Pub Date : 2019-12-20DOI: 10.3389/fmech.2019.00066
K. Judd, R. Handler
{"title":"Editorial: Applications of Infrared Methods in Fluid Mechanics","authors":"K. Judd, R. Handler","doi":"10.3389/fmech.2019.00066","DOIUrl":"https://doi.org/10.3389/fmech.2019.00066","url":null,"abstract":"","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"96 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90519291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-06DOI: 10.3389/fmech.2019.00067
Yunong Zhou, Anle Wang, M. Müser
Contact problems as they occur in tribology and colloid science are often solved with the assumption of hard-wall and hard-disk repulsion between locally smooth surfaces. This approximation is certainly meaningful at sufficiently coarse scales. However, at small scales, thermal fluctuations can become relevant. In this study, we address the question how they render non-overlap constraints into finite-range repulsion. To this end, we derive a closed-form analytical expression for the potential of mean force between a hard wall and a thermally fluctuating, linearly elastic counterface. Theoretical results are validated with numerical simulations based on the Green's function molecular dynamics technique, which is generalized to include thermal noise while allowing for hard-wall interactions. Applications consist of the validation of our method for flat surfaces and the generalization of the Hertzian contact to finite temperature. In both cases, similar force-distance relationships are produced with effective potentials as with fully thermostatted simulations. Analytical expressions are identified that allow the thermal corrections to the Hertzian load-displacement relation to be accurately estimated. While these corrections are not necessarily small, they turn out surprisingly insensitive to the applied load.
{"title":"How Thermal Fluctuations Affect Hard-Wall Repulsion and Thereby Hertzian Contact Mechanics","authors":"Yunong Zhou, Anle Wang, M. Müser","doi":"10.3389/fmech.2019.00067","DOIUrl":"https://doi.org/10.3389/fmech.2019.00067","url":null,"abstract":"Contact problems as they occur in tribology and colloid science are often solved with the assumption of hard-wall and hard-disk repulsion between locally smooth surfaces. This approximation is certainly meaningful at sufficiently coarse scales. However, at small scales, thermal fluctuations can become relevant. In this study, we address the question how they render non-overlap constraints into finite-range repulsion. To this end, we derive a closed-form analytical expression for the potential of mean force between a hard wall and a thermally fluctuating, linearly elastic counterface. Theoretical results are validated with numerical simulations based on the Green's function molecular dynamics technique, which is generalized to include thermal noise while allowing for hard-wall interactions. Applications consist of the validation of our method for flat surfaces and the generalization of the Hertzian contact to finite temperature. In both cases, similar force-distance relationships are produced with effective potentials as with fully thermostatted simulations. Analytical expressions are identified that allow the thermal corrections to the Hertzian load-displacement relation to be accurately estimated. While these corrections are not necessarily small, they turn out surprisingly insensitive to the applied load.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"9 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78232476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-03DOI: 10.3389/fmech.2019.00064
A. Boretti
The pros and the cons of lean-burn, compression ignition (CI), direct injection (DI) internal combustion engines (ICE) are reviewed for transport applications. Fueling options considered include diesel only and dual-fuel applications with diesel and a gaseous fuel (CNG, LNG and LPG). CIDI ICEs have higher fuel conversion efficiencies than stoichiometric, spark ignition (SI) ICEs, whether DI or port fuel injected (PFI). However, diesel-fueled CIDI ICEs have higher particulate matter (PM) and NOx engine-out emissions. The tail-pipe NOx emissions in real-world driving of diesel-powered vehicles have been, in the past, above the limits requested over the simplified cold start driving cycles used for certification. This issue has recently been resolved. The newest diesel-powered vehicles are now compliant with new laboratory test cycles and real-world-driving schedules and have no disadvantages in terms of criteria air pollutants compared to older diesel vehicles, while delivering improvements in fuel economy and CO2 emissions. Dual-fuel CIDI ICEs offer the opportunity for enhanced environmental friendliness. Dual-fuel CIDI ICEs have lower engine-out NOx and PM emissions compared to diesel-only CIDI ICEs. The latest diesel-only vehicles and vehicles with dual-fuel ICEs deliver dramatic reductions in tail-pipe PM emissions compared to older diesel-only vehicles. Moreover, they deliver tail-pipe PM emissions well below the ambient conditions in most city areas that are highly polluted, thereby helping to clean the air. The diesel-fueled CIDI ICEs may be further improved to deliver better fuel economy and further reduced tail-pipe emissions. The dual-fuel CIDI ICE has more room for improvement to produce similar or better steady state and transient performance in terms of torque, power output and fuel conversion efficiency compared to diesel-fueled CIDI ICEs, while drastically reducing CO2 and PM tail-pipe emissions, and improving NOx tail-pipe emissions. This is due to the ability to modulate the premixed and diffusion phases of combustion with a second fuel that is much easier to vaporize and is less prone to auto-ignition. Further development of the fuel injection system for the second fuel will lead to novel dual-fuel CIDI ICE designs with better performance.
{"title":"Advantages and Disadvantages of Diesel Single and Dual-Fuel Engines","authors":"A. Boretti","doi":"10.3389/fmech.2019.00064","DOIUrl":"https://doi.org/10.3389/fmech.2019.00064","url":null,"abstract":"The pros and the cons of lean-burn, compression ignition (CI), direct injection (DI) internal combustion engines (ICE) are reviewed for transport applications. Fueling options considered include diesel only and dual-fuel applications with diesel and a gaseous fuel (CNG, LNG and LPG). CIDI ICEs have higher fuel conversion efficiencies than stoichiometric, spark ignition (SI) ICEs, whether DI or port fuel injected (PFI). However, diesel-fueled CIDI ICEs have higher particulate matter (PM) and NOx engine-out emissions. The tail-pipe NOx emissions in real-world driving of diesel-powered vehicles have been, in the past, above the limits requested over the simplified cold start driving cycles used for certification. This issue has recently been resolved. The newest diesel-powered vehicles are now compliant with new laboratory test cycles and real-world-driving schedules and have no disadvantages in terms of criteria air pollutants compared to older diesel vehicles, while delivering improvements in fuel economy and CO2 emissions. Dual-fuel CIDI ICEs offer the opportunity for enhanced environmental friendliness. Dual-fuel CIDI ICEs have lower engine-out NOx and PM emissions compared to diesel-only CIDI ICEs. The latest diesel-only vehicles and vehicles with dual-fuel ICEs deliver dramatic reductions in tail-pipe PM emissions compared to older diesel-only vehicles. Moreover, they deliver tail-pipe PM emissions well below the ambient conditions in most city areas that are highly polluted, thereby helping to clean the air. The diesel-fueled CIDI ICEs may be further improved to deliver better fuel economy and further reduced tail-pipe emissions. The dual-fuel CIDI ICE has more room for improvement to produce similar or better steady state and transient performance in terms of torque, power output and fuel conversion efficiency compared to diesel-fueled CIDI ICEs, while drastically reducing CO2 and PM tail-pipe emissions, and improving NOx tail-pipe emissions. This is due to the ability to modulate the premixed and diffusion phases of combustion with a second fuel that is much easier to vaporize and is less prone to auto-ignition. Further development of the fuel injection system for the second fuel will lead to novel dual-fuel CIDI ICE designs with better performance.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"74 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80714356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-03DOI: 10.3389/fmech.2019.00062
A. Dimaratos, Z. Toumasatos, S. Doulgeris, Georgios Triantafyllopoulos, A. Kontses, Z. Samaras
The objective of this study is the assessment of the real-world environmental performance, and the comparison with laboratory measurements, of two Euro 6 passenger cars. The first is equipped with a common-rail diesel engine, Lean NOx Trap (LNT) and Diesel Particulate Filter (DPF), and the second is a bi-fuel gasoline/CNG (Compressed Natural Gas) one, equipped with Three Way Catalyst (TWC). The experimental campaign consisted of on-road and chassis dynamometer measurements. In the former test set, two driving routes were followed, one complying with the Real Driving Emissions (RDE) regulation, and another characterized by more dynamic driving. The aim of the latter route was to go beyond the regulatory limits and cover a wider range of real-world conditions and engine operating area. In the laboratory, the WLTC (Worldwide harmonized Light vehicles Test Cycle) was tested, applying the real-world road load of the vehicles. Both cars underwent the same tests, and these were repeated for the primary (CNG) and the secondary (gasoline) fuel of the bi-fuel vehicle. In all the tests, CO2 and NOx emissions were measured with a Portable Emissions Measurement System (PEMS). The results were analyzed on two levels, the aggregated and the instantaneous, in order to highlight the different emissions attributes under varying driving conditions. The application of the realistic road load in the WLTC limited its difference with the RDE compliant route, in terms of CO2 emissions. However, the aggressive driver behavior and the uphill roads of the Dynamic driving schedule resulted in around double CO2 emissions for both cars. The potential of natural gas to reduce CO2 emissions was also highlighted. Concerning the diesel car NOx emissions, the real-world results were significantly higher than the respective WLTC levels. On the other hand, the bi-fuel car exhibited very low NOx emissions with both fuels. Natural gas resulted in increased NOx emissions, compared to gasoline, always remaining below the Euro 6 limit, with only exception the Dynamic driving schedule. Finally, it was found that the overall cycle dynamics are not sufficient for the complete assessment of transient emissions and the instantaneous engine and aftertreatment behavior can reveal additional details.
{"title":"Assessment of CO2 and NOx Emissions of One Diesel and One Bi-Fuel Gasoline/CNG Euro 6 Vehicles During Real-World Driving and Laboratory Testing","authors":"A. Dimaratos, Z. Toumasatos, S. Doulgeris, Georgios Triantafyllopoulos, A. Kontses, Z. Samaras","doi":"10.3389/fmech.2019.00062","DOIUrl":"https://doi.org/10.3389/fmech.2019.00062","url":null,"abstract":"The objective of this study is the assessment of the real-world environmental performance, and the comparison with laboratory measurements, of two Euro 6 passenger cars. The first is equipped with a common-rail diesel engine, Lean NOx Trap (LNT) and Diesel Particulate Filter (DPF), and the second is a bi-fuel gasoline/CNG (Compressed Natural Gas) one, equipped with Three Way Catalyst (TWC). The experimental campaign consisted of on-road and chassis dynamometer measurements. In the former test set, two driving routes were followed, one complying with the Real Driving Emissions (RDE) regulation, and another characterized by more dynamic driving. The aim of the latter route was to go beyond the regulatory limits and cover a wider range of real-world conditions and engine operating area. In the laboratory, the WLTC (Worldwide harmonized Light vehicles Test Cycle) was tested, applying the real-world road load of the vehicles. Both cars underwent the same tests, and these were repeated for the primary (CNG) and the secondary (gasoline) fuel of the bi-fuel vehicle. In all the tests, CO2 and NOx emissions were measured with a Portable Emissions Measurement System (PEMS). The results were analyzed on two levels, the aggregated and the instantaneous, in order to highlight the different emissions attributes under varying driving conditions. The application of the realistic road load in the WLTC limited its difference with the RDE compliant route, in terms of CO2 emissions. However, the aggressive driver behavior and the uphill roads of the Dynamic driving schedule resulted in around double CO2 emissions for both cars. The potential of natural gas to reduce CO2 emissions was also highlighted. Concerning the diesel car NOx emissions, the real-world results were significantly higher than the respective WLTC levels. On the other hand, the bi-fuel car exhibited very low NOx emissions with both fuels. Natural gas resulted in increased NOx emissions, compared to gasoline, always remaining below the Euro 6 limit, with only exception the Dynamic driving schedule. Finally, it was found that the overall cycle dynamics are not sufficient for the complete assessment of transient emissions and the instantaneous engine and aftertreatment behavior can reveal additional details.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"36 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-12-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86635983","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-11-29DOI: 10.3389/fmech.2019.00065
M. Evans, P. Medwell
There is a wealth of existing experimental data of flames collected using laser diagnostics. The primary objective of this review is to provide context and guidance in interpreting these laser diagnostic data. This educational piece is intended to benefit those new to laser diagnostics or with specialisation in other facets of combustion science, such as computational modelling. This review focuses on laser-diagnostics in the context of the commonly used canonical jet-in-hot-coflow (JHC) burner, although the content is applicable to a wide variety of configurations including, but not restricted to, simple jet, bluff body, swirling and stratified flames. The JHC burner configuration has been used for fundamental studies of moderate or intense low oxygen dilution (MILD) combustion, autoignition and flame stabilisation in hot environments. These environments emulate sequential combustion or exhaust gas recirculation. The JHC configuration has been applied in several burners for parametric studies of MILD combustion, flame reaction zone structure, behaviour of fuels covering a significant range of chemical complexity, and the collection of data for numerical model validation. Studies of unconfined JHC burners using gaseous fuels have employed point-based Rayleigh-Raman or two-dimensional Rayleigh scattering measurements for the temperature field. While the former also provides simultaneous measurements of major species concentrations, the latter has often been used in conjunction with planar laser-induced fluorescence (PLIF) to simultaneously provide quantitative or qualitative measurements of radical and intermediary species. These established scattering-based thermography techniques are not, however, effective in droplet or particle laden flows, or in confined burners with significant background scattering. Techniques including coherent anti-Stokes Raman scattering (CARS) and non-linear excitation regime two-line atomic fluorescence (NTLAF) have, however, been successfully demonstrated in both sooting and spray flames. This review gives an overview of diagnostics techniques undertaken in canonical burners, with the intention of providing an introduction to laser-based measurements in combustion. The efficacy, applicability and accuracy of the experimental techniques are also discussed, with examples from studies of flames in JHC burners. Finally, current and future directions for studies of flames using the JHC configuration including spray flames and studies and elevated pressures are summarised.
{"title":"Understanding and Interpreting Laser Diagnostics in Flames: A Review of Experimental Measurement Techniques","authors":"M. Evans, P. Medwell","doi":"10.3389/fmech.2019.00065","DOIUrl":"https://doi.org/10.3389/fmech.2019.00065","url":null,"abstract":"There is a wealth of existing experimental data of flames collected using laser diagnostics. The primary objective of this review is to provide context and guidance in interpreting these laser diagnostic data. This educational piece is intended to benefit those new to laser diagnostics or with specialisation in other facets of combustion science, such as computational modelling. This review focuses on laser-diagnostics in the context of the commonly used canonical jet-in-hot-coflow (JHC) burner, although the content is applicable to a wide variety of configurations including, but not restricted to, simple jet, bluff body, swirling and stratified flames. The JHC burner configuration has been used for fundamental studies of moderate or intense low oxygen dilution (MILD) combustion, autoignition and flame stabilisation in hot environments. These environments emulate sequential combustion or exhaust gas recirculation. The JHC configuration has been applied in several burners for parametric studies of MILD combustion, flame reaction zone structure, behaviour of fuels covering a significant range of chemical complexity, and the collection of data for numerical model validation. Studies of unconfined JHC burners using gaseous fuels have employed point-based Rayleigh-Raman or two-dimensional Rayleigh scattering measurements for the temperature field. While the former also provides simultaneous measurements of major species concentrations, the latter has often been used in conjunction with planar laser-induced fluorescence (PLIF) to simultaneously provide quantitative or qualitative measurements of radical and intermediary species. These established scattering-based thermography techniques are not, however, effective in droplet or particle laden flows, or in confined burners with significant background scattering. Techniques including coherent anti-Stokes Raman scattering (CARS) and non-linear excitation regime two-line atomic fluorescence (NTLAF) have, however, been successfully demonstrated in both sooting and spray flames. This review gives an overview of diagnostics techniques undertaken in canonical burners, with the intention of providing an introduction to laser-based measurements in combustion. The efficacy, applicability and accuracy of the experimental techniques are also discussed, with examples from studies of flames in JHC burners. Finally, current and future directions for studies of flames using the JHC configuration including spray flames and studies and elevated pressures are summarised.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"11 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75774785","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-11-26DOI: 10.3389/fmech.2019.00063
A. Perpignan, Rishikesh Sampat, A. Gangoli Rao
The Flameless Combustion (FC) regime has been pointed out as a promising combustion technique to lower the emissions of nitrogen oxides (NOx) while maintaining low CO and soot emissions, as well as high efficiencies. However, its accurate modeling remains a challenge. The prediction of pollutant species, especially NOx, is affected by the usually low total values that require higher precision from computational tools, as well as the incorporation of relevant formation pathways within the overall reaction mechanism that are usually neglected. The present work explores a multiple step modeling approach to tackle these issues. Initially, a CFD solution with simplified chemistry is generated [both the Eddy Dissipation Model (EDM) as well as the Flamelet Generated Manifolds (FGM) approach are employed]. Subsequently, its computational cells are clustered to form ideal reactors by user-defined criteria, and the resulting Chemical Reactor Network (CRN) is subsequently solved with a detailed chemical reaction mechanism. The capabilities of the clustering and CRN solving computational tool (AGNES—Automatic Generation of Networks for Emission Simulation) are explored with a test case related to FC. The test case is non-premixed burner based on jet mixing and fueled with CH4 tested for various equivalence ratios. Results show that the prediction of CO emissions was improved significantly with respect to the CFD solution and are in good agreement with the experimental data. As for the NOx emissions, the CRN results were capable of reproducing the non-monotonic behavior with equivalence ratio, which the CFD simulations could not capture. However, the agreement between experimental values and those predicted by CRN for NOx is not fully satisfactory. The clustering criteria employed to generate the CRNs from the CFD solutions were shown to affect the results to a great extent, pointing to future opportunities in improving the multi-step procedure and its application.
{"title":"Modeling Pollutant Emissions of Flameless Combustion With a Joint CFD and Chemical Reactor Network Approach","authors":"A. Perpignan, Rishikesh Sampat, A. Gangoli Rao","doi":"10.3389/fmech.2019.00063","DOIUrl":"https://doi.org/10.3389/fmech.2019.00063","url":null,"abstract":"The Flameless Combustion (FC) regime has been pointed out as a promising combustion technique to lower the emissions of nitrogen oxides (NOx) while maintaining low CO and soot emissions, as well as high efficiencies. However, its accurate modeling remains a challenge. The prediction of pollutant species, especially NOx, is affected by the usually low total values that require higher precision from computational tools, as well as the incorporation of relevant formation pathways within the overall reaction mechanism that are usually neglected. The present work explores a multiple step modeling approach to tackle these issues. Initially, a CFD solution with simplified chemistry is generated [both the Eddy Dissipation Model (EDM) as well as the Flamelet Generated Manifolds (FGM) approach are employed]. Subsequently, its computational cells are clustered to form ideal reactors by user-defined criteria, and the resulting Chemical Reactor Network (CRN) is subsequently solved with a detailed chemical reaction mechanism. The capabilities of the clustering and CRN solving computational tool (AGNES—Automatic Generation of Networks for Emission Simulation) are explored with a test case related to FC. The test case is non-premixed burner based on jet mixing and fueled with CH4 tested for various equivalence ratios. Results show that the prediction of CO emissions was improved significantly with respect to the CFD solution and are in good agreement with the experimental data. As for the NOx emissions, the CRN results were capable of reproducing the non-monotonic behavior with equivalence ratio, which the CFD simulations could not capture. However, the agreement between experimental values and those predicted by CRN for NOx is not fully satisfactory. The clustering criteria employed to generate the CRNs from the CFD solutions were shown to affect the results to a great extent, pointing to future opportunities in improving the multi-step procedure and its application.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"36 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84363175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-22DOI: 10.3389/fmech.2019.00061
A. Chinnici, G. Nathan, B. Dally
The intermittent nature of solar energy limits its further deployment to applications where firm supply and constant output is required. While energy storage is a viable option to increase solar share, in itself is not sufficient without an additional dispatchable energy source. Combustion of both fossil-based and renewable fuels can provide the demand ready energy source required and lends itself to hybridisation with tower based Concentrated Solar Thermal, CST, energy. The Hybrid Solar Receiver Combustor, HSRC, is a novel technology that integrates both sources of energy in one device and offers tangible benefits in increased solar share, thermal efficiency and reduced capital and operation costs. This paper reports a brief review of the different findings from experimental and computational research carried out at the Centre for Energy Technology of the University of Adelaide into optimizing the HSRC design, developing the first-of-a-kind laboratory-scale HSRC unit and evaluating its performance under different fuels, operating conditions and modes of operation. It highlights the benefits and need for utilizing MILD combustion in the HSRC to match the heat transfer characteristics and stability required to achieve similar operational range and efficiency from both sources of energy. A 5-kWel xenon-arc solar simulator and the combustion of a wide variety of fuels are used as the energy sources. This paper reports on the effectiveness of MILD combustion under these conditions and in particular it discusses flame stability envelop and its relation to heat extraction, temperature and pollutant emissions. It also reports on thermal efficiency, heat losses and heat flux distribution within the cavity for all fuels and operating conditions. It is found that the HSRC thermal performance is similar under the three operation modes (solar, combustion and combined) and that operating under MILD combustion mode allowed fuel flexibility, homogeneous heat distribution and very low emission of NOx and CO. Also found that H/C ratio plays a minor role in the radiated energy to the heat exchanger within the cavity. Future research and further technology development need is also discussed in this paper.
{"title":"Hybrid Solar-MILD Combustion for Renewable Energy Generation","authors":"A. Chinnici, G. Nathan, B. Dally","doi":"10.3389/fmech.2019.00061","DOIUrl":"https://doi.org/10.3389/fmech.2019.00061","url":null,"abstract":"The intermittent nature of solar energy limits its further deployment to applications where firm supply and constant output is required. While energy storage is a viable option to increase solar share, in itself is not sufficient without an additional dispatchable energy source. Combustion of both fossil-based and renewable fuels can provide the demand ready energy source required and lends itself to hybridisation with tower based Concentrated Solar Thermal, CST, energy. The Hybrid Solar Receiver Combustor, HSRC, is a novel technology that integrates both sources of energy in one device and offers tangible benefits in increased solar share, thermal efficiency and reduced capital and operation costs. This paper reports a brief review of the different findings from experimental and computational research carried out at the Centre for Energy Technology of the University of Adelaide into optimizing the HSRC design, developing the first-of-a-kind laboratory-scale HSRC unit and evaluating its performance under different fuels, operating conditions and modes of operation. It highlights the benefits and need for utilizing MILD combustion in the HSRC to match the heat transfer characteristics and stability required to achieve similar operational range and efficiency from both sources of energy. A 5-kWel xenon-arc solar simulator and the combustion of a wide variety of fuels are used as the energy sources. This paper reports on the effectiveness of MILD combustion under these conditions and in particular it discusses flame stability envelop and its relation to heat extraction, temperature and pollutant emissions. It also reports on thermal efficiency, heat losses and heat flux distribution within the cavity for all fuels and operating conditions. It is found that the HSRC thermal performance is similar under the three operation modes (solar, combustion and combined) and that operating under MILD combustion mode allowed fuel flexibility, homogeneous heat distribution and very low emission of NOx and CO. Also found that H/C ratio plays a minor role in the radiated energy to the heat exchanger within the cavity. Future research and further technology development need is also discussed in this paper.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"4 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82092539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-15DOI: 10.3389/fmech.2019.00060
F. Takahashi
Each year, fires in the wildland-urban interface (WUI)—the place where homes and wildlands meet or intermingle—have caused significant damage to communities. To contribute to firefighter and public safety by reducing the risk of structure ignition, fire blankets for wrapping a whole house have been investigated in the laboratory and prescribed wildland fires. The fire blankets aim to prevent structure ignition (1) by blocking firebrands to enter homes through vulnerable spots (gutters, eaves, vents, broken windows, and roofs); (2) by keeping homes from making direct contact with flames of surrounding combustibles (vegetation, mulch, etc.); and (3) by reflecting thermal radiation from a large fire within close range (adjacent burning houses or surface-to-crown forest fires) for a sustained period of time. In the laboratory experiment, two-layer thin fabric assemblies were able to block up to 92 % of the convective heat and up to 96 % of the radiation (with an aluminized surface). A series of proof-of-concept experiments were conducted by placing instrumented wooden structures, covered with different fire blankets, in various fires in ascending order of size. First, birdhouse-sized boxes were exposed to burning wood pallets in a burn room. Second, wall-and-eaves panels were exposed to prescribed fires climbing up slopes with chaparral vegetation in California. Finally, a cedar shed was placed in the passage of the prescribed head fire in the Pine Barrens in New Jersey. The experiments demonstrated both successful performance and technical limitations of thin fire blankets. The key success factors in protecting the WUI structure are (1) the fire blanket’s heat-blocking capability, (2) endurance under severe heat-exposure high-wind conditions, and (3) proper installation. Additional studies are needed in the areas of advanced material/layer development, blanket deployment methods, and multi-structure protection strategies.
{"title":"Whole-House Fire Blanket Protection From Wildland-Urban Interface Fires","authors":"F. Takahashi","doi":"10.3389/fmech.2019.00060","DOIUrl":"https://doi.org/10.3389/fmech.2019.00060","url":null,"abstract":"Each year, fires in the wildland-urban interface (WUI)—the place where homes and wildlands meet or intermingle—have caused significant damage to communities. To contribute to firefighter and public safety by reducing the risk of structure ignition, fire blankets for wrapping a whole house have been investigated in the laboratory and prescribed wildland fires. The fire blankets aim to prevent structure ignition (1) by blocking firebrands to enter homes through vulnerable spots (gutters, eaves, vents, broken windows, and roofs); (2) by keeping homes from making direct contact with flames of surrounding combustibles (vegetation, mulch, etc.); and (3) by reflecting thermal radiation from a large fire within close range (adjacent burning houses or surface-to-crown forest fires) for a sustained period of time. In the laboratory experiment, two-layer thin fabric assemblies were able to block up to 92 % of the convective heat and up to 96 % of the radiation (with an aluminized surface). A series of proof-of-concept experiments were conducted by placing instrumented wooden structures, covered with different fire blankets, in various fires in ascending order of size. First, birdhouse-sized boxes were exposed to burning wood pallets in a burn room. Second, wall-and-eaves panels were exposed to prescribed fires climbing up slopes with chaparral vegetation in California. Finally, a cedar shed was placed in the passage of the prescribed head fire in the Pine Barrens in New Jersey. The experiments demonstrated both successful performance and technical limitations of thin fire blankets. The key success factors in protecting the WUI structure are (1) the fire blanket’s heat-blocking capability, (2) endurance under severe heat-exposure high-wind conditions, and (3) proper installation. Additional studies are needed in the areas of advanced material/layer development, blanket deployment methods, and multi-structure protection strategies.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"16 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-10-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78457335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-02DOI: 10.3389/fmech.2019.00059
N. Swaminathan
MILD combustion is gaining interest in recent times because it is attractive for “green” combustion technology. However, its fundamental aspects are not well understood. Recent progresses made on this topic using direct numerical simulation data are presented and discussed in a broader perspective. It is shown that a revised theory involving at least two chemical timescales is required to describe the inception of this combustion not only showing both autoignition and flame characteristics but also a strong interaction between these two phenomena. The reaction zones have complex morphological and topological features and the most probable shape is pancake-like structure implying micro-volume combustion under MILD conditions unlike the sheet-combustion in conventional cases. Relevance of the MILD (micro-volume) combustion to supersonic combustion is explored theoretically and qualitative support is shown and discussed using experimental and numerical Schlieren images.
{"title":"Physical Insights on MILD Combustion From DNS","authors":"N. Swaminathan","doi":"10.3389/fmech.2019.00059","DOIUrl":"https://doi.org/10.3389/fmech.2019.00059","url":null,"abstract":"MILD combustion is gaining interest in recent times because it is attractive for “green” combustion technology. However, its fundamental aspects are not well understood. Recent progresses made on this topic using direct numerical simulation data are presented and discussed in a broader perspective. It is shown that a revised theory involving at least two chemical timescales is required to describe the inception of this combustion not only showing both autoignition and flame characteristics but also a strong interaction between these two phenomena. The reaction zones have complex morphological and topological features and the most probable shape is pancake-like structure implying micro-volume combustion under MILD conditions unlike the sheet-combustion in conventional cases. Relevance of the MILD (micro-volume) combustion to supersonic combustion is explored theoretically and qualitative support is shown and discussed using experimental and numerical Schlieren images.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"153 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88130024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-27DOI: 10.3389/fmech.2019.00056
Félix E. Montero, R. Rezende, J. D. da Silva, M. Sabino
Biofabrication is an incipient and fast-growing field of research that continues to develop groundbreaking innovations. Considerable progress has also been made in additive manufacturing technologies, which are used for the production of complex geometry using biomaterials, such as scaffolds and, most recently, bioink-based structures. Some of the topics related to these new breakthroughs in tissue engineering and bioprinting will be discussed. Additionally, the obtained experimental results in this work contribute to the recent advances in such sciences. Formulations of sodium alginate (NaAlg)/Poly(N-Isopropylacrylamide) (PNIPAm)/ZnSO4-based smart bioinks were developed and characterized. The lower critical solution temperature (LCST), viscosity and thermal stability were determined through UV-Visible spectroscopy, a rheological analysis and a thermogravimetric analysis (TGA), respectively. Furthermore, an injectability test was performed in order to assess the influence of the extrusion process in the morphology of the bioinks like scaffolds (after lyophilization) using scanning electron microscopy SEM. According to the obtained results, the scaffolds presented a structure composed of interconnected pore systems, which were affected by the presence of the Zn2+ ion, and the extrusion process. The biocompatibility of the gels was tested through a hemolysis assay using erythrocytes and the obtained results indicate that have not cytotoxic effects. For all these reasons these formulations are candidates for the obtention of intelligent bioinks applicable for bioprinting and tissue engineering.
{"title":"Development of a Smart Bioink for Bioprinting Applications","authors":"Félix E. Montero, R. Rezende, J. D. da Silva, M. Sabino","doi":"10.3389/fmech.2019.00056","DOIUrl":"https://doi.org/10.3389/fmech.2019.00056","url":null,"abstract":"Biofabrication is an incipient and fast-growing field of research that continues to develop groundbreaking innovations. Considerable progress has also been made in additive manufacturing technologies, which are used for the production of complex geometry using biomaterials, such as scaffolds and, most recently, bioink-based structures. Some of the topics related to these new breakthroughs in tissue engineering and bioprinting will be discussed. Additionally, the obtained experimental results in this work contribute to the recent advances in such sciences. Formulations of sodium alginate (NaAlg)/Poly(N-Isopropylacrylamide) (PNIPAm)/ZnSO4-based smart bioinks were developed and characterized. The lower critical solution temperature (LCST), viscosity and thermal stability were determined through UV-Visible spectroscopy, a rheological analysis and a thermogravimetric analysis (TGA), respectively. Furthermore, an injectability test was performed in order to assess the influence of the extrusion process in the morphology of the bioinks like scaffolds (after lyophilization) using scanning electron microscopy SEM. According to the obtained results, the scaffolds presented a structure composed of interconnected pore systems, which were affected by the presence of the Zn2+ ion, and the extrusion process. The biocompatibility of the gels was tested through a hemolysis assay using erythrocytes and the obtained results indicate that have not cytotoxic effects. For all these reasons these formulations are candidates for the obtention of intelligent bioinks applicable for bioprinting and tissue engineering.","PeriodicalId":53220,"journal":{"name":"Frontiers in Mechanical Engineering","volume":"410 1","pages":""},"PeriodicalIF":2.3,"publicationDate":"2019-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85506083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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