* and OH*/C 2 * chemiluminescence intensity ratios along the axis showed a divergent behavior in all the analyzed cases. Nevertheless, CH*/C 2 * chemiluminescence intensity ratio decreased only slightly, showing low sensitivity to the position of the spectrometer. The findings may be directly applied in steady operating combustion systems, i. e., gas turbines, boilers, and furnaces.
To reduce our dependence on primer energy resources, renewable fuels are appearing in an increasi... more To reduce our dependence on primer energy resources, renewable fuels are appearing in an increasing number of fields. Environment has a major effect on theoperating conditions of a gas turbine. Thermal efficiency and power loss occurs, due to higher ambient temperature in summers. There are certain methods to reduce gas turbine inlet temperature, e.g. water evaporation, adsorption and mechanical cooling. Ours is the following: inject bioethanol into the inlet air, which will evaporate , so it reduces inlet temperature. Emission and efficiency measurements were taken to evaluate this method. The Depart-ment's Capstone C330 gas turbine use airblast atomizers for liquid fuel evaporation. Air, as auxiliary medium was replaced with ethanol-water compound steam,which can be easily produced with waste heat of the gas turbine. A test pad was built to examine an isolated fuel nozzle in operation. Pictures and high frame rate videos were taken for visual evaluation. This information helped us to fine-tune our system, and then optimal operating conditions were determined. Keywords gas turbine · renewable fuel · bioethanol · evaporation Acknowledgement Thanks to Krisztián Sztankó, Attila Kun-Balog and Sándor Könczöl for theoretical and technical support, employees of laboratory , who helped me so much in assembling the measurement devices. This project was supported by ÁMFT TÁMOP-4.2.1/B-09/1/KMR-[2010-0002] and also supported by the grant
Utilizing crude vegetable oils in all types of heat engines can be a part of a sustainable econom... more Utilizing crude vegetable oils in all types of heat engines can be a part of a sustainable economy in the future. Fo-cusing on their local usage, they can possibly compete with fossil fuels. Furthermore, to keep the pollutant emissions at the lowest possible level, the feedback control of the equivalence ratio is essential. Regarding the harsh environment of the combustion chambers, optical flame diagnostics is a potential tool. Therefore, in order to examine its feasibility, the comparison of flame emission spectroscopy (FES) of rapeseed oil with standard diesel oil was carried out at atmospheric conditions in a lean premixed prevaporized (LPP) burner at 15 kW of firing power. The well-known chemiluminescence intensity ratios of OH*, CH*, and C 2 * at 516 nm (C 2, 516 *) were investigated. A further significant peak was found at 554 nm in case of rapeseed oil firing, which probably corresponds to C 2 * (C 2, 554 *). The corrected chemiluminescence intensity ratios as a function of air-fuel equivalence ratio are shown in the current work. It was found that these ratios involving C 2 * at either 516 or 554 nm show less sensitivity to the pressure of atomizing air than OH*/CH*, therefore they are more suitable for diagnostics and for the control of the equivalence ratio of liquid fired burners.
The last decades have emphasized the requirement for alternative energy sources, particularly in ... more The last decades have emphasized the requirement for alternative energy sources, particularly in the transport sector, where combustible liquid fuels are expected to dominate in the foreseeable future. In such applications, the fuel must be efficiently atomized, evaporated, and mixed with the combustion air before it reaches the flame front, in order to meet the latest pollutant emission standards. Hence, this paper investigates the utilization of nine different fossil and renewable liquid fuels. The domain of the analysis is a lean premixed prevaporized burner equipped with an air blast atomizer and a mixing tube. Analytical calculations are performed to determine the evaporation process after the atomization; then the evaporation time is compared to the residence time of the droplets in the mixing tube. The effect of pre-heating both the fuel and the combustion air is also examined to determine proper combustion conditions even for the low volatile crude vegetable oils.
