In order to optimize the design of the submerged combustion vaporizer(SCV), an experimental apparatus was set up to investigate the heat transfer character outside the tube bundle in SCV. Several experiments were cond...In order to optimize the design of the submerged combustion vaporizer(SCV), an experimental apparatus was set up to investigate the heat transfer character outside the tube bundle in SCV. Several experiments were conducted using water and CO_2 as the heat transfer media in the tubes, respectively. The results indicated that hot air flux, the initial liquid level height and the tube pitch ratio had great influence on the heat transfer coefficient outside the tube bundle(ho). Finally, the air flux associated factor β and height associated factor γ were introduced to propose a new hocorrelation. After verified by experiments using cold water, high pressure CO_2 and liquid N_2 as heat transfer media, respectively, it was found that the biggest deviation between the predicted and the experimental values was less than 25%.展开更多
Existing droplet evaporation/combustion mod- els in computational fluid dynamics （CFD） simulation of spray combustion are based on simplified 1-D models. Both these models and recently developed 3-D models of single...Existing droplet evaporation/combustion mod- els in computational fluid dynamics （CFD） simulation of spray combustion are based on simplified 1-D models. Both these models and recently developed 3-D models of single- droplet combustion do not give the conditions for the different existing droplet combustion modes. In this paper, droplet evaporation and combustion are studied both analytically and numerically. In the analytical solution, a 2-D axisymmetric flow surrounding an evaporating and combusting droplet was considered. The governing equations were solved using an integral method, similar to the Karman-Pohlhausen method for solving boundary-layer flows with pressure gradient. The results give a local evaporation rate and flame radius in agree- ment with experimental results. In numerical simulation, 3-D combusting gas flows surrounding an ethanol droplet were studied. The prediction results show three modes of droplet combustion under different relative velocities, explaining the change in the evaporation constant with an increase in relative velocity observed in experiments. This implies that different droplet combustion models should be developed in simu- lating spray combustion. The predicted local evaporation rate and flame radius by numerical simulation are in agree- ment with the analytical solution in the range of azimuthal angles 0° 〈 θ 〈 90°. The numerical results indicate that the drag force of an evaporating and combusting droplet is much smaller than that of a cold solid particle, and thus the currently used drag models should be modified.展开更多
The accelerated depletion of oil reserves and the often exorbitant cost of fossil fuels contribute to the development of fuels from renewable sources. The objective of this work is to analyze the influence of the prop...The accelerated depletion of oil reserves and the often exorbitant cost of fossil fuels contribute to the development of fuels from renewable sources. The objective of this work is to analyze the influence of the properties of renewable fuels on their evaporation in natural convection, their combustion and their use in internal combustion engines. A summary of the various numerical and experimental works from the literature has been presented in this work. This work focuses on the numerical modelling of the natural convection evaporation of an isolated drop of a liquid fuel in natural convection. The transfers in the liquid and vapour phases are described by the conservation equations of mass and species, momentum and energy. The main feature of this work is the consideration of advection, azimuthal angle and thickness of the vapour phase of the drop during evaporation of the drop.展开更多
This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but...This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but faces challenges in NO_(x)emissions.Strategies like nonpremixed direct injection,increased intake boost pressure,and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines.Control of hydrogen start of injection(SOI)and water injection(WI)are identified as effective techniques for reducing NO_(x)emissions.Ammonia shows inferior combustion and higher NO_(x)and unburned NH_(3)emissions in the same conditions as conventional fuels with conventional engines.Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice,thereby improving combustion and emission reduction.Increasing intake pressure,injection pressure,and EGR rate,employing a turbulent jet,and preheating ammonia improve efficiency and reduce NO_(x)emissions.Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH_(3)adsorber and De NO_(x)catalysts to mitigate unburned NH_(3)and NO_(x)emissions.Biodiesel affects the fuel supply system,combustion,and emission characteristics according to its viscosity and density.Increasing injection pressure and blending with volatile fuels enhance spray and combustion.Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation.By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions,there is potential to improve thermal efficiency and PMNO_(x)trade-off.Therefore,carbon-neutral fuel adoption should be accelerated to mitigate CO_(2)emissions,highlighting the importance of combustion techniques and emissions reduction strategies.展开更多
文摘In order to optimize the design of the submerged combustion vaporizer(SCV), an experimental apparatus was set up to investigate the heat transfer character outside the tube bundle in SCV. Several experiments were conducted using water and CO_2 as the heat transfer media in the tubes, respectively. The results indicated that hot air flux, the initial liquid level height and the tube pitch ratio had great influence on the heat transfer coefficient outside the tube bundle(ho). Finally, the air flux associated factor β and height associated factor γ were introduced to propose a new hocorrelation. After verified by experiments using cold water, high pressure CO_2 and liquid N_2 as heat transfer media, respectively, it was found that the biggest deviation between the predicted and the experimental values was less than 25%.
基金supported by the National Natural Science Foundation of China(Grants 51390493 and 51266008)
文摘Existing droplet evaporation/combustion mod- els in computational fluid dynamics （CFD） simulation of spray combustion are based on simplified 1-D models. Both these models and recently developed 3-D models of single- droplet combustion do not give the conditions for the different existing droplet combustion modes. In this paper, droplet evaporation and combustion are studied both analytically and numerically. In the analytical solution, a 2-D axisymmetric flow surrounding an evaporating and combusting droplet was considered. The governing equations were solved using an integral method, similar to the Karman-Pohlhausen method for solving boundary-layer flows with pressure gradient. The results give a local evaporation rate and flame radius in agree- ment with experimental results. In numerical simulation, 3-D combusting gas flows surrounding an ethanol droplet were studied. The prediction results show three modes of droplet combustion under different relative velocities, explaining the change in the evaporation constant with an increase in relative velocity observed in experiments. This implies that different droplet combustion models should be developed in simu- lating spray combustion. The predicted local evaporation rate and flame radius by numerical simulation are in agree- ment with the analytical solution in the range of azimuthal angles 0° 〈 θ 〈 90°. The numerical results indicate that the drag force of an evaporating and combusting droplet is much smaller than that of a cold solid particle, and thus the currently used drag models should be modified.
文摘The accelerated depletion of oil reserves and the often exorbitant cost of fossil fuels contribute to the development of fuels from renewable sources. The objective of this work is to analyze the influence of the properties of renewable fuels on their evaporation in natural convection, their combustion and their use in internal combustion engines. A summary of the various numerical and experimental works from the literature has been presented in this work. This work focuses on the numerical modelling of the natural convection evaporation of an isolated drop of a liquid fuel in natural convection. The transfers in the liquid and vapour phases are described by the conservation equations of mass and species, momentum and energy. The main feature of this work is the consideration of advection, azimuthal angle and thickness of the vapour phase of the drop during evaporation of the drop.
基金supported by the Laboratory of Space Utilization and D-Drive Project,Hokkaido University,Japan。
文摘This review examines the potential of hydrogen,ammonia,and biodiesel as alternative fuels,focusing on spray dynamics,droplet evaporation,combustion,and emissions.Hydrogen offers superior combustion characteristics but faces challenges in NO_(x)emissions.Strategies like nonpremixed direct injection,increased intake boost pressure,and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines.Control of hydrogen start of injection(SOI)and water injection(WI)are identified as effective techniques for reducing NO_(x)emissions.Ammonia shows inferior combustion and higher NO_(x)and unburned NH_(3)emissions in the same conditions as conventional fuels with conventional engines.Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice,thereby improving combustion and emission reduction.Increasing intake pressure,injection pressure,and EGR rate,employing a turbulent jet,and preheating ammonia improve efficiency and reduce NO_(x)emissions.Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH_(3)adsorber and De NO_(x)catalysts to mitigate unburned NH_(3)and NO_(x)emissions.Biodiesel affects the fuel supply system,combustion,and emission characteristics according to its viscosity and density.Increasing injection pressure and blending with volatile fuels enhance spray and combustion.Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation.By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions,there is potential to improve thermal efficiency and PMNO_(x)trade-off.Therefore,carbon-neutral fuel adoption should be accelerated to mitigate CO_(2)emissions,highlighting the importance of combustion techniques and emissions reduction strategies.
