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The main results of VTI's investigations into low-emission combustors for gas-turbine units (GTU) are presented. In recent years, the combustion of a premixed fuel-air mixture (FAM) in a swirling flow in a limited space has been under development for this purpose to attain more complete combustion, stable fluctuation-free operation of a combustor in a wide range of parameters, and compliance with environmental protection requirements. To solve the problems encountered in this field, a procedure has been developed for assessing the effect of temperature in the combustion zone, flow velocity, combustor pressure, and other factors on the combustion stability. A review is presented of a comprehensive approach employed by VTI's specialists to study the processes in combustors using numerical and experimental methods enabling them to cut down the cost and time of activities on development of low-emission combustors. For example, a relationship is presented between the numerically estimated quality of the produced fuel-air mixture and the experimental nitrogen oxide concentrations. A design parameter relating the process conditions in a flame tube with the vibration combustion amplitude is proposed. The experiments demonstrated a good correlation of the proposed parameter with measured pressure fluctuation amplitude. Of real interest are the presented examples of changes in the velocity and temperature fields with an increase in the working pressure, which should be considered in designing and bench testing the combustor. The low-emission combustors (LEC) developed for large- and medium-power GTUs are presented. The potential for scaling the combustors for other GTUs is examined. [ABSTRACT FROM AUTHOR]

Results are presented of the experimental investigation of gaseous fuel combustion in a combustor comprising two zones in series each of which has its own burner unit (BU). The first burner unit (BU1) is a conventional one for low-emission combustors. It contains swirlers, a fuel-air mixing zone, a pilot burner, and a main burner. BU1 is fed with a premixed fuel-air mixture (FAM). The second burner unit (BU2) is located downstream along the flow, behind the first combustion zone. It is supplied with gaseous fuel (i.e., natural gas) without premixing with air. Diffusion combustion occurs in the second zone. The potential was studied for extending the stable operation range of the first combustion zone to the range of low excess air factors by creating radial nonuniformity in the FAM concentration at the BU1 outlet. This is accomplished by feed air in one hole in the fuel tubes above the vanes of the main burner swirler. The best FAM concentration at the first stage minimizing NOx and CO emission during joint operation of two combustion stages installed in series was determined. The results of the experiments with BU2, which is a thick hollow disk with a nozzle-shaped orifice with holes in the bore surface for fuel injection, are presented. The experiments were carried out with a model combustor in the test facility at OAO VTI. [ABSTRACT FROM AUTHOR]

An investigation of the low-emission premixed combustion in a conventional combustor is presented. The main problem encountered is the pressure fluctuations induced under certain operating conditions of the combustor. Low-emission operation of the combustor was studied numerically and experimentally. The effect of the concentration distribution at the outlet from the mixing zone on the position and macrostructure of the flame and the combustion stability was investigated at various excess air factors corresponding various GTU loads. It is demonstrated that, for a given excess air factor, there exists the concentration profile such that the interaction of the flame front with dominating flow structures results in excitation of the low-frequency combustion instability. The factors responsible for high-amplitude pressure fluctuations are examined. It is shown that the combustion stability can be estimated using a calculated criterion. Its direct relationship with pressure fluctuation amplitudes is described. The effect of the air pressure in a combustor on the flame macrostructure and the combustion stability was studied. It is shown that an increase in the combustor pressure has no considerable effect on the processes in the combustor. However, a change in the chemical reaction rates affects the stable combustion boundary. In this case, the combustion stability is achieved with higher nonuniformity of the fuel-air mixture entering the combustion zone. The experimental boundaries of stable combustion envelope at an air pressure of 350 and 1500 kPa are presented. [ABSTRACT FROM AUTHOR]

A computational and experimental investigation of the processes occurring in premix combustors with swirl stabilization similar to that used in modern gas-turbine engines is described. The combustor burner consists of main and pilot burners. The combustor operates on a mixture of natural gas and air with excess air coefficient from 10 to 2.6. The influence of the fuel fraction in the pilot burner (PFR) with fixed excess air coefficient á on the macrostructure of the flame - the relation between the shape and position of the flame front and the dominating structures of the flow - is examined. The flame front is investigated by means of three-dimensional numerical modeling. Four ma xxx crostructures are observed in the experimental PFR range from 0 to 100% with fixed excess air coefficient á. It is shown that each form of high-frequency combustion instability corresponds to a definite macrostructure of the flame. It is noted that the fuel fractions in the pilot burner at which changes are observed in the flame configuration are associated with the appearance of thermo-acoustic instability. [ABSTRACT FROM AUTHOR]