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The combustion instability of turbulent flames is the most important problem of the gas turbine combustor. Thus improved understanding of mechanisms of combustion instability is necessary for the design and operation of gas turbine combustors. In this study, the cause of the combustion instability in a rearward-step dump combustor was investigated with respect to the fuel flow modulation; choked fuel flow, unchoked fuel flow and fully premixed mixture flow. We observed various types of combustion instabilities with respect to the change of equivalence ratio, fuel flow conditions and fuel injection location. Particularly in the unchoked fuel flow condition, it was found that the oscillation time of combustion instability is strongly related to the convection time of the fuel and that the pressure fluctuation in a lab-scale combustor is highly related to the vortex and the equivalence ratio fluctuations due to fuel flow modulation and unmixedness of the fuel and air.
The present study conducted experimental study of spray combustion to investigate the effect of the inlet conditions of fuel and air on the flame structure, the flame stability and the characteristics of emission in the can-type model of a gas turbine combustor. In the experiment, the diameter of fuel droplet was measured using Malvern particle size analyser and temperatures in the combustion chamber were measured with R-type shielded thermocouple. In addition, flame structure was taken picture with camera and analysed. Gas analyser was also used to analyse the concentration of each components of exhausting gas. The experimental results showed that the flame condition was optimal with swirl number, 0.63 and equivalence ratio, 0.5 for controlling the flame stability, the combustion temperature and the NOx concentration. The present study concluded that both the flame structure and the emission formation were strongly affected by the swirl intensity, which selection was found as an important parameter for either stabilizing flame or lowering the quantity of NOx.
??In this study, a swirl hollow cone injector, which has a good atomization performance at the low injection pressure relatively, was designed to apply the Urea-SCR. In order to investigate the spray pattern and SMD of a swirl injector, the spray visualization was conducted by using the simple swirl injector, and the images of the spray cross-section were obtained from a sheet beam of Nd-Yag laser and CCD camera. The SMD of the swirl injector was measured with the axial of stance from the nozzle exit. The shape of the spray was converted from the hollow cone to solid cone along the distance from the injector exit. The spray angle is increased and the SMD is decreased with increasing injection pressure respectively.
본 연구에서는 디젤 인젝터의 거시적 분무특성을 실험적으로 알아 보았다. 커먼레일 디젤 인젝터의 본사를 위해 보쉬 커먼레일 시스템을 사용하였다. 본 연구를 위한 대상 인젝터는 6-hole 보쉬 디젤 인젝터였다. 다양한 분사 조건에서 디젤 인젝터의 거시적 분무특성인 분무도달거리 및 분무각을 측정하였다. 본 연구에 따르면, 인젝터의 분사압력이 높을수록 분무달거리는 증가 하였다. 또한 동일 분사압력에서 분사되는 곳의 분위기 압력이 증가 할수록 분무도달거리는 감소하였고, 분무각은 증가하였다. In this study, we conducted the experimental study to investigate the macroscopic spray characteristics with a CRDI injector. A Bosch common rail system has been equipped for this study. We used a Bosch injector with 6 holes for nozzle in this study. The spray tip penetration and sprat angle was measured with the various test conditions. According to this study, the spray tip penetration increased with increase of the injection pressure. Furthermore, as the ambient pressure increase, the spray tip penetration decreased and the spray angle increased although the injection pressure was same.
In this study, a swirl hollow cone injector, which has a good atomization performance at the low injection pressure relatively, was designed to apply the Urea-SCR. In order to investigate the spray pattern and SMD of a swirl injector, the spray visualization was conducted by using the simple swirl injector, and the images of the axial of stance from the nozzle exit. The shape of the spray was converted from the hollow cone to solid cone along the distance from the injector exit. The spray angle is increased and the SMD is decreased with increasing injection pressure respectively.
A study was performed to understand self-excited pressure fluctuations in the lean premixed flames and to evaluate the effect of Helmholtz resonator on the pressure fluctuations. As low-frequency pressure fluctuations have been reported to cause fatal damage to the combustor and the entire system, Helmholtz-type resonators, which reduce the damage by low-frequency pressure fluctuation in the combustor, are attached to the channel of unburned mixture flow. It is found that the range of low-frequency pressure fluctuations of flame mode 2 is narrowed by the attachment of Helmholtz resonators. From this result, if Helmholtz-type resonators are applied to actual gas turbine combustor, it is confirmed that Helmholtz resonators attached on the fuel discharge hole are also effective for narrowing the range of flame mode 2
An experimental study was conducted to investigate the atomization characteristics of a circular nozzle and elliptical nozzles of small diameter (0.5mm) under the high injection pressure (1MPa~9MPa). Furthermore, num erical simulations were attempted to investigate the internal flow structure in the circular and elliptical nozzles. This study showed that the disintegration characteristics of the liquid jet of elliptical nozzles were much differ ent from those of the circular nozzle. In the case of the circular nozzle, the surface of liquid jet was much smooth near the nozzle exit under the injection pressures of this study. But, in the case of the elliptical nozzles, surface waves on liquid jet have been generated and grown with increase of the injection pressure. As a result, surface breakup was observed with the increase of injection pressure because a rough column surface caused by growth of surface wave is disintegrated to ligament as the relative velocity between the liquid jet and ambient air increases. Furthermore, the numerical simulations informed that the internal flow structure of elliptical nozzle was quite different from that of the circular nozzle. The internal flow structure of the elliptical nozzle in hydraulic flip was reattached to the orifice wall of the minor axis unlike the flow in the circular nozzle which is detached from orifice wall. It has been concluded that the internal flow structure of the elliptical nozzle has influence on the disintegration characteristics of the liquid jet issued from the elliptical nozzle.