摘要:

Quantitative laser-induced fluorescence (LIF) measurements of NO concentration ([NO]) have been obtained along the centerline of prompt-NO dominated, methane-air counterflow diffusion flames at two to five atm, Global strain rates of 20, 30 and 40 s−1were investigated at each pressure, with the addition of a 15 s−1case at three and four atm. Linear LIF measurements of [NO] are corrected for variations in the electronic quenching rate coefficient by using major species profiles generated by an opposed-flow flame code and quenching cross-sections for NO available from the literature. Corrected linear LIF measurements of [NO] are compared with numerical predictions from the opposed-flow flame code by utilizing the GRI (version 2.11) mechanism for the NO kinetics. The effect of radiative heat loss on code predictions is accounted for by using an optically thin radiation model. A modest decrease in predicted temperature owing to radiative heat loss causes a significant decrease in predicted [NO], indicating the temperature sensitivity of the prompt-NO kinetics. Comparisons between [NO] measurements and predictions show that the GRI mechanism underpredicts prompt-NO by a factor of two to three at all pressures. The underprediction peaks at 2 to 3 atm, and decreases with pressure from 3 to 5 atm. Although the GRI mechanism does not display this trend, predictions with a modified rate coefficient for the prompt-NO initiation reaction give qualitative agreement with the experimentally observed variation. However, modifying the prompt-NO initiation reaction is not sufficient to account for the differences between measurements and predictions, thus indicating a need for refinement of the CH chemistry.

ISSN:0010-2202    

DOI:10.1080/00102200008947318

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Post cylinder oxidation of unburned hydrocarbons (UHC) was studied using a 35 kW lest engine. The engine was equipped with an insulated exhaust reactor to extend the residence time. The exhaust reactor performance has been characterised under the basic engine operating conditions, and under conditions where temperature and composition (NOxlevel) of the exhaust were modified independent of engine settings. The experiments studied spanned a wide range of moderately lean-bum conditions. The composition at the exhaust port was as follows: O25-9% (engine excess air ratios of 1.28-1.75), UHC 1000-7000 ppm, CO 550 ppm, NOx0-1400 ppm. The temperature varied from 600 to 700°C, In addition, experiments with injection of hydrogen peroxide to promote UHC oxidation in the exhaust system were conducted.

ISSN:0010-2202    

DOI:10.1080/00102200008947319

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Turbulent premixed flame propagation in a closed spherical vessel with a homogeneous and isotropic turbulent flow field is modelled using the one-point transport equation for the probability density function (pdf) in the thermodynamic space. The pdf equation is discretized using the control volume formulation on a one-dimensional spherical grid. Then the discretized equation is solved using the Monte Carlo method to follow particles with variable volumes on a grid moving with the expansion radial velocity. The mixing term is modelled using the Curl model, and the modified Curl model. The source term is simulated delerministically using a one-step chemical reaction mechanism. Transient solutions are obtained for spherical benzene-air flames using frozen turbulent flow. The pressure rise, the mass fraction burned, the flame speed, the entrainment speed, the burning speed, and the burned gas speed are calculated. The calculated entrainment speeds are compared with the ones reported in Bradley et al (1992) for KLc>5.3 where distributed reaction zones are assumed to govern the flame propagation. The effects of different turbulent flow field (uvS1) and the effect of the product (KLe) are discussed.

ISSN:0010-2202    

DOI:10.1080/00102200008947320

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Based on the influence of chemical equivalence ratio on the combustion stability of utility pulverized coal-fired boilers and the control theory about system stability, a combustion stability index, CSI, which refers to the maximum reduction ratio of the fuel mass flow rate that can be overcome by the stable combustion process under a constant air mass flow rate, was proposed to assess quantitatively the combustion stability in the boilers. MLO, the Minimum Load of Operation with stable combustion not supported by firing oil, and MCQ, the Minimum Coal Quality, which gives the lowest heat values of coals with different volatile matter contents for stable operation of boilers, are defined on the basis of CSI. In order to predict MLO and MCQ, a simple chemical reaction system model has been modified by means of the concept of lean flammability of gaseous fuels. A three-dimensional combustion simulation code integrated with the modified model was used to study the stability of combustion process in a 200MWe pulverized coal fired utility boiler. The predictions of MLO and MCQ agreed confidently with operational experiences.

ISSN:0010-2202    

DOI:10.1080/00102200008947321

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102200008947322

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor