Weiguang An

Bio: Weiguang An is an academic researcher from University of Science and Technology of China. The author has contributed to research in topics: Flame spread & Combustion. The author has an hindex of 11, co-authored 16 publications receiving 398 citations. Previous affiliations of Weiguang An include China University of Mining and Technology & City University of Hong Kong.

Correlation study between flammability and the width of organic thermal insulation materials for building exterior walls

Abstract: Considering the sustainable energy strategy for buildings, external wall insulation system is expected to play an important role in building energy conversation. And higher energy efficiency drives our demands for much thicker thermal insulation materials. However, it does not mean that the thicker the better, especially considering various requirements and properties. Among these are materials mechanical strength, aging durability, water resistance, construction difficulty and even fire safety performance. In the following paper to explore fire safety of organic thermal insulation, polyurethane foam (PUF) and extruded polystyrene (XPS) were selected to carry out a series of lab-scale tests over a wide range of widths. What is more, some fire safety aspects have been studied and compared: temperature variation in solid and gas phase, heat and mass transfer process, flame propagation over material surface, flame height, material melting and charring, etc. The aim of exploring relationship between material flammability and width is to help to select a proper width when considering fire safety, and lay a foundation for us to conduct real fire disaster of external insulation system in following study.

Correlation analysis of sample thickness, heat flux, and cone calorimetry test data of polystyrene foam

Abstract: This paper deals with thermal and fire performance evaluation of expanded polystyrene (EPS) and extruded polystyrene (XPS) in a cone calorimeter with a piloted ignition. The correlation analysis of sample thickness, heat flux ( $$ \dot{q}^{\prime \prime } $$ ), and experimental results is performed. It is found that the heat flux follows a linear function of the vertical distance from the standard horizontal level to the sample. An optimization ignition model is established considering the effects of sample thickness (or radiant distance). The modified ignition time ( $$ \bar{t}_{\text{ig}} $$ ) decreases with the increase of the sample thickness. Both t ig (ignition time) and $$ \bar{t}_{\text{ig}} $$ drop as external heat flux rises. EPS’s t ig is more sensitive to the variation of external heat flux. Thermal thickness (δ P) decreases with the intensifying of heat flux, and δ P is in linear correlation with $$ \rho /\dot{q}^{\prime \prime } $$ . When sample is quite thin or the irradiance level is low (2 cm-thick PS under 35 kW m−2 and 3 cm-thick EPS under 25 kW m−2), single peak heat release rate (HRR) is present. Under other situations, there are at least two peak values. For EPS, the first peak value is higher than the last, while the reverse is true for XPS (exclusive of 5 cm-thick XPS at 35 kW m−2). Both peak and mean HRR rise linearly with the increase of external heat flux. t ig, $$ \bar{t}_{\text{ig}} $$ , critical heat flux and δ P of XPS are smaller than those of EPS, while the reverse is true for mean HRR. The ignition and heat release risk of PS drop with the decrease of external heat flux, and these hazards of XPS are higher than those of EPS.

An experimental study of premixed hydrogen/air flame propagation in a partially open duct

Abstract: High-speed schlieren cinematography and pressure records are used to investigate the dynamics of premixed hydrogen/air flame propagation and pressure build up in a partially open duct with an opening located in the upper wall near the right end of the duct. This work provides basic understanding of flame behaviors and the effects of opening ratio on the combustion dynamics. The flame behaves differently under different opening conditions. The opening ratio has an important influence on the flame propagation and pressure dynamics. When the opening ratio α ≤ 0.075 a significant distorted tulip flame can be formed after the full formation of a classical tulip flame. The propagation speed of flame leading tip increases with the opening ratio. The coupling of flame front with the pressure wave is strong at low opening ratio. Both the pressure growth rate and oscillation amplitude inside the duct increases as the opening ratio decreases. The formation times of tulip and distorted tulip flames and the corresponding distances of flame front increase with the increase of the opening ratio.

Theoretical and experimental study of width effects on horizontal flame spread over extruded and expanded polystyrene foam surfaces

Abstract: In order to explore the mechanisms of horizontal flame spread over thermal insulation foam surfaces, extruded polystyrene and expanded polystyrene foams were selected to carry out a series of experiments with different sample widths ranging from 4 to 16 cm. Temperatures in both the solid phase and the gas phase were measured, with considerable differences being found between extruded polystyrene and expanded polystyrene in their temperature profiles. Extruded polystyrene also showed a distinct pyrolysis stage, while expanded polystyrene showed a lengthy melting stage differences that may be explained from their different thermal properties. The flame spread rates of both materials first decreased and then increased with increasing sample widths. The minimum flame spread rates were at widths of 8 and 10 cm for extruded polystyrene and expanded polystyrene, respectively, resulting from the relative differences between convection and radiation heat flux, which were different for the two foams. Numerical equa...

Dynamics of premixed hydrogen/air flame in a closed combustion vessel

Abstract: The dynamics of a premixed hydrogen/air flame propagating in a closed vessel is investigated using high-speed schlieren cinematography, pressure measurement and numerical simulation. A dynamically thickened flame approach with a 19-step detailed chemistry is employed in the numerical simulation to model the premixed combustion. The schlieren photographs show that a remarkable distorted tulip flame is initiated after a classical tulip flame has been fully produced. A second distorted tulip flame is generated with a cascade of indentations created in succession before the vanishing of the first one. The flame dynamics observed in the experiments is well reproduced in the numerical simulation. The burnt region near the flame front is entirely dominated by a reverse flow during the formation of the distorted tulip flame. The distorted tulip flame can be formed in the absence of vortex motion. The pressure wave leads to periodic flame deceleration and plays an essential role in the distorted tulip formation. The numerical results corroborate the mechanism that the distorted tulip flame formation is a manifestation of Taylor instability.

Traditional, state-of-the-art and renewable thermal building insulation materials: An overview

Abstract: Energy saving has become a strategic goal in the whole world, that will lead to protect the environment and conserve natural resources. The energy consumption in buildings for heating and cooling is considered as one of the major sources of energy consumption in a lot of countries. Therefore, there is an ongoing search for finding the proper alternatives to preserve energy and minimize energy losses. Subsequently, heat insulators, part of building materials, are steadily getting their importance as a means of saving energy. Although, a lot of insulation materials are used commercially, this part of building construction still faces different difficulties and challenges such as the cost, thermal and mechanical properties, health problems, etc. Current insulation materials used in construction industry are generally polymer based materials such as polystyrene and polyurethane foam. Although these materials have a high performance in thermal insulation, but the environmental impacts in their production processes are significant. Consequently, the researchers find that there is a necessity to develop and come up with insulating materials that possess excellent properties and at the same time, they have less environmental impacts, and are relatively cheap. In this review paper, the researches carried out in the formulation and development of different kinds of thermal insulation in the last decades are presented. The focus was placed on researches utilized of renewable resources and wastes in thermal insulations development. In addition, the light was shed on the composites materials which was developed as a construction material with high thermal insulation capacity.

Formation and evolution of distorted tulip flames

Abstract: The development and evolution of tulip and distorted tulip flames in closed channels were simulated by solving the fully compressible reactive Navier–Stokes equations using a high-order numerical method and a single-step Arrhenius model for the reactions and energy release in a stoichiometric mixture of hydrogen and air. Important features of the simulations include (1) the development and propagation of acoustic waves and their effects on flame evolution, (2) the formation and collapse of flame cusps, both at the flame front and near the sidewalls, and the effects of cusp collapse on flame propagation, and (3) the appearance of adverse pressure gradients at the onset of the tulip or a distorted tulip flame, which result in reverse flow in the unburned gas. The simulations highlight the coupling between pressure waves, adverse pressure gradients, boundary layers, and the propagating flame front. Whereas the formation of the tulip flame can be attributed to several effects (such as pressure waves, vortex motion and Landau–Darrieus instabilities), the onset of the distorted tulip flame is strongly influenced by the Rayleigh–Taylor instability.

Flames: Their Structure, Radiation and Temperature

Abstract: A G Gaydon and H G Wolfhard London: Chapman and Hall 1970 pp + 365 price £6 With the rapid expansion of combustion science in and over so many fields in the last decade, it is a relief to learn of a new edition of this well known book. Although the framework of this volume will be reassuringly recognizable to first edition veterans, the contents, which include the extra chapter topics of the second edition, have been thoroughly sifted to bring the frontier information up to date.

Premixed flame propagation in hydrogen explosions

Abstract: Hydrogen as an energy carrier is a very promising alternative fuel in the future. Accidental hydrogen explosions remain one of the major concerns in hydrogen energy utilization and process industries. This paper summarizes recent experimental and numerical efforts towards understanding combustion wave propagation in hydrogen explosions, including flame instabilities, flame acceleration, deflagrations, and deflagration-to-detonation transition (DDT). The fundamental problems involve understanding physical mechanisms that significantly influence the dynamic flame behavior in hydrogen explosions, such as combustion/hydrodynamic instabilities, vortex motion, pressure waves and flow turbulence. Advances achieved over recent years in new experimental observations, theoretical models and numerical simulations are discussed. Future research is required to quantitatively understand flame instabilities, turbulence properties and DDT in hydrogen explosions and improve reliability of theoretical and numerical predictions for hydrogen safety applications.

Eco-friendly geopolymer materials: A review of performance improvement, potential application and sustainability assessment

Abstract: The traditional cement production wastes a large amount of natural resources and energy, and causes environmental pollution, which cannot meet the green and sustainable development needs of modern building materials. Geopolymer is an environmentally friendly materials that can utilize industrial solid wastes and have low environmental load and energy consumption, which is expected to become a substitute for OPC. However, geopolymers also have shortcomings in some properties that need to be improved. This paper reviews the recent research progress on the performance improvement, potential new applicationw and sustainability assessment of geopolymer materials. Discussion from this paper showed that the properties of geopolymer materials, including rheology, hardening properties, toughness, etc., can be significantly improved by some methods such as chemical additives, mineral admixtures, nanoparticles, fibers, etc. Furthermore, this paper proves that geopolymers have great application potential as porous thermal insulation materials and 3D printing building materials, and points out some performance optimization methods for geopolymer-based porous materials and 3D printing materials. In this work, it was also concluded that geopolymer shows significant advantages over OPC in sustainable analysis index such as E-energy and E-CO2 (Energy and CO2 emission) based on LCA method. Finally, a few potential opportunities and development directions have been suggested for future research on geopolymer materials.