Cool flame characteristics of methane/oxygen mixtures

As one of the most important clean fuels, methane plays a significant role in the energy supply system, and its combustion characteristics directly affect the efficiency and emission. In order to avoid the production of a large number of nitrogen oxides, the low temperature combustion associated with cool flame is getting more and more attention. But until now the cool flame characteristics of methane is still unclear, even its existence is controversial. In this work, the property of premixed methane/oxygen cool flame has been experimentally studied in a cylindrical reactor and numerically analyzed using different mechanisms. The effects of pressure, temperature and equivalence ratio on methane cool flame have been investigated experimentally. The experimental results show that the cool flame can be obtained in the range of 0.2–4.8 equivalent ratio. The lower limit of pressure of the cool flame region decreases with the increasing initial temperature. The sensitivity and reaction path have been analyzed through the numerical simulation, which reveals that the bifurcation in CH₃ oxidation process has remarkable effects on cool flame formation.     

Cool flame partial oxidation and its role in combustion and reforming of fuels for fuel cell systems

The purpose of this review was to integrate the most recent and relevant investigations on the auto-oxidation of fuel oils and their reforming into hydrogen-rich gas that could serve as a feed for fuel cells and combustion systems. We consider the incorporation of partial oxidation under cool flame conditions to be a significant step in the reforming process for generation of hydrogen-rich gas. Therefore, we have paid particular attention to the partial oxidation of fuels at low temperature in the cool flame region. This is still not a well-understood feature in the oxidation of fuels and can potentially serve as a precursor to low NO_x emissions and low soot formation. Pretreatment, including atomization, vaporization and burner technology are also briefly reviewed. The oxidation of reference fuels (n-heptane C₇H₁₆, iso-octane C₈H₁₈ and to a lesser extent cetane C₁₆H₃₄) in the intermediate and high temperature ranges have been studied extensively and it is examined here to show the significant progress made in modeling the kinetics and mechanisms, and in the evaluation of ignition delay times. However, due to the complex nature of real fuels such as petroleum distillates (diesel and jet fuel) and biofuels, much less is known on the kinetics and mechanisms of their oxidation, as well as on the resulting reaction products formed during partial oxidation. The rich literature on the oxidation of fuels is, hence, limited to the cited main reference fuels. We have also covered recent developments in the catalytic reforming of fuels. In the presence of catalysts, the fuels can be reformed through partial oxidation, steam reforming and autothermal reforming (ATR) to generate hydrogen. But optimum routes to produce cost effective hydrogen fuel from conventional or derivative fuels are still debatable. It is suggested that the use of products emanating from partial oxidation of fuels under cool flame conditions could be attractive in such reforming processes, but this is as yet untested. The exploitation of developments in oxidation, combustion and reforming processes is always impacted by the resulting emission of pollutants, including NO_x, SO_x, CO and soot, which have an impact on the health of the fragile ecosystem. Attention is paid to the progress made in innovative techniques developed to reduce the level of pollutants resulting from oxidation and reforming processes. In the last part, we summarize the present status of the topics covered and present prospects for future research. This information forms the basis for recommended themes that are vital in developing the next generation energy-efficient combustion and fuel cell technologies.     

Correlation of true quench temperature for water

A new true quench temperature correlation is formulated based on Groeneveld and Stewart's data (2–9 MPa, ?0.1250?0.1155 (quality), 26–625 kg/m²s), Fung's data (0.1 MPa, ?0.0215?0.0253 (quality), 50–500 kg/m²s) and Cheung, Lau and Poon's data (0.1?1.0 MPa, ?0.0315?0.1990 (quality), 50–682 kg/m²s). Comparison is made with Groeneveld and Stewart's correlation and discussion of the new correlation is also included.     

蓄冷式冷藏运输

通过对易腐货物运输市场需求变化的分析，对各种冷藏运输方式进行了比较，研究了蓄冷式冷藏运输的优越性，为发展新型的冷藏运输方式提供了参考依据。     

Cool sooting flames of hydrocarbons

IntroductionThe stUdy of the smicbe of soot formation flamesgives the valuable information on cheInical and physicalprocesses occtrig before and in hme of soot fonnaon.Whcs inveshgation of hydrDcarbon combushon is ofgreat scientific and prachcal intebesL in prtcular inconnechon with the problems of Protection of tbeenviroIUnnt hom the ProductS of incomPletecombushon in Pebol and diesel engines['].In spite of the gnat number of inveshgations ofhytherton combushon now, there is no comPlete …     

Parametric studies of a side wall quench layer

A parametric study of the structure of the side wall quench layer has been performed. An atmospheric pressure premixed hydrocarbonair flame was stabilized on a porous sintered bronze disk and flat plate was located perpendicular to the undisturbed flame. Spontaneous Raman spectroscopy was used to measure temperature and hydrocarbon number densities, with emphasis on the near wall fields. A propane flame with a cooled copper side wall at fuel lean stoichiometric ratio φ = 0.87 was studied as a nominal case. Various combinations of stoichiometry (φ = 0.69, 0.87, 1.0), fuel species (propane, butane, ethylene), and wall conditions (cooled copper, platinum, and Teflon and heated cast iron) were studied.     

Cool thinking: Unlocking earth's energy

The ground is as universal as air and solar radiation. Over the past twenty years, as the hunt for natural low-carbon energy sources has intensified, there has been an increased endeavour to investigate and develop both earth and ground water thermal energy storage and usage. Bill Holdsworth reports on some recent pioneering developments in the Netherlands and UK.     

浅议热电冷联产

文章论述了热电冷联产节能原理,压缩制冷吸收制冷的比较,热电冷联产的市场前景。     

Safety distances: Definition and values

In order to facilitate the introduction of a new technology, as is the utilization of hydrogen as an energy carrier, development of safety codes and standards, besides the conduction of demonstrative projects, becomes a very important achievement to be realized.     

Tulip flame - the mechanism of flame front inversion

The paper explains the mechanism of tulip flame formation in horizontal combustion chambers closed at the ignition end. The explanations are based essentially on the PIV images and the direct visualization of the process. The obtained results demonstrate that the tulip flame is a purely hydrodynamic phenomenon which results from the competition between the backward movement of deflected burned gases expanding from the lateral flame skirts and the forward movement of unburned gases accelerated in the phase of finger-shaped flame. In some configurations a supplementary global movement imposed by the confinement (for example: acoustic waves) is superposed on the two above mentioned, and modifies the parameters of the process. The results also prove that the intrinsic instabilities of the flame front (Rayleigh–Taylor, Richtmyer–Meshkov or Darrieus–Landau) are not involved in this process. The convex shape of the flame front has no influence on the phenomenon.     

生物质水煤浆及其相关技术(下)

水煤浆技术不仅能很好地解决污泥(废液)资源化难题,又能简化污泥(废液)处理与处置流程.生物质水煤浆作为分布式能源的"一次能源"多样性的重要内容,使企业、工业园区或城镇社区变污染负效益为资源正效益,拥有了自己的"能源工厂".充分体现出制浆技术在能源结构调整、资源合理利用以及清洁生产等方面的综合作用,从而奠定水煤浆技术在循环经济中的应有地位.     

Radiation effects on flame stabilization on flat flame burners

This study investigates the impact of radiative heat transfer on the behavior of flat flame burners within the framework of a simplified one-dimensional model. Flat flame burners stabilize planar premixed flames downstream of a porous plug. Within this study, the porous plug is modeled as a thermally conducting, optically thick medium, allowing for both conductive and radiative heat transfer. Based on the simplified model, the impact of radiative heat exchange between the porous plug exit and the downstream environment is investigated. In “surface” combustion, flame stabilization occurs due to heat transfer between gas phase and porous solid. Results demonstrate that radiative heat transfer from a hot downstream environment to the porous plug significantly increases maximum attainable mass fluxes. For a cold downstream environment, plug properties do not affect the maximum supportable mass flux, although plug porosity and heat transfer between gas and solid have a significant impact on the “stand-off” distance between flame and plug exit. In addition, the model provides insight to a second “submerged” combustion mode, where the flame is stabilized within the porous plug of the burner. Here, increased flame temperatures lead to a dramatic increase of the maximum supportable mass flux. Overall, results show that radiative heat losses play a critical role in both combustion modes: in surface combustion, they are an important mode of heat dissipation, where they can prevent “flash-back” conditions with the flame moving into the porous matrix; in submerged combustion, they prevent flame stabilization close to inlet and exit faces and enable a “slow” solution branch that does not exist without radiative losses.     

Development of a 1 MJ SMES with quench enthalpy protection

As a quench protection method in an SMES, a dumping resistor method and an enthalpy method are considered. The former is a conventional method, but the latter has not been experimentally examined yet, although it has been shown to be suitable for future SMES. In addition, a new control method, QI simultaneous control, has been also developed as a practical application of the SMES. The performance or the enthalpy protection technique is verified by a helium dumping method, and the QI simultaneous control is also successfully examined using a power network simulator     

直接接触式放冷试验的初步研究

本文考察了不同水流量下的放冷时间的变化,探讨了不同工况下蓄冷缸内的温度分布。     

Dynamics of upstream flame propagation in a hydrogen-enriched premixed flame

An unconfined strongly swirled flow is investigated to study the effect of hydrogen addition on upstream flame propagation in a methane-air premixed flame using Large Eddy Simulation (LES) with a Thickened Flame (TF) model. A laboratory-scale swirled premixed combustor operated under atmospheric conditions for which experimental data for validation is available has been chosen for the numerical study. In the LES-TF approach, the flame front is resolved on the computational grid through artificial thickening and the individual species transport equations are directly solved with the reaction rates specified using Arrhenius chemistry. Good agreement is found when comparing predictions with the published experimental data including the predicted RMS fluctuations. Also, the results show that the initiation of upstream flame propagation is associated with balanced maintained between hydrodynamics and reaction. This process is associated with the upstream propagation of the center recirculation bubble, which pushes the flame front in the upstream mixing tube. Once the upstream movement of the flame front is initiated, the hydrogen-enriched mixture exhibits more unstable behavior; while in contrast, the CH₄ flame shows stable behavior.     

Risk-informed separation distances for hydrogen refueling stations

As part of the US Department of Energy Hydrogen, Fuel Cells & Infrastructure Technologies Program, Sandia National Laboratories is developing the technical basis for assessing the safety of hydrogen-based systems for use in the development/modification of relevant codes and standards. This work includes quantitative risk assessments (QRA) of hydrogen facilities. The QRAs are used to identify and quantify scenarios for the unintended release of hydrogen and thus help identify the code requirements that would reduce the risk at hydrogen facilities to acceptable levels.     

Cool currents: superconductors' evolution for power transmission

Researchers and engineers toil at discovering new solutions and technologies that could make the recent northeastern U.S blackout a rare occasion in the future. One of the prominent technologies that has captured a great deal of attention is superconducting power cable. Studies by major corporations and organizations have concluded that major investments in the power grid in the United States will be necessary to meet the need for reliable and affordable electric power and that HTS cables could lay a significant role in meeting this need. It is apparent that HTS technology will progressively set the stage for applications in large markets where cost as well as size, weight, efficiency and performance are important.     

Numerical analysis of the Cambridge stratified flame series using artificial thickened flame LES with tabulated premixed flame chemistry

Detailed comparisons of LES results against measurement data are presented for the turbulent lean and rich stratified Cambridge flame series. The co-annular methane/air burner with a central bluff body for flame stabilization has been investigated experimentally by Sweeney et al.  and . Three cases with varying levels of stratification in the lean and rich combustion regime are taken into account. Turbulent combustion is modeled by using the artificial thickened flame (ATF) approach in combination with flamelet generated manifolds (FGM) lookup tables. The model is adapted for stratified combustion and an alternative formulation for the flame sensor is presented. Three different grids are used to investigate the influence of the filter width and the sub-filter modeling on the overall results. Velocities, temperatures, equivalence ratios, and major species mass fractions predictions are compared with measurements for three different stratification rates and an overall good overall agreement was found between simulation and experiment. Some deviations occur near the bluff body, which are analyzed further by evaluation of atomic and species mass fractions. The stratified combustion process was further investigated and characterized by probability density functions extracted from the simulation results.