Search

The gas temperature fields of axisymmetric co-annular laminar diffusion ethylene flame jets in air and oxygen-enriched atmospheres were measured and visualized using large lateral shearing interferometry technique. Seven cases of reconstructed temperature fields were investigated using various compositions of fuel/oxidant with an average correction factor. The phase difference field were obtained using a fringe trace algorithm. A discrete Abel inversion process was adopted to resolve the refractive index distribution from the line-of-sight integrated data. The peak temperatures of the flame varied between 1980 K and 2050 K using air as the oxidant and increased to more than 2150 K when oxygen was added. Two separate high temperature zones, one located at the side edge of the flame, the other in the upper part of the flame around the centerline of the burner were observed in four of the seven instances of high mixture stoichiometry. The proposed methodology was verified to be suitable for the reconstruction of temperature distributions from the experimental measurement results. [ABSTRACT FROM AUTHOR]

This paper presents a method to invert the two-dimensional distribution of a temperature and volume concentration of soot particles from color images. By using numerical simulation, the temperature field and particle volume-concentration field of a non-uniform soot flame are simultaneously reconstructed using the wide-response spectrum of a color CCD camera without adding monochromatic filters. The influence of number of cameras, error of camera position angle, measurement noise and different reconstruction algorithms on measurement accuracy are analyzed. The numerical-simulation results demonstrate that camera-position angle errors play a crucial role in the reconstruction accuracy. In addition, increasing the number of cameras can improve the reconstruction result accuracy. Compared with the least squares algorithm, the Tikhonov-regularization algorithm has a stronger anti-noise ability and can resist 39 dB of noise. The conclusions obtained in this paper are helpful to guide following experimental studies. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a new conception of in-situ combustion control schemes for pulverized coal-fired boilers to improve the installed conventional control equipment of power plant units. In this paper, radiant energy signal (RES), based on a flame image processing technique, is put forward and an optimal on-line combustion supervisory strategy is developed for introducing RES into the combustion control circuit. The results show that better combustion efficiency can be obtained in association with the control property. Also a decrease in fuel consumption with a corresponding decrease in the consumption of energy, as well as a reduction of emissions, has been studied and tested for the optimization. In this paper, the optimal scheme is proved to be practical and economical, and it can be used to optimize the combustion control design and operation of pulverized coal-burning boilers, when considering both the stability of steam pressure as a traditional calorific value signal and the rapidity of response by using RES. [Copyright &y& Elsevier]

In the field of micro and mesoscale combustion, the feature of flame-wall thermal coupling is of great significance because of its small scale nature. Thus, this work provides a comprehensive heat transfer analysis in cylindrical combustors from the perspective of numerical simulation. The combustor has a fixed length-to-diameter aspect ratio of 10, and the channel diameter is scaling up from 1 mm to 11 mm to explore the influence of chamber dimension on heat transfer and flame structure. The distribution of convective and radiative heat flux on inner surface, contribution of thermal radiation are given. Moreover, the role of radiation in flame structure is analyzed, and the convective and radiative heat losses are quantitatively analyzed. We find that radiative heat flux is smaller compared to convective heat flux, and the proportion of radiative heat flux becomes larger with an increasing diameter. Thermal radiation does not change the flame structure when the diameter is less than 3 mm. When the diameter is greater than 5 mm, thermal radiation changes the location of flame front. The heat loss becomes larger at a smaller diameter, and heat loss ratio can reach approximately 73.6% in the combustor with diameter of 1 mm. [Display omitted] • Comprehensive heat transfer analyses in micro combustors are revealed. • The contributions of thermal radiation in combustors with different scales are investigated. • The role of radiation in the flame structure is analyzed. • Heat losses in cylindrical combustors from microscale to mesoscale are quantified. [ABSTRACT FROM AUTHOR]

Effects of radiation reabsorption on the burning flux of freely propagating laminar premixed flames at atmospheric and elevated pressures were numerically investigated for CH 4 /O 2 /N 2 /CO 2 mixtures. Models with SNBCK 9 bands and 7 bands based on the spectral band lumping for H 2 O, CO 2 , CO and CH 4 were developed to improve the computational efficiency. It is found that the burning flux is promoted by the upstream radiation reabsorption and with increasing CO 2 concentration. Furthermore, with increasing pressure, radiation reabsorption first increases and then reduces the burning flux because of the corresponding increases of the reabsorption efficiency and the optical thickness, respectively. The blockage of radiation emission from the burnt mixture due to the increased optical thickness is dominant with the addition of the stronger radiative species CO 2 at higher pressures. Extensive computation further demonstrates that, compared with the benchmark case of 367 bands, the SNBCK 9 bands lumping retains good accuracy while substantially facilitates the computational efficiency. [ABSTRACT FROM AUTHOR]

A candle flame is experimentally studied using a hyperspectral imaging device in this paper. The distributions of temperature and wavelength-dependent emissivity are calculated using a Newton-type iterative method. The results show that the spectral radiation intensity increases from the outside to the inside in the candle flame, and at the same spatial point, the intensity increases as the wavelength increases. The highest temperature of the candle flame is about 1980 K, occurs close to the flame border, indicating the most vigorous reaction. Additionally, the radiation characteristics of the candle flame differ from a gray-body, and the emissivity of the flame decreases as the wavelength increases. [ABSTRACT FROM AUTHOR]

• An experimental design was used to investigate the effects of different torrefaction conditions on the properties of biomass. • Two spectrometers were simultaneously used to capture high SNR signals of continuous spectrum and characteristic spectrum. • In-situ detection of the temperature and K release concentration of torrefied biomass pellet combustion was achieved. • Changes in combustion characteristics and K release characteristics of torrefied biomass were evaluated. The orthogonal experiment designed in this paper investigated the effect of changes in experimental parameters such as biomass species, torrefaction temperature, torrefaction time, torrefaction oxygen concentration on the physicochemical properties and combustion characteristics of the torrefaction products. Two optical fiber spectrometers were used to capture the spontaneous emission spectra of the combustion flame of compressed pellets of torrefied biomass, and the in-situ measurement of pellet combustion temperature and K release concentration at high heating rate was realized by multi-spectral analysis algorithm. The experimental results indicate that for biomass, torrefaction will lead to a decrease of volatile and moisture content and an increase of fixed carbon and ash content in components, a decrease of O and H and an increase of C content in elements, a certain loss of biomass quality, an increase of high heat value, and each indicator move closer to coal. The effects of various experimental parameters on the volatile content, mass yield, high heat value increase rate and energy yield in biomass torrefaction products have similar laws, i.e., biomass species / torrefaction oxygen concentration > torrefaction temperature > torrefaction time. The mild torrefaction product pellets have a shorter ignition delay, increased volatile combustion flame height and peak temperature, longer volatile and char combustion duration, but lower peak char combustion temperature, among which the selected torrefaction products of rice straw and pine wood showed an increase in peak temperature of 0.56 % (11 K) and 0.61 % (12 K) for the volatile stage respectively, and a decrease of and 1.29 % (20 K) and 1.29 % (21 K) for the char stage respectively. In addition, the peak K release concentration during combustion of the mild torrefaction product pellets was reduced, among which the peak K release concentrations during the volatile and char stage were reduced by 43.22 % (3.89 ppm) and 52.93 % (51.55 ppm) of the rice straw torrefaction product respectively, and by 73.14 % (1.28 ppm) and 62.08 % (15.01 ppm) for the pine wood torrefaction product respectively. Biomass torrefaction products have fuel properties closer to coal, less K released from the combustion process, which have the potential to become an alternative to coal. [ABSTRACT FROM AUTHOR]

A novel planar micro-combustor with four-corner entrances is proposed by considering high and uniform outer wall temperature distribution used in micro thermo-photovoltaic generator. For this, a three-dimensional numerical model with detailed chemical mechanism, transport, and heat transfer and a thermo-photovoltaic energy conversion model are developed to examine its performance. Results show that the proposed micro-combustor has excellent wall temperature uniformity because a uniform distribution of high-temperature zones of four individual flames is formed in the combustion chamber. Thermal performance and energy efficiency of the proposed micro-combustor are better than conventional micro-combustor at a low flow rate (m) and large equivalence ratio (φ). Additionally, the implemented plate-insertion strategy effectively overcome the deterioration of combustor performance under higher m or lower φ. Proposed micro-combustor with plates insertion has the largest wall temperature and energy efficiency, no matter what φ and m are adopted. Plates extend the fluid ravel path and produce some recirculation zones, which promotes heat transfer, preferential diffusion, and flame anchoring, while its pressure loss is larger. Of all the tested cases, the system efficiency reaches a maximum of 6.39%, corresponding to 12.1 W electricity output. This work provides effective combustor design and research insights to develop high-efficiency micro-power system. • A novel micro-combustor with four entrances is proposed for micro-TPV system. • Excellent performance of wall temperature uniformity is obtained. • Inserting plates boosts thermal performance and energy conversion efficiency. • A maximum system efficiency of 6.39% is achieved with 12.1 W electric output. [ABSTRACT FROM AUTHOR]