摘要:

This paper presents the results of a study of the potential causes of frequently observed combustion instabilities in low NOx gas turbines (LNGT) that burn gaseous fuels in a premixed mode. The study was motivated by indications that such systems are highly sensitive to equivalence ratio perturbations. An unsteady well-stirred reactor model was developed and used to determine the magnitude of the reaction rate and heat release oscillations produced by periodic flow rate, temperature or equivalence ratio perturbations in the combustor's inlet flow at different mean equivalence ratios. This study shows that the magnitudes of the reaction rate and heat release oscillations produced by these perturbations remains practically unchanged, decreases, and significantly (i.e., by a factor of 5-100) increases, respectively, as the equivalence ratio decreases. These results strongly suggest that equivalence ratio perturbations, which are an indication of reactants unmixedness, playa key role in the driving of combustion instabilities in LNGT operating under lean conditions.

ISSN:0010-2202    

DOI:10.1080/00102209808924157

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Active Control of thermoacoustic instabilities in continuous premixed combustion processes is being increasingly investigated for operating at lean low NOxconditions. Recently, we have developed a model-based approach for active control design which accounts for the underlying acoustics, heat release dynamics, and sensor and actuator dynamics. While this model captures a number of the dominant dynamic features of a premixed laminar combustor, there are a number of uncertainties associated with it as well. In this paper, we study the sensitivity of this model with respect to parametric uncertainties, and the efficacy of a fixed control design for suppressing pressure oscillations. We show that under certain conditions, the fixed controller is inadequate and present a self-tuning controller which is capable of delivering the desired performance in the presence of these uncertainties. The controller proposed is based on a rigorous analytical foundation, and is shown through simulation results to lead to better performance than corresponding fixed controllers. Adaptive algorithms based on the LMS-filter are shown to result in numerical instabilities.

ISSN:0010-2202    

DOI:10.1080/00102209808924158

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Combustion of magnesium in carbon oxides is of great interest because of the prospects for CO2/metal propulsion on Mars. In this paper pulsating combustion of single magnesium particles in the atmosphere of carbon monoxide is experimentally studied. A closed chamber and a gas flow reactor are employed in this study. Thermocouple measurements of particle and gas temperature as well as microscopic observations throughout the entire ignition and combustion process are carried out. The pulsation frequency significantly increases with increasing the ambient temperature and decreases with increasing the gas velocity. The experimental results are discussed with consideration of thermodynamic peculiarities of Mg combustion in carbon oxides.

ISSN:0010-2202    

DOI:10.1080/00102209808924159

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The subject of the present work is to report an experimental comparative study of the effect of dispersion-induced turbulence on dust combustion in constant volume vessel, carried out both in normal gravity and in microgravity environment. Dispersion system with small scale of turbulence, creating uniform homogeneous mixture, was used in experiments. To improve reproducibility of the explosion data an ignitor of small energy, with local soft ignition was developed. Both factors contributed to acquisition of more reproducible experimental data. In experiments under microgravity conditions a dust suspension during combustion remains constant. This makes possible to study dust explosion under stationary dust suspension without influence of turbulence.

ISSN:0010-2202    

DOI:10.1080/00102209808924160

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Alex powder (an ultra-fine aluminum powder produced by the plasma-explosion process) has been shown to be a very effective burning rate enhancer for solid propellants and fuels. The objective of this research is to investigate the mechanisms responsible for the beneficial effect of Alex. A TGA and DTA were employed to examine the thermal bahavior of Alex and regular aluminum particles in different gases. An environmental scanning electron microscope (ESEM) was utilized to study the particle surface bahavior when samples were heated in air and nitrogen. A transmission electron microscope (TEM) was employed for examining the microstructure of Alex particles. Alex powder was demonstrated in TGA and DTA experiments to behave very differently from the regular aluminum in air, oxygen and nitrogen. Rapid weight gain of Alex particles in air and nitrogen environment occurred around 548°C and 700°C, respectively. The low-temperature reaction in air corresponds to an oxidation reaction. Comparing DTA traces of Alex and regular aluminum in air, it was found that oxidation of Alex particles occurs at a lower temperature with a higher degree of reaction. This is believed to be mainly due to the higher reactivity associated with greater surface area of the Alex particles. In the comparison of DTA traces of Alex and regular aluminum in nitrogen, the rapid nitridation reaction of Alex particles occurs at temperature around 680°C and proceeds to near completion.

ISSN:0010-2202    

DOI:10.1080/00102209808924161

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor