Influence of ignition position and obstacles on explosion development in methane–air mixture in closed vessels

The paper outlines an experimental study of influence of the ignition position and obstacles on explosion development in premixed methane–air mixtures in an elongated explosion vessel. As the explosion vessel, 1325 mm length tube with 128.5 mm diameter was used. Location of the ignition was changeable, i.e., fitted in the centre or at one of ends of the tube, when the tube was in a horizontal position. When it was in a vertical position, three locations of the ignition (bottom, centre and top) were used. In the performed study, the influence of obstacles on the course of pressure was investigated. Two identical steel grids were used as the obstacles. They were placed 405 mm from either end of the tube. Their blockage ratio (grid area to tube cross-section area) was determined as 0.33 for most of experiments. A few additional experiments (with smaller blockage ratio—0.16) were also conducted in order to compare the influence of the blockage ratio on the explosion development. Also some experiments were conducted in a semi-cylindrical vessel with volume close to 40 l.

All the experiments were performed under stabilized conditions, with the temperature and pressure inside the vessel settled to room values and controlled by means of electronic devices. The pressure–time profiles from two transducers placed in the centreline of the inner wall of the explosion vessel were obtained for stoichiometric (9.5%), lean (7%) and rich (12%) methane–air mixture. The results obtained in the study, including maximum pressures and pressure–time profiles, illustrate a quite distinct influence of the above listed factors upon the explosion characteristics. The effect of ignition position, obstacles location and their BR parameters is discussed.

The additional aim of the performed experiments was to find the data necessary to validate a new computer code, developed to calculate an explosion hazard in industrial installations.     

Formation and destruction of PCDD/F inside a grate furnace

Formation and destruction of polychlorinated dibenzo-p-dioxins and dibenzofurans PCDD/F during the combustion process was investigated experimentally in a pilot plant. All important process steps like the burnout of the fuel bed on the grate, the burnout of the flue gas inside the combustion chamber, the heat recovery in a boiler as well as influences of the fuel composition are described in detail.

High concentrations especially of PCDF are formed during the burnout of the fuel bed. The formation reaction is mainly influenced by the fuel composition and the burnout characteristic of the fuel bed. Fuels with low chlorine and low metal content (Cu) result only in negligible concentrations of PCDD/F.

Under stable combustion conditions characterized by an excellent flue gas burnout PCDD/F will almost be completely destroyed already inside the combustion chamber. “Cold strands” of unburned flue gas (high CO concentrations) caused by disturbed combustion conditions will result in high concentrations of PCDD and especially of PCDF in the raw gas.

A second place of PCDD/F formation is the well-known boiler section. Here fly ash deposits containing residual carbon (mainly soot particles) are the source for the formation reaction. Under stationary effective combustion conditions, they are dominant for PCDD/F concentrations in the raw gas over a very long period of time.

Stationary efficient flue gas burnout (especially soot) together with effective boiler cleaning will guaranty low concentrations of PCDD/F in the flue gas in front of the flue gas cleaning system.     

火灾中建材燃烧毒性的试验研究

通过探讨火灾中燃烧毒性对人体的危害和分析国外主要的毒性研究方法，研制了毒气热分解仪并对部分有一定代表性的建材进行了实测研究。根据研究结果提出了相应的结论意见。     

Detailed and reduced chemistry for hydrogen autoignition

Reaction-rate parameters are given for the detailed chemistry of gas-phase hydrogen combustion, involving 21 reversible elementary steps. It is indicated that, when attention is restricted to specific combustion processes and particular conditions of interest, fewer elementary steps are needed. In particular, for calculating autoignition times over a wide range of pressures for temperatures between about 1000 and 2000 K, five irreversible elementary steps suffice, yielding a remarkable reduction in complexity. It is explained that, from a mathematical viewpoint, in terms of global reaction-kinetic mechanisms, the hydrogen–oxygen system in principle comprises only six overall steps. Rational reduced chemical mechanisms for hydrogen combustion therefore necessarily must have fewer than six overall steps. For autoignition over the range of conditions specified above, ignition times can be determined accurately by considering, in addition to an elementary initiation step and an elementary termination step, at most three overall steps for reaction intermediaries, which reduce to two for very fuel-lean conditions and to one for stoichiometric or fuel-rich conditions. The resulting reductions can simplify computations that need to be performed in risk analyses for hydrogen storage and utilization.     

