• 대한기계학회논문집B
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• 제32권9호
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• pp.659-668
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• 2008

Combustion instability has been considered as very important issue for developing gas turbine and rocket engine. There is a need for fundamental understanding of combustion instability. In this study, combustion instability was numerically and experimentally investigated in a dump combustor with bluff body. The fuel and air mixture had overall equivalence ratio of 0.9 and was injected toward dump combustor. The pressure oscillation with approximately 256Hz was experimentally obtained. For numerical simulation, the standard k-$\varepsilon$ model was used for turbulence and the hybrid combustion model (eddy dissipation model and kinetically controlled model) was applied. After calculating steady solution, unsteady calculation was performed with forcing small perturbation on initial that solution. Pressure amplitude and frequency measured by pressure sensor is nearly the same as those predicted by numerical simulation. Furthermore, it is clear that a combustion instability involving vortex shedding is affected by acoustic-vortex-combustion interaction. The phase difference between the pressure and velocity is $\pi$/2, and that between the pressure and heat release rate is in excitation range described by Rayleigh, which is obvious that combustion instability for the bluff body combustor meets thermoacoustic instability criterion.

• 한국자동차공학회논문집
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• 제3권5호
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• pp.122-134
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• 1995

The present study was investigated combustion characteristics of methane-air mixtures at stratified charge in a constant volume combustion chamber. The main results obtained from this study can be summarized as follows. In case of ${\phi}_s=1.0$, total burning times greatly affected rather than initial time of pressure increase and maximum combustion pressure. In case of ${\phi}_t=1.0$, initial time of pressure increase and total burning times were affected considerably in comparison with the case of ${\phi}_s=1.0$. Also, even the very lean mixture which total equivalence ratio is ${\phi}_t=0.69$(${\phi}_s=1.0$, ${\phi}_m=0.65$), by changing configuration of the critical passage-hole and using a stratified mixture, it is possible to decrease substantially the initial time of pressure increase. total burning times and NOx concentration without deteriorating combustion characteristics such as maximum combustion pressure, rate of heat release etc. in comparison with the use of single chamber(in case of ${\phi}=1.0$) only. Specifically, our trends were revealed remarkably in the case of Type D which is reduced a flame contact area of sub-chamber side of the passage-hole.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1999년도 추계 학술발표회 논문집
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• pp.23-29
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• 1999

Experimental studies are conducted to investigate the flame stability and the thermal/fuel NOx formation characteristics of the low calorific value (LCV) coal derived gas fuel. Synthetic LCV fuel gas is produced by mixing carbon monoxide, hydrogen, nitrogen and ammonia on the basis that the thermal input of the syngas fuel into a burner is identical to that of natural gas. The syngas mixture is fed to and burnt with air on flat flame burner. With the variation of the equivalence ratio for specific syngas fuel, flame behaviors are observed to identify the flame instability due to blow-off or flashback and to define stable combustion range. Measurements of NOx content in combustion gas are made for comparing thermal and fuel NOx from the LCV syngas combustion with those of the natural gas one. In addition, the nitrogen dilution of the LCV syngas is preliminarily attempted as a NOx reduction technique, and its effects on thermal and fuel NOx production are discussed.

• 한국폐기물자원순환학회지
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• 제35권7호
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• pp.600-605
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• 2018

In this study, the combustion characteristics were investigated based on the biodrying solid recovered fuel (SRF) in a 5 Ton/day scale combustion boiler. The composition of the combustion gas containing the biodrying SRF was analyzed, the particulate matter, and its HCl content was determined with the air pollutant process test method. Mass balance, carbon balance, and combustion efficiency were calculated according to the equivalence ratio (ER) method; the energy recovery efficiency of the combustion boiler was also analyzed. The overall combustion efficiency of the biodrying SRF was 97.3 % and the energy recovery efficiency was 80.2%.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.79-84
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• 2004

For the non-premixed interacting jet flames, it has been reported that if eight small nozzles are arranged along the circle of 40 $^{\sim}$ 72 times the diameter of single jet, the flames are not extinguished over 2oom/s. In this research, experiments were extended to the partially premixed cases to reduce both flame temperature and NOx emission. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric centre. The space between nozzles, S, the equivalence ratio, ${\Phi}$, the exit velocity and the role of the jet from the centre nozzle were considered. Normally, flame was lifted and flame base was located inside the imaginary circle made by the nozzle. As nozzles went away from each other, blowout velocity increased and then decreased. The maximum blowout velocity diminished with the addition of air to the fuel stream. When the fuel and/or oxidizer were not fed through the centre nozzle, the maximum blowout velocity obtained by varying Sand ${\Phi}$ was around 160m/s. Optimum nozzle separation distance at which peak blowout velocity obtained also decreased with ${\Phi}$ decrease. Flame base became leaner as approaching to the blowout. It seemed that lots of air was supplied to the flame stabilizing region by the entrainment and partially premixing. To approve this idea and to enhance the blowout velocity, fuel was supplied to the centre region. With the small amount of fuel through the centre nozzle, partially premixed flame could be sustained till sonic velocities. It seemed that the stabilizing mechanism in partially premixed interacting flame was different from that of non-premixed case because one was stabilized by the fuel supply through the centre nozzle but the other destabilized.

• 한국추진공학회지
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• 제16권5호
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• pp.10-19
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• 2012

연소불안정 현상을 제거하거나 효과적으로 제어하기 위해서는 화염구조에 대한 이해가 매우 중요하다. 이에 본 연구에서는 OH 자발광 및 He-Ne 레이저 광흡수 계측기법을 이용하여 연소불안정과 화염 구조사이의 상관관계에 대한 실험적 연구를 다양한 실험조건에서 수행하였다. 실험에서는 673 K로 가열된 swirl 형태로 공급되는 건조한 공기와 LNG($CH_4$) 연료를 사용하였으며 전체 당량비는 1.2 조건에서 속도를 25 ~ 70 m/s까지 바꾸어가며 실험을 수행하였다. 이를 통하여 연소불안정 현상이 낮은 속도조건과 높은 속도조건에서 발생하는 것을 확인할 수 있었고, 낮은 속도조건의 불안정에서는 화염의 와동구조가 연소불안정현상에 영향을 끼친다는 것을 확인할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1116-1121
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• 2004

In this study, the effect of central fuel injection on a coaxial laminar $CH_{4}/air$ flame was experimented at the defined premixing condition(${\Phi}=1.90$, ${\sigma}=50/75/100%$, x/D=10). The partial premixing parameter are the equivalence ratio that total fuel is fixed at 200cc/min, the fuel split degree which means the percentage of fuel entering the outer tube to the total amount, and the mixing distance indicating the nonreactant mixture's homogeneity between inner tube top and burner exit. The object is to investigate the flame structure and chemiluminescence characteristics of laminar partial premixed flame as changing mixing parameters. The radical signal was acquired from ICCD camera and PMT. Each intensity was compared with Abel inverted value for measuring the effect of background light on the peak signal location and the intensity at central preheat zone. The results show that the peak location of each radical was broaden as the fuel split degree increasing because the mixing quality was enhanced. and $OH^{\ast}$ is a good indicator for flame front between reaction and preheat zone. At last $CH_{2}^{\ast}$ has the same tendency with $CH^{\ast}$ but a thinner reaction zone than $CH^{\ast}$ due to a rapid decay on the burned gas side.

• 대한기계학회논문집B
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• 제36권2호
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• pp.225-232
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• 2012

희박 예혼합 가스터빈 연소기에서 배출되는 NOx, CO 와 같은 오염물질을 예측하기 위해서 화학반응기 네트워크 모델을 개발했다. 본 연구에서는 CHEMKIN 코드와 4 가지 NO 생성 메커니즘을 포함한 GRI 3.0 메탄-공기 연소 메커니즘을 이용해서 가스터빈의 부하조건을 변화시키며 NOx 및 CO 배출의 예측을 수행하였다. 모델의 검증을 위해서 계산된 결과를 모사연소기의 실험 데이터와 비교하였다. 여러부하조건에 따른 4 가지 NO 경로의 기여도를 조사하였다. 또한 인젝터의 질량유동 및 당량비의 불균일성이 NOx 배출이 끼치는 영향을 고찰하고 10ppm 이하의 저 NOx 연소기 개발을 위한 저감 방법을 제안했다.

• 대한기계학회논문집B
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• 제29권1호
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• pp.71-79
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• 2005

For the non-premixed interacting jet flames, it has been reported that if eight small nozzles are arranged along the circle of $40{\sim}72$ times the diameter of single jet, the flames are not extinguished even in 200m/s. In this research, experiments were extended to the partially premixed cases to reduce both flame temperature and NOx emission. Nine nozzles were used- eight was evenly located along the perimeter of the imaginary circle and one at the geometric centre. The space between nozzles, S, the equivalence ratio, ${\phi}$, the exit velocity and the role of the jet from the centre nozzle were considered. Normally, flame was lifted and flame base was located inside the imaginary circle made by the nozzle. As nozzles went away from each other, blowout velocity increased and then decreased. The maximum blowout velocity diminished with the addition of air to the fuel stream. When the fuel and/or oxidizer were not fed through the centre nozzle, the maximum blowout velocity obtained by varying S and ${\phi}$ was around 160m/s. Optimum nozzle separation distance at which peak blowout velocity obtained also decreased with ${\phi}$ decrease. Flame base became leaner as approaching to the blowout. It seemed that lots of air was supplied to the flame stabilizing region by the entrainment and partially premixing. To approve this idea and to enhance the blowout velocity, fuel was supplied to the centre region. With the small amount of fuel through the centre nozzle, partially premixed flame could be sustained till sonic velocities. It seemed that the stabilizing mechanism in partially premixed interacting flame was different from that of non-premixed case because one was stabilized by the fuel supply through the centre nozzle but the other destabilized.

• International Journal of Automotive Technology
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• 제7권1호
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• pp.1-7
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• 2006

The ignition delay of a dual fuel system has been numerically investigated by adopting a constant volume chamber as a model problem simulating diesel engine relevant conditions. A detailed chemical kinetic mechanism, consisting of 28 species and 135 elementary reactions, of dimethyl ether (DME) with methane ($CH_{4}$) sub-mechanism has been used in conjunction with the multi-dimensional reactive flow KIVA-3V code to simulate the autoignition process. The start of ignition was defined as the moment when the maximum temperature in the combustion vessel reached to 1900 K with which a best agreement with existing experiment was achieved. Ignition delays of liquid DME injected into air at various high pressures and temperatures compared well with the existing experimental results in a combustion bomb. When a small quantity of liquid DME was injected into premixtures of $CH_{4}$/air, the ignition delay times of the dual fuel system are longer than that observed with DME only, especially at higher initial temperatures. The variation in the ignition delay between DME only and dual fuel case tend to be constant for lower initial temperatures. It was also found that the predicted values of the ignition delay in dual fuel operation are dependent on the concentration of the gaseous $CH_{4}$ in the chamber charge and less dependent on the injected mass of DME. Temperature and equivalence ratio contours of the combustion process showed that the ignition commonly starts in the boundary at which near stoichiometric mixtures could exists. Parametric studies are also conducted to show the effect of additive such as hydrogen peroxide in the ignition delay. Apart from accurate predictions of ignition delay, the coupling between multi-dimensional flow and multi-step chemistry is essential to reveal detailed features of the ignition process.