The investigation of renewable liquid fuels has received high attention in the combustion science... more The investigation of renewable liquid fuels has received high attention in the combustion science of the past decades. However, the combustion of crude rapeseed oil has received less attention due to its poor combustion properties. Therefore, the scope of the current paper is to experimentally investigate its utilization in an atmospheric test rig designed for 15 kW combustion power. For the current investigation, a lean premixing and prevaporizing burner equipped with an airblast atomizer was used. During the investigation, the combustion air flow rate and the atomizing pressure were varied. For comparison, the same measurement series were carried out utilizing diesel oil. Stable combustion of rapeseed oil was limited by inadequate atomization, critical swirl number, and blowout. By contrast, diesel oil combustion was only limited by blowout. The emission of CO and NOX were compared to an actual decree from which emphasized that CO governed the overall emissions. The optima are located at similar atomizing pressure and primary equivalence ratio for both fuels. Therefore, crude rapeseed oil might be an appropriate substitute for diesel oil in steady combustion.
Airblast atomizers are especially useful and commonplace in liquid fuel combustion applications. ... more Airblast atomizers are especially useful and commonplace in liquid fuel combustion applications. However, the spray formation processes, the droplet dynamics and the final drop size distributions are still not sufficiently understood due to the coupled gas-liquid interactions and turbulence generation. Therefore, empirical and semi-empirical approaches are typically used to estimate the global spray parameters. To develop a physical understanding of the spray evolution, a plain-jet airblast atomizer was investigated in an atmospheric spray rig using the Phase-Doppler technique. The simultaneous drop size and axial and radial velocity components were measured on radial traverses across the spray at various axial distances from the nozzle for a range of atomizing pressures. The droplet turbulent and mean kinetic energies were found to be proportional to the atomizing pressure. Hence, the scatter of the radial motion of the droplets increased with the atomizing pressure. A droplet stability analysis was performed to locate the regions characterized by ongoing secondary atomization. The volume-to-surface diameter, D32, of the fully developed spray was compared with estimates provided by five published formulae. The role of liquid viscosity, hence the Ohnesorge number, was found to be negligible in the investigated regime. Three commonly used size distribution functions were fitted to the measured data to analyze their dependence on the atomizing pressure. The Gamma distribution function was found to give the best approximation to the atomization process.
Hydrous ethanol is produced to the largest extent among all renewable liquid fuels. The utilizati... more Hydrous ethanol is produced to the largest extent among all renewable liquid fuels. The utilization of aqueous ethanol, however, seems to be a more economical solution due to considerable savings on the production costs while the combustion performance is affected slightly. In the present paper, the energy balance of aqueous bioethanol distillation was analyzed using a 12% ethanol-water solution by volume as feed. The results showed that the distillation energy-to-lower heating value ratio of 92–52% solutions are only 0.394 of that of hydrous ethanol. Combustion tests were performed at 15 kW combustion power and an air-to-fuel equivalence ratio of 1.17, utilizing 96–50% ethanol-water solutions by volume injected in both gaseous and liquid form. From a pollutant emissions perspective, all the tested alcohols are in line with the present Hungarian standard. Considering the upcoming regulations of 2018, 90–50% liquid alcohols and 80–50% evaporated alcohols already fulfill the stricter limitations.
Atomization involves mass, energy, and impulse transfer, in such a complex way that the overall p... more Atomization involves mass, energy, and impulse transfer, in such a complex way that the overall process can only be described by empirical and semi-empirical correlations to date. The phenomenon of atomization is used in numerous applications, e.g., in combustion technology and metallurgy. However, many formulae are available in the literature to derive mean diameters of the spray, size distribution functions are barely discussed. Based on the measurement results performed earlier by a Phase Doppler Anemometer, twenty probability density functions were evaluated and seven are discussed in detail over the course of the present paper. The atomization pressure was varied, and characteristic regimes of the spray were measured. Interestingly, the analysis showed that not only the three most commonly used probability density functions (Nukiyama-Tanasawa, Rosin-Rammler, and Gamma) are eligible for describing the size distribution of the spray.
