Emissions measurements and OH* chemiluminescence imaging were performed on a novel multipoint lean direct injection combustor designed for low-NOx emissions and with the flexibility to operate at both high- and low-power settings. The combustor has five rows of fuel nozzles that can be staged in three independent circuits as required. The fuel nozzle stages are not identical; instead, they are optimized for different power settings. NOx, CO, and unburned hydrocarbons were measured for a variety of settings, including lean blowout, idle, intermediate power, and simulated full power. Effects of pressure, inlet temperature, equivalence ratio, and fuel flow distribution were studied. OH* chemiluminescence was used to observe flame structure and interpret emissions trends. The local equivalence ratio, calculated with the fuel and air flow rates particular to each combustor stage, was a useful parameter for interpreting emissions. The combustor demonstrated the ability to operate at a wide range of conditions, ...

Experimental Study of a Multinozzle Combustor at Elevated Pressures

In this paper, we perform a comparative numerical analysis of turbulent combustion and harmful substance emission from a homogeneous combustion chamber operating on pure n-decane and mixed n-decane/hydrogen or n-decane/syngas fuels. The calculations were performed using the ANSYS Fluent program, and a reduced kinetic mechanism describing the oxidation of the fuels under consideration was developed. The hydrogen or syngas addition to n-decane in a 50/50 volume ratio is shown to lead to a decrease in temperature both inside the combustion chamber and in its outlet section. There is a simultaneous decrease in the carbon oxides and nitrogen emission. The depletion of the air–fuel mixture with an excess air coefficient of α = 2.3–2.5 sharply reduces the nitric oxide emission and simultaneously increases significantly the carbon monoxide emission. In this depletion, total NO and CO emission index increases more than twofold.

Numerical Study of the Effect of Hydrogen or Syngas Additions to n-Decane on the Harmful Substance Emission from a Homogeneous Combustion Chamber

A multiple-nozzle staged combustor with lean direct injection nozzles which experiences self-sustained thermoacoustic coupling under certain conditions is examined. This combustor has three fuel stages: a high-swirl pilot stage, a low-swirl intermediate stage, and a low-swirl outer stage. When the lower-stability fuel stages are supplied fuel, coupling with a fundamental frequency of 540 Hz can occur depending on the equivalence ratio and the fuel distribution. Generally, increasing either the equivalence ratio or sending more of the total fuel to the low-stability airblast nozzles results in an increase in the amplitude of the pressure oscillations. Time-resolved chemiluminescence images reveal dramatic changes in the reaction zone over a period of oscillation. This fluctuation in the OH* emission is dominated by recurrent extinction and re-ignition in the reaction zone of the low-emission intermediate and outer fuel stages. One condition displays an oscillation which is highly intermittent in that bursts of high-amplitude pressure waves appear and disappear about 5.5 times a second. Proper orthogonal decomposition shows that the modes characterizing the periodic fluctuations in the reaction zone have frequencies at 5.5 Hz (associated with the intermittent dynamics) and 540 Hz (from the thermoacoustic coupling).

High-Speed Imaging of Combustion Oscillations in a Multiple Nozzle Staged Combustor

Periodic behavior in the reaction zone of a multiple-nozzle combustor undergoing self-sustaining combustion oscillations is examined. Understanding of the thermoacoustic interactions among heterogeneous arrays of swirl cups is important to enable the implementation of this low NOx approach. This combustor has three stages: a high-swirl pilot stage, a low-swirl intermediate stage, and a low-swirl outer stage. Liquid jet A fuel is supplied to all three fuel stages, which is characteristic of the high-power operation mode. Four test conditions are examined in which thermoacoustic coupling is observed at a well-defined frequency. Phase-averaged images of the OH* chemiluminescence emission show dramatic changes in the OH* emission, which is dominated by recurrent weakening and reignition downstream of the low-stability intermediate and outer fuel stages. The pilot stage reaction zone also displays periodic variation in intensity that is 90 deg out of phase and precedes the intermediate and outer fuel stages. O...

Thermoacoustic Coupling in a Multinozzle Staged Combustor

Numerical simulation of the V-shaped turbulent combustion of a homogeneous methane-air mixture has been performed using the program Fluent from the ANSYS-CFD software package. The combustion process was described by the two-dimensional unsteady Navier-Stokes equations and the one-step kinetic mechanism. The unsteady profiles of the velocity components at the input domain of the calculation area were modeled by means of the artificial turbulence algorithms. These algorithms made it possible to set the pulsation intensity and the integral turbulence scale in the oncoming flow. Comparison of the calculated and experimental data has shown that experimentally observed broadening of the combustion front can be a result of its instability to the perturbations of the velocity in the oncoming flow.

Computer study of the effect of the turbulence of an oncoming flow on the V-shaped combustion of a homogeneous methane-air mixture

A one-dimensional problem of propagation of a laminar flame front through a uniform methane-air mixture was solved using the GRI-Mech 3.0 reaction mechanism. An analysis of the composition of the combustion products behind the flame front at a pressure of 10 atm, an initial mixture temperature of 600 K, and two values of the air-to-fuel equivalence ratio (α = 1.8 and 2.5) was performed. It was demonstrated that, at short residence times, the carbon oxide emission increases as the mixture is made leaner, with the opposite tendency being observed at long residence times. Numerical calculations of the characteristics of turbulent flow and combustion in two axisymmetric homogeneous-combustion model chambers with relatively long residence times were performed within the framework of a bulk (quasi-laminar) combustion model. In calculations, the methane-air mixture composition and the wall temperature of one of the chambers were varied. The case of cooling air inflow through the chamber wall was considered. It was demonstrated that, over a wide range of parameters in the combustion chamber and on its wall, the CO emission monotonically decreases as the degree of mixture leaning grows, but it increases when the chamber wall is cooled and when cooling air is blown through the wall.

Emission of carbon oxides during the combustion of lean methane-air premixed mixtures

The effect of recirculation zone on the magnitude of NO x emissions in a low-emission combustion chamber

The process of combustion of a premixed lean methane/air mixture in the model low-emission combustor is studied. Several known mechanisms of the self-oscillation generation and the flame flashback are analyzed. Numerical LES and SAS calculations of several combustors of typical configurations and regime parameters are presented. Some means of suppressing the flame flashback are proposed and analyzed.

Possible mechanism of self-oscillations in a combustor working on a premixed methane/air mixture

Two methods for calculating the noise of turbulent exhaust jets of civil aircraft nozzles are considered. The first method is chiefly intended for engineering mass-volume calculations and is based on the solution of the averaged Navier-Stokes equations closed by a two-equation turbulence model. The second method uses direct numerical simulation of large eddies in a turbulent jet and the Kirchhoff surface for calculating noise spectra and radiation patterns in the far field. The possibilities and certain important restrictions of these methods are analyzed. The results obtained using these methods are compared with experimental data.

Analysis of the possibilities of the methods for calculating turbulent jet noise

The structure functions in homogeneous isotropic turbulence are numerically investigated. Both one-dimensional and three-dimensional turbulences are considered. The methods for constructing the compressible turbulence are analyzed.

A. N. Sekundov

Papers

Emission of carbon oxides during the combustion of lean methane-air premixed mixtures

The effect of recirculation zone on the magnitude of NO x emissions in a low-emission combustion chamber

Possible mechanism of self-oscillations in a combustor working on a premixed methane/air mixture

Analysis of the possibilities of the methods for calculating turbulent jet noise

Analysis of Kolmogorov's Hypotheses in a Compressible Turbulent Flow