Effects of thermal barrier coating on the performance and combustion characteristics of a diesel engine fueled with biodiesel produced from waste frying cottonseed oil and ultra-low sulfur diesel

In this study, the top surfaces of piston and valves of a four-strokes and direct-injection diesel engine have been coated—with no change in the compression ratio—with a 100 μm of NiCrAl lining layer via plasma spray method and this layer has later been coated with main coating material with a mixture of 88% of ZrO₂, 4% of MgO and 8% of Al₂O₃ (400 μm). Then, after the engine-coating process, ultra-low sulfur diesel (ULSD) as base fuels and its blend with used frying cottonseed oil derived biodiesel in proportion of 20%, volumetrically, have been tested in the coated engine and data of combustion and performance characteristics on full load and at different speeds have been noted. The results, which were compared with those obtained by uncoated-engine operation, showed that thermal efficiency increased, and engine noise reduced. Cylinder gas pressure values obtained from the diesel engine which has been coated with thermal barriers have been found to be somewhat higher than those of the uncoated-engine. Also, maximum pressure values measured in both engines and under the same experimental conditions through the use of test fuel have been obtained after TDC. Moreover, heat release rate and heat release have occurred earlier in the coated-engine. NOx emissions were increased while CO and HC emissions were remained almost the same with a little bit decrease.     

城市生活垃圾焚烧过程中的二恶英污染

城市生活垃圾的焚烧处理虽有其优点，但同时又是剧毒污染物二恶英类物质产生的主要来源。为有助于开发城市固体废弃物的洁净能源化利用的新技术，介绍了二恶英类物质的结构、物理和毒理性质、在焚烧过程中产生的机制等内容。     

燃烧源超细颗粒物及其排放控制研究进展

对燃烧过程超细颗粒物的国内外研究现状及其排放控制进行了综述.介绍了国内外近期开展的有关超细颗粒物的研究课题、研究方向,简述了常用的超细颗粒物的采样、分析及其控制方法,并对超细颗粒物研究的发展趋势进行了预测,由此提出了目前应该开展研究的重点和方向.     

Emission and burnt smell characteristics from combustion experiments with defined materials

Typical burnt smell often results from fire accidents or in general from incomplete combustion. Recently, eleven compounds were identified, which are basically responsible for this odour. When analyzing residual materials from different fire accidents, the pattern that means the relative ratios of these compounds among each other varies strongly, although always causing a burnt smelling. Consequently, lab-scale combustion experiments were performed in order to investigate the influence of defined materials from domestic environment on the burnt-smell fingerprints. Furthermore, the occurrence of other polar and higher molecular combustion products was studied. It was found that under good combustion conditions, the burnt smell patterns resulting from the single materials were astonishingly consistent, mostly dominated by methylphenols or naphthalene. No correlation could be found between these ‘fingerprints’ and combustion product groups identified by GC/MS-screenings. LC/MS/MS-measurements especially pointed at the existence of higher molecular weight phenolic and acidic functionalized compounds in the combustion residues.     

Polybrominated diphenyl ethers in various atmospheric environments of Taiwan: their levels, source identification and influence of combustion sources

In this study, ambient air samples from different atmospheric environments were examined for both PBDE and PCDD/F characteristics to verify that combustion is a significant PBDE emission source. The mean ± SD atmospheric PBDE concentrations were 165 ± 65.0 pg Nm⁻³ in the heavy steel complex area and 93.9 ± 24.5 pg Nm⁻³ in the metals complex areas, 4.7 and 2.7 times higher than that (35.3 ± 15.5 pg Nm⁻³) in the urban areas, respectively. The statistically high correlation (r = 0.871, p < 0.001) found between the atmospheric PBDE and PCDD/F concentrations reveals that the combustion sources are the most likely PBDE emission sources. Correspondence analysis shows the atmospheric PBDEs of the heavy steel and metals complex areas are associated with BDE-209, -203, -207, -208, indicative of combustion source contributions. Furthermore, the PBDEs in urban ambient air experience the influence of the evaporative releases of the commercial penta- and octa-BDE mixtures, as well as combustion source emissions. By comparing the PBDE homologues of indoor air, urban ambient air, and stack flue gases of combustion sources, we found that the lighter brominated PBDEs in urban ambient air were contributed by the indoor air, while their highly brominated ones were from the combustion sources, such as vehicles. The developed source identification measure can be used to clarify possible PBDE sources not only for Taiwanese atmosphere but also for other environmental media in other countries associated with various emission sources in the future.     

Effect of organic matter and moisture on the calorific value of solid wastes: An update of the Tanner diagram

Objective of the work was to experimentally determine the effect of the organic matter and moisture contents on the calorific value of organic solid wastes. Nine substrates (i.e. newsprint, biodried municipal solid wastes, municipal solid waste derived composts, wastewater sludges, and sea weed derived compost), with organic matter contents that ranged from 12% to 91% (dry weight) were used in the experiments. All substrates were dried and ground and deionized water was artificially added in order to achieve certain target moisture contents per substrate. The higher heating value (HHV) was, then, determined experimentally for each sample using a bomb calorimeter. Best reduced models were developed to describe the higher and lower heating values as a function of organic matter, ash and moisture contents. A triangular plot was constructed and the self-sustained combustion area was determined and compared to that of the Tanner diagram. Response surfaces were drawn to visually assess the effect of organic matter and moisture contents on the calorific value of the wastes.