Stringent emissions standards for NOx and carbon monoxide (CO) prompt lean combustor development.... more Stringent emissions standards for NOx and carbon monoxide (CO) prompt lean combustor development. With this motivation, combustion stability issues emerge since the desired operating point approaches the lean blowout limit. In this paper, an atmospheric, 15 kW lean premixed prevaporizing-type swirl burner, equipped with a plain jet airblast atomizer, was investigated at various atomizing pressures and combustion air flow rates, using quarls from 0 deg to 60 deg in 15 deg steps. Both the 15 deg and the 30 deg quarls provided a 42% higher lean blowout stability on average in terms of mean mixing tube discharge velocity, compared to the baseline burner. However, the superior stability regime was encumbered by a rapidly increasing CO emission. In parallel, the NOx emission vanished due to the more dilution air and incomplete combustion. The 60deg quarl provided a moderately extended blowout stability limitation, while the NOx emission slightly increased and the CO emission reduced compared to the baseline burner.
CubeSats have revolutionized the space industry in the past two decades. Its successor, the Pocke... more CubeSats have revolutionized the space industry in the past two decades. Its successor, the PocketQube class seems to be a lower size limit for a satellite which can operate continuously and can be received by radio amateur equipment. The present paper discusses the simulation of the thermal environment of the SMOG-1 PocketQube satellite at low Earth orbit by both thermal network and finite element models. The major findings of the analyses are the following. Even a single node per printed circuit board model can provide adequate information about the thermal behavior without tuning the physical parameters. By applying a finite element model with few magnitudes more nodes, the predicted inner temperature increased as the losses were reduced in the radiation-dominant environment compared to the thermal network model. Therefore, this latter method provides a more conservative temperature estimation. The most sensitive component of small-sized satellites is the battery which remains in the desired positive temperature regime even in this satellite class according to the finite element model. However, the thermal network model predicted a restricted battery charging protocol to ∼50% of the lit duration. Nevertheless, this condition still results in a positive energy balance by a factor of 1.5.
Airblast atomization is a suitable model platform to understand atomization physics since the ato... more 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.
Calculation of evaporation requires accurate thermophysical properties of the liquid. Such data a... more Calculation of evaporation requires accurate thermophysical properties of the liquid. Such data are well-known for conventional fossil fuels. In contrast, e.g., thermal conductivity or dynamic viscosity of the fuel vapor are rarely available for modern liquid fuels. To overcome this problem, molecular models can be used. Currently, the measurement-based properties of n-heptane and diesel oil are compared with estimated values, using the state-of-the-art molecular models to derive the temperature-dependent material properties. Then their effect on droplet evaporation was evaluated. The critical parameters were liquid density, latent heat of vaporization, boiling temperature, and vapor thermal conductivity where the estimation affected the evaporation time notably. Besides a general sensitivity analysis, evaporation modeling in a practical burner ended up with similar results. By calculating droplet motion, the evaporation number, the evaporation-to-residence time ratio can be derived. An empirical cumulative distribution function is used for the spray of the analyzed burner to evaluate evaporation in the mixing tube. Evaporation number did not exceed 0.4, meaning a full evaporation prior to reaching the burner lip in all cases. As droplet inertia depends upon its size, the residence time has a minimum value due to the phenomenon of overshooting.
