In order to obtain the cold flow structures inside a model scramjet combustor, direct-connected experiments have been conducted on the inlet Mach number of 2.0. The length to height ratio of the isolator is 6 and 8. The static pressure along the wall is measured with varied back pressure. The Schlieren technique is employed for visualizing the typical shock train structures in the model. The results indicate that the flowfield in the scramjet combustor is rather complicated because of shock wave/boundary layer interaction. The first shock of the normal shock train is bifurcated at the foot, while the subsequent shocks are seen to be of nearly normal shock. Each successive shock is weaker. The shock train moves towards the isolator entrance as back pressure increases. The position of the leading edge of shock train is sensitive to the pressure variation. The isolator of Liso/ h=8 can sustain pressure rise better than Liso/ h=6.
In this article, the ignition characteristics of the gaseous ethylene hydrocarbon fuel is investigated in a supersonic clean airstream experimental facility with resistance heaters. A generic cavity flame holder is used to create a recirculation region and promote the fuel/air mixing at the lower wall of the combustor. Three different injection concepts are considered in this research: (a) ethylene injection upstream of the cavity; (b) ethylene and hydrogen injection upstream of the cavity simultaneously; and (c) ethylene injection preceded by pilot hydrogen injection. The pilot injection is a supportive tool for holding the flame of the main normal ethylene fuel injection. Therefore, using pilot hydrogen injection and cavity configuration necessitates optimizing the combustor length to ensure complete combustion and full liberation of the chemical energy stored in the fuel before exiting the combustor. This study proved the possibility of igniting the ethylene and maintaining its flame in the supersonic airstreams.
The objective of this study is to gain a fundamental understanding of the flow-field and flame behaviors associated with a low-swirl burner. A vane-type low-swirl burner with different swirl numbers has been developed. The velocity field measurements are carried out with particle image velocimetry. The basic flame structures are characterized using OH radicals measured by planar laser-induced fluorescence. Three combustion regimes of low-swirl flames are identified depending on the operating conditions. For the same low-swirl injector under atmospheric conditions, attached flame is first observed when the incoming velocity is too low to generate vortex breakdown. Then, W-shaped flame is formed above the burner at moderate incoming velocity. Bowl-shaped flame structure is formed as the mixture velocity increases until it extinct. Local extinction and relight zones are observed in the low-swirl flame. Flow-field features and flame stability limits are obtained for the present burner.
In aero-engine combustor, the primary and secondary dilution air jets play a vital role to achieve efficient combustion and provide a satisfactory temperature profile at the combustor exit. In the current research, seven kinds of three-dome combustor sector associated with different dilution holes arrangements are simulated using Flamelet model. The influences of location, number and diameter of dilution air holes on flow field and performance of combustor are analysed in detail. The results demonstrate that the variation of airflow distribution, while keeping the total admission area constant, impact the combustion efficiency and pattern profile considerably, yet has insignificant effect on the total pressure coefficient. The maximum combustion efficiency and minimum pattern factor can be achieved simultaneously with deliberate dilution jet holes arrangement.
To predict the pollutant emissions and lean blowout, chemical reactor network (CRN) model is applied to the modern aircraft engine combustion chamber. In this study, the CRN which represent the major features of aerodynamics and combustion in the combustion chamber is set up based on the OpenFOAM simulation results. The boundary and the initial conditions used for the CRN derive from the operating modes of typical aircraft engine cycle. A 21 species 30 steps chemical mechanism of kerosene is employed in the CRN method. The levels of pollutant emissions are obtained under four ICAO engine power settings of idle, approach climb and take off. The lean blowout equivalent ratio is evaluated at the idle power setting. The results will be helpful to predict the aircraft engine exhaust emissions and lean blowout (LBO).
The characteristic of the spray within combustion chamber is one of the determining factors that affect the performance and exhaust gas emissions of an aero-engine. Recently, the holography technique has been successfully applied to spray atomization measurement due to its significant advances. In this article, an atmospheric test rig of pressure-swirl nozzle is built. The kerosene spray generated at the atmospheric condition and in an aero-engine combustor is measured. The Sauter mean diameter of the spray droplets is obtained. In addition, the theoretical analysis of film formation and sheet breakup processes are conducted. Comparison of theoretical analysis and experimental results on the spray atomization of a pressure-swirl nozzle is presented.
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