Combustion Science and Technology

Kummer, Johann-Robert; Essmann, Stefan; Markus, Detlev; Grosshans, Holger; Maas, Ulrich

doi: 10.1080/00102202.2021.1931153pmid: N/A

Spark ignition by low-energetic electrical discharges in combustible fuel/air mixtures is a significant safety risk in various industries. In the present paper, OH-LIF measurements and numerical simulations of the ignition and early flame propagation of hydrogen/air, propane/air and ethene/air mixtures are reported. The experiments, carried out at four energy levels close to the respective minimum ignition energy (MIE), show that higher energy input leads to a wider flame radius, which is in agreement with one-dimensional numerical simulations. Further, the evaluation of the radial OH distribution reveals the highly stochastic nature of this process if the introduced energy is near the respective MIE. By utilizing the combined methodical approach of experiments and simulations, the key factors impairing the experimental repeatability are identified. The numerical results indicate at lower energies a longer time delay between source time and ignition, during which loss processes and perturbations may lead to extinction. One important influencing factor is the three-dimensional flow induced by the discharge, effectively increasing the experimental scatter. The presented work facilitates a detailed view on the complex physiochemical mechanisms dominating ignitions of explosive gas mixtures by low-energetic electrical discharges.

Duan, Yulong; Yang, Yanling; Li, Yuanbing; Xu, Jun; Zhang, Yuzhu; Jia, Hailin

doi: 10.1080/00102202.2021.1932851pmid: N/A

Many gas explosion accidents show that gas explosion can easily cause a large number of casualties and huge property losses in coal mines. Therefore, the sliding device is established to study its explosion suppression effect, and the influence of the initial position of the sliding device on the explosion is analyzed. The results show that when the sliding device is close to the ignition source, due to the strong reverse action of the spring, the sliding baffle has a reverse secondary acceleration movement, thus forming a crescent-shaped forward compression flame, forming a reverse acceleration inhibition effect and rapidly extinguishing, and this rapid reverse movement is the key technology of accelerating chain breaking and wall collision effect in methanation reaction. Generally speaking, the sliding device can effectively control the overpressure and can make the flame extinguish quickly. At the same time, the possibility of secondary fire and explosion caused by the spread of explosion in other areas is prevented. Thus, the sliding device has a good effect of explosion-proof and suppression in coal mines.

Xiao, Yang; Zhang, Hong-Mei; Yin, Lan; Shu, Chi-Min; Li, Qing-Wei

doi: 10.1080/00102202.2021.1933961pmid: N/A

Coal-based activated carbon (CBAC) is widely used in several industrial processes and daily life, however, it is susceptible to spontaneous combustion during storage and transportation. Therefore, it is essential to probe the spontaneous combustion risk of CBAC. The oxidation process of briquetting material sample (BM), carbonized material sample (CM), and activated material sample (AM) was studied via thermogravimetric (TG–DTG) analysis. The oxidation mechanism of the samples was investigated via the proximate and ultimate analyses, Fourier transform Infrared (FTIR) spectroscopy, and nitrogen adsorption. Kinetic characteristics of the samples during the combustion were determined using the Kissinger–Akahira–Sunose (KAS) method. Five characteristic temperature points and the five stages of the samples during oxidation were obtained. With an increase in the heating rate, the hysteresis phenomenon was observed during thermal decomposition and combustion of AM in TG–DTG curves. The heating value of BM, CM, and AM were 6678, 6705, and 6776 cal g–1, respectively. AM has a developed pore structure that leads to enhanced oxygen adsorption and limited heat transfer, easy to induce spontaneous combustion. The main functional groups of AM were hydroxyl groups and aromatic hydrocarbons, especially hydroxyl groups that played a key role in the spontaneous combustion of AM. The apparent activation energy (E a) during the combustion of BM, CM, and AM were 110.70, 85.90, and 111.80 kJ mol–1 from the KAS method, respectively. These results are expected to facilitate a better understanding of CBAC spontaneous combustion.

Niu, Yanqing; Lei, Yu; Lv, Yuan; Wang, Guangyao; Liu, Siqi; Hui, Shi’En

doi: 10.1080/00102202.2021.1935906pmid: N/A

Liquid slag tapping at low operation temperature is a major challenge for the application of entrained-flow slagging gasifier. To obtain and elucidate a regulation on stable liquid slag tapping, the SiO2-Al2O3-(CaO+MgO+Na2O+K2O)-Fe2O3 phase diagrams of ash fusion temperatures as well as the ash viscosity and components were studied with ash fusibility apparatus, high-temperature viscometer, SEM-EDS and FactSage software. Meanwhile, the potential slagging properties were analyzed by the difference between soften temperature and deformation temperature (DSI), base/acid ratio (B/A) and slag viscosity index G. Results indicated that the contours of fluid temperature (FT) in the SiO2-Al2O3-(CaO+MgO+Na2O+K2O) pseudo-ternary diagrams presented inverted V-shaped distribution. Attributing to the positive effect of Al2O3 and the downward parabola effect of SiO2, the FT first decreased and then increased with the increased SiO2/Al2O3 at the minimum value of around 3.25. Also, with the increase of (SiO2+ Al2O3+ CaO+MgO+Na2O+K2O)/Fe2O3, the FT showed a V-type distribution with a minimum value at 94:6, yet the effect of Fe2O3 was slight. Besides, high content of CaO+MgO+Na2O+K2O effectively reduced the FT, which favored the formation of molten slag and operation economy; but it shortened the DSI, disadvantaging the formation of long slag and the operation stability. Moreover, decreased ratio of (CaO+MgO)/(Na2O+K2O) not only reduced the FT, but also enlarged the DSI. Finally, a regulation method concerning stable liquid slag tapping at low operation temperature based on ash fusion and slagging properties was proposed: adjusting SiO2/Al2O3 to 3.25 and the mass ratio of Fe2O3 nearby 6.0 wt.%, and doping CaO+MgO+Na2O+K2O with low (CaO+MgO)/(Na2O+K2O) ratio could effectively reduce the FT and viscosity and enlarge the DSI simultaneously, and vice versa.

Lu, Wei; Gao, Liyang; Zhang, Wenrui; Hu, Xiangming; Zhang, Mingguang; Xin, Lin; Ni, Guanhua; Li, Jialiang; Kong, Biao

doi: 10.1080/00102202.2021.1935907pmid: N/A

Once fires occur in a coalfield, large quantities of coal in the coalfield will be baked at high temperatures. The changes and differences in the microscopic and spontaneous combustion properties of coals in high-temperature environments (ambient temperature or even after high-temperature baking) in the fire zone have not been studied yet. In this paper, three types of different-rank coals were baked at five different temperatures to investigate their changes in microcrystalline compositions, functional groups and combustion characteristics. The following results were obtained. The temperature treatment causes damage to the microcrystalline structure of different-rank coals. As the baking temperature rises, the aromatic layer spacing decreases, while the ductility and stacking height gradually increase. The aromatic ether content and the aliphatic hydrocarbon content gradually decline, while the -COOH content goes first and then falls. The spontaneous combustion activities of coals around the fire area gradually weaken with the rise of baking temperature. This research is crucial for revealing the effect of temperature, especially fire baking, on the spontaneous combustion characteristics of coal.

Radyjowski, Patryk P.; Schoegl, Ingmar; Ellzey, Janet L.

doi: 10.1080/00102202.2021.1938017pmid: N/A

Heat recirculating reactors have many potential applications as thermal oxidizers, combustors, and fuel reformers due to their extensive operating range. Low emissions and fuel flexibility make such devices highly desirable as heat sources as well as chemical reactors. The dependence on the solid/gas heat transfer implies that wall characteristics and operating conditions significantly influence the stable range. In this paper, the importance of various combustor parameters is examined through an analytical model, and an experimental reactor is fabricated from a new ceramic-metal composite using additive manufacturing. A full range of possible operation modes, from flashback to blow-off, was observed together with characteristic temperature distributions at various firing rates. The new combustor showed improved operational flexibility as compared to a traditionally assembled counterpart. Low CO and NOx emission levels were observed together with an audible sound in the range between 825 Hz and 1000 Hz. The combustor operated for over 70 hours without visible damage to the material. The overall thermal performance, low emissions, and high power density make the heat recirculating reactor a viable solution for combustion applications.

Price-Allison, Andrew; Mason, Patrick E; Jones, Jenny M.; Barimah, Eric K.; Jose, Gin; Brown, Aaron E.; Ross, Andrew B; Williams, Alan

doi: 10.1080/00102202.2021.1938559pmid: N/A

The amount of moisture in wood fuel has a significant influence on the emissions of particulate matter (PM) and gaseous pollutants when burned in small-scale domestic appliances. Previous studies have shown that higher moisture content generally produces higher particulate emissions factors. As well as quantity of material emitted, it is also important to understand the effects of moisture on particle qualities including size, composition and morphology – since these can influence the human-toxicity and environmental impacts of the particles. In this study, emissions were quantified and the particulate qualities were also examined using chemical, optical and thermogravimetric analysis as well as size-graded sampling. By comparing the results from the use of batches of beech wood fuel with differing moisture content, it was shown that there are consistent and significant differences in both the quantity and qualities of the resulting emissions when burned under the same conditions. This has important consequences for emission inventories which currently only assume an emission factor from a proscribed combustion situation

Du, Qinglei; Liang, Huimin; Zhang, Qi

doi: 10.1080/00102202.2021.1939320pmid: N/A

Explosion often has a chain reaction in the accident field. The aerosol is injected into the high-temperature and high-pressure area produced in the first explosion and a superimposed explosion may be induced. To study this chain process, hazards in the secondary explosion of propylene oxide aerosol was numerically simulated. The superimposed explosion overpressure and temperature of propylene oxide aerosol produced in the secondary explosion are much higher than those in the first explosion. The overpressure of 0.5MPa and the temperature of 2200 K in the first explosion are increased to higher than 2.6 MPa and 3300 K in the secondary explosion, respectively. The secondary explosions of fuel aerosol are even more terrifying in the accident field. More attention should be paid to the superimposed explosion effect. The aerosols with the smaller droplet sizes react more quickly after they are injected into the high-temperature area produced in the first explosion. The superimposed pressure of aerosol with the smaller droplet sizes is higher in near field, but its effect range is shorter than that with the larger droplet sizes. The effect of droplet sizes on superimposed explosion overpressures for the PO aerosol with droplet sizes smaller than 0.2 mm is slight.