Original scientific paper https://doi.org/10.2298/TSCI150616062J Control and online monitoring of... more Original scientific paper https://doi.org/10.2298/TSCI150616062J Control and online monitoring of combustion have become critical to meet the increasingly strict pollutant emission standards. For such a purpose, optical sensing methods, like flame emission spectrometry, seem to be the most feasible technique. Spectrometry is capable to provide information about the local equivalence ratio inside the flame through the chemiluminescence intensity ratio measurement of various radicals. In the present study, a 15 kW atmospheric burner was analyzed utilizing standard diesel fuel. Its plain jet type atomizer was operated with both air and steam atomizing mediums. Up to now, injection of steam into the reaction zone has attracted less scientific attention contrary to its practical importance. Spatial plots of OH*, CH*, and C 2 * excited radicals were analyzed at 0.35, 0.7, and 1 bar atomization gauge pressures, utilizing both at-omizing mediums. The C 2 * was found to decrease strongly with increasing steam addition. The OH*/CH* and OH*/C 2 * chemiluminescence intensity ratios along the axis showed a divergent behavior in all the analyzed cases. Nevertheless, CH*/C 2 * chemiluminescence intensity ratio decreased only slightly, showing low sensitivity to the position of the spectrometer. The findings may be directly applied in steady operating combustion systems, i. e., gas turbines, boilers, and furnaces.
To reduce our dependence on primer energy resources, renewable fuels are appearing in an increasi... more To reduce our dependence on primer energy resources, renewable fuels are appearing in an increasing number of fields. Environment has a major effect on theoperating conditions of a gas turbine. Thermal efficiency and power loss occurs, due to higher ambient temperature in summers. There are certain methods to reduce gas turbine inlet temperature, e.g. water evaporation, adsorption and mechanical cooling. Ours is the following: inject bioethanol into the inlet air, which will evaporate , so it reduces inlet temperature. Emission and efficiency measurements were taken to evaluate this method. The Depart-ment's Capstone C330 gas turbine use airblast atomizers for liquid fuel evaporation. Air, as auxiliary medium was replaced with ethanol-water compound steam,which can be easily produced with waste heat of the gas turbine. A test pad was built to examine an isolated fuel nozzle in operation. Pictures and high frame rate videos were taken for visual evaluation. This information helped us to fine-tune our system, and then optimal operating conditions were determined. Keywords gas turbine · renewable fuel · bioethanol · evaporation Acknowledgement Thanks to Krisztián Sztankó, Attila Kun-Balog and Sándor Könczöl for theoretical and technical support, employees of laboratory , who helped me so much in assembling the measurement devices. This project was supported by ÁMFT TÁMOP-4.2.1/B-09/1/KMR-[2010-0002] and also supported by the grant
Utilizing crude vegetable oils in all types of heat engines can be a part of a sustainable econom... more Utilizing crude vegetable oils in all types of heat engines can be a part of a sustainable economy in the future. Fo-cusing on their local usage, they can possibly compete with fossil fuels. Furthermore, to keep the pollutant emissions at the lowest possible level, the feedback control of the equivalence ratio is essential. Regarding the harsh environment of the combustion chambers, optical flame diagnostics is a potential tool. Therefore, in order to examine its feasibility, the comparison of flame emission spectroscopy (FES) of rapeseed oil with standard diesel oil was carried out at atmospheric conditions in a lean premixed prevaporized (LPP) burner at 15 kW of firing power. The well-known chemiluminescence intensity ratios of OH*, CH*, and C 2 * at 516 nm (C 2, 516 *) were investigated. A further significant peak was found at 554 nm in case of rapeseed oil firing, which probably corresponds to C 2 * (C 2, 554 *). The corrected chemiluminescence intensity ratios as a function of air-fuel equivalence ratio are shown in the current work. It was found that these ratios involving C 2 * at either 516 or 554 nm show less sensitivity to the pressure of atomizing air than OH*/CH*, therefore they are more suitable for diagnostics and for the control of the equivalence ratio of liquid fired burners.
The last decades have emphasized the requirement for alternative energy sources, particularly in ... more The last decades have emphasized the requirement for alternative energy sources, particularly in the transport sector, where combustible liquid fuels are expected to dominate in the foreseeable future. In such applications, the fuel must be efficiently atomized, evaporated, and mixed with the combustion air before it reaches the flame front, in order to meet the latest pollutant emission standards. Hence, this paper investigates the utilization of nine different fossil and renewable liquid fuels. The domain of the analysis is a lean premixed prevaporized burner equipped with an air blast atomizer and a mixing tube. Analytical calculations are performed to determine the evaporation process after the atomization; then the evaporation time is compared to the residence time of the droplets in the mixing tube. The effect of pre-heating both the fuel and the combustion air is also examined to determine proper combustion conditions even for the low volatile crude vegetable oils.
The investigation of renewable liquid fuels has received high attention in the combustion science... more The investigation of renewable liquid fuels has received high attention in the combustion science of the past decades. However, the combustion of crude rapeseed oil has received less attention due to its poor combustion properties. Therefore, the scope of the current paper is to experimentally investigate its utilization in an atmospheric test rig designed for 15 kW combustion power. For the current investigation, a lean premixing and prevaporizing burner equipped with an airblast atomizer was used. During the investigation, the combustion air flow rate and the atomizing pressure were varied. For comparison, the same measurement series were carried out utilizing diesel oil. Stable combustion of rapeseed oil was limited by inadequate atomization, critical swirl number, and blowout. By contrast, diesel oil combustion was only limited by blowout. The emission of CO and NOX were compared to an actual decree from which emphasized that CO governed the overall emissions. The optima are located at similar atomizing pressure and primary equivalence ratio for both fuels. Therefore, crude rapeseed oil might be an appropriate substitute for diesel oil in steady combustion.
Airblast atomizers are especially useful and commonplace in liquid fuel combustion applications. ... more Airblast atomizers are especially useful and commonplace in liquid fuel combustion applications. However, the spray formation processes, the droplet dynamics and the final drop size distributions are still not sufficiently understood due to the coupled gas-liquid interactions and turbulence generation. Therefore, empirical and semi-empirical approaches are typically used to estimate the global spray parameters. To develop a physical understanding of the spray evolution, a plain-jet airblast atomizer was investigated in an atmospheric spray rig using the Phase-Doppler technique. The simultaneous drop size and axial and radial velocity components were measured on radial traverses across the spray at various axial distances from the nozzle for a range of atomizing pressures. The droplet turbulent and mean kinetic energies were found to be proportional to the atomizing pressure. Hence, the scatter of the radial motion of the droplets increased with the atomizing pressure. A droplet stability analysis was performed to locate the regions characterized by ongoing secondary atomization. The volume-to-surface diameter, D32, of the fully developed spray was compared with estimates provided by five published formulae. The role of liquid viscosity, hence the Ohnesorge number, was found to be negligible in the investigated regime. Three commonly used size distribution functions were fitted to the measured data to analyze their dependence on the atomizing pressure. The Gamma distribution function was found to give the best approximation to the atomization process.
Hydrous ethanol is produced to the largest extent among all renewable liquid fuels. The utilizati... more Hydrous ethanol is produced to the largest extent among all renewable liquid fuels. The utilization of aqueous ethanol, however, seems to be a more economical solution due to considerable savings on the production costs while the combustion performance is affected slightly. In the present paper, the energy balance of aqueous bioethanol distillation was analyzed using a 12% ethanol-water solution by volume as feed. The results showed that the distillation energy-to-lower heating value ratio of 92–52% solutions are only 0.394 of that of hydrous ethanol. Combustion tests were performed at 15 kW combustion power and an air-to-fuel equivalence ratio of 1.17, utilizing 96–50% ethanol-water solutions by volume injected in both gaseous and liquid form. From a pollutant emissions perspective, all the tested alcohols are in line with the present Hungarian standard. Considering the upcoming regulations of 2018, 90–50% liquid alcohols and 80–50% evaporated alcohols already fulfill the stricter limitations.
Atomization involves mass, energy, and impulse transfer, in such a complex way that the overall p... more Atomization involves mass, energy, and impulse transfer, in such a complex way that the overall process can only be described by empirical and semi-empirical correlations to date. The phenomenon of atomization is used in numerous applications, e.g., in combustion technology and metallurgy. However, many formulae are available in the literature to derive mean diameters of the spray, size distribution functions are barely discussed. Based on the measurement results performed earlier by a Phase Doppler Anemometer, twenty probability density functions were evaluated and seven are discussed in detail over the course of the present paper. The atomization pressure was varied, and characteristic regimes of the spray were measured. Interestingly, the analysis showed that not only the three most commonly used probability density functions (Nukiyama-Tanasawa, Rosin-Rammler, and Gamma) are eligible for describing the size distribution of the spray.
Stringent emissions standards for NOx and carbon monoxide (CO) prompt lean combustor development.... more Stringent emissions standards for NOx and carbon monoxide (CO) prompt lean combustor development. With this motivation, combustion stability issues emerge since the desired operating point approaches the lean blowout limit. In this paper, an atmospheric, 15 kW lean premixed prevaporizing-type swirl burner, equipped with a plain jet airblast atomizer, was investigated at various atomizing pressures and combustion air flow rates, using quarls from 0 deg to 60 deg in 15 deg steps. Both the 15 deg and the 30 deg quarls provided a 42% higher lean blowout stability on average in terms of mean mixing tube discharge velocity, compared to the baseline burner. However, the superior stability regime was encumbered by a rapidly increasing CO emission. In parallel, the NOx emission vanished due to the more dilution air and incomplete combustion. The 60deg quarl provided a moderately extended blowout stability limitation, while the NOx emission slightly increased and the CO emission reduced compared to the baseline burner.
CubeSats have revolutionized the space industry in the past two decades. Its successor, the Pocke... more CubeSats have revolutionized the space industry in the past two decades. Its successor, the PocketQube class seems to be a lower size limit for a satellite which can operate continuously and can be received by radio amateur equipment. The present paper discusses the simulation of the thermal environment of the SMOG-1 PocketQube satellite at low Earth orbit by both thermal network and finite element models. The major findings of the analyses are the following. Even a single node per printed circuit board model can provide adequate information about the thermal behavior without tuning the physical parameters. By applying a finite element model with few magnitudes more nodes, the predicted inner temperature increased as the losses were reduced in the radiation-dominant environment compared to the thermal network model. Therefore, this latter method provides a more conservative temperature estimation. The most sensitive component of small-sized satellites is the battery which remains in the desired positive temperature regime even in this satellite class according to the finite element model. However, the thermal network model predicted a restricted battery charging protocol to ∼50% of the lit duration. Nevertheless, this condition still results in a positive energy balance by a factor of 1.5.
Airblast atomization is a suitable model platform to understand atomization physics since the ato... more 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.
Calculation of evaporation requires accurate thermophysical properties of the liquid. Such data a... more Calculation of evaporation requires accurate thermophysical properties of the liquid. Such data are well-known for conventional fossil fuels. In contrast, e.g., thermal conductivity or dynamic viscosity of the fuel vapor are rarely available for modern liquid fuels. To overcome this problem, molecular models can be used. Currently, the measurement-based properties of n-heptane and diesel oil are compared with estimated values, using the state-of-the-art molecular models to derive the temperature-dependent material properties. Then their effect on droplet evaporation was evaluated. The critical parameters were liquid density, latent heat of vaporization, boiling temperature, and vapor thermal conductivity where the estimation affected the evaporation time notably. Besides a general sensitivity analysis, evaporation modeling in a practical burner ended up with similar results. By calculating droplet motion, the evaporation number, the evaporation-to-residence time ratio can be derived. An empirical cumulative distribution function is used for the spray of the analyzed burner to evaluate evaporation in the mixing tube. Evaporation number did not exceed 0.4, meaning a full evaporation prior to reaching the burner lip in all cases. As droplet inertia depends upon its size, the residence time has a minimum value due to the phenomenon of overshooting.
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Papers by Viktor